CHEMICAL AND PHYSICAL CHARACTERIZATION OF
THE DEGRADATION OF WLCANIZED NATURAL
RUBBER IN THE MUSEUM ENVIRONMENT
SANDRA AND& CONNORS
A thesis submitted to the Department of Art
in conformity with the requirements for the
degree of Master of Art Conservation
Queen's University
Kingston, Ontario, Canada
September, 1998
copyright@ Sandra André Connors, September, 1998 Nationai Library Bibiiièque nationale du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington ûüawaON K1AW OrtawaON K1AW canada Canada
The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or sell reproduire, prêter, distribuer ou copies of this thesis in microform. vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique.
The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Numerous types of polymenc materials are found in history, technology and fine an museums throughout the world. Vulcanized natural rubber, one of the rnost widely used polyrners, is a component in many museum artifacts. Those in charge of the daily carz and preservation of vulcanized natural rubber collections have found it dificult to conserve these artifacts because of the severe degradation that develops. These artifacts cm exhibit bloom, random and linear cracking patterns, hardening and brittleness as well as softening and tackiness. Cmently, there is relatively littie known regarding what type of analytical instrumentation is best suited to evaiuate the degradation of this material.
Finding suitable instrumentation is made more difficult by the presence of carbon black in most vulcanized natural mbber material. There is even less known about how the chemical and physical degradation of nlcanized natural rubber are interrelated.
Vulcanized natural rubber was chemically charactenzed using three Fourier- transform infrared spectroscopy techniques: attenuated total reflec tance-microscop y-
Fourier-transform infrared spectroscopy, attenuated total reflectance-Fourier-transform infrared spectroscopy, and photoacousric-Fourier-transfomi infrared spectroscopy. Two thermal analysis techniques were also used: thermogravimetry and thermogravimetr).-
Fourier-transform infiared spectroscopy. Physical characterization of vulcanized natural rubber was done using scanning electron microscopy as weil as mechanical testing. The chemical and physical data were correlated to determine if any consistencies between changes in physical and chemical properties were present. Ir was found that the physical changes occurring in the artificially aged samples closely resembled the changes found in many museum artifacts. These physical changes- inciuded: cracking, hardening and embrinlernent as weU as softening of the material.
Chernical analysis indicates that oxidative degradation of the material has occurred due to accelerated aging of the samples; howver, there was no specific structural change occhg in the material that was found to be linked to a specific physical sign of degradation. I wodd paaicularly like to thank Dr. Mison Murray for her never-endhg enthusiasrn for this research, encouragement and friendship.
Special thanks are due to Dr. Ralph Paroii, Dr. Karen Lui, Ms. Ana Delgado and
Ms. Jayne hui. This research could not have moved forward without their invaluable contribution of expertise and instrumentation.
1 would also like to acknowledge Ms. Clara Deck of the Henry Ford Museum &
Greenfield Village, for her generosity and invaluable assistance with die collection of naturally aged vulcanized natdnibber samples fiom museum aaifacts.
Thanks are dso due to Dr. Warren Baker for his interest in this research as well as his ideas about how to bring this research to hition.
This research would not have been possible without the financial support of
Queen's University Faculty of Arts and Sciences and the National Science and
Engineering Research Council of Canada.
Acknowledgement is also due to the Faculty, Staff and Students of the An
Conservation Program at Queen's University for their constant suppon.
Finally, I would like to thank my farnily and friends, particularly David and
Shirley Connors, Janice and Ben Cranston and Nicole Yantzi, for their unconditional love and support. T-LE OF CONTENTS
-. ABSTRACT ...... -11
ACKVOWLEDGEMENTS ...... iv
TABLE OF CONTENTS...... v
LIST OF TABLES ...... ix . LIST OF FIGURES ...... --..--...----...-....~.-...... ~....-.-...-..-..-~-.---.--~..~...x~l
CHAPTER 1. INTRODUCTION ...... 1
CWTER 2. HTSTORY ...... 3
7.1 History of Polymers ...... 3
3.2 History of Natural Rubber ...... 6
CHAPTER 3. CHEMISTRY AND PRODUCTION OF NATUILAL RUBBER ...... 10
3.1 Source of Nanual Rubber ...... -.-...... 1 O
3 -2 Vulcanization ...... 1 1
5 -3 Degradation of Vulcanized Natural Rub ber ...... 13
CHAPTER 4. PREVIOUS RESE-4RCH...... 22
4- 1 Previous Research: Polymenc mate rials ...... 73
4.2 ProbIems -4ssociated \?th Natural Rubber Artifacts ...... -30
9 - 4.3 Previous Research: Natural Rubber Materials ...... 33
CHAPTER 5. LMETHOÛOLOGY...... -39
5.1 Fourier-Transform Infrared Spectroscopy (FTIR) ...... -39 5 .1.1 Attenuated Total Reflectance-Microscopy-Fourier-Transform
bedSpectroscopy (ATR-Microscopy-FTR) ...... 12
5- 1 -2 Attenuated Total Reflectance-Fourier-Transform Infked
Spectroscopy with the Avatar OmI-Sarnpler Atîachment
(OMNbSampler)...... -44
5 .1.3 Photoacoustic-Fourier-Transform Infiared Spectroscopy
(PAS-FTIR) ...... 46
5.2 Thrrmogravimetry (TG) ...... --...... *.*..*. -48
5.3 Themogravimetry-Fourier-Transfom Infrared Specnoscopy
...... (TG-FTIR) ...... 51
5.4 Scanning Electron Microscopy ...... 52
5.5 iMechanica1 Testing S ystem ...... 55
CHAPTER 6 . EXPERIMENTAL ...... -56
6.1 Surrogate Sample Formulation ...... 56
6.2 Naturally Aged Samples ...... 56
6.3 Accelerated Aging ...... -37
6.4 Chernical Analysis ...... 59
6.4.1 Attenuated Total Reflectance-Fourier-Transform Infrared
Spectroscopy (ATR-Microscopy-FTIR)...... 59
6.4.2 Avatar OMNI-Sampler Attachent (OMNI-Sampler) ...... 60
6.4.3 Photoacoustic-Fourier-Transforrn-Infiared
Spectroscopy (PAS-FTIR) ...... 60
6.4.4 Thermogravimetry (TG) ...... 1
8.7 TeeDa ...... 111
C K.TER 9. CONCLUSIONS ...... 113
BIBLIOGRAPHY ...... 116
APPENDIX A ...... 125 APPENDIX B ...... 129
APPENDIX C ...... , ...... 131 APPENDIX D ...... 132 APPENDIX E ...... 135
APPENDE F ...... , ...... 138
VITA ...... 145 LIST OF T-ABLES
Tablz 6.1 Standard Formula 2A hrBlack Filied Vdcanized Natural Rubber ...... 56
Table 6.2 Henry Ford Museum & Greenfield Village Artifacts Sampied
for this Project ...... 57
Table 7.1 Identification of Peaks for ATR-microscopy-FTIR Spectrum of
an ünexposed Vulcanized Naniral Rubber Smogate Sarnple ...... 6 j
Table 7.2 Identification of Peaks for ATR-Microscopy-FTIR Spectnim of a
One Week Exposed Vulcanized Naturai Rubber Sample ...... 66
Table 7.3 Identification of Peaks for OMNI-Sarnpler Spectnim of Unexposed
Vulcanized Natural Rubber ...... 68
Tabie 7.1 Identification of Peaks for OMNI-Sampler Spectrum of Vulcanized
Naturai Rubber after Two Months of QUV Exposure ...... 70
Table 7.5 Identification of Peaks for OMNI-Sampler Spectnim of Vulcanized Natural
Rubber derFour Months of QUV Exposure ...... 7 1
Table 7.6 Identification of Peaks for OMNI-Sampler Spectm of the
c. 1880 DmCylinder Press Sample ...... 73
Table 7.7 Identification of Pe&s for PAS-FTIR Spectrum of Unrxposed
Vulcanized Natural Rubber ...... 75
Table 7.8 Identification of Peaks for PAS-FTIR Spectrum of a Vulcanized
Naml Rubber Surrogate Sarnple after Two Months of
QUV Exposure ...... -.76
Table 7.9 Identification of Peaks for PAS-JiTIR Spectm of a Vulcanized NaWRubber Surrogate Sample after Four Months of
QW Exposure ...... -77
Table 7-10 Identification of Peaks for PAS-FTIR Spectrum of the
c. 19 10 Washing Machine ...... 79
Table 7.1 1 Identification of Peaks for PAS-FTIR Spectnim of the
c. 18 80 Dnim Cylinder Press Sample ...... -80
Table 7.12 Activation Energy and Degradation Time Calculations for Vulcanized
Natural Rubber at 136"C,230°and 250°C ...... 82
Table 7.13 Changes at the Surface of Vulcanized Natural Rubber Surrogate
Samples As a Result of QW Exposure ...... -88
Table 7.14 Changes in Fracture of Vulcanized Natural Rubber Specimens
as a Resul t of QW Exposure ...... 93
Table F. 1 Mechanical Testing Data for Unexposed Vulcanized Natural Rubber ..... 138
Table F.2 Mechanical Testing Data for Unexposed Vulcanized Natural Rub ber
(continued) ...... 1 3 8
Table F.3 Mechanical Testing Data for Vulcanized Natural Rubber after
One Week of Exposure ...... 139
Table F.4 Mechanical Testing Data for Vulcanized NaturaI Rubber after
One Week of Exposure (continued) ...... ~...... ~...... 1 3 9
Table F.5 Mechanical Testing Data for Vulcanized Natural Rubber afier
One Month of Exposure ...... 140
Table F.6 Mechanical Testing Data for Vulcanized Natural Rubber afler
One Month of Exposure (continued) ...... 140 Table F.7 Mechanical Testuig Data for Vulcanized Naniral Rubber after
Two Months of Exposure ...... 14 1
Table F.8 Mechanical Testing Data for Vulcanized Nanirai Rubber der
Two Months of Evposure (conrinued)...... 141
Table F.9 Mechanical Testing Data for Vuicanized Naturd Rubber afier
Three Months of Exposure ...... -142
Table F. 1 0 Mechanicd Testing Data for Vulcanized NadRubber afier
Three Months of Exposure (continued)...... 132
Table F. 1 1 Mechanical Testing Data for Vulcanized Natural Rubber afier
Four Months of Exposure ...... 143
Table F. 12 Mechanicd Testing Data for Vulcanized NatdRubber afier
Four Months of Exposure (continued) ...... 143 sii
LIST OF FIGURES
Figure 3.1 Chernical Smcture of Cis- 1. 4Polyisoprene ...... 10
Fibgre 3 -2 Vuicanization of Natural Rubber ...... 12
Figure 3 -3 Free-Radical Mechanism for Sul* Vulcanization of Natural
Rubber ...... -13
Figure 3.4 Fra-gnentation of Peroxy Groups ...... 14
Figure 3.5 Fragmentation of Carbonyl Groups ...... 14
Figure 3 -6Free-Radical Formation on the Polymer Chain ...... *...... 15
Figure 3 -7 Mechanism for Photo-Oxidation which Results in Chain Scission ...... 15
Figure 3.8 Mechanism for Photo-Oxidation which Results in Cross-Linking ...... 17
Figure 3.9 Production of Stable Products fkorn Two Free-Radicals ...... 18
Figure 3 .IO Ozone Attack of Natural Rubber ...... 19
Figure 5.1 Types of Molecular Vibrations ...... 40
Figure 5.2 Schematic Diagram of Nicolet 800 Fourier-Transform Infrared
Spectrometer ...... 42
Figure 5.3 General Schematic Diagm of Attenuated Total Reflectance
Sarnpling System ...... -43
Figure 5.4 Infrared Objective for Nicolet Nic-Plan Microscope ...... -44
Figure 5.5 Diagram of Avatar OMNI-Sampler Attachent ...... 45
Figure 5.6 Schematic Diagram of PAS-FTIR ...... 47
Figure 5.7 Main Types of Thermogravimetric Curves ...... 48
Figure 5.8 Schematic Diagram of Thermogravimetry Instrumentation...... 50 Figure 5.9 Diagram of Thermogravimeq-Fourier-Transform infrared
Spectroscopic hstmmentation ...... 52
Figure 5.1 O Schematic Diagram of a Scanning Electron Microscope ...... j4
Figue 6.1 Lamp and Sample Placement Diagram for QWApparatus ...... 58
Figure 7.1 ATR-Microscopy-FTIR Specmim of an Unexposed Vulcanized
Naturai Rub ber Surrogate Sample ...... 64
Figure 7.2 Chernical Structure of Cis- 1. 4.Polyisoprene ...... 65
Figure 7.3 ATR-Microscopy-FTIR Spectnim of a Vulcanized NaWRubber
Surrogate Sample after One Week of QUV Exposure ...... 66
Figure 7.4 Attempted ATR-Microscopy-FTIR Spectrum of a Waturaily Ajed
Washing Machine Sample ...... 67
Figure 7.5 OMNI-Sampler Spectnim of Unexposed Vulcanized Natural Rubber ....68
Figure 7.6 OMNI-Sampler Spectnim of Vulcanized Natural Rubber after
Two Months of QUV Exposure ...... 69
Figure 7.7 OMNI-Sampler Spectnim of Vulcanized Natural Rubber afier
Four iMonths of QUV Exposure ...... 70
Figure 7.8 OMNI-Sarnpler Spectnim of Vulcanized Natural Rubber afier
Three Months of QUV Exposure (Version 1) ...... 7 1
Figure 7.9 OMNI-Sarnpler Specuum of Vulcanized Natural Rubber afier
Three Months of QUV Exposure (Version 2) ...... 72
Figure 7.10 OMNI-Sampler Spectrum of Vulcanized Nahird Rubber der
Three Months of QUV Exposure (Version 3) ...... 72
Figure 7.1 1 OMNI-Sampler Spectm of c . 1880 Drum Cylinder Press Sample...... 73 xiv
Figure 7.12 P AS-FTIR Spectmm of Unexposed Vuicanized Nanual
Rubber ...... -.,.,.... *.*...... *...-.....*...... *...... *.74
Figure 7-13 PAS-FTK Spectrum of Vulcanùed Natural Rubber
afier Two Months of QW Exposure ...... 76
Figure 7.14 PAS-FTIR Spectrum of Vulcanized Naturai Rubber
after Four 1Mont.h~of QWExposure ...... 77
Figure 7.15 PAS-FTIR Spectnun of a c. 19 10 Washing Machine Sample ...... 78
Figure 7.16 PAS-FTIR Spectrum of a c. 1880 Drum Cylinder Press Sample ...... 79
Figure 7.1 7 Thermogravimetric and Derivative Thermogravimetric Cmes
for Unexposed Vulcanized Natural Rubber ...... S 1
Figure 7.18 Activation Energy and Degradation Time Determinations
for Vulcanized Natural Rubber at 1 36°C ...... 8 1
Figure 7.19 TG and DTG Curves of Vulcanized NatdRubber afier
70 Hours at 23 O°C Oven Exposure ...... -83
Figure 7.20 TG and DTG Curves of Vulcanized Naturai Rubber afier
1 18 Hours at 230°C Oven Exposure ...... 83
Figure 7.2 1 TG and DTG Curves of Vulcanized Natural Rubber afier
1 9 Hom of Oven Exposure at 250°C ...... 84
Figure 7.22 TG and DTG Curves of Vulcanized Natural Rubber afier
23 Hours of Oven Exposure at 250°C ...... 85
Figure 7.23 TG and DTG Curves of Vulcanized Natural Rubber &er
Tiuee Months of Q UV Exposure ...... 8 5
Figure 7.24 TG-FTIR Spectra of Unexposed Vulcanized Natural Rubber ...... 86 Figure 7.25 TG-FTIR Spectra of Vdcanized Nanual Rubber der
Three Months of QUV Exposure ...... 87
Figure 7.26 SEM Image of Unexposed Vulcanized Natural Rubber
(200X ~Magnification)...... -89
Figure 7.27 SEM Image of Vulcanized Natural Rubber after
One Week of QW Exposure (200X Magnification) ...... --89
Figure 7.28 SEM Image of Vulcanized NatdRubber after One
Month of QUV Exposure (200X Magdication) ...... 90
Figure 7.29 SEM Image of Vulcanized Naturai Rubber after Two
Months of QLTV Exposure (200X Magnification)...... -90
Figure 7.30 SEM Image of Vulcanized Natural Rubber afier Three
Months of QUV Exposure (200X Magnification)...... 9 1
Figure 7.3 1 SEM Image of Vulcanized Natural Rubber after Four
Months of QUV Exposure (200X Magnification)...... 9 1
Figure 7.32 Detail of 1907 Harley Davidson Motorcycle Tire ...... 93
Figure 7.33 SEM Image of Fracture Point of an Unexposed Vulcanized Natural
Rubber Specimen (5OX Magnification) ...... 939
Figure 7.34 SEM Image of Fracture Point of a Vulcanized Naturai Rubber
Specimen derOne Week of QUV Exposure (50X Magnification)...... 94
Figure 7-35 SEM Image of Fracture Point of a Vulcanized Naturai Rubber
Specimen derOne Month of QUV Exposure
(5OX Magni fication) ...... 94 Fi-we 7.36 SEM Image of Fracture Point of a Vulcanized Natural Rubber
Specimen after Two Months of Q W Exposure
(jOX Magnification) ...... 9 j
Fiawe 7.3 7 SEM Image of Fracture Point of a Vulcanized Natural Rubber
Specimen after Three Months of QUV Exposure
(5OX Magnification) ...... 95
Figure- 7.38 SEM Image of Fracture Point of a Vuicanized Natuai Rubber
Specimen after Four Months of QUV Exposure
(5OX Magni fication) ...... 96
Figure 7.39 Changes in l'ensile Strength of Vulcanized Natural Rubber
Specimens as a Function of Q W Exposure ...... 97
Figure 7.40 Changes in Percent Elongation of Vulcanized Natural Rubber
Specimens as a Function of QW Exposure Time ...... 98
Figure 7.4 1 Calculation for Percent Elongation ...... 98
Figure A. 1 PAS-FTIR Spectrum of a 19 15 Cadillac Tire Sample ...... 125
Figure A.2 PAS-FTIR Spectrum of a 1903 Cadillac Hom Bulb Sarnple ...... 123
Figure A.3 PAS-FTIR Spectnim of a 1903 Ford Mode1 A Hom Bulb Sample ...... 126
Figure A.4 PAS-FTIR Spectnun of a Harley Davidson Tire Sample...... 126
Figure A.5 PAS-FTIR Spectnun of a 1899 Locomobile Sample ...... 127
Figure A.6 PAS-FTIR Specmim of a Rubber Shoe Sample ...... 127
Figure A.7 PAS-FTIR Spectnim of a c. 1864 Gordon Osciliating Cylinder
Press Sample ...... 128 Figure B. 1 Activation Energy and Degradation Tirne Determinations
for 230O C ...... -.-. 129
Figure B.2 Activation Energy and Degradation Time Deteminations
for 250°C ...... 130
Figure C. 1 Gram-Schmidt Reconstruction for Unexposed Vulcanized
NaW Rubber ...... 13 1
Figure C.2 GramSchmidt Reconstruction for Vulcanized Natural
Rubber after Three Months of QUV Exposure ...... 13 1
Figure D.1 SEM Image of Unexposed Vulcanized Naturai Rubber ...... 132
Figure D.2 SEM Image of Vulcanized Naturai Rubber after One Week
of QW Exposure ...... 132
Figure D.3 SEM Image of Vulcanized Natural Rubber derOne Month
9- of QUV Exposure ...... 1JJ
Figure D.4 SEM Image of Vulcanized Naturd Rubber after Two Months
1% of QUV Exposure ...... 1 J 3
Figure D.5 SEM Image of Vuicanized Naturai Rubber after Three Months
of QUV Exposure ...... 134
Figure D.6 SEM Image of Vulcanized Nanird Rubber after Four Months
of QUV Exposure ...... 134
Figure E. 1 SEM Image of a Vulcanized Natural Rubber Specimen afier
One Week of QUV Exposure ...... 1 35
Figure E.2 SEM Image of a Vulcanized Naniral Rubber Specimen afier
One Month of QUV Exposure ...... 135 Figure E.3 SEM Image of a Vulcanized Na& Rubber Specimen afker
Two Months of QUV Exposure ...... 13 6
Fiwe.. E.4 SEM Image of a Vulcanized Natural Rubber Specirnen after
Three Months of QUV Exposure ...... 136
Figure E. j SEM Image of a Vuicanized Nanual Rubber Specimen after
Four Months of QUV Exposure ...... 13 7 1. INTRODUCTION
Artifacts made of polymeric materials can be found in almost every museum
throughout the world. Machinery, household goods, medical equipment, as well as, fine
art objects have al1 been made, at least in part, fiom polymers. These collections are the
concern of conservators and conservation scientists who have to make decisions
regarding their exhibition, dorage and care. Most artifacts made of polymenc materials
are diEcult to conserve and evaluate, but vulcanized naturai rubber artifacts pose a
particular problem because of the severity of degradation frequently found in these
artifacts. This degradation cm manifest itself as bloom, random or linear cracking
patterns, hardening and brittleness or softening and tackiness. These physical changes
that occur in vulcanized natural rubber are visible to the human eye. There is, however,
relatively little known about what chemical and physical changes are occumng in this
material as it ages. It is essential to have a thorough understanding of these changes
before attempting conservation, as treatments done to vulcanized natural rubber artifacts
may inflict irrevenible damage andor acceierate the rate of detenoration. This study will, rherefore, focus on evaluating the chemical and physical changes occumng in vulcanized natural rubber as a result of degradation, as well as look for any correlation between the changes.
The chemical characterization is made dificuit by the presence of carbon black in most vulcanized natual rubber formulations. Three Fourier-transform infiared spectroscopy techniques will be evaluated for their usefulness in characterization of vulcanized natural rubber, which has been either naturally or artificially aged. These techniques include: attenuated total reflectance-microscopy-Fourier-tram form ieed spectroscopy (ATR-microscopy-FTIR), attenuated total refl ectance-Fourier-transfonn i-ed spectroscopy (ATR-ETIR), and photoacounic-Fourier-transfom infrared spectroscopy (PAS-FTIR). Two thermal analysis techniques wil1 also be evaiuated for their use fulness in charac tenzation of this matenal including themogravimetry (TG) and themogravimew-Fourier-mfom infiared spectroscopy (TG-FTIR). Physical characterization of artificially aged vulcanized natural rubber samples will be done to determine if chernical changes occurring in the materiai correlate with physical changes.
Scanning electron microscopy (SEM) and mechanical testing will be used to evaluate changes in the tende properties and morphoiogy of the aaificially aged samples.
This thesis will first provide a brief history of natural and semi-synthetic polymenc materials, a background into the chemistry and production of vulcanized natural rubber, and a literatue review that focuses on art conservation research of polymeric materials. This will be followed by the methodology for the instrumentation used, the experimentai protocois used for each instrument, as well as al1 experimental results. Finally, a discussion is given regarding the results and conclusions of this researc h. 2.1 History of Polymers
One of the most important developrnents in materials science over the last 150 years has been the invention and manufacture of several types of polymeric materids.
Polymenc materials were originally developed to replace more expensive natural materials such as hom and tortoiseshell. More recently, polymeric materials have been produced for their specific physicd and mechanical properties which can be changed depending on what additives are included in the rnanufacturing processes. Products made fiom polymeric materiais have been used al1 over the world. The development of and increase in consumer goods used by the middle class, cari be traced by examination of household goods, clothing and toys made fkom polymers. Automotive and machinery objects containing polymenc materids were an intrinsic part of the industrial revolution as we11 as an intricate part of North Amencan culture. Plastics have also played a large part in military history. These new materials allowed for communication and transportation advances, which were not possible prior to their development. As polymeric matenals became part of everyday life, they also became of interest to artists who were looking for materials with which to mate new and innovative works of art.
For ail these reasons, objects made of polymeric materials have been collected by fine art, living history, military, and science and technology museums throughout the world.
The development of polymenc matenais between 1800 and 1940 will be discussed. This includes only naturai polymers and semi-synthetic polymers, the latter of which were developed through die manipulation of naturally occurring material.
Gutta-percha is a completely nadpolymer whose main component is trans-
1,4,-polyisoprene. This material is initially hard and must be scraped fiom the Palaquium tree. Gutta-percha becomes soft and malleable in hot water. Once sofi, it
may be molded into almost any shape. It has been used for commercial products such as
buckets, containers, tubing, smail sculptures and tool handles. Because gîta-percha also
has very good insdating properties, it was chosen as the insulating matenal for the fist
undenvater telegraph link between England and France. It was used for al1 undenvater
cables for approxirnately 100 years. Gutta-percha was also widely used to mold
decorative objects, such as Victorian era jeweiry and ink wells (Katz 1986).
Cellulose was the fhand most popular natural polymer to be used as a semi-
synthetic plastic. In 186 1, Alexander Parkes patented a process, which combined Cotton
fiben or wood flou with nitric and sulfuric acids. He used additives such as camphor and caster oil to plasticize the matenal (Maltby 1997). This process created a cellulose ester, cellulose nitrate which could be molded into decorative shapes. Parkes named this matenal Parkesine. This material degraded relatively rapidly, becoming badly cracked and warped. These eariy problems with cellulose based polymers were solved concurrently by the Hyan brothers in the United States, and Spill in Britain. They developed a different process of using camphor as a plasticizer. Spill patented his material in 1869 under the name Xylonite and the Hyan brothers patented this process and material under the name Celluloid in 1870. Celluloid and Xylonite were used extensively as imitation tortoise shell and ivory. Cellulose nitrate products include buttons, hair combs, shirt coilars and cuffs, billiard balls and, most recently, ping pong balls (Maltby 1997). Cellulose nitrate was also used as cinema film, cells for animation and children's toys. Its main drawback is that it is flarnmable (Katz 1986). Even with this drawback, cellulose nitrate was a material which artists appreciated and used fiequently (Derrick, et al. 1993). Naum Gabo, for example, was able to produce sculptural effects using cellulose nitrate, which no other materiai available at the time
would ailow. Cellulose nitrate continued to be used in the United States until 1952 for
several materiais, including film (Katz 1986).
Casein is another of the semi-synthetic plastics developed during the 1800s. This
material cornes fiom the protein found in mi&, which consists of long chain molecules.
The milk is treated with lactic acid in order to separate the curds and whey. The curds
are then dried and ground into a powder, mixed into a dough, and extnided into lengths
(Katz 1986). The material hardens over the course of several days or weeks to produce a
thermosetting material, which can be polished and machined into desired shape. Spitteler
and kische first patented this matenal, in Germany, in 1899. It is similar to cellulose
nitrate and cellulose acetate in that it may be colored with any number of bright and/or
natural colors to give the desired effect (Katz 1986).
Cellulose waç also used in the production of cellulose acetate. This ester was first
developed in 1905 by treating Cotton fibers with acetic anhydride instead of nitnc acid. It
was thought to be more stable than cellulose nitrate because it was not flammable.
Initially cellulose acetate was used for waterproofing aircraft fabric. It was not until 1928 that it repiaced the use of cellulose nitrate for creating moided decorative objects such as combs and hair clips (Katz 1986). It was also used for film, although cellulose nitrate remained the preferred film base until 1952 (Katz 1986). Naum Gabo also used cellulose acetate as a material for his sculptures, some of which are currently in the collection of the Tate Gallery in England. 2.2 History of Na- Rubber
The Mayan and Aztec peoples of equatoriai South America used nanual rubber
for many purposes. The moa famous of these uses was to make a bal1 that was wdin a
game, which consisted of playea attempting to hit the rubber bail into a hole on the stone
wall of an I-shaped court (Loadman 1995). Naturai nibber was also used by the natives
of the Amazon and Penivian regions. The Inca people had a very well developed
network of roads, which were usudly traveled on foot. This created a need for protective
covering for the feet. By dipping their feet directly into liquid naturai rubber! the people
created a perfectly fined pair of shoes (Loadman 1995).
As Europeans were exploring the Americas, several exploren wrote of rubber and
its uses by the native peoples of the region. Captain Gonzalo Fernadez de Oviedo and
Antonio de Herrera Tordesillas wrote about the bal1 games rnentioned above in 153.
During the same period, Torquemada described how natives taught soldien to waterproof
their clothing and boots with natuml rubber. He also described how natural rubber was
used to create waterproof vessels for carrying liquids (Loadrnan 1995).
After this initial period of interest in rubber by Europeans, there was a 121-year period when virtually no work was published on the subject. In 1736, the interest in
natural rubber was renewed. Two French explorers, Charles de la Condamine and
Francois Fresneau, traveled independently to South Amenca in order to determine the esact shape of the earth; however, during their years in South Amenca, they also collected information and samples regarding the harvesting, processing and production of natural rubber objects. This information was sent to the Paris Academy of Science. Even though de la Condamine retumed to France afier carrying out his work, he remained a fiiend to Fresneau, who stayed in South America studying and recording al1 aspects of rubber production. The information coliected by Fresneau would be the foundation of the
fmt scientific papers wnaen about mbber (Loadman, 1995). Upon rehirning to France in
1739, Fresneau devoted the rest of his life to research into rubber as an industrial
materiai; he became known as the father of the rubber industry.
Unfomuiately, the raw naWrubber (latex) was dificult to transport fiom South
hencato Europe. If lefi untreated, the rubber wouid develop fûngal growdi or it would
dry out during transportation and become to hard to use. For these reasons, Euopeans
developed many techniques for processing nanual rubber, making the mbber easier to
use.
There were several attempts to find suitable solvents for natural rubber. In 1780,
R. Bemiard performed experiments that attempted to use lavender oil, tqentine, carnphor oii, olive oil, almond oii and linseed oii as solvents for rubber. In 179 1, G. V.
M. Fabbroni successfully used rectified petroleum for this purpose. The sarne year
Samuel Peal patented the use of turpentine oil (in the presence of heat) for the dissolution of rubber. In 1797, Henry Johnson patented a process of using a mixture of turpentine essence and alcohol as a solvent. Once solvents were found, the hardened rubber fiom
South Amenca could be dissoived ùito a liquid which, in tum, would be used to coat fabric, shoes and containers to make them waterproof. This process was also used to coat fabric for balloons. In the late 1700's bdloon ascents were becoming popular, and in
1785 ascents were made in rubberized balloons filled with hydrogen (Schidrowitz and
Dawson 1952).
Another advance to prove useful for processing rubber was the invention of the masticator. The British inventor of this machine, Thomas Hancock, initiaily started a factory for the preparation of rubber solutions for the waterproofing and coating of fabncs. When he did not nicceed in producing a suitable coating material, he began to produce elastic threads, which could be used for gloves and undergarments. Hancock devised a machine, which, he believed, would heat the large arnounts of waste rubber resulting from this process and dry it out, increasing the ease of disposal. In fact, this machine heated the waste rubber under pressure, which created one solid mass of rubber
(Schidrowitz and Dawson 1952). This provided the oppormnity for solid molded objects to be created.
Charles Macintosh acquired a patent, in 1823, for a process for waterproohg double textures by dissolving the mbber in coai-tar naphtha (Schidrowitz and Dawson
1952). Using coal-tar naphtha as a solvent was the solution Hancock had been looking for when he first started in the rubber industry. In 1826, Hancock and Macintosh entered into a working agreement for the manufacture of waterproof garments.
Even with al1 the advancements of the 18" and 19" centuries, natural rubber still had problems. As a thermoplastic polymer, it would soften when hot and become hard and brittle when cold. This problem was solved by the development of vulcanization, a process which revolutionized the rubber industry.
Charles Goodyear accidentally discovered the process in 1839. He fond that when raw rubber was heated with sulfur and litharge (lead monoxide or PbO), it became resistant to changes in temperature while retaining its elastic properties (Kauffman and
Seymour 1990). He initiaily called the resulting matenal Metallic Gurn-Elastic. Thomas
Hancock was subsequently successful in making the material cornmercially profitable under the name Vulcanized Indian Rubber. Development of this process allowed the eventual production of the wide range of vulcanized naniral rubber objects. The process of vulcanization alters the physical properties of naniral rubber
dramatically, so that it is changed hma themioplastic polymer to a thennosetting
pol>mer, while retainîng its elasticity. The material becomes very durable and pliable,
yer is impermeable to air as well as to most gases and liquids (Schidrowitz and Dawson
i 952).
When a mail amount of sulfur was used, a soft and resilient materid was created.
This soft form of vulcanized natural rubber found wide use in the automobile and
rnachinery industries where it was used in making tires, O-rings, seals and belts. This
material was also used heavily during World War 1, for example, to make gas masks.
Vulcanized naturai rubber was also used in household goods, such as bathing suits, caps
and shoes, imer tubes, toys, dolls, bandages, sheets, and gloves (Allington 1988; Katz
1986; Loadman 1993).
When a large arnount of sulfur was used, a hard rubber was produceci which was
knokvn as wlcanite and ebonite. The matenal resembled ebony and was frequently used to make such items as jewelry, buttons, doorknobs and fountain pens. Hard rubber was particularly chernical and heat resistant and was therefore used for pumps, valves, banery boxes, electrical parts, and telephones. It was also used in making pipe stems and dentures (Allington 1988; Katz 1986). 3. CHEMISTRY AND PRODUCTION OF NATURAL RUBBER
3.1 Source of Natural Rubber
Natural rubber cornes fiom many bofanical sources most commonly being the
Havea Brisilienris tree. This is a tro~icaltree which originaily could not be found outside the equatoriai region in South Amenca. Naturai rubber is harvested through a process of tapping. A sharp kniie is used to cut the bark approximately 1 mm wide and 2 mm deep. The cut is made at a 25' angle, downward from horizontal. The latex, a mikj liquid, oozes fkom the tree and collects in a pan under the cut. Latex is an ernulsion of approximately 30% nibber by weight in water (Sowry 1977).
Natural rubber is a polymer whose main component is cis-1,4-polyisoprene.
(Figure 3.1) The rest is composed of natural impurities, including proteins, fatty acids, resins and sterols (Kauffman and Seymour 1990).
Figure 3.1 Chernical Structure of Cis- l &Polyisoprene
cis- 1,4-polyisoprene
Cis-1 3-polyisoprene, as mentioned before, is a thermoplastic polymer in its natural state.
It has very few, if any, cross-linkages between polyrner chahs. It becomes soft when exposed to high temperatures (above 50°C) and becomes brittle when exposed to cold ternperatures, having a glas transition temperature of -70°C. When naturai rubber is strerched, random coils of polymeric chahs are unwound and become aligned, forming crystals. In other words, the pol ymer chains become more ordered and there is a decrease in entropy. Because of the maIl number of cross-linkages, the polymer chah may slip past one another as the material is stretched (Kauffman and Seymour 1990). Naniral rubber is dso very adhesive; two pieces will become one mass when put in contact wirh one another. Natural mbber is also very soluble, dissolving easily when in contact with grease or oil and haan unpleasant odor (Schidrowitz and Dawson 1952).
3 -2 Vulcanization
Vulcanization of natural rubber is achieved through the combination of sulfur with natural rubber. This was historically done in one of two ways. The fmt was a process in which natural mbber was dipped into molten sulfur. The second was a process, known as cold cure, in which sulfur chloride and carbon disulfide were combined with polyisoprene. This allowed the vulcanization to take place at Iower temperatures.
Two chemical reactions are of concem when naturai rubber is being vulcanized.
The first reaction is the oxidation of polyisoprene resulting in chain scission; this reaction is described in detail in the next section. The second reaction is the developrnent of suhr cross-Iinkages between polyisoprene chains (Figure 3-2). This reaction is a general mechanism for vulcanization of natural nibber (Stem 1967). Even though the mechanism for creation of sulfur cross-linkages is not completely undentood, one possible mechanisms have been put forth. It proceeds through fiee-radical attack (Figure
3.3) (Eirich 1978). It is also thought that cross-linking involves polysulfide cross- linkages attaching at a secondary carbon (Kauffman and Seymour 1990) and that monosulfide bonds would occur at a tertiary carbon (Stem 1967). It is necessary to 12 optimize the sulfur cross-linkage reaction, while minimi;ring the oxidation reaction, in order to produce a vuicanizate with useful physical properties.
Figure 3 .Z Vulcanization of Natural Rubber
CH; CH3 1 I -CH2-C=CH-CH2-Cb-C=CH-CH2- + Sd6~-
CH; C H3
Figure 3 -3 Frse-Radical Mechanism for Sulfur Vulcanization of Natuni Rubber
CH; I -CH2- C= CH- CH2- I CH; CH3 CH; 1 - I
SuhCross Linkage
3 -3 Degradation of Vulcanized Natural Rubber
There are several ways in which wlcanized natural rubber may deteriorate. The most common process of degradation, occuning in rnuseurn artifacts, is fice-radical oxidation. This reaction will occur without a cataiyst but is accelerated in the presence of light. The light wi11 react with a chromophore (any material which will reacr with light).
Perosy groups (0-0)and carbonyl groups (GO) are particularly photosensitive and frequently act as chromophores. They are usually found as additives in the formula or an impurity from processing. The chromophore will absorb a photon of light, usually in the ultra-violet region of the spectrum. Once absorbed, the energy from the photon wvivill iniriate chain scission, which will result in free-radical formation (Graaan 1978). In the case of peroxy groups, chain scission occurs at the oxygen-oxygen bond (Figure 3-41.
Carbonyl groups usually fragment behveen the carbon bonds, thus separating the carbonyl group fiom part of the polymer chain (Figure 3.5). Fi_= 3 .l Fragmentation of Peroxy Groups
photon R-O-O-R - R-O* + *O-R peroxide
photon R-O-O-FI - R-O* + *O-H
hy droperoxide
Figure 3 -5 Fragmentation of Carbonyl Groups
R \ photon C=O - Re c 'C=O R' R' carbony 1
The fiee-radicals, being very reactive, will react with molecules around them to create more free-radicals. Free-radical formation on the polymer chah is inevitable (Figure
3.6). Once this occurs, photo-oxidative degradation of the polymer will begin. The mechanisms for oxidation of vulcanized natural rubber are not cornpletely understood at this point, although two possible mechanisms are worth discussing. In the first mechanism (Figure 3.7) the polymer chah must fint undergo a rearrangement, placing the fiee-radical on the tertiary carbon. The free-radical will then react with molecular oxygen to create a peroxide. Figure 3.6 Free-Radical Formation on the NaturaI Rubber Chain
CH3 1 -CH2-C=C&-CH- + Rom I - H cis- 1,4-polyisoprene
-CH*-&CH-CH- . + ROH
fiee-radical
This is followed by reaction with a hydrogen-containhg compound, which may be an impurity or another portion of the polymer chah to produce a hydroperoxide. The hydroperoxide may again react with a photon of light, causing fragmentation between the oxygen-oxygen bond. The resulting fiee-radical will undergo remangement and chain scission will occur between two carbon bonds, creating a carbonyl containing compound and another fiee-radical (Grattan 1978). In cases where chah scission results fiom degradation, the physical properties of the wlcanized natural rubber artifact will change.
It will become softer and more tacky than its original state because of the decrease in cross-link density of the material.
Figure 2.7 Mechanism for Photo-Oxidation Which Results in Chain Scission
fiee-radical fkee-radical (Fi_oure 2.7 Continued)
CH; CH3 I I -C&-C-CH=CH- + O2 -CH-C-CH=CH- 0 - I fiee-radical
peroxide
CH; CH3 I I -CH--CH=CH- + -CH2-C=CH2-CH- - I I O W I 0. hydrogen containing material peroxide
O I O-H hy droperoxide
CH; l -CH2-C-CH=CH- Y Photon I -
O I H hydroperoxide (Fi,gure 37Continued)
CH; CH3 I l -CH2-C-CH=CH- __T -CH2-C + -CH=CH- I '$ 0. O
chain scission
In the second mechanism for oxidation (Figure 3.8), the fiee-radical goes through the same rearrangement as in the first mechanism. The he-radical on the polymer chah attaches to another natural rubber chah at the double bond, thereby developing a new cross linkage between the chah (Grattan 1978). In this case there is an increase in the cross-link density of the material, resuiting in a hardening and embrittiement of the rubber. As the matenal becomes harder, random cracking patterns will develop. This will expose new rubber to molecular oxygen and perpetuate the degradation process.
Free-radicals may also react with other fiee-radicds to create stable products (Figure
3 -9).
Figure 3.8. Mechanism for Photo-Oxidation Which Result in Cross-linking.
CH3 I CH3I -CH2-C=CH-CH- -CH2-C-CH=CH- - O fiee-radical fiee-radical (Figure 3.8 Continued)
CH; CH3 I I
CH; I -CHrC-CH- CH2- 1 -CH=CH-C-CH2- 1 CH3 chah linkage
Figure 3.9 Production of Stable Products fiom Two Free-Radicals
CH; CH3 I I -CH-C-CH=CH- + -CH-C-CH=CH- I I O O 1 I O* O-
CH; I -CH2-C-CH=CH- 1 O I O I -CH2-C-CH=CH- 1 CH3 stable product
The second type of degradation, commonly found in vulcanized natural rubber museum objects is the result of ozone aaack (Figure 3.10). Ozone, being more corrosive then molecular oxygen, will attack the polymer directly, at the carbon-carbon double bond. The ozone molecule wvill attach itself to the double bond creating a C203ring.
Chain scission will occur, resulting in products containing carbonyl groups. Ozone degradation of vulcanized natural rubber exhibits a very specific cracking pattern which usudly only develop if the rubber is under mess. A linear cracking pattern will form perpendicular to the direction of the stress or elongation. If the matenal is not under stress, it will develop a hard surface layer while the rest of the rubber retains its original physical properties.
Figure 3.10 Ozone Attack of Natural Rubber
cis- l ,l-poly isoprene
CH?, C-O H' H'
+ O ther species which rnay be hroperoxides or peroxides
The third type of degradation is related to the presence of sulfur in vulcanized natural rubber objects. Three problems rnay arise nom the presence of sulfur. The first cornes fiom the fact that the vdcanUation process does not gop when the Milcanizing temperature is reduced; the process wiil continue slowly at ambient temperature
(Loadman 1991). This will lead to the development of more and more cross-linkages, which will significantly alter the physical properties of the materiai. It will become harder as it ages.
The sulfûr cross-linkages developed through the vulcanization process may be formed with monosulfide or polysulfide linkages, as mentioned before. These sulfur cross-linkages will cause problems for artifacts which are stored or displayed under stress, for example, when a tire is innated or an object is stretched from its original shape.
The sulfur cross-linkages cm and will break when under stress. The polysulfide cross- linkages are more likely to break than the monosuifide cross-linkages because a carbon- sulfur bond has greater strength than a sulfür-sulfùr bond. When the cross-linkages break, the bond will re-form either at the original site, or Merdown the polymer chain in such a way as to relieve the stress on the object. This is known as "relaxation" or
"slippage" of the polymer. The slippage of many bonds will result in the irreversible de formation of the obj ect into its stretched shape (Loadman 199 1).
Oxygen will also interact with the sulfur in vulcanized naturai rubber. This is a particular problem when the concentration of sulh used in the formulation is relatively hi@. for example in ebonite artifacts. The excess of sulfur will migrate to the surface and the reaction of sulfur and oxygen will result in the production of sulfuric acid
(Loadman 1994). The sulfuric acid will ultimately cause streaking through acid attack of the surface (Stevenson 199 1).
The fourth type of degradation cornes from the presence of metal around vulcanized naturai rubber. Some metals, particulariy copper and manganese, catalyze the degradation reactions of nibber. This phenornenon, generally termed "metal poisoning", is mon active with compounds which have a high solubiiity in rubber. For example, copper resinate is more soluble than copper sdfide and therefore causes a more accelerated rate of degradation (McCord and Daniels 1988). Metal poisonhg causes an increase in brittieness of the rubber and leads to depolymerïzation (McCord and Daniels
1988). 1. PREVIOUS RESEARCH
Al1 the materials found in museum collections are of concern to both conservators and consemation scientists. Polymers in general pose some of the most dficult questions regarding degradation and evennial conservation. Below is a general sumrnq of research into the degradation mechanisms in polymenc materials and possible preventive measures. Problems associated with vulcanized natural rubber are discussed in this chapter to put the present snidy into context.
4.1 Previous Research: Polymeric Materials
There is limited understanding of polymer chernistry in the field of art conservation. There has been an attempt to introduce polymer chemistry to the conservation community through summary articles giving basic information on polymerization techniques, the chemical and physical properties of polymen and the general vocabulary necessary to discuss the topic (Blank 1990; Tement 1988; Baker
1995,). There are also general sources for the identification of polymers (Coxon 1993;
Blank 1990) and the theory of polyrnenc degradation in specific situations (Wiles 1993).
Conservation research into polymers can generally be divided into three categones: chemical and physical degradation initiated from the object itsel f, chemical and physical degradation initiated from external conditions, and preventive conservation of polyrnenc objects. These categories will be discussed in this section
Degradation caused by inherent problems in the polymer has been an area of research for conservation scientists. One article written by D. Grattan of the Canadian
Conservation Institute (CCI) in Ottawa, Ontario, thoroughly describes oxidative degradation of organic materials in conservation (Grattan 1978). Grattan gives a good introduction to the types of materids, which oxidative degradation will apply to, dong
with the symptoms used to recognize oxidation and the problems that these symptoms
will cause over time (Gram 1978). The article describes in some detail the chemistry of
oxidation, using polypropylene, natural rubber, proteins and cellulose as examples of
polyrners that undergo oxidation (Gratta. 1978). In addition to this publication being a
summary article, it also discusses the usefulness of analytical instrumentation, such as,
Fourier-û-ansform infitared spectroscopy and chemiluminescence (a phenomenon in
which a chemical reaction produces an excited species, which emits light upon its rem
to ground state), for the evduation of degraded materials (Grattan 1978). Some
preventive mesures are dso discussed.
The degradation of the cellulose esters, cellulose acetate and cellulose nitrate, has
been of particular concem to the art conservation community. These materiais are
unstable and they have been the fiat and most obvious semi-synthetic matenais to begin
de,mding. There have been several studies on the deterioration of cellulose acetate and
cellulose nitrate film bases, but one relatively comprehensive study was performed by the
Image Permanence Institute of Rochester, New York, USA (Adelstein, et al. 1991). Film
bases of several manufacturers were studied under conditions of variable temperature and relative humidity after different penods of accelerated aging. The intrinsic viscosity of the base polper, tensile properties, acidity, emuision wet strength, emulsion rnelting point and emulsion flow were ail measured at each time interval of aging. The Arrhenius equation was used for the data obtained and extrapolations were made in order to predict the life span of each type of film base (Adelstein, et al. 1991). Cornparisons were made betsveen long-term stability in various environmentai conditions (Adelstein, et al. 199 1).
This study made several conclusions: first, the film base stability can be evaluated by the tende stress at break of the Nm base; second the chernical stability of celiulose acetate and cellulose nitrate fi bases are similar; Wy,the beneficial effects of low relative humidity and low temperature storage a~ additive.
Conservators and conse~ationscientists at the Tate Gallery in London, Engiand have been concerned about the condition and longevity of cellulose acetate sculptures by
Naurn Gabo. The sculptures have exhibited warping, midl oily droplets on the surface, cracking, an acetic acid odor and delarnination of the cellulose acetate sheets (Pullen and
Heuman 1988). The severe degradation of these sculptures prompted scientists to do accelerated aging tests on cellulose acetate sheets, which were obtained fiom the artist's studio. The scientists attempted to simulate the conditions in which the Gabo sculptures, in the Tate collection, had been stored. Samples were aiso exposed to acidic vapors and high relative hurnidity, to compare the rates of degradation. It was determined that the oily droplets were plasticizen which had migrated to the surface. This migration of plasticizer was always followed by other forms of detenoration, such as cracking and color change; however, the specific reason for this migration was not determined. This research also showed that the rate of degradation of cellulose acetate increases in the presence of acetic acid vapor- Since acetic acid is a byproduct of cellulose acetate degradation, this study showed the importance of proper ventilation when storing and exhibiting cellulose acetate objects (Pullen and Heurnan 1988). A similar snidy of cellulose acetate film degradation was done through the collaboration of Manchester
Polytechnic and the Manchester Museum, at the University of Manchester. The authors proposed a possible mechanism, which consisted of the removal of an acetate group fiom the cellulose acetate molecule. It was found that the acetate group combined with a water molecde to create acetic acid vapor, which has been observed as a byproduct of cellulose
acetate degradahon in the Nam Gabo sculpture mentioned above (Edge. et al. 1988).
Cellulose nitrate has aiso been the subject of much examination. It has been
found to be very unstable, especially when used in thin films. Accelerated aging tests of
cellulose nitrate were performed through the collaborative efforts of the University of
Strathclyde and the National Museums of Scotland. The presence of trace levels of
sulfates in the material, most likely lefi fkom the manufachuing process, was linked to
eventual degradation of the matenal. Measuring these trace levels of sdates was
proposed as a possible method for predicting the degradation rate of cellulose nitrate
(Stewart, et al. 1996).
ffiowledge of the additives used in polymer production is essential to
understanding how these additives may prevent or contribute to a polymer's degradation.
S. Williams at CC1 did a comprehensive study, which looked into how the additives, used
in plastics, affect the life span of the materiai. Any additive put into a mixture with a
polymer alters the chemical and physical properties of the resulting material. Relatively
recent advances in the polymer industry have given manufactures the ability to use
additives to create very specific matenals, for example ones that can endure harsh
environments. These additives cm fall into four categories, plasticizers, stabilizers.
processing aids, and end-use modifiers. It is important to know what these additives do
in order to understand the resulting material and its limitations (Williams 1993).
The degradation of polymeric materials due to extemal conditions is the second category of research typically pursued by conservation scientists. Atmosphenc polluüints are one type of extemai condition that has been addressed. There are several categories of pollutant type, but those that are of concem for polymes, both natural and synthetic, are oxides of suifur, oxides of nitrogen and particulate matter (Cook 1976). Sulfur compounds enter the atmosphere through non-ferrous metal smelting, petro leum refining, and fuel burning. SuLfur dioxide itself is known to cause deterioration in some polymers by reacting directiy with saturated and unsaturated polymers in the presence of ultraviolet light (Cook 1976). The conversion of sulfur dioxide into suifuric acid is also of concem.
Sulfuric acid, once in the atmosphere, may be deposited on objects though condensation or rain water. The presence of acidic residue on almost any polymer will accelerate its rate of deterioration.
Nitrogen dioxide is found nahlrally in the atmosphere but its levels have been increased by man-made agents, such as automobile exhaust. Reaction with nitrogen dioxide can cause chain scissions to occur in many polymeric materiais. Chain scissions result in a reduction of the molecular weight of the polymer and, therefore, a change in its physical and mechanicd properties (Cook 1976). Nitrogen dioxide is converted into ozone when it is in the presence of sunlight. Ozone causes a similar eflect in that it may attack unsaturated polymers at the carbon, carbon double bond, causing chain scissions
(Cook 1976).
Particulate matter may cause damage to objects both directly and indirectly.
Particles that deposit themselves on the surface of an object may cause mechanical damage due to abrasion resulting in the irreversible loss of material. If particulate matter is continually deposited on the surface of an object, cleaning that surface is an inevitable necessity (Cook 1976). Frequent cleaning could cause Ieaching of important additives in the polymer leading to mechanical damage through abrasion and chemical damage.
Either one of these will accelerate the eventual detenoration of the object. Another area of concem, with respect to degradation due to extemal conditions, is
conservator's fiequent use of solvents, as diluents for adhesives, coatings, inpainting
media and cleaning solutions. One study examines the efTect of ten different solvents,
commonly used by conservators, on polymenc materials (Sale 1988). Four dinerent
polymer bases were chosen as being representative of many museum artifacts: poly(methy1 methacrylate), poly(viny1 chioride), polyethylene and naturai rubber (Sale
1988). This study measured the absorption of or extraction by solvents through changes in molecular weight and dimensions of the test samples; weight gain and increase in dimension indicated absorption of the solvents and weight loss and decrease in dimension indicated extraction of material from the samples (Sale 1988). Changes in physical appearance and surface texture were also recorded. It was possible that some of the solutions tests had left residues on the surface of the samples (Sale 1988). Al1 of the solvents af5ected the polymenc samples to varying degrees. The solvents tested were not found to be safe enough for use on museum artifacts (Sale 1988). This poses a difficult problem, particularly for the cataloging and organization of a collection, because solvents are frequently used to apply labels and identification numbers to artifacts.
Another study focuses on the problem of labeling artifacts in a collection. Most museums label their artifacts immediately upon their arriva1 in the collection. The standard process of labeling is to apply an isoiation layer of varnish ont0 the object, then the registration nurnber, and hally a protective layer of varnish. The organic solvents used to prepare the vamish may dissolve or swell the polymer substrate. Even if this is not the case, the solvent may still cause stress cracking or crazuig, particularly on hard and brittle polymen (Fenn 1993). inks and dyes typically used for labeling may also cause damage. Depending on the subsirate and dye used, the dye may chemicaily bond to the substrate making the label irreversible. Dyes may aiso catdyze photo-degradation
of the substrate, because of the photosensitivity of the dye (Fenn 1993). Labelhg
anifacts is essential to the orgdtion of any rnuseum collection, but it seems that
indirect labeling is the safest method for plastic amfacts. Labeling the storage container
or mount for an artifact would be acceptable. When this is not possible, the use of Teflon
tape or other rags made of chemicaily resistant matenal is preferred (Fenn 1993).
The third area of research is preventive conservation for polymers. .4 number of
articles have been men about an oxygen-absorbing material named ~~eless'~<.'
AgeIessTM is a product rhat contains finely divided iron; it scavenges molecular oxygen
fÎom the atmosphere (Shashoua and Thomsen 1993): It therefore absorbs most of the
oxygen in an enclosed environment. It has been examined as a possible environment for polymeric materials. Since polyrners degrade prirnarily through oxidation reactions it is
proposed that AgelessTL*be used to create an oxygen fiee environment for storage and exhibition of polymenc rnateds. It was deteimùied that oxidation of the material would be limited if AgelessTMcould decrease the oxygen level inside the enclosure below the amount consurned by a deteriorathg object (Gram 1994).
Efforts have also been made to find a suitable polymer stabilizer for use widi conservation materials. The stabilizer would extend the useful lifetime of polymers being used as conservation treatments. An overview of the types of stabilizers cornmercially available and their stabilizing mechanisms is available as sumrnarîes in the conservation literature (Williams 1993; de la Rie 1998). The concem with using any additive with a conservation material, is whether or not the additive will have adverse effects on the end product. In other words, how will the additive change the materid's visible appearance
' AgeIessrm is a mde name of the Mitsubishi Gas Chernical Company Inc. of Japan. and aging ability? This question has been researched to some extent Antioxidants, one type of stabilizer, have been studied to determine ifthey will discolor in the presence of niaogen containing amiospheric pollutants (NOa (Gleeson and Loadman 1996). This mrdy tested 21 different antioxidants for their resistance to color change in the presence of NO, fumes. Those antioxidants found to discolor were then examined uing gas chromatography-mass spectrometry (GC-MS), to determine the chernical change responsible for the discoloration. The oxides of nitrogen were folmd to introduce into the antioxidant structure either nitro groups through electrophilic substitution and or carbonyl aoups through oxidation of phenols. These functional groups reflect light in the yellow C region of the electrornagnetic spectnun, accounting for its yellow color (Gleeson and
Loadman 1996). This study showed the importance of choosing an antidegradant that would not do more harm than good.
There has also been research into non-intrusive ways of evaluating the extent of polyner degradation. The dye m-cresolsulphonephthalein (cresol purple) has been shom to be a useful indicator for the advanced degradation of celluLose nitrate artifacts
(km1996). This dye is sensitive to oxides of nitrogen, which are produced through the degradation of cellulose nitrate. The dye changes color fiom yellow to red when in the presence of nitrogen oxide gases. Once the artifact is off-gassing it poses a significant danger to other artifacts because of the corrosive nature of nitrogen oxide gases. The indicator, therefore, will alert conservators ro the off-gassing artifact, which may be rernoved and isolated to protect the rest of the collection (Fenn 1996). 4.2 Problems Associated with Natural Rubber Arufacts
The relatively fast rates of chemical and physicai degradation of natural rubber have forced conservators to treat naniral rubber artifacts. Unfortunately, the conservation community is far from having any widely accepted conclusions for dealing with naniral rubber or other polymeric materiais. The following paragraphs explain some techniques conservators have used to conserve naturd rubber artifacts.
As mentioned in Chapter 2, natinal rubber was fiequently used as a waterproofmg agent. A 20"-cenniry rubberized raincoat in the collection of the Textile Conservation
Centre, Surrey, UK,was found to be degradhg severely only five years after acquisition.
Nadrubber and neoprene (polychloroprene) were both used as waterproofing agents on the raincoat. The rubbenzed lining (made of neoprene) was hardened and beginning to crack, while the rubberized collar (made of natural rubber) still remained sornewhat flexible (Stoughton-Harris 1993). The relatively good preservation of the natural mbber ma. be due to the presence of carbon black; the nanirai rubber was filled with carbon black. which absorbs Iight, thereby hindering the process of photo-degradation, while the light-colored neoprene lining was not and therefore it does not have the same light absorbing ability. A wet cleaning treatment was chosen for the a.rtifact because of its ability to remove dirt, reduce the acidity of the textile and plasticize the hardened neoprene (Stoughton-Harris 1993). Loss of antidegradents due to the wet cleaning process was mentioned briefly in the article; however, there should dso be concem for the loss of plasticizer and low molecular weight neoprene fragments, since wet cleaning cm leach important additives. Wet cleaning may, in fact, accelerate the deterioration rate of the neoprene and nadrubber. Long-term effects of this treatment will be monitored by the Conservation Textile Centre staff (Stoughton-Harris 1993). Hard rubber (ebonite or vulcanite) objects pose their own set of problems for
conservators. Migration of sdfur to the naface of these objects is of panicdar concem.
The A. W. McCurdy Developing Tank exemplifies this problem very rvell (Stevenson
1993). The surface of this hard rubber tank was covered with brownish droplets, which
were discovered to be sulfunc acid having a pH of 0.5 (Stevenson 1993). Presurnably, escess sulfur migrates to the surface where it combines with water to create sulfunc acid.
Attempted removal of the acid is a problem in and of itself since it may cause streatcing; yet leaving the acid on the surface will Merdeteriorate the object. I\ treatment was devised for removal of the acid where severd solvents were used in succession
(Stevenson 1993). This process did remove the sdfunc acid but may have removed other surface materiai as well and may have increased the likelihood of Mer sulf'ur migration.
Natural rubber artifacts are also found in archaeological sites. An example of this is the discovery of three waterlogged mbber shoes, found during the excavation of the
Oficee' Latrine at Artillery Park, in Quebec, Canada in a stratigraphie layer dating to before 1871. Al1 three shoes appeared to be made of vulcanized natural mbber. One of the shoes exhibited soft and tacky areas as well as hard, brinle areas. The other nvo shoes exhibited an overall hardening and brittleness. Tests done to evaluate the effect of slow drying on the shoes determined that the water was held in the mbber creating a colloidal effect. Approximatel y 9% linear shrinkage occurred on the test specimens, which were dned. Instead of nsking darnage to the artifacts by dryhg hem, they were stored under water, in a tank of de-ionized water from which the oxygen had been removed, until options for treatment could be evaluated. The tank was protected fiorn light exposure by covering it with a black cloth and plastic. There are some drawbacks to underwater storage: it requires regular maintenance to prevent the growth of alga, and it renden examination of the amfacts difficuit and exhibition almost impossible. In the mamient evennially decided upon, the shoes were slowly dried out, away fiom light exposure. It was thought that the dried dimensions would be the most historicaily accurate. Areas which were soft and tacky became very sticky upon drying. Armor
NIDf was used as a consolidant on the sticky areas of one shoe in order to seal the surface. The nvo remaining shoes did not receive treatment with Armor AllTM because the long-terni eEects of the treatment are not known (ClaW 1982).
Rubber artifacts can exhibit multiple types of degradation at the sarne the. In this case the conservator must detemine what action to take, if any. A good example of this problem tvas a pair of natural rubber bathing shoes treated by Susan Maltby at CCI.
The shoes exhibi ted areas of extreme brittleness and cracking, areas that had become so fi and üicky, and areas that remained elastic and pliable. The shoes were deformed and sticking to each other in many places (Maltby 1988). They were reshaped using heated sandbags (55-60°C) to soften the rubber. Ripstop nylon was used to cover the sandbags wherever the. might corne into contact with the tacky areas on the shoe. The heating process most likely removed the crystallinity of the rubber, restoring some of iü flesibility (Baker 1995b). Areas of loss were filled with toned Japanese tissue to give continuity to the shoes (Maltby 1988). During treatment, a previously non-degraded area began showing active signs of degradation, in the form of blisters. An unsuccessfbl atternpt was made to stop the degradation through application of the antioxidant, Irganox
1076nf. It became necessary to store the shoes in an inert environment; in this case, nitrogen was used (Maltby 1988). 4.3 Previous Research: NaturaI Rubber Matends
Chemists in the mbber industry and conservation scientists pumie research uith
hdamentally different goals. The main goal in the rubber industry is to make new
materials more stable, and with the desired physical and chernical properties. The goal of
conservation science is to stabiiize deteriorathg polymen. For this reason, a relatively
small amount of the technical literature is directly usefd for the conservation scientin.
There are a few exceptions, which could prove helpful.
Most of the conservation science research dealing with natuml rubber rnuseum
artifacts to date has been a discussion of their historic significance, (Allington 1988;
Kaminitz 1988; Hills 1971 ; Schidrowitz and Dawson 1952; Stern 1967; Loadman 1995)
summaries of degradation mechanisms, (Loadman 1993; McCord and Daniels 1988;
Gram 1978) and case studies of naturd rubber artifacts, which have been treated
(Shashoua and Thomsen 1993; Maltby 1988; Clavir 1982; Stoughton-Harris 1993;
Stevenson 1993). There bas been, however, some research done on the degradation and stabilization of naturai rubber (McCord and Daniels 1988; Shashoua and Oddy 1990;
Grartan 1978; Shashoua and Thornsen 1993; Grattan 1993; Grattan and Gilberg 1994;
Baker 1995b; Baker 1995~;Williams 1993).
One of the most thorough review articles dealing with natural rubber artifacts is by M.J.R. Loadman of the Malaysia Rubber Producers; Research Association (Loadman
1993). This article focuses on the development of the rubber industry by Europeans, as well as discussing some techniques for analyzhg natural rubber and its additives. For identification, either pyrolysis infrared spectroscopy or pyrolysis gas chromatography would be usefùi (Loadman 1993). The article dso discusses the use of scanning electron microscopy and electron microprobe for evaluation of morphological changes and inorganic elements present in the material (Loadman 1993). The most useful part of this
article is the description of the types of suface appeafatlce changes that rnay occur as the
rubber degrades and their probable cause (Loadman 1993). The article also gives a
similar description of the types of degradation natural rubber will undergo and descriptions of the visible changes in appearance associated with a given mechanism of degradation (Loadman 1993).
Research has been published giving recommendations for the storage conditions of natural rubber artifacts. These recomrnendations include storage at low temperatures
(below fkeezing), little to no light exposure, elimination of al1 mechanical stress and removal of al1 ozone generating equipment (photocopien, air cleanen, etc.) from storage areas (McCord and Daniels 1988). Reducing the level of oxygen in the storage area would also reduce the rate of deterioration. This may be done by using a nitrogen atrnosphere (McCord and Daniels 19881, although this is usually an expensive and therefore impractical option.
In theory, a protective bmier on the surface of artifacts would decrease the chance of oxygen anack on the base polymer- Conservators have, therefore, thought that the addition of a surface coating may be useful for inhibiting oxidative degradation of natural rubber. Four plasticizers (di-isodecyl adipate, dioctyl adipate, di-isononyl phthalate and di-isodecyl phthalate) and four commercially available surface coatings
(Dunlop Tyre Protection Paint, Armor AilM, a Carboxymethyl Chitosan (NOCC) and
BM Protective Coating) have been evaluated in an attempt to find a treatment that would be reversible and would inhibit oxidative degradation without changing the visible appearance or tensile strength of a natural rubber object (Shashoua and Oddy 1990).
Two methods of accelerated aging were used. The fint was light aging using a Miscroscal light fastness tester with an MBTL 500 Watt daylight specmim bdb and the
second was heat aging at 45OC (Shashoua and Oddy 1990). The plasticizers were not
found to be useful because they drarnatically softened the rubber as it aged. 'Ihe
plasticizers also appeared to be leached out fiom the accelerated aging process (Shashoua and Oddy 1990). The dace coatings, on the other hand, showed varying degrees of success. Ail of the coatings exhibited some change in appearance. The Dunlop Tyre
Protection Paint produced a brown coating which obscured the surface. Armor Allm produced a slight sheen to the surface, as well as, imparting a crepe-like texture afier aging. NOCC developed a glossy, inflexible film and BM Protective Coating produced a white, inflexible film (Shashoua and Oddy 1990). The only coating that exhibited a Iess than 10% loss in breaking strength was Armor AIlY It showed only 3.9% loss in breaking strength afier accelerated aging (Shashoua and Oddy 1990). The intlexible film produced by NOCC cracked and exposed the nibber after a relativeiy short aging penod
(14-20 days). Cracks began to form on the exposed rubber 50-75 days after the protective film was cracked. Dunlop Tyre Protection Paint &ordeci some protection to the rubber, but cracks and bloom did forrn after 100-1 10 days. The Amor Allm and BM
Protective Coatings were both successful in preventing bloom and crack formation on the treated rubber samples (Shashoua and Oddy 1990). Unformnately, the plasticizers and surface coatings tested did not show complete revenibility, with the exception of NOCC, which proved to be completely revenible in water. Armor AHTM W~Snot reversible with any of the solvents tested (Shashoua and Oddy 1990). Even though this study did not achieve its goal, it was usehl for its evaluation of commerciaily available products, which may have applications for extrerne conservation problems. Some research has been done into the use of antioxidants applied to museum artifacts as a stabilizing tool for naniral rubber artifacts (Grattan 1987). For example,
Irganox 1076m broduced by Ciba-Geigy, Ltd.) was used at varying concentrations in acetone. The naturai nibber samples were coated with the antioxidant and aged in darkness at X°C, 50°C, 65°C and 85°C. The antioxidant was found to reduce the oxidation rate considerably when used in 1% wlv concentration (Grattan 1987).
Unfortunately, the use of solvents to apply the antioxidant can be dangerous and may darnage rubber that has softened with age (Grattan 1988).
Research has also been done to investigate the use of Agelessm, mentioned earlier, to create an oxygen-free environment for natual rubber artifacts (Shashoua and
Thomsen 1993). The materials used for the enclosure are of particdar concem. One study examined enclosure materials using five critena: stability, impermeable to molecular oxygen, mechanicaliy safe, transparent to facilitate visual study of the artifact and, easily resealable to facilitate physical examination of the artifact (Shashoua and
Thornsen 1993). Accelerated aging tests were done to determine any difference in the rate of deterioration between rubber in the presence of oxygen and in the oxygen- depleted environment. The rubber aged in the presence of oxygen showed more severe cracking than the rubber enclosed with AgelessTM(Shashoua and Thomsen 1993). Use of
AgeIessTMhas proved to be a successful way of depleting oxygen From an enclosed area, although it does have its faults. AgelessTMwiI1 only work if it is a more successful oxygen scavenger than the object itself. The oxygen mut be more likely to react with the iron in the Agelessm sachet than with the rubber in its oxidizing reaction (Grattan
1993). The leak rate of oxygen through the walls of the enclosure, which will be different for each type of barrier, must be taken into account when determinhg the volume of AgelessSM matenal needed in the enclosure (Grattan 1993). The duation of
storage in a particular enclosure must also be considered. Agelessm will scavenge
oxygen, but the reaction is temiinal (Shashoua and Thomsen 1993); therefore, then! is a
finite amount of oxygen that cm be scavenged and a finite amount of time that Ageless"
will remain useful. Al1 of these problems need to be considered and resolved before an
artifact is stored in an enclosure with AgelessTMsachets.
Research is also being pursued into the oxidative degradation and crystallinity of
natural rubber (Baker 1995b; Baker 1995~).Naturai rubber samples fiom both ancient
and modem sources have been evaiuated. It was found that low temperature storage
(recommended for natural rubber artifacts) increases the degree of crystallinity in the
material. Fourier-transform uifrared spectroscopy and differential scanning calorimetry were used to evaluate the extent of oxidation and crystallinity of naturd rubber. It was fond that al1 of the rubber samples crynallized and oxidized over tirne (Baker 199jb).
Oxidation of natural rubber was discussed in the previous chapter. Crystallization, a physical change, is a phenomenon in which polymer chah begin to fold in a regular marner. These chahs are incorporated into the growth of crystals (Baker 199%).
Crystallization does occur at room temperature, although the crystallization rate increases as the temperature decreases to a maximum at around -25°C; and it reduces to a minimum around 40°C (Baker 1995b). The size and shape of the crystals are dependent on the crystallization temperature. Thin crystals are formed at low temperatures while thick crystals are formed at higher temperatures (Baker 1995b).
One of the ancient samples (Mexican nibber fiom the collection at the Amencan
Museum of Natural History in New York City) and rubber obtained fiom an Apollo spacesuit (in the collection at the National Air and Space Museum in Washington, DC) still retain rubber-like properties, for example a glass transition temperature even though the materials appear hard and brittie (Baker 199%). Oxidation is irrevenible; however, it
\vas observed that crynallization couid be removed by heating (Baker 1995~).fis may enable some of the physicd properties of unaged rubber to be regained, although, the process of heating must be done with care to ensure that there are no adverse effects such as the evaporation of additives (Baker 1995~).
Research has been done on the deterioration of natural rubber through attack of microorganisms (Williams 1982). This study found Penicillin variabile to be of particular concern for both natural and synthetic polyisoprene polymers. The organism is present in soil, which rnay pose problems for nahual rubber in archaeologicai sites. The rubber samples tested had a 15% reduction in molecular weight, dthough no changes were detected using infrared spectroscopy and x-ray photoelecnon spectroscopy
(Williams 1982). This sugges~sthat mic~oorganismsattack the polymer fiom the chah end, although more research must be done to determine a definite mechanism of attack
(Williams 1982). 5. METHODOLOGY
This chapter will discuss the techniques that have been used for chemicd and physical analysis of the naturally and artificially aged wlcanized nahiral rubber used in this study. A general explanation of each technique wiiI be given first, followed by a more specific explanation of each attachment Also outlined will be the reasons why each technique waç chosen as well as how the technique has been used by other conservators and conservation scientists.
5.1 Fourier-Transfomi Infnired Spectroscopy (FTIR)
FTIE2 uses infrared radiation to evaluate a sample. AU experiments perfonned in this mdy used infrared radiation in the mid-infrared region (4,000 cm-'to 400 cm").
There are, however, a number of applications for near-infrared (12,800 cm-' to 4,000 cm-') radiation and far-infrared (400 cm*' to 10 cm-') radiation. For any of these regions, the interaction between infiared radiation and the sample is fiindamentally the same.
Each molecule has a naturd fiequency at which it vibrates. For a molecule to be infiarecl active it must undergo a change in dipole moment as a resdt of interacting with infrared radiation. Many molecules will undergo a change in dipole moment but some will not.
Any molecule with a high degree of symmetry such as homonuclear species (e.g. O*)will not undergo a change in dipole moment as a result of vibrational motion. When the natural vibrational fiequency of the molecule is the same as the frequency of infrared radiation behg applied to the sample, there is a net transfer of energy resuiting in the absorption of the irhred radiation (Skoog and Leary 1992). There are two main types of molecdar vibrations: bending and stretching.
Graphic depictions of ail types of molecula. vibrations are located in Figure 5.1. A bending motion consists of a change in bond angle while a stretching motion is characterized by a change in bond length. There are four types of bending motions
(scissoring, rocking, wagging and twisting) and two types of stretching motions
(symmetric and asymmetric) (Skoog and Leary 1992).
Figure 5.1 Types of Molecular Vibrations (Note: O indicates motion toward the reader and O indicates motion away from the reader.) (Skoog and Leary 1992)
In-plane rocking In-plane scissoring
Out-of plane wagging Out-of -plane twisting
a) Bending Vibrations (Figure 5.1 Continued)
symmebic asymmetric
6) Stretching Vibrations
The absorption of hfkired radiation by the sample at a specific fiequency resuits in a peak on the infi.ared spectrum at that frequency. The infraed spectrurn is produced through proprietary software. A schematic diagram of the Nicolet 800 Fourier-transfomi infked spectrometer is shown in Figure 5.2. This is the main spectrometer used for this study; however for the attenuated total reflectance-FTIR with Omni-Sampler attachment experiments a Nicolet Avatar System 360 spectrometer was used. There are many attachments that can be used for FTIR experiments. These attachments dlow the IR beam to interact with the sample in difTerent ways and therefore obtain varied information about the sample.
FTIR instrumentation has been used fiequently by conservation scientists. The wide variety of materials that cm be analyzed using this instnunentation has made it a useful tool for answering several conservation research questions. In one study, FTIR was used to evaluate changes occurring in cellulose nitrate as a result of accelerated aging
(Stewart, et al. 1996). Another study shows the use of FTIR to determine degradation mechanisms in unsized and shed paper (Calvini 1996). Figure 5.2 Schematic Diagrarn of Nicolet 800 Fouier-Tdonn Infiared Spectrometer (Nicolet Analytical Instruments 1989)
5.1.1 Attenuated Total Reflectance-Microscopy-Fourier-TransformInfiared
Spectroscopy (Am-Microscopy-FTIR)
The ATR-microscopy objective works in the same way as a standard ATR.
Figure 5.3 shows the general diagram of an ATR attachment. The ATR crystal must be
of higher rehctive index than the sample and the sample dace must be reflective to
infked radiation. If this is the case the infhred beam will travel through the crystal and reflect off the surface of the sample. As the infrared beam reflects off the sample it is actuaily penetrating Uito the surface and the absorption of infhred radiation takes place.
The ATR-microscopy objective is a single bounce system, therefore, the in.6-ared beam will interact with the sample only once before moving on to the detector (ürban 1996).
The ATR attachment was placed into the hfked objective (of the Nicolet Nic-Plan
microscope) show in Figure 5.4.
ATR-microscopy-FTIR was chosen as a possible diagnostic tool for two reasons.
The first was the ability of this method to evaluate the surface of material; the oxidative degradation reactions mentioned in Chapter 3 begin at the surface of the matenal. The second reason was its ability to evaluate very smaii samples; smaii sample size is essential for evaluation of museum artifacts because of the ethicd problems associated with removal of material fiom a work of histonc and artistic significance.
Figure 5.3 Generai Schematic Diagram of Attenuated Totai Reflectance Sarnpling System
a pplied pressure
sample /
IR beam
/ ATR crystal evanescent wave
This type of ATR has been used by conservation scientists to evaluate many different materids. ATR-FTIR instrumentation was used by S. Simon and CO-authorsto determine what effect surfactants have on the dace of marble (Simon, et al. 1992). It has dso been used to evduate weathered polymer nIms (Carter, et al. 1989).
Figure 5.4 Innared Objective for Nicolet Nic-Plan Microscope (Nicolet Analytical Instruments 1990)
1OX gbss objective
5.1.2 Attenuated Total Reflectmce-Fourier Transform Mared Spectroscopy with the
Avatar OMM-Sampler Attachment (Avatar OMNI-Sampler)
The Avatar OMM-Sampler is also a single bounce ATR and works in the same way as the ATR-microscopy objective. It was chosen as a possible diagnostic tool for the same reasons the ATR-microscopy-FTIR instrumentation was chosen; however, it was useful in the evaluation of vulcaLLized natural rubber. Figure 5.5 shows a general diagram of the Avatar Omni-Sampler attachment.
Figure 5.5 Diagram of ATR-FTIR with Omni-Sampler Attachment (Nicolet Analytical Instruments 1998)
pressure tower
sample
The ATR crystal in this attachment has a sampling point 2 mm in diameter at the top of the crystal. This satisfies the need for a smaiI sample size when analyzing samples f?om museum artifacts. The pressure tower on this attachent works using a 'slip-clutch' mechanism which ailows for pressure to be exerted on the sample. The mechanism will be set a specifïc amount of pressure, after which the mechanism can no longer be tightened. The level of pressure this attachment cm reach without damaging the ATR crystal is higher than the level that can be reached using the ATR-mimscopy-FTIR instrumentation.
According to the research done by this author, there has been no published work referencing the use of the Avatar Omni-Sampler attachent to evaluate conservation materials or artifacts-
5.1.3 Photoacoustic-Fourier-Transform Infrared Spectroscopy (PAS-FTR)
The PAS-FTIR attachment works differedy fiom ail other FTR attachments discussed in this chapter. Figure 5.6 depicts a schematic diagram of a PAS-FTIR attachent. The sample chamber is filled with an inert gas (usually helium). The IR barn is focused on to the sample using optics which direct the beam through the IR transparent window above the sample and on to the sarnple. As the IR beam interacts with the sample, the latter will warm up due to the absorption of &ed radiation. The infked radiation will penetrate into the sample, where it is converted to heat. The heat fiom the inner layers of the sample will diffuse toward the top (cooler) surface of the sample in a movement known as a thermal wave. When the thermal wave reaches the top of the sample it will =fer the heat to the inert gas which fills the chamber, causing the gas to expand. The expansion of the gas causes a pressure wave which propagates through the gas until being detected by the microphone. The pressure wave is then himed into an electrical signal, which is ultimately tumed into an innared spectm (Smith
1996; McC leiland, et al 1992).
The degree of contact between the sample and the ATR crystai raised concens about the usefulness of these techniques for severely degraded rubber samples (e.g. they harden). It was thought that PAS-FTIR would be particularly useful for samples which
had becorne hard and brittle with age, because it does not require contact to be made
between the objective and the sample.
Figure 5.6 Schematic Diagram of Photoacoustic-FI1R (Harrick Scientific Corporation 1987)
window inert gas \ incident radiation
removable sample \ sample pan microphone
PAS-FTIR has been used to evaluate keratin fibers which can usually be found in ethnographie artifacts (Jurdana, et al. 1995). It has also ken used to characterize photo- oxidation occumbg in cotton cellulose (Yang and Freeman 1991), as well as, characterization of weathered polymer films (Carter, et al. 1989). 5.2 Thennogravimetry (TG)
In thermogravimetry, a mass of a sample is precisely monitored as a fimction of time or temperature. The sample is heated at a known rate fiom a known starting temperature to a known ending temperature. Any change in the mass is recorded and is usually displayed as a percent weight change as a function of time or temperature. The resulting plot is known as a thermogravimetric or thermal decomposition curve (Skoog and Leary 1992). Seven types of thermogravimetric cwes cm be produced, depending on what happens to the sample, as it is heated. Figure 5.7 shows idealized versions of these seven types of thermogravimetric curves (Brown 1988).
Figure 5.7 Main Types of Thermogravimetric Curves (Brown 1988) Curve (1) redts fiom a sample that does not undergo any decomposition, resulting in the loss of volatile products over the temperature range analyzed. Curve (2) results fÎom the rapid weight loss characteristic of drying or desorption of a component in the sample.
Curve (3) exhibits the decomposition of the sample in a single stage, over the temperature range shown. Curve (4) results fkom the multi-stage decomposition of the sample when there are stable intermediates in the decomposition mechanism. Curve (5) also redts fkom a multi-stage decomposition of the sample; however, this cwe is typical when there are no stable intermediates in the decomposition reaction. Cuve (6) shows a weight gain, as opposed to a weight los, as a result of heating. This is typical of when the sampie interacts with the surrounding atrnosphere, for example, in an oxidatioo reaction. Curve (7) generally results fiom the intedon of the sample and atmosphere to create a product which is subsequently decomposed at a higher temperature in the same heating cycle (Brown 1988).
Thermogravimetric instrumentation consists of four main components: a sensitive analyticai balance, a fumace, a purge gas system and a computer which enables instrument control, data acquisition and data display. Figure 5.8 shows a schematic diagram of a typical thermogravimetric instrument. The balance measures changes in weight as a result of heating the sample using a computer controiled fumace at a specified heating rate. The purge gas is generally nitrogen or oxygen; nitrogen is used when an inert atmosphere is desired and oxygen is used when the reactions of interest are oxidative. It is also possible to switch fiom one gas to another in the middle of an expriment if both atmospheres are desirable. When working with a material, it may be useful to evaluate the derivative therrnogravimetric (DTG) curve in order to resolve the different stages in a complex thermogravimetric curve. Some materials may appear to give a one-stage thermogravimetric curve but the derivative themogravimetric curve will exhibit multiple peaks indicating a more complex decomposition reaction than was originally expected.
Figure 5.8 Schematic Diagram of Thennogravimetry Instrumentation (Brown 1988)
electronic weig hing rnechanism r-l
recorder fumace r #' tare sample I 8 programmer \
Thennogravimetry was chosen as a possible diagnostic tool for vulcanized naturai rubber because of its ability to produce information regarding the thermal stability of the matenal. Through the application of kinetics, this technique may also provide information about the degradation tirne of the material when stored or exhibited at specific ternperatures. This information could be usefid for deteminhg standards for storage and exhibition of rubber amfacts. Thermogravimetry has been used by other conservation scientists to make lifebe predictions for materials includuig polyurethane-based recording media bhders (Baker
1995) and commercial PVC resins (Marcilla and Beltran 1996). It has also been used to determine the effect of heat on wools (Crighton and Hole 1976).
5.3 Themogravimetry-Fourier-Tmfom hhedSpectroscopy (TG-FTIR)
?hemogravimetry-Fourier-transfonn hfked spectroscopy belongs to the family of hyphenated techniques. The basic theory for the two techniques can be found in sections 5.1 and 5.2 respectively. It is a convenient combination because TG provides quantitative data while FTIR provides qualitative data. This section will, therefore, focus on how these two techniques work together. Figure 5.9 depicts a diagram of the TG-
FTIR steup.
The software (Nicolet Instruments) for this instrumentation scans the glass sarnple cell giving a spectnim for the evolved gases fiom the sample at many points as it degrades. This will provide information about how the vulcanized natural rubber sample is degrading, for example, what sections of the polymer chain are breaking off first.
This instrument was chosen as a possible diagnostic tool for vulcanized natural rubber because it is able to provide information about structurai changes which occur in the rubber as a result of accelerated aging, particuiarly, if there is a significant breakdown in the polymer backbone. A structural change in the materid would be indicated by the appearance or disappearance of a peak in the spectm
According to the research done by this author, TG-FTIR has not been used by other conservation scientists for the evaluation of conservation and artistic materials. Figure 5.9 Diagram of Thermogravimetry-Fourier-Transfomi Inn;ued Spectroscopie instrumentation (Paroli and Delgado 1994)
5.4 Scanning Electron Microscopy (SEM)
A scanning electron microscope allows one to gain morphological and topographical information about a sample. The magnification can be as little as 10X and as great as 100,000X. In this study, a scanning electron microscope was used to evaluate the morphological changes occurring in the vulcanized ~turalrubber as a result of accelerated aging; specincally, the development of cracking patterns was evaluated.
Figure 5.10 shows the schematic diagram of a typical scanning electron microscope. In this system, an electron gun is used to fom and emit an electron beam which is focused on the sample using the magnetic condenser and objectives lenses. The finai spot size of this electron beam is between 5 and 200 nm. The process of scanning is done using two pair of electronic coils located with in the objective lem. One pair of coils deflects the electron beam in the X direction and the other pair of coils deflects it in the Y direction. The electron beam is controlied by the electrical signal to each pair of coiis. The beam is scanned in a straight line across the X direction and returned to the original position before moving dom the sample. This is repeated until the whole sample is scanned in the X direction. In this way the entire dace of the sample is irradiated with the electron beam (Skoog and Leary 1992).
When the electron beam interacts with the surface of a sample backscattered electrons are produced. This occurs when the electrons corne in contact with the surface of the sample. The electrons are elastically scattered upon entering the sample. The majority of these electrons will undergo many colîisions and ultimately be excited fiom the surface of the sample. The incident electron beam usually has a diameter of Snm.
The backscattered electron beam, however, has a diameter of severai microns. The resolution which can be obtained using SEM is, in part, dependant on the diameter of the backscattered electron beam (Skoog and Leary 1992).
To create an SEM image a cathode-ray tube scans dong the X and Y directions of the sample at the same time as the incident electron beam. The output of an electron detector is used to control the intensity of the spot on the cathode-ray tube. This produces a map of the sample surface which has a one-to-one correlation between a point on the sample and a point on the cathode-ray tube display (Skoog and Leary 1992).
SEM has ken used by conservation scientists for the evaluation of many different types of materials. Conservation scientists who focus on paper and fiber chemistry have fiequently used this technique because of the somewhat limited number of andytical tools that can be used to evaluate paper One example of this is a study which discusses the adysis of modem Chinese papa (Tsai and van der Reyden 1997). SEM has also been used to detennine the morphology of modem and fossil poilen (Piicher 1968) as weU as studying the techniques of Mayau Iapidary production (Gana-Valdes 1985).
Figure 5.10 Schematic Diagram of a Scanning Electron Microscope (Skoog and Leary 1992) variable hi&-voltage electron gun power SUPP~Y
electron 1 beam - I
magnetic I condenser : m..: : ...... * lens ,... ,-.*.. . S.. *. . I .... ,.-. ... S.. I *... S...... S.. - l l...... I ..* I I I I I sczln (mag nification) coi1 controls
detector ,...
sample chamber 5.5 Mechanicd Testing System
MechiUrical testing techniques (tensile and elongation) gives information regarding the physical changes which occur in a materid as a result of accelerated aging.
This instrumentation measures the stress, strain and displacement of a material as it is stretched to the point of rupture. Changes in the tensile properties of the material cm indicate the degradation of the material, although it does not indicate what type of reaction is in progress. The drawback with this technique is that greater amounts of sarnples are required.
Mechanical testing has ken used by many conservation scientists, especially those interested in any physical property changes that may result from a consewation treatment. One study discusses the changes in tensile properties of paper before and after washing (Smith 1997). Another discusses the use of mechanical testing to evaluate the effect fluctuations in relative humidity have on modern paint films (Douglas 1996). Yet another study discusses the effect of moishue on the mechanical properties of collagen
(Mecklenburg 1988). 6.1 Surrogate Sample Formulation
Vulcanized naturai rubber surrogate samples were prepared by Alcron Rubber
Development Laboratory, Inc. Akron, Ohio, using ASTM standard D 3 184 formula 24 as
a guidehe. The formulation is outiined in Table 6.1. The mixing and vu1cani;lation
procedures coaform to ASTM standard D 3 182 with a cure temperature of 284°F and a
curing tirne of 40 minutes.
Table 6.1 Standard Formula 2A for Black Filled Vuicanized Natural Rubber
MATERIAL NAME QUANTIIY PARTS BY MASS FORMULA NUMBER
1 natural rubber 100.00 zinc oxide 5-00 Sulfirr 225 stearic acid 2.00 oil fiirnace biack 35.00 n-tert-buryl-2-benzothiazole su! fenamide 0.70 1 Total 1 144.95 1
6.2 Naturally Aged Samples
Naturally aged vulcanized natural rubber sarnples were obtained fiom artifacts in
the collection at Henry Ford Museum & Greenfiield Village. When possible, pieces of
rubber which had fallen off the object were used. If no detached pieces were available, a
sample was cut, using a scalpel, fkom an already damaged area or a portion which couid
not be seen when the artifact is exhibited. Samples were obtained fiom artifacts with
varying degrees of visible degradation. Samples taken from artifacts are listed in Table
6.2, Table 6.2 Henry Ford Museum Br Greenfield Village Artifacts Sampled for this Project
HENRY FORD iMUSEUM & GREENFELD VISIBLE SfGNS OF DEGRADATION VILLAGE ARTIFACTS 1 1880 DmCylinder Press ' severe cracking rubber L soft and tac@ 1907 Harley Davidson tire severe cracking mbkr is hard and brinle it has begun hlling off the fabnc substrate of the tire GE vacuum cleaner fine cracking rubber is hard but not very britile 1864 Gordon OscilIating Cylinder Press severe cracking 1 1 mbber is sofi and racky dirt has become imbedded in the soft area of rubber Model A hom bulb moderate cracking I 1 rubber is hard and brinle 1 1 more severe cracking around areas of stress on the artifact Cadiliac hom bulb fine to moderate cracking rubber is hard and brittle 1 1 more severe cracking around the areas of stress on the artifact 19 15 Cadilfac tire moderate cracking dent in one side of the tire fiom storage on its end rubber is hard c. 19 1 O washinj machine fine cracking 1 1 rubber is still sornewhat flexible although may have hudened hmits original s&e 1 899 LocomobiIe tire severe cracking
6.3 Accelerated Aging
The vulcanized natural rubber swogate samples were artificially aged using a Q- panel QUV. Fony eight (7cm x 14cm) specimens of vulcanized natural rubber were cut out of the original 144cm x 144cm panels received fiom Alcron Rubber Developmenr
Laboratory. Sis of the surrogate samples were retained as unexposed (control) samples.
The remaining samples were put into the QW (Figure 6.1). W-A fluorescent bulbs
(40W) were used that had a peak emission at 340 nm. The bulbs and samples were rotated, accordhg to ASTM standard G 53, every 400 and 168 hours, respectively. Six samples were removed afier one week, one month, two months, three months and four months of QW exposure. At each tirne interval, chernical and physical analyses were done on the samples.
The vulcanized na- rubber surrogate samples were also artificially aged using a circulahg oven with an Omega temperature controller. Five specimens (1Ocm x 14cm) were put into the oven and heated at 250°C for 19 hours and 23 houn of exposure. One specimen was removed after 19 hours and the rest &er 23 hours. Five specimens (IOcm x 14cm) were put into the oven and heated at 230°C. One specimen was removed afier
70 hours of exposure, and the remaining specimens were removed after 118 hours of exposure.
Figure 6.1 Lamp and Sample Placement Diagram for QUV Apparatus (Q-Panel Company 1985)
Condensation Thermostat Scnsor
Watcr Hcaur Blowu (Condaration Cycle) 6.4 Chernical Anaiysis
Three Fourier-transform infrared spectroscopy techniques and two thermal analysis technique were evaluated as possible diagnostic tools for evaluation of the degradation of vulcanized naturai rubber. The procedure used for each technique is described below.
6.4.1 Attenuated Total Reflectance-Microscopy-Fourier-Transform Infrared
Spectroscopy (ATR-Microscopy-FTIR)
Five specimens (A-E) fiom each sample were analyzed using a Nicolet Nic-Plan microscope equipped with an MCT-A detector. No preparation was needed prior to analysis of the specimens. Spectra were collected using an attenuated total reflectance
(ATR) attachment with a 45" germanium (Ge) crystal. Each specirnen vas placed on the microscope siide attached to a contact alm. A 10X-glass objective was used to select the area to be sampled and to focus the microscope. Once in focus, contact was made benveen the ATR objective and the specimen. The collection parameters were: 1.jmm aperture, 500 scans, mirror velocity set to 55 (3.16 cmlsec), 8 cm" resolution and Happ-
Genzel apodization. The contact alarm was kept at 2-4 rnA when the specimens were being scmed to ensure good contact benveen the specimen and the germanium crystal.
The ATR and baseline correction routines fiom the Omnic software (Nicolet instruments) were applied to al1 spectra before plotîing. 6-42 Avatar OLWI-SamplerAmchment
Five specimens (one korn each sample &er zero, one month, two months, three months, and four months of QW exposure) dong with one ~turdlyaged museum sample were anal yzed using an Avatar System 360 with OMNI-Sampler amchment. The
ObNI-Sampler was equipped with a Ge crystal for ATR. After each specimen was placed on top of the germanium crystai, pressure was applied by tightening the pressure towr. to create good contact between the specimen and the crystal. The collection parameten were: aperture set to 100, 50 scans, 0.6329cdsec rnirror velocity, 4 cm" resolution, and Happ-Genzel apodization. ATR and baseline correction routines fiom the
Omnic software (Nicolet Instruments) were applied to al1 spectra before plotting.
6.4.3 Photoacoustic-Fourier-Transfomi Infrared Spectroscopy (PAS-FTIR)
Five trial specimens (A-E) fiom each sample were cut using a hole punch. Each specimen was approximately 6 mm in diameter and approximately 2 mm in thickness.
Each specimen was cut in half, widthwise, using a utility knife to reduce the thickness to approximately 1 mm. Analysis of the specimens was done using a Nicolet 800 inhed spectrometer equipped with a photoacoustic cell and detector, mode1 200 (MTEC
Photoacoustics). Each specimen was placed in the sample pan with the newly weathered side of the sample facing upward. The pan was introduced into the ce11 and purged with helium gas (5mVsec) for 1-2 minutes. The specimens were scanned using die following esperimental parameters: 8 cm-' resolution, 300 scans, and mirror velocity set to 20 (0.32 cdsec). The sample spectra were ratioed against a carbon black standard reference membrane background collected the same day. Omnic software fkom Nicolet
Insûuments was used to correct for the non-linearity of the PAS detector.
6.4.4 Thermogravimetry (TG)
Thermopravimetrïc analysis of unexposed vulcanized naniral rubber wm performed using a Seiko Simultaneous ThedAndyzer (STA) mode1 TGIDTAj20.
Approximately 10 mg of ùie specirnen (fiom an unexposed vulcanized na- rubber sarnple) was placed in the sample pan and heated fiom 20°C to 600°C using different heating rates (3'C/min, j°C/min, 1O°C/min and 20°C/min). Two trials were perfomed for each of the heating rates. The kinetics software was used to calculate the activation energies and degradation time determinations for each trial. The averaged values were reporred.
6-43 Thermogravimetry-Fourier-Transfomilnfiared Spectroscopy (TG-FTIR)
Unexposed and exposed vulcanized natural rubber specimens were evduated usine TG-FTIR. A Seiko Simultaneous Thermal Analyzer (STA) mode1 TGIDTAjîO connected to a Nicolet 800 Fourier-transform inhed spectrorneter \vas used. The TG and FTIR were comected using a TG interface kit (Nicolet Instruments). The kit contained a Teflon adapter, heated transfer line, and a glas ce11 enclosed in an insulated chamber. In both the transfer iine and the glass cell, the temperature was kept at 265°C to prevent condensation.
A specimen of approximately 10 mg (fiom the unexposed and the three months
QW exposed samples) was placed in the TG pan and heated fkom 40°C to 600°C at 10°C/min under a nitrogen atmosphere (15Odmin). The evolved gas was tramferred to the ETIR through the heated tramfer line. Data nom the FTIR narted to be collected using Nicolet SID software when the sample temperature on the STA reached 150°C.
Spectra were collected at 8 cm" resolution and mirmr velocity set to 30 (0.63 cdsec).
6.5 Physical Testing
6.5.1 Scanning Electron Microscopy (SEM)
A Joel JSM-T300scanning electron microscope was used to obtain morphological information about the sarnples. Specimens were eut approximately 1 cm square fiom unexposed and exposed samples. Each specimen was attached to a mount using double- sided tape and a Kummer VI-A Sputtering System was used to coat the speciniens with gold. Tensile strength specimens were also examined using the SEiM. The fracture point for the tensile strength specimens was evaluated. These specimens were mounted ushg hot glue and coated with gold ushg the same apparatus mentioned earlier. Micrographs were obtained for each specimen.
6-52Tensile Data
Ten dog-bone specimens were cut for each sample with die C, as specified in
ASTM D 41 2, using a Neaf hydraulic punch press. The thickness of each specimen was precisely measured, taking an average of five points measured along the length of the specimen using a Mitutoyo digital micrometer. The samples were tested using an Instron 4502 Automated Materials Testing
Systern with Senes IX software. The room was kept at constant temperature of 23 f 2°C and relative humidity of 50 +: 5%.
The specimens were tested at a speed of 50Omm/min using a lkN capacity load cell. Pneumatic grips were used to hold the specimens. A sarnpling rate of 10 ptdsec and a gauge lenath of 25 mm were used. An Inmon XL Extensiometer was used to mesure displacement. 7. RESULTS
This section will discuss the results obtained using the insûumentation techniques and observation methods, menhoned in Chapter 6. Spectra, images and sunimary tables will be used to explain the data.
7.1 Attenuated Total Reflectance-Microscopy-Fourier-Transfom lnfrared Spectroscopy
(ATR-microscopy-FTIR)
Al1 spectra were ATR and baseline corrected using the Omnic Software routines
(Nicoiet Instruments). Figure 7.1 shows the spectrum of an unexposed vulcanized natural mbber surrogate sample.
Figure 7.1 ATR-Microscopy-FTIR Spectnim of an Unexposed Vulcanized Natural Rubber Surrogate Sample
Wavenum bers (cm-') Table 7.1 lists the significant peaks in the specmim of an unexposed vuicanized natural rubber surrogate sample, as well as identifies each peak. The primary peaks in this specmun are due to cis- 1,4-polyisoprene (see Figure 7.2)
Figure 7.2 Chernical Structure of Cis- 1,bPolyisoprene
cis- 1,4-poly isoprene
Table 7.1 Identification of Peaks for ATR-Microscopy-FTIR spectrum of an Unexposed Vuicanized Naturai Rubber Surrogate Sample
- 1 PEAK LOCATION 1 IDENTIFICATION OF PEAK* 1 (cm-') 2958 CH3 syrnmetric stretching motion 29 13 CHI asymmetric stretching motion 2846 CH2 symmetric stretching motion 1594 This broad band between 1700 and 1500 cm" is due to the C=C 146 CH2 r CM3 and bending 1373 CH, bending 1084 May be due to an additive or CH3 rocking vibration 836 RIC=CHR (=CHwa-gging) a Identification of peaks made using (Colthup, et ai. 1990) and (Silverstein, et. al. 1991).
The surrogate samples were also analyzed after one week of QLN exposure as well. Figure 7.3 shows the spectnim of a sample exposed for one week. Table 7.2 depicts the peak locations and peak identifications for al1 peaks in the spectrum in Figure
ATR-microscopy-FTIR was also used to analyze one naturally aged museum sample. This sample was obtained fiom a c. 19 10 washing machine. Figure 7.1 shows this sample. Figure 7.3 ATR-rMicroscopy-FTIR Spectnm of a Vuicauized Natural Rubber Surrogateu Sample afier One Week of Q W Exposure
3000 2000 Wavenum bers (cm")
Table 7.2 Identification of Peaks for ATR-Microscopy-FTIR Spectrum of a One Week Exposed Vulcanized NaruraI Rubber Surrogate Sample
PEAK LOCATION PEAK IDENTIFICATION (cm*') 1 2959 CH3 symmetric stretching motion 2916 CH2 asyrnrnetric stretching motion 2848 CH2asymmetric stretchïng motion 1539 May be due to an additive 1447 CH3 and CH2 asyrnmenic bending 1375 CH3 symmetric bending 1085 May be due to an additive or CH3rocking vibration 83 1 R2C=CHR (=CHwa-%in%) Identification of peaks made using (Colthup, et al. 1990) and (Silverstein, et. al. 199 1). Figure 7.4 Attempted ATR-Microscopy-FTR Spectm of a Natlnally Aged Washing Machine Sample
Wavenumben (cm")
7.2 Avatar with OiMNI-Sarnpler Attachment
OMM-Sarnpler was used as a diagnostic tool to evaluate nlcanized natural rubber as it degrades. The following results show the usefulness of this technique for this purpose. Figure 7.5 shows the spectnim of unexposed wlcanized natural rubber. Table
7.2 sumarizes the peak locations and identities for those peaks found in the spectrum of unexposed vulcanized natural rubber. Figure 7.5 OMNI-Sampler Spectnim of C'nexposed Vulcanized Natural Rubber
Wavenumbers (cm-')
Table 7.3 Identification of Peaks for OMM-Sampler Spectrum of Unexposed Vulcanized Natural Ru bber
PEAK LOCATION PEAK IDENTIFICATION* (cm-') 1 1 3375 OH stretching vibration 3036 =CH stretching vibration 2960 CH3 asymmetric stretching vibration 2917 CH2 asymmetric stretching vibration 2850 CH2 symrnetric stretching vibration 1654 C=C metching vibration 1540 May be due to an additive I4lS CH2 and CH3 asymmetric bending 1375 CH3 syrnmetric bending 12 12 RCH2-(S-S)- (CH2 wagging) 1 154 May be due to an additive or C-C-Obonds resulting fiom premature de,gradation 838 R2C=CHR (=CH wacging) Identification of peaks made using (Colthup, et al. 1990) and (Silventein. et. al. 1991).
Figure 7.6 depicts the vulcanized natural rubber spectnvn after two months of QUV exposure. The locations of peaks, in this spectnim, are summarized in Table 7.4. Figure 7.7 shows the OMNI-Sampler spectmm of vulcanized nahirai rubber after four months of
QUV exposure and Table 7.5 summarized the peaks found in this spectrum. Figures 7.8-
7.10, however, show three different spectra of the material after three months of QUV exposure. There are noticeable differences in these three spectra. Finally, Figure 7.1 1 depicts the OMNI-Sampler spectrum of a c. 1880 dnim cylinder press sampie.
Fi=we 7.6 OMNI-Sarnpler Spectnim of Vulcanized Natural Rubber after Two Months of QW Exposure
4000 3000 2000 1O00 Wavenumbers (cm-') Table 7.4 Identification of Peaks for OMM-Sampler Spectrum of Vulcanized Nad Rubber derTwo Months of QW Exposure
i PEAK LOCATION I PEAK IDENTIFIACTION* 1 1 1 (cm-') l l 1 32 19 l OH stretching vibration I 1 2965 ! CH, asymmeaic stretching vibration 1 ! 29 17 CHz asymmetric stretching vibration 1707 C=O stretching vi'bration - - 1638 1 May be due to absorbed water or C=C siretchin%vibration 1-- -- 1 154 1 1 May be due to an additive t 377 CH3symmetiic bending 1229 RCHI-(S-S)- (CH?wagging) 11 15 May be due to an additive or C-C-O sîretching vibration IO59 May be due to an additive or CH3 rocking vibration 82 1 R2C=CHR (=CH wagging) * Identification of peaks made using (Colthup, et al. IWO) and (Silverstein, et, al. 199 1).
Figure 7.7 OMNI-Sampler Spectrum of Vulcanized Natural Rubber after Four Months of QUV Exposure
3000 2000 Wavenumbers (cm-') Table 7.5 Identification of Peak for OMNI-Sampler Spectnim of Vulcanized Naniral Rubber after Four Months of QUV Exposure
f PEAK LOCATION PEAK IDENTIFICATION* [ (cm") ! 3224 OH stretching vibration 1 1707 C=O metching vibration 1638 May be due to absorbed water or C=C smtching vibration 154 1 May be due to an additive l 1428 CH-, and CH3 asymrnetric bending I I 1377 CH3 symrnetric bending 1 1230 RCH?-(S-S)-(CH2 wagging) 1141 May be due to an additive or C-C-O sfretching vibration 1070 May be due to an additive or CH; rocking vibration 82 1 RIC=CHR (=CHwagging) * Identifica~ionof peaks made ushg (Colthup, et al. 1990) and (Silventein, et. ai. 199 1).
Figure 7.8 OMNI-Sampler Spectrum of Vulcanized Natural Rubber afier Three Months of QW Exposure (Version 1)
Wavenum bers (cm-') Figure 7.9 OMNI-Sampler Specmun of Vulcanized Naturai Rubber after Three Months of QUV Exposure (Version 2) i
1 I
4000 3000 2000 1O00 Wavenum bers (cm'')
Figure 7.10 OiMNI-Sampler Spectrum of Vulcanized Natural Rubber afier Three Months of QUV Exposure (Version 3)
Wavenumbers (cm") Fi-me 7.1 1 OMM-Sampler Specmim of c. 1880 lhm Cylinder Press Sample
3000 2000 Wavenumbers (cm-')
Table 7.6 Identification of Peaks for OMNI-Sarnpler Spectnim of the c. 1880 Dnun Cylinder Press Sample
1 PEAK LOCATION fEAK IDENTIFICATION* 1 t (cm-') 3366 OH stretching vibration 1 1920 CH2 asyrnmetric stretching 1 2850 CH2 symmetric stretching 164 May be due to absorbed water or C=C stretching vibration f 1420 CH2 and CH; asymmetric bending 1 1362 CH; symmetric bending i 1110 C-C-O r May be due to stretching motion or an additive I 1041 May be due to an additive or CH3 rocking vibration 1 820 RIC=CHR (=CH wagging) * Identification of peaks made using (Colthup. et al. IWO)and (Siiventein, et al. 199 1). 7.3 Photoacoustic-Fourier-Transfom mdSpectroscopy (PAS-FTIR)
Al1 spectra obtained were only correcteci for the non-lùiearity of the PAS detector using the PAS routine in the Omnic software fiom Nicolet Instruments. Automatic baseline correction did not work for any of the PAS-FTIR spectra and manual baseline correction did not give repmducible resuits. The specm of an unexposed Milceed natural rubber surrogate sample is show in Figure 7.12. Table 7.7 identifies di peaks in the PAS-FTIR spectnim of unexposed vulcanized natural rubber.
Figure 7.12 PAS-FTIR Spectm of Unexposed Vulcanized Naniral Rubber
3000 2000 1000 Wavenumbers (cm-') Table 7.7 Identification of Peaks for PAS-FTR Spectnm of Unexposed Vulcanized Narural Rubber
1 PEAKLOCATION 1 PEAK IDENTIFICATION* 1 (cm") 2959 CH3 symmetric stretching motion 292 1 1 CH2 asymmetric stretching motion 2854 CH2 synunetrïc metching motion 1661 C=C stretching motion 1447 CH2 and CH3 asymmetric bending 1376 CH-, symmetric bendina 1217 RCH2-(S-S)- (CH?w~iag) 1089 May be due to an additive 1 834 1 R~C=CHR(=CH wa~ing) l * Identification of peaks made usin; (Colthup, et al. 1990) and (Silverstein, et- al- 1991).
The peaks at 13 12 cm'', 1217 cm", and 987 cm-' may be peaks, although it is difficult to obtain a conclusive identification with such a high baseline in the spectnim. The peak at
1089 cm-', however, is consistent throughout ail FTIR spectra of the vulcanized natural rubber surrogate samples. It is therefore believed that this peak is due to an additive in the polymer system.
Figure 7.13 shows the PAS-FTIR spectnim of a vulcanized natural rubber surrogate sample afier two months of QUV exposure. Table 7.8 identifies all peaks in the
PAS-FTIR spectrum of a vulcanized nahuai rubber surrogate sample afier two months of exposure. Figure 7.14 shows the spectrum of a vulcanized natural rubber surrogate sample after four months of QUV exposure. Table 7.9 shows the identification of each peak in Figure 7.14. Figure 7.13 PAS-FTR Specmmi of Vdcanized Nahaal Rubber after Two Months of
3000 2000
Wavenumbers (cm-')
Table 7.8 Identification for Peaks for PAS-FTIR Spectnim of a Vulcanized Natural Rubber Surrogate Sampie after Two Months of QUV Exposure
PEAK LOCATION PEAK IDENTIFICATION*
L (cm"). . I 1 2959 CH3symmetric stretching motion 166 1 C=C stretching motion 1447 CH2 and CH3 asymmetric bending motion 1376 CH3 symmetric bending motion 834 R2C=CHR (=CHwagging) Identification of peaks made using (Coithup, et al. IWO) and (Sitverstein, et. ai. 199 1). n
Fipe 7.14 PAS-FTIR Spectmm of Vdcanized Naniral Rubber der Four Months of Q W Exposure
Wavenumben (cm")
Table 7.9 Identification of Peaks for PAS-FT?R Spectnim of a Vulcanized Naturai Rubber Surrogate Sarnple afier Four Months of QUV Exposure
PEAK LOCATION PEAK IDENTIFICATION* (cm-'1 2959 CH3 symmetric stretchüig motion 1661 C=C stretching motion andfor C=O stretching motion 1447 CHI and CH3 asymmetric bending 1376 CHj symmetric bendifig 834 RLC=CHR(=CH wagging) * Identification of peaks made using (Cofthup,et al. 1990) and (SiIverstein, et. al. 199 1).
PAS-FTIR was aiso used to evaluate the samples from naturaily aged rnuseum artifacts collected for this study. Most of the spectra of these samples had well defined peaks and a low signal-to-noise ratio. Two of the spectra collected using PAS-FTIR of the museum samples will be presented here. Ml other spectra of museun samples col1ected using PAS-FIIR may be found in AppendLu A. Figure 7.15 shows the PAS-
FTIR spectnim of a c. 1910 washing machine sampie. Table 7.10 iists al1 peaks in the washing machine spectnim as well as identifies them.
Figure 7.15 PAS-FTIR Spectnim of c. 19 10 Washing Machine Sample
O 3000 2000 1O00 Wavenurnbers (cm")
The other naturally aged museum sample which will be discussed here, is a c.
1880 drum cylinder press. This museum sample, show in Figure 6.16, was also analyzed using PAS-FTIR. Table 7.1 1 identifies ail the peaks in the PAS-FTIR specuum of the dmcylinder press sample. Table 7.10 Identification of Peaks for PAS-FTIR Spectrum of the c. 1910 Washg Machine
[ PEAKLOCATION 1 PEAK IDEMIFICATION* 1
Figure 7.16 PAS-FTIR Specmof a c. 1880 Drum Cylinder Press Sample
6
5 - ,3 344 1 542
fr
4000 3000 2000 I O00 Wavenumbers (cm-') Table 7.1 1 Identification of Peaks for PAS-FTIR Spectrum of the c. 1880 Dnmi Cylinder Press Sample
PEAK LOCATION PEAK IDENfIFICATiON* (cm") . r 3 344 OH metchhg vibration 2933 CH2 and CH3 asymmemc stretching vibrations mis band may also represent CH2 and CH3 symmetric stretching vibrations. although the peak is not wei1 defined) 1653 May be due to absorbed water or C=C stretching vibration 1542 May be due to an additive 1420 CH2 and CH3 asymmetric bending (This band is not well defined and may also represent CH3 symmetric bending) II16 C-C-Ostretching vibration 1036 May be due to an additive or CH3 rocking vibration 854 R2C=CHR (=CH wagging) i - 1 672 1 This peak may be due to carbon dioxide in the air Identification of peaks made using (Colthup, et al. 1990) and (Siiverstein, et. al. 199 1).
7.1 Thermogravimetry (TG)
The following is the results from thermogravimetric analysis of ~ulcanizednahiral rubber surrogate samples. Figure 7.1 7 shows the thermogravirnetric (TG) curve and the derivative thermogravirnetric (DTG)curve of unerposed vulcanized natural mbber.
Kinetics calculations were canied out on the unexposed vulcanized natural rubber matenal using the kinetics software of the Seiko STA instrument to give the activation energies and degradation times for vulcanized natural rubber at 136°C. Figure 7.18 show the results of these caIcuIations. Table 7.12 sununarizes the results of activation energ and degradation time calculations for 136'C, 230°C and 250°C. The graphic results for the Z30°C and 250°C calculations cm be found in Appendix B. Fise 7.17 Thermogravhetric and Derivative Thermogravimetric curves for Unexposed Vulcanized Natual Rubber
30r
25.
2D
C IS- * E \Y 10. s3 C O 5.
0 -.
Figure 7.18 Activation Energy and Degradation Time Determinations for Vulcanized Naturai Rubber at 136°C
calcdations gave an accurate lifetime prediction for the vulcanized naturai rubber.
Vulcanized nadrubber was exposed in an oven at 230°C. Samples were removed
from the oven after 70 and 118 hours and run in the TG. Figures 7.19 and 7.20 show the resuiting TG and DTG cwes.
Table 7.12 Activation Energy and Degradation Time Calculations for Vulcanized Naturd Rubber at l36"C, 230°C and 250°C.
R.F. (Yo) 136°C 230°C 250°C Delta E Life fie Delta E Life Time Delta E Life Time (Wrnol) (year) (Ufmol) (day) (kJ/mo t) Oiour) 1 13 1.6 0.0046575 131.6 0.00 12358 13 1.6 0.0089098 7 147.23 0.045478 142.23 0,0067305 142.23 0.044033 3 159.93 0.536 17 159.93 0.0300 19 159.93 O. 16706 4 184.84 1 1.822 184.84 O. 16858 184.84 0.7472 5 195.00 76,273 195.00 0.6223 1 195.00 2.5 136 6 196.18 17524 196.18 1.3398 196.18 5.3534 7 199.17 370.69 199.17 2.4055 199.17 93529 8 199.77 556.02 199.77 3 -4908 199.77 13 -498 9 199.19 693.6 199.19 4.496 199.19 17.478 1O 300.24 945.03 200.24 5.7817 1 200.24 22.26 Figue 7.19 TG and DTG Curves for Vulcanized Naturai Rubber after 70 Hours at 230°C Oven Exponne
200 400 Teno. C
Figure 7.20 TG and DTG Cwes of Vulcanized Natural Rubber afier 1 18 Hours at 230°C Oven Exposure The kinetics caiculations were also checked at ZSO°C. Table 7.11 shows uiat, according to the kinetics calcdations, the material will degrade by approximately 10% after 5 days (ai 230°C) and after 22 hom (at Z50°C). Oven aging of the samples was done to compare the TGlDTG curves afier exposure for the duration specified by the kinetics calculations. Figure 7.21 and Figure 7.22 show the TG and DTG curves of vulcanized nadrubber after 19 hours and 23 hotus of oven exposure at 250°C, respectively. Figure 7.23 shows the TG and DTG curves of vdcanized naniral rubber afier four months of QUV exposure.
Figure 7.21 TG and DTG Cumes of Vulcanized Natural Rubber after 19 Hours of Oven Exposure at 250°C
~eiperaturemgr= unents: [CI I-t.11 [min! [xtj 19 nours in =OC !3: O2 !a 20- 600 M 1 10 Check Klnetrcs 10.03r3 ng Re f ercnct: A 1203 11.315 mg
200 400 Teno. C Figure 7.22 TG and DTG Curves of Vuicanized Naturai Rubber after 23 Hom of Oven Exposure at 250°C
Figure 7.23 TG and DTG Cwes of Vulcanized Natural Rubber after Three Months of Q W Exposure
cc TCIDT&> 2 ~cw~trdLurePropran- cnm=n*~ 0a1a Msrr rs -3 [CI Itctil Cwnl Ltetl 3 aontn cxposure. trral A. Samule takon Oite 9616/17r4:03 1. 20- 603 t 1 frontheeurface sarnii: re 7.5 Themogravimev-Fourier-Tdom Mked Spectroscopy (TG-FTIR)
TG-FTR results have given information regardhg mucnual changes in the vulcanized natural rubber nirrogates samples as a result of QUV exposure. The Graham-
Schmidt reconstruction curves for vulcanized natural rubber, both unexposed and exposed for four months, are located in Appendix C. The GrahamSchmidt reconstruction was produced by the Nicolet software for this instrument. The software was originally designed for chromatography, therefore, the resulting cuve fiinctiom the same way as a reco~ctedchromatograrn. The curves show the retention time of the components as they evolve fiom the sample. Figure 7.24 shows the TG-FTIR spectra of unexposed vulcanized naturai rubber at temperatures ranging from 300°C to 500°C at
50°C intervals. Figure 7.25 shows the TG-FTIR spectra of the vulcanized nadmbber surrogate sample afier three rnonths of QUV exposure.
Figure 7.24 TG-FTIR Spectra of Unexposed Vulcanized Natural Rubber
Unexposed at 500 OC
Unexposed at 450 OC
Unexposed at 400 OC
Unexposed at 350 OC A
Unexposed at 300°C
3000 2000 Wavenumoers (cm-') 87
Figure 7.25 TG-FTIR Spectra of Vulcanized Narurai Rubber after Three Months of QUV Exposure
3 Months Exposure (50 1OC)
3 Months E-xposure (45 1OC)
3 Months Exposure (40 1 OC)
3 Months Exposure (3 5 1 OC) A- a_J
3 Months Exposure (30 1 OC) h
Wavenumben (cm-')
7.6 Scanning Electron Microscopy (SEM)
Scanning electron microscopic images were taken of al1 vulcanized natural rubber surrogate samples after QUV erposure. Table 7.13 shows the type and seventy of changes that occurred at the surface of the surrogate samples as a result of QUV exposure. SEM Images at 200X rnagnification follow; SEM images at 5OX and 1500X are located in Appendix D and Appendix E, respectively. Figure 7-37shows a detail of a
1907 Harley Davidson motorcycle tire. Table 7.13 Changes at the Surfiace of Vulcanized Natural Rubber Surrogate Samples As a Result of QUV Expowe
Exposure Time Appearance of Vulcanized Naniral Rubber Smgate Sample - - O black shiny nocracks 1 week slightly Merblack slightly speckled appearance morematte no visible cracks/ very fine cracks at 200x mgnification cracks are in randorn cracking pattern datker black more speckled appearance morematte very fine cracking visible to human eye £iae cracking at 2Oûx mapification cracks are in random cracking pattern with some more severe than others edges of cracks appear jagged and pulied at 1500~magnification there is a mottledlorange peel appearance to the surfàce 2 months black color is the same as 1 month cxposure reduction in speckled appearance morematte fine cracking visible to human eye cracking at 200x magnification becoming more severe large amount of jagged and pulled edges dong the mcks cracks are wider than 1 month of exposure fine cracking pattern between the larger cracks at 1500x magnification the mottled/orange peel appearance of the surface is more severe 3 months black color is the same as 1 month exposure matte appearance is the same as 2 months' exposure fine cracking visible to human eye cracking is becoming more severe the jagged and pulled edges are noticeable at 50x magnification at 1SOOx magnification the mottled/orange peel appearance of the surface is more severe 4 months black color is the same as in 1 month exposure matte appearance is the same as 2 months' of exposure fine cracking visible to the human eye cracking is more severe the jagged and pulled edges are visible at 5Ox magnification at 150x magnification the mottled/orange pee1 appearance of the surfàce is more severe 89
Figure 7.26 SEM Image of Unexposed Vdcanized Naturai Rubber (200X Mapification)
Figure 7.27 SEM Image of Vdcanized Natural Rubber One Week of QUV Exposure (200X Magnification) Figure 728 SEM Image of Vulcaaized Nanirat Rubber der One Month of QUV Exposure (200X Magnincation)
Figure 7.29 SEM image of Vulcanized Naturd Rubber after Two Months of QW Exposure (200X Magnincation) Figure 7.30 SEM Image of Vulcanized Naturai Rubber afkThree Months of QW Exposure (200X Magnification)
Figure 7.31 SEM Image of Vulcaaized Naturai Rubber after Four Months of QUV Exposure (200X Magnification) 92
Figure 7.32 Detaii of Tire nom a 1907 Haley Davidson Motorcycle
SEM images at 50X magnification were also taken of the hcture point of each of the exposed vulcanized natural rubber specimens. These images show the changes in fracture as a result of QUV exposure; these are summarized in Table 7.14. Table 7.14 Changes in Fracture of Vulcanized NadRubber Specimens as a Result of QUV Exposure
CHANGES iN FRACTURE no qpearance changes the ûacture is uneven, consistent with rubbery material no visible change in appearance hcture is still uneven the fiacture appears to be becoming more brittle the lines of fiachne are becomiag straighter, indicating a more brittle hcture the bcture swfbce is smooth compared to unexposed mirror shape has just started to fonn the lines moving away hmhcture point are straighter 3 months mirror shape is more prominent ~UrfSlCeissmootb Ilines are very well defmed, indicating a more brittle hcture 4 months mirror shape is very prominent typical of britîie hcture Ilines are well dehed and -&ter
Figure 7.33 SEM Image of Fracture Point of an Unexposed Vuicanized Nahuai Rubber Specimen (50X Magnïfïcation) Figure 7.34 SEM Image of Fracture Point of a Vulcanized Naturai Rubber Specirnen after One Week of QW Exposure (50X Magnification)
Figure 7.35 SEM Image of Fracture Point of a Vulcanized Naturai Rubber Specimen der One Month of QW Exposure (50X Magnification) Figure 7.36 SEM Image of Fracture Point of a Vulcanized NamRubber Specimen afler Two Months of QUV Exposure (50X M-cation)
Figure 7.37 SEM Image of Fracture Point of a Vulcanized Naturai Rubber Specimen afler Three Months of Q W Exposure (50X Magnification) Figure 7.38 SEM Image of Fracture Point of a Vdcanized Natural Rubber Specimen after Four Months of QUV Exposure (50X Magnincation)
7.7 Tensile Data
The tende data provides information regarding changes in the tensile properties of vulcanized naairal rubber as a resuit of QUV exposure. Figure 7.39 shows the change in tensile strength as a function of QUV exposure. Tensile strength refers to the maximum engineering stress, in tension, that may be sustallied without hcture (Callister
1997). Further data are located in Appendix F. Figure 7.40 shows the percent elongation of the vulcanized naturai nibber specimens as a result of QW exposure. Percent elongation was calculated using the equation in Figure 7.41 Figure 7.39 Changes in Tende Strength of Vulcanized NamRubber as a Function of QUV Exposure
0.03 1
T e 0.0251 n S i I 0.02- e
S t r 0.015- e +Temile n Strength 4 t 0.01 - h
(kNI mm2) 0.00s-
O+ 1 c 5 I 1 O 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (Months) Figure 7.40 Changes in Percent Elongation of Vulcanized Naturai Rubber Specimens as a Function of QUV Exposure
ooc
S(M
400
300
+Percent Elongation (%) zoo -
IO0
O 0.5 1 1.5 2 2.5 3 3.5 4 4.5 T ime (Months)
Figure 7.4 1 Calculation for Percent Elongation
% Elongation = (Displacement at Break + Gauge Length) x 100 8. DISCUSSION
This section will discuss the mults for each technique and how the results are
interrelated.
8.1 Xttenuated Total Reflectance-~Microscopy-Fourier-TransformMked Spectroscopy
The ATR-microscopy-FTIR spectnim of unexposed vulcanized natural rubber
(Figure 7.1) shows al1 of the peaks which are typical of cis-l,4-polyisoprene. The peak at
1539 cm-' in, Figure 7.2 was also present in many spectra of the unexposed samples,
hoviever, it did not consistently appear. This suggests that it may be the result of a
processing agent or additive which is not mixed uniforrnly through the polymer system.
ATR-microscopy-FTlR has only shown limited usefulness for the evaluation of
the surrogate and naturally aged samples. Two problems have misen in using this
technique for evaluation of the material. The first is the high level of carbon black in the
surrogate samples. Carbon black is used in vulcanized natural rubber formulations as a
filler and to provide some protection against photo-degradation. Because of its strong absorbing power in the inftared region, carbon black masks functional group information about the polymer system. Due to this interference, the spectra of matenal containing carbon black tend to be noisy and the peaks have Iow intensity. As matenal containing carbon black ages, the carbon black migraes to the surface. This compounds die problem of spectral interference by masking changes, which might indicate the presence of degradation products.
The second problem with using the ATR-microscopy-FTIR is that the samples are hardened and embrialed as a resuit of aging. Most museum artifacts, as weil as the surrogate samples which have undergone QUV exposure, undergo degradation, resuiting in cross-linking of the materiai, which causes it to becorne hard and brittle with age. The germanium (ATR crystai) cannot withstand a great deal of pressure. When the IR-ATR objective is put into contact with the sample, the sample material must bc sofi enough to allow good contact with only a mal1 amount of pressure. Naturally aged and artificially aged samples have usually becorne hard and can no longer yield enough to give the necessary good contact. The spectrum in Figure 7.4 is of a naturally aged museum sample (c. 19 10 washing machine) and it is typical of the spectra obtained fiom rnuseum samples using this technique. The only peaks present (2362 cm-' and 2342 cm-') are due to carbon dioxide in the surroundhg atmosphere. This indicates that good contact was not made between the crystal and sample.
8.2 Avatar OMNI-Sampler Attachment
The spectrum of unexposed vulcanized nadrubber shows ail peaks which are typicai of cis- 1,4-polyisoprene. The peak at 1540 cm-', present in the ATR-rnicroscopy-
FTIR spectrum is aiso present here. In cornparison to the ATR-microscopy-FTIR spectra of esposed samples, however, the OMM-Sampler spectra give a much better indication of dekgadation of the wlcanized natural rubber. Afier two months of exposure (Figure
7.6) there is already a noticeable decrease in the intensity of peaks due to CH2 and CHj stretching and bending vibrations (2965 cm-', 2917 cm-' and 1377 cm-'). After four months of exposure the peaks around 2900 cm" (due to CH2 and CH3 stretching vibrations) are no longer noticeable. In both the two-month exposure and the four-month exposure spectra there appears to be a broadening of the peak at 1638 cm" to include a 10 1 greatcr intensity at 1707 cm-'. This may indicate the presence of oxidative deCigradation occurring in the material.
The area sampled by this instrument is 2mm in diarneter. This is good nom the standpoint of conservation science which requires the sample size to be as mail as possible. It does, however, run the risk of having the sample not be representative of degradation occurring rhroughout the object. Figures 7.8-7.10 show spectra of a surrogate sample afrer three months of QW exposure. Each figure ivas taken from a different area on the same sample. There are noticeable differences in the spectra. particularly in the region between 3000 cm" and 2850 cm-'.The difference in intensities of these peaks (due to CH2 and CH3 stretching vibrations) indicates some difference in the degree of degradation occwhg over the entire surface of the sample. Further work needs to be done to determine if changes in chernical structure, due to degradation, are consistent with visual changes at different points on the sarnple.
Figure 7.1 1 shows the spectrum of a c. 1880 dmcylinder press sample. Al1 the peaks typical of cis-1,4-polyisoprene are present in the spectnun. This spectrum is also similar to the spectrum in Figure 7.16 (taken using PAS-FTIR). There is, however. slightly more definition of peaks between 1450 cm-' and 1300 cm" in rhe OMNI-Sampler spectrum, as well as a greater relative intensity of the peaks at 3366 cm" and 1641 cm-'.
This is most likely due to the fact that the sample spent seven days in a desiccator prior to being analyzed with PAS-FTIR and the sarnple was not desiccated prior to analysis with the OiMNI-Sampler attachent. This indicates a greater degree of absorbed water in the sample when analyzed using the OMNI-Sampler attachent. The two problems that arose when evaluating the naturally aged and artificially
aged samples using ATR-microscopy-FTIR were not major factors in this second
technique. The area sampled with the OMNI-Sampler amchment (2mm) is larger than
the area sampled by the ATR-microscopy-FTR instrumentation. The larger area being sampled minimizes the interference caused by the carbon black in the sample. The second problem in using the ATR-microscopy-FTIR instrument, was the small arnount of pressure which could be put on the germanium crystal. The germanium crystal in the
OMNI-Sampler attachment has a curved surface. When the sample is placed on the crystal, a pressure tower is used to create uniform pressure on the sarnple by pressing it against the crystal. A slipclutch mechanism on the pressure tower allows the maximum amount of pressure the crystal can withstand to be achieved each time the aitachment is used. It is possible, therefore, to obtain better contact between the crystal and sample even when the sample has become cracked and bnttle.
Both ATR-FTIR techniques (ATR-microscopy-FTIR and OMNI-Sampler attachent) are useful for evaluation of the surrogate samples, although rhe OMNI-
Sarnpler attachment has proven to be more useful for hard and brinle samples, including both the surrogate samples and some of the nahirally aged rnuseurn samples.
8.3 Photoacoustic-Fourier-Transform Inffared Spectroscopy
The results obtained using PAS-FTIR show varying degrees of success. The spectra of surrogate samples initially showed great promise, as ail functionai groups typical of cis-1,4-polyisoprene were present in the spectmn of the unexposed surrogate sarnple (Figure 7.12). The baseline, however, is very high for this spectrum as well as for the spectra of surrogate samples exposed for two and four months (Figures 7.13 and 7.14, respectively), as a result of the high level of carbon black in the polymer systexn. As rnentioned previously, when wlcanized nanual rubber samples age (either nanually or artificially) the carbon black migrates to the dace. Carbon black absorbs very well in the infrared region. As the amount of carbon black at the surface increases. so does the amount of infrared signal which it absorbs. The baseline, therefore, will increase as the material ages until the Uitensity of the peaks (due to cis-l,4-polyisoprene) is masked and eventually obscured by the carbon black. This problem is intensified by the fact that the background is scanned against a carbon black reference membrane, which adds to the high baseline of the spectra.
There appears to be some change in the functional groups of the surrogate sample spectnim, afier only two months of QW exposure (Figure 7.13). The peak at 1661 cm-'has been identified as the stretching motion of the carbon, carbon double bond. This peak, however, seems to have broadened as a result of QUV exposure. The peak at 166 1 cm" diminishes and a peak around 1710 cm-' appears, compared to the PAS-FTIR spectrum of the unexposed vulcanized natural rubber sample. This increase in intensiy near 17 10 cm'' may be the result of oxidative degradation of the mlcanized natural mbber sample. An increase in this area wouid indicate an increase in the amount of carbonyl-containing groups which would be consistent with the oxidative degradation of vulcanized natual rubber as outlined in Chapter 3. After four months of exposure
(Figure 7.14), however, almost dl functional group information is obscured. The peaks due to CH2 and CH3 stretching motion are no longer visible. The baseline of the specmun has increased signifcantly, making it very difficdt to distin,esh any of the
peaks from the background with absolute certainty.
The naturally aged museum samples were aIso evaluated using the PAS-FTIR
technique. The baseline of museum samples using this technique is higher than would be
expected because of the carbon black in the polymer system; however, functional group
information is present in the spectra. The baseline in the rnuseurn sample spectra is lower
than that found in the surrogate sample spectra. This may be due to a lower level of
carbon black in the rnuseum sample formulations compared to that of the surrogate
sarnples. A11 peaks typical of cis-1,4-polyisoprene are present dong with some peaks
which indicate the presence of degradation products. The specm of the c. 1910
washing machine sample (Figure 7.15) exhibits two peaks (3388 cm-' and 1668 cm-'),
which rnay be due to absorbed water in the sample. There is also a peak at 1712 cm",
which is most likely due to degradation products that contain carbonyl groups. It is also
possible that the peaks at 3388 cm", 1668 cm" and 1712 cm" may be due to plasticizen
or other formulation components not present in the surrogate sample fomulation. The
rubber roller from which the washing machine sample was taken exhibits some hardening and development of a fine cracking pattern. This spectnim is typical of the spectra obtained frorn museum samples which have hardened as a result of age. The spectra of other museum samples that exhibit hardening are located in Appendix A, Figures A.l -
A.S.
The spectrum of the c. 1880 dnim cylinder press sarnple (Figure 7.16) exhibits peaks similar to those found in the washing machine sarnple spectra. This specintm exhibits al1 the peaks that are typical of cis-1,4-polyisoprene. The peaks at 3344 cm" and 1612 cm-', which may be due to absorbed water, are present. The peak at 1652 cm-' may
ais0 be due to the carbon, carbon double bond stretching motion. The peak at 1712 cm-',
present in the spectnun of the washing machine sample, is, however, not present in the
spectrum of the dnun cylinder press. The stmng peak at 1652 cm" may be masking the
presence of the carbonyl peak around 1712 cm-'.
One other difference between the washing machine and dmcylinder press
spectra is in the region between 1500 cm-' and 1300 cm-'. The two peaks at 1450 cm-'
and 1376 cm-' in the washing machine spectrum are well defined, yet there is no
defuiition of peaks in this region of the drum cylinder press spectrum. This may indicate
a greater degree of degradation in the dmcylinder press sample. ïhe peaks in this region are due to CH2 and CH3 bending vibrations. A decrease in these peaks would be expected as a result of aging. A decrease in the CH2 and CH3 stretching vibration region befiveen 2950 cm-' and 2850 cm-' wodd aiso be expected. The drum cylinder press specmim rnay indicate this because of the lack of definition in the peaks around 2932 cm-'.
8.4 Thennogravimetry
Thermogavimetric analysis of the surrogate sarnples and application of kinetics calculations to the resulting data yielded information on the usehl lifetime of the vulcanized natural rubber matenai when stored at a specific temperature. The TG curve of an unexposed smogate sample (Figure 7.17) indicates a weight loss between 300°C and 550°C. From the TG cuve it appears that this weight loss is a one-step process; however, examination of the DTG cuve for the same sample (Figure 7.1 7) suggests that two materials are evolving between 300°C and 550°C as thcre are two peaks on the DTG
curve. The first, at 380°CI is most likely due to the degradation of the main polymer, cis-
1.4-polyisoprene. The second peak, at 420°C, may result fkom the refomllng of
de-gradation products fiom the main polymer and the subsequent degradation of those
byproducts or it may be a component in the polymer system, which has a higher thermal
stability than cis- 1-4-polyisoprene.
Afier accelerated aging, either by oven or QW,the DTG curves of sunogate
samples (Figures 7.19-7.23) show a decrease in the 380°C peak. due to cis-1,4-
polyisoprene. The DTG curves of oven-exposed samples (Figures 7.19-7.22) also show
an increase in the peak at 420°C. There is only a slight decrease in the 380°C peak and
no noticeable increase in the DTG curve of a surrogate sample exposed in the QW for
three months (Figure 7.23).
Oven exposure took place at higher temperatures (230°C and 250°C). After only
70 hours of esposure, at 230°C, there was a noticeable decrease in the 280°C peak, as
well as an increase in the peak at 42O0C. The 380°C peak continued to decrease and the
330°C peak continued to increase as the duration of exposure continued. By 1 18 hours of
oven exposure, at 230°C, there was a marked decrease of the 580°C peak as well as an
increase in the 420°C peak. This decrease in the peak at 380°C is due to the degradation
of the cis-1 ,il-polyisoprene polymer backbone. The increase in the 47O0C peak may be
the result of the recombination of degradation products fiom cis-1,4-polyisoprene and
their subsequent degradation. There may, however, not be an actual increase in the arnount of material degrading at 470°C. If the main polymer has degraded, a larger percentage of the exposed sample's weight would be due to the component degrading at IZO°C than wouid have been found in the unexposed sample; therefore, the qwtity of
the component at 420°C may actually remain the same even though the peak appean ro
incrase.
The physical changes occurring in the samples after exposure at 230°C and 250°C
are slightly different. The samples exposed at 230°C appear to become brittie (after 70
hours of exposure) then become sofier and tacky (afler 1 18 hours of exposure). The
samples exposed at 250°C, however, do not appear to go through this brittle stage.
Samples examined afier 19 hours and 23 hours of exposure both showed a severe
softening of the material, to a much greater extent than the samples exposed at 230°C.
This may indicate that different degradation mechanisms are occmïng at different
temperatures.
The DTG curves of a surrogate sample afier oven exposure at 250°C (Figure
7.21 -7.22) shows the same phenornenon as the surrogate sample after oven exposure at
230°C. There is a decrease in the 380°C peak and an increase in the 420°C pe*.
According to the kinetics calculations, however, oven exposure at 250°C for 72 hous
should cause the same approsimate degadation (10%) of the material as found for the oven exposure at 230°C for 118 hours. By cornparison of the two DTG curves (Figures
7.20 and 7.22) there is a rnuch greater decrease in the 380°C peak than for the sample exposed at Z30°C for 118 hours. These changes in the DTG curves of QUV and oven exposed surrogate samples, however, indicate that the kinetics calculations do offer a good approximation of degradation time for the vulcanized natural rubber surrogate samples. 83Thermogravimetry-Fourier-Transform lnfiared Spectroscopy
Themogravimeq-Fourier-dom infrared spectroscopy was used in order to detemiine if any stnictural changes had occurred in the vdcanized natural rubber surrogate sarnples as a resdt of accelerated aging. Figure 7.24 indicates that most of the cis-i,l-polyisoprene is degrading around 400°C. In the spectnim at 400°C, dl of the peaks .pical of cis- 1,4-polyisoprene are present. Specifically this includes: the peaks at
3080 cm-'and 830 cm" (due to the =CH metchùig and wagging vibrations, respectively), the peaks around 2900 cm-' (due to CH2 and CH3 stretching vibrations), and the ow peaks around 1450 cm-'and 1370 cm-' (due to the CH, CH2 and CH3 bending vibrations).
Cis- 1+polyisoprene begins degrading between 300°C and 3S0°C. B y 3 50°C, the CHI and CH3 stretching bands are present in the spectrum. This is consistent with the TG cwe of the sme sample showing the main weight loss beginning at approximately
300°C. The intensity of al1 peaks increase to a maximum at 400°C, then slowly decreases as higher temperatures are reached. The CH2 and CH3 stretching bands are still present at
500°C. This is also consistent with the TG curve of this sample, which indicates that the weight loss due to cis- l ,I-polyisoprene ends between 500°C and 550°C.
TG-FTIR was also used to analyze a surrogate sample which was exposed in the
QW for three months. Figure 7.25 shows the spectra From this sample. These specm are almost identical to the spectra of the unexposed surrogate sample in Figure 7.14.
There is no indication of structurai change in the material, which would be seen by the disappearance or formation of a significant peak. There is, however, one change in the specm: at 45 1OC and 501 OC, the region between 1800 cm" and 1500 cm-' appears very noisy and goes below the baseline of the rest of the spectmn. This may be due to water vapor in the sample cell.
8.6 Scanriing Elecîron Microscopy
Significant changes in appearance occur in the vuicanized natural rubber material as a result of accelerated aging (both QWand oven). Table 7.13 summarized these changes, the most prominent of which is the random cracking pattern on the surface of the material, which developed very early (afier one week of exposure) in the accelerated aging process. The main cracks in this random cracking pattern meet one another to form polygon shapes which are relatively uniform in size; smaller cracks do branch off the main cracks which results in a similar cracking pattern within each polygon shape. These cracks propagate dom into the center of the rubber material rather than along the surface. As a result, the tops of the cracks (at the surface of the matenal) widen, creating a V-shape, ahose base is toward the center of the material. The edges of the cracks appear very jagged, especially, afier two months of QüV exposure (Figures 7.29-7.3 1).
This random cracking pattern is very similar to the cracking pattern found in naturally aged museum artifacts. The cracking found on the tires of a 1907 Harle?
Davidson motorcycle (in the coilection of the Henry Ford Museum and Greenfield
Village, Dearbom, Michigan) (Figure 7.32) is similar to that found on the vulcanized natural rubber surrogate samples exposed in a QUV. The cracks on the Harley Davidson tire also show the formation of polygon shapes in the nibber.
The random cracking pattern found on both the QUV exposed samples and the naturally aged rnüseum sample is different fiom the cracking pattern that developed on the oven-aged surrogate samples. The cracks that fomed after oven exposure do not
meet to form polygon shapes and have a more tented appearance than cracks found in the
samples exposed to QUV.
By magnimg the samples l5OOX (photomicrographs Iocated in Appendix E),
there aiso appean to be a change in the surface texture of the material. There is an
increase in the appearance of an orange peei pattern on the surface of the rubber. This may be due to erosion of the surface as a result of accelerated aging.
Another physical change in the vulcanized naturai rubber, resulting from accelerated aging, is the hardness of the matenal. The rubber in the QW-exposed samples exhibits hardening and ernbrittlement. The SEM images of the hcture points for the QW-exposed samples, seen in Figures 7.33-7.38 and described in Table 7.14, exhibit a significant change in the type of fracture in the matenal at different exposure times. The fractures become smoother than fractures in the unexposed vulcanized natural rubber. The mirror (serni-circular) shape, typicai of a more bnttle fracture, appears after two months of exposure and becomes more prominent with Licreased QUV exposure.
The lines formed in fracture become straighter and more defined. These changes in appearance indicate that the material is becoming more brinle as a result of QW exposure. In Figure 7.33, the fracture of the unexposed wlcanized natural rubber sarnple is tom and uneven. and begins at the upper corner of the sarnple (the upper lefi corner of the image). The most common fracture point for these specimens was a corner, as seen in
Figure 7.33; however, on occasion the fracture point was in the center of the specimen as seen in Figure 7.38. Tensile properties of the oven-aged samples were not evaluated because of their advanced state of degradation. Oven exposure at 230°C resulted in a marked change in the physicai properties of the matenal. .Mer 70 hours of oven exposure. the material had hardened and a severe cracking pattern had developed, most likely due to the loss of components which made the material soft and flexible (e-g. oit) or ÿicreased cross- linking. Afier 1 18 hours of oven exposure, however, the samples became noticeably sofier (likely due to the breakdown of the polymer backbone) and the cracking pattern became more severe. Breakdown of the polymer backbone will result in a decrease in cross-link density of the materid and, therefore, a sofier material.
This phenornenon was also noticed for the vulcanized natural rubber samples exposed in an oven at 250°C for 19 hours and 23 hours. These samples became very soft and tacky. It would be expected that the more severe conditions of a 30°C oven would lead to the breakdown of the polymer backbone in a shorter exposure time than those in the 230°C oven; however, as was seen in the TG data, the polymer backbone (the 380°C peak in the TG curve) did not appear as degraded From 250°C as it did from 230°C exposure.
5.7 Tensile Data
Evaluation of tensile properties of the surrogate samples has provided information about the changes in the physical properties of this material as a result of acceleraied aging. From Figure 7.39 we cm see that (as a result of QUV exposure) the tensile svength of the vulcanized natural rubber decreases as does the percent elongation of the specimens (Figure 7.10). Both of these charts indicate that the dcanized naturai rubber specimens become bnttle as a resdt of QW exposure. 9. CONCLUSIONS
This study has provided the author and, it is hoped, other conservation
professionals with information regarding the physicd and chemicai changes in
vulcanized nadrubber as a result of accelerated aging. The diagnostic tools evaluated
during this mtdy have shown varied degrees of usefulness for evaluatinp the degradation
of vulcanized natural rubber. The three Fourier-transfom infiared spectroscopy
techniques, especially, Vary in the* ability to evaluate the materiai. ATR-microscopy-
FTIR showed only a minor ability to do so. The inability of the germanium ATR crystal
to nithstand pressure prevented the achievement of good contact between the crystal and
the sample and, consequently, prevented reproducible spectra fiom being obtained. The high carbon black content of the vulcanized naniral rubber also compounded the problem by producing very noisy spectra with low peak intensity.
The Avatar OMNI-Sampler (Am) attachent was a much more reliable tool for evaluating the vulcanized natual rubber samples. The pressure tower on this attachrnenr was able to consistently provide enough pressure on the sample to achieve good contact
\vithout damaging the crystal, even when the surface of the material was uneven and crackcd (Le. on the degraded surrogate and rnuseum samples).
PAS-FTIR was found to be very useful for evaluating the severely degraded museum samples, which had become hard and brinle with age. The museum sample spectra exhibited good resolution of the peaks and good signal-to-noise ratio. The quality of the PAS-FTIR spectra was, however, dependent on the carbon black content of the mattrial. If the carbon black content is too hi&, as in the case of the surrogate samples, the hi& baseline of the specmim will obscure any functional group information. The
nanirally aged museum samples appear to have less carbon black, because of the
significantiy bener quality of the spectra obtained, compared to the surrogate sarnples;
however, tiis could not be confhmed without chemical analysis of the carbon bIack
loading in each sample.
Thermal analysis of the vuicanized natural mbber produced information on the thermal stability of the material. Kinetics calculations revealed that the vulcanized nadrubber surrogate samples have an expected iifespan of 945 years if stored at
136°C. These calculations were show to be relatively accurate for the aged surrogate samplrs; however. the museum sarnples have become severeiy degraded in a far shorter time penod (60-80 years). This suggests that thermal degradation rnay not be the main agent of degradation to which vuicanized natural mbber is subjected in a museum environment.
Therrnogravimetry-Fourier-transform infrared spectroscopy was usefil in that it showed no significant chemical change in the vulcanized naniral rubber as a result of three months of QUV exposure. This, however, does not conclusively indicate that no chemical changes were occurring in the material; rather it indicates that degradation occhng in the bulk of the matenal has not caused significant changes to the matenal's chemical structure or that the changes were not IR active. The resulü using the Avatar
OMNI-Sampler anachment, however, show a structural change at the surface of the material, indicating that there are chemical changes occurring at the surface.
Accelerated aging caused significant physical changes to wlcanized natural rubber. These physical changes differed depending on the type of accelerated aging (QUV or oven exposure) to which the sample was subjected. Samples became harder and more brittle with increased QW exposure, as was indicated by the decrease in tensile strength and percent elongation of the material. The randorn cracking pattern that developed as a resdt of QUV exposure is typical of the cracking found on mwum artifacts rhat have become hard and brittle over the. Therefore, it was concluded that chernical changes occurring in vulcanized natural rubber to produce a hardened material with a random cracking pattem are due the matenal's exposure to ultraviolet light.
Mer oven exposure, the wlcanized naniral rubber ulhately became very sofi and tacky, and revealed a cracking pattern that was noticeably different from that of the
QUV exposed samples, indicating that a different degradation mechanism had occurred.
In future research, experiments will be designed in order to appiy kinetics calculations to light aging methods such as QW andor Weatherometer exposure. The thermogravimetric analysis of other modem materials, particularly those currently being used by artists, would be of interest to this author and other conservation scientists investigating the degradation and preservation of modem artists' materials. Further research using the Avatar OMNI-Sarnpler attachment would also be useful. This technique shows promise for the evaluation of minute samples and materials containing carbon black. Expenmental protocols also need to be deveioped for quantieing the degradation of the vulcanized natural rubber material. Adelsrein, Peter Z., Reilly, James M., Nishimm Douglas W., and Erbiand, C. J., Recent
Findings on d cetate Film Stabi[is, ( 199 1),78-90.
Mlington, Caroline, "The Treatment of Social History O bjects Made of Natural Rubber,"
SSCR Modern Orgunic iMateriaIs: Edinburgh 1998, Edinburgh: SSCR Publication,
(1988), 123-132.
Baker. Mary T., "Conservation Issues for Modem Materials," Presening the Recent
Past, Chicago. iMarch 30 - April 1, 1995, ( 1995a), 1 1- 18.
Baker, Mary T., "Thermal Studies on Ancient and Modem Rubber: Environmental
Information Contained in Crystallised Rubber," Resins: Ancient and Modern,
Edinburgh: SSCR Publication, (1 995b), 53-56.
Baker. iMary T., "Ancient Mexican Rubber Artifacts and Modem Amencan Spacesuits:
Studies in Crystallization and Oxidation," MarerioIs Issues in Art and Archaeology
IV. vol. 4, ( 1995~), 213 -23 1.
Baker, iMary T., "Lifetime Predictions for Polyurethane-Based Recording Media Binders:
Determination of the 'Shelf-Lifeof Videotape Collections,"' Resins Ancient and
Modern, Edinburgh: SSCR Publication, (1995d), 106- 1 10.
Blank, Sharon, "An Introduction to Plastics and Rubber in Collections," Sudies in
Conservarion,35, (199O), 53-63.
Brovm, Michael E., Introduction to Thermal Analysis: Techniques and Applications,
London: Chapman and Hall, Ltd., (1988), 1-2 1.
Callister, Jr., William, Materials Science and Engineering: An Introduction. dfhed., New
York: John Wiley & Sons, Inc., (1 997), 109- 140. Calvini, P., Fransceschi, E. and Palk,D., "Artificially induced Slow-Fire in Shed
Papers; îTR, TG DTA and SEM," Science und Technologyfor Cultural Herirage,
vol. 5, no. 1, (19961, 1-11.
Carter. R. O.. Paputa Peck, M. C. and Bauer, D. R., "The Characterization of Polyrner
Surfaces by Photoacoustic-Fourier-Transfomi Infrared Spectroscopy," Polymer
Degradation andSîubility, vol. 23, (1989), 121-134.
Clavir, Miriam, "An Initial Approach to the Stabilization of Rubber from Archaeological
Sites and in Museum Collections," J. IIC-CG, vol. 7,nos. 1&2, (1 982), 3- 10.
Colrhup, Norman B., Daly, Lawrence H. and Wiberley, Stephen E., Introduction to
Infroed and Raman Spectroscopy, Boston: Academic Press, (1 990).
Cook. Ian, "Air Pollution and Aspects of Polymer Degradation," ICCM Bulletin, vol. 2,
no. 4, December, (1 976), 4-24.
Coson, Helen C., "Practical Pitfidls in the Identification of Plastics," Symposium 'Pi -
Saving the 2Q'11Cenlury.. The Conservafion of Modern Materiuls, 1 5 to 20 September
199 1, Ottawa, (1993, 395107.
Crighton, 1. S. and Hole, P. N., "The Effect of Hear on Wools: Thermogravimetry of
Keratin Fibres." Proceedings of the 5" lniernational Wool Textile Research
Conference, Aachen, (1976), 499-509. de la Rie, E. Rene. "Polymer Stabilizers. A Suwey with Reference to Possible
r\pplications in the Conservation Field," Studies in Conservation,33, (1 988), 9-22.
Derrick, Michele, Stulik, Dusan and Ordonez, Eugena, "Deterioration of Cellulose
Ninate Sculptures by Gabo and Pevsner," Symposium '91 - Saving the 2fhCentzuy: The Conservation of Modem &lrteriaZs IS to 20 Seprember 1991, Ottawa, ( 19931,
16% 180.
Douglas, Alison, The Mechanical Testing offree Film Acrylic and Oil Paint A4Lxture.s
and Lqyering at Various Percentages of Relative Humidity, Kingston: Queen's
University, (1 996).
Edge, M., Allen, N. S., Jewitt. T. S., Appleyard, I. H. and Horie. C. V., "Cellulose
Acetate an Archival Polymer Falls Apart," SSCR Modern Organic Materialsr
Edinburgh 1988, Edinburgh: SSCR Publication, (1 988), 67-79.
Einch, Fredenck R., Science and Technology oflubber, New York: Academic Press,
(1978),291-453.
Fenn, Julia, "Labelling Plastic Artifacts," Symposium '91 - Saving the 7flhCentu~: The
Conservation of Modern ~Clateriais,1 j tu 20 Septernber 1991,Ottawa, ( 1 9%)' 34 1 -
349.
Fenn, Julia, "Monitoring Cellulose Nitrate Emissions: A New Use for an Old Indicator,"
Polyrner Preprints, vol. 37, no. 2, ACS The Division of Polymer Chemistry, Inc.,
(1996), 170-171.
Garza-Valdes, Leonico A., "The Study of Maya Lapidary Techniques," Analytical Tools
in Archaeorneiry I. Newark. ( 1 985), 12.
Gleeson, J. D. andloadman, M. J. R., ''hInvestigation into the Yellowing of
Supposedly Non-staining Antioxidants," Polyrner Preprints, vol. 3 7, no. 2, ACS The
Division of PoIymer Chemistry, Inc., (1W6), 172- 173.
Grattan, D. W., "Rubber Deterioration: Cm Antioxidants Heip Save Artifacts?," IX-CG
Nerosletter. vol. XII, no. 3, (1986),12-14. Granan, David W. and Gilberg, Mark, "Ageless Oxygen Absorber: Chemicai and
Physicai Properties?" Studies in Come17ration,39, (1994), 2 10-2 14.
Granan, David W., "Degradation Rates for Some Hiaoric Polymers and the Potential of
Various Conservation Measures for MÙwriizing Oxidative Degradation," Symposium
'9 1 - S.@ the 2ghCentury: The Consemution of iWodern Mareri&, Ijto 20
September 1991. ûttawa, (1993),35 1-36 1.
Grartan, David W., "The Problern of Rubber Conservation," MnCentwy 1Materi~is,
Testing and Textile Conservation Harper 's Ferry: Harpers Ferry Teaile Group,
(1988), 125-128.
Grattan, David, The Oxidative Degradation of Organic Materiais and Its Importance in
Deterioration of Artifacts," J.IZC-CG, vol. 4, no. 1, (1 W8), 17-26.
Harrick Scientific Corporation, Optical Spectroscopy: Surnpling Techniques iknual,
Ossining: Harrick Scientific Corp., (1 987), PAS-2.
Hills, D. A., Heat Transfer and Vulcanisation of Rubber, Amsterdam: Elsevier
Publishing Co. Ltd., (1 97 l), 1-8.
Jurdana, Lucia E., Ghiggino, Kenneth P.. Leaver, Ian H. and Cole-Clarke, Peter,
"Applications of FT-IR Step-Scan Photoacoustic Phase Modulation Methods to
Keratin Fibers," AppliedSpectroscopy, vol. 49, no. 3, (1 999, 36 1-366.
Kaminitz, Marian, "Arnazonian Ethnographic Rubber Artifacts," SSCR Modern Organic
Mu~erials:Edinbwgh 1998, Edinburgh: SSCR Publication, (1 98 8), 143 - 150.
Katz, Sylvia, Eurly Plastics, Shire Publications Ltd., (1986).
Kauffman, G. B. and Seymour, R. B., "Elastorners,"Journal of Chemicai Education, vol.
67, no. 5, (1 990),422-423. Loadman, M. J. R., Trospects for Rubber Conservation in Museums," Rubber Division:
drnerican Chernicul Society meeting April19-22, 1994, Hertford, Tun Abdul Razak
Laboratory, (1994).
Loadman, M. J. R., "Rubber: Its History, Composition, and Prospects for Conse~ation,"
Symposium '91 - Sming rhe 2@ Century: The Conservation of Modern ~Matetia1.s.15
to 20 Seprember 1991, Ottawa, (1993), 59-80.
Loadman. M. I. R., The Exploitation of Nafural Rubber, Tun Abdul Razak Laboratory,
Hertford, (1 995).
Mdtby, Susan, "From the Conservatory.. .," Vintage Times,Jd y ( 1997).
Maltby, Susan, "Rubber: The Problem that becomes a Solution," SSCR Modern Organic
!Cï~rerials:Edinburgh 1998, Edinburgh: SSCR Publication, (1 988), 15 1- 1 57.
Marcilla, A. and Belnan, M., "Kinetics Models for the Thermal Decomposition of
Commercial PVC Resins", Polymer Degradation and Stability, voi -53, no. 2, ( 1W6),
25 1-260.
McCord, Margaret and Daniels, Vincent, "The Deterioration and Preservation of Rubber
in Museums: A Literature Review and Survey of the British Museum's Collections,"
SSCR Modern Organic hfaierials: Edinburgh 1998, Edinburgh: SSCR Publication,
(1988), 133-141.
Mecklenburg, LM.F.. '-The Effects of Atmosphenc Moisture on the Mechanical Properties
of Collagen Under Equilibrium Conditions," AIC 161h Annual Meeting, New Orleans,
June I-5, 1988, Washington: AIC, ( 198 8), 23 1-244.
Nicolet halytical Instruments, Mc-PlanTMOpernrion, Madison, Nicolet Instrument
Corporation, (1 990). Nicolet halytical Inmuments, Systern 800 Refrence, Mudison, Nicolet Instrument
Corporation, (1 989).
Paroii, Rdph M. and Delgado, Ana H., "Applications of Thermogravimetry-Fourier-
Transform IR Spectroscopy in the Characterization of Weathered Sealants," From
Provder, Theodore, et al. Hjphenated Techniques in Polymer Chmacterization:
Specnoscopic and Other Methods, ACS Symposium Senes No. 58 1. /unencan
Chernical Society, (1994), 129- 148.
Pilcher, J. R., "Some Applications of Scanning Electron Microscopy to the Study of
iModern and Fossil Pollen," Uster J. Archaeoiogy, vol. 3 1, (1968), 87-9 1.
Pullen, Derek and Heuman, Jackie, "Cellulose acetate Deterioration in the Sculptures of
Naum Gabo," SSCR Modern Organic Materials: Edinburgh 1998, Edinburgh: SSCR
Publication, (1 988), 57-66.
Sale, Jr., Don?'The Effect of Solvents on Four Plastics Found in Museum Collections: A
Treatment Dilemma," SSCR Modern Organic Materialsi Edinburgh 1998,
Edinburgh: SSCR Publication, (1 988), 105- 144.
Schidrowitz, P. and Dawson, T. R., History of the Rubber Industry, Cambridge: W.
Heffer and Sons Ltd., (1952), 1-63.
Shashoua, Y.and Oddy, W. A., "inhibitive Treatrnents for Rubber," Conservation
Research Interna[ Report, The British Museum, Department of Conservation, (1990),
1-10.
Shashoua, Yvonne and Thomsen, Scott, "A Field Trial for the Use of Ageeless in the
Preservation of Rubber in Museum Collections," Symposium '91 - Saving the 2gh Centzry: The Conservation of iwodern Materials, 15 ro 20 September 1991, Onawa,
(1 993), 363-372.
Silverstein, R-M.,Bassler. G. Clayton and Mord, Terence C ., Spectromenic
Identijkation of Organic Compoundr. 5" ed , New York: John Wiley & Sons, Inc.,
(1991), 91-102.
Simon, S., Boehm, H. P. and Snethiage, R., "A Smface-Chernical Approach to Marble
Conservation," Proceedings of the 7' lntemtional Congress on Deterioration and
Conservafion of Stone. Lisbon. 15-18 June 1992, Lisbon: Laboratono Nacional de
Engenharia Civil, (1 9E), 85 1-859.
Skoog, Douglas A. and Leary, James J., Principies of lnrhtmentai Analysis, 4" ed, Fon
Worth: Saunders College Publishing, (1 992).
Smith, Anthony W., "Effects of Aqueous Treatments on the Mechanical Properties of
Paper," The Interface Between Science and Conservation, no. 16, London: The British
Museum, ( 1997), 59-65.
Smith, Brian C.. Fundamentais of Fourier-Transform lnfrareed Spectroscopy, Boca
Raton: CRC Press, (1 996).
Sowy. JO, Rirbber, New York: Crane, Russak & Company, Inc., (1 977),8-19.
Stern, H. J., Rzibber: iVatwaI and Syntheric. yd ed., London: Maclaren and Sons, Ltd.,
( 1967), 1 -254.
Stevenson, Robert D., "A. W. McCurdyTsDeveloping Tank: Degradation of an Early
Plastic," Svmposium '91 - Saving the 2dh Centuryr The Consemation of Modern
Lbfateriak i j to 20 September 1991. Ottawa, (1 993), 183- 187. Stewart. R., Linlejohn, D., Pethrick, R A. and Tement, N. H., "The Use of Accelerated
;\ging Tests for Shidying the Degradation of Cellulose," ICOM Cornmitteefor
Consermtion, I 1" Triennid Meeting in Edinburgh. 1-6 Spe ternber 1996. London:
James & James, Ltd., (1996), 967-970.
Stewart, R., Linlejohn, D., Pethrick, R. A., Tement, N. H., and Quye, A., "halytical
Studies of the Degradtion of Cellulose Nitrate Plastics in Museums," Polymer
Preprints. vol. 37, no. 2, ACS The Division of Polyrner Chemistrv, Inc., (1996), 168-
169.
Stoughton-Harris, Clare, "Treatrnent of 70"~entu-yRubberized Multimedia Costume:
Conservation of a Mary Quant Raincoat (ca. 1967)," Symposium '91 - Saving the 2Vh
Ceniury : The Conservation of Modern Muteriak. l 5 to 20 September 1 991. Ottawa.
(I993), 213-221.
Tement, Norman, "An Introduction to Poiymer Chemistry Relevant to Plastic
Collections," SSCR Modern Organic Materials: Edinburgh 1998, Edinburgh: SSCR
Publication. (1 988),3- 10.
Tsai. Fei Wen and van der Reyden, Dianne, "Analysis of Modem Chinese Paper and
Treatment of Chinese Woodblock Pnnt," The Poper Conservator. vol. 2 1, (1 997), 18-
62.
Urban, Marek W ., A ttenuated Toial Reflecrance Spearoscopy of PoZymers: Theory and
Procrice, Polper Surfaces and Interfaces Series, Washington, DC: Arnerican
Chernical Society, (1 W6), 3-62. Wiles, David M., "Changes in Polyrneric va te rials with The," Symposium '91 - Sming
the 2tfh Cenhqy: The Comervution of Modern Materiais, I 5 to 20 September 1991,
Ottawa, (i993), 105-1 11.
Williams, G. R., "The Breakdown of Rubber Polymers by Microorganism," Infernational
Biodeterioration Bulletin, vol. 18, no. 2, (1982), 3 1-36.
Williams, Scott, "Composition Implications of Plastic Artifacts: A Survey of Additives
and Their Effects on the Longevity of Plastics, " Symposium '91 - Saving the 2th
Century: The Conservation of Modern Materiak, 15 fo 20 Septerder 199 1, Ottawa,
(1993), 135-152.
Yang, C. Q. and Freeman, J. M., "Photo-oxidation of Cotton Cellulose Studied by FR-IR
Photoacoustic," AppZied Spectroscopy, vol. 45, no. 10, (1 99 1), 16%- 1698. APPENDIX A: Photoacoustic-Fourier-Transform Infkmd Spectra of Naturally Aged Museum Samples
Fi-mire A. 1 PAS-ETIR Spectnim of a 19 15 Cadillac Tire Sample
W avenumbers (cm-')
Figure A.2 PAS-FTIR Spectnim of 1903 Cadillac Hom Bulb Sample Fi-me A.3 PAS-FTIR Specmun of 1903 Ford Mode1 A Hom Bulb Sarnple
O 4000 3000 2000 1O00 Wavenumbers (cm-')
Figure A.4 PAS-FTIR Spectm of Harley Davidson Tire Sarnple
W avenum bers (cm") Fi-me A.5 PAS-FTIR Spectm of 1899 Locomobile Sample
Wavenurnbers (cm-')
Figure A.6 PAS-FTIR Spectnim of Rubber Shoes SampIe
O 1 4000 3000 2000 f O00 Wavenum bers (cm") Fi-me A.7 PAS-FTIR Spectruxn of c. 1864 Gordon Oscillating Cylinder Press Sample
7 4I 1651
4000 3000 2000 1O00 W avenumbers (cm-') APPENDM B: Resdts of Activation Energy and Degradation Time Determinations
Fiaure B. 1 Activation Energy and Degradation Time Determinations for 230°C Fi+me B.? Activation Energy and Degradation Tirne Detemination for 250°C APPENDIX C: Graham-Schmidt Reconstniction Cwes
Fi-gxe C. 1 Gram-Schmidt Reconstruction for Unexposed Vulcanized Naniral Rubber
..m...... W... 1.w. W...... 1- ...1...1. =r.T.d d. 00 {o. 00 $0.00 i0.00 40.00 RE'TENfION TI= (MIN) I B 1 160 166 237 3b6 3% 993 si2 SB 1 650 ORTa POINTS
Figure C.2 Gram-Schmidt Reconstruction for Vulcanized Naturd Rubber after Three Months of Q W Exposure APPENDM D: Scanning Electron Microscopy Images of Unexposed and Exposed Vdc&ed Natural Rubber at 50X Magnification
Figure D.1 SEM Image of Unexposed Vulcanized Natural Rubber
Figure D.2 SEM Image of Vulcanized Natural Rubber after One Week of Exposure Figure D.3 SEM Image of Vulcanized Natural Rubber after One Month of Exposure
Figure D.4 SEM Image of Vulcanized Natural Rubber after Two Months of Exposure 134
Figure D.5 SEM Image of Vdcanized Naturd Rubber afler Three Months of Exposure
Figure D.6 SEM Image of Vulcanized Nahiral Rubber &er Four Months of Exposure APPENDM E: Scanning Electron Microscopy Images of Exposed Vulcanized Naturd Rubber at L 500X Mapification
Figure E. I SEM Image of Vulcanized Natural Rubber after One Week of Exposure
Figure E.2 SEM [mage of Vuicanized NadRubber after One Month of Exposure Figure E.3 SEM Image of Vulcanized Natural Rubber after Two Months of Exposure
Figure E.4 SEM Image of Vulcanized Natural Rubber after Three Months of Exposure Figure ES SEM Image of Vdcanwd Na- Rubber after Four Months of Exposure APPENDM F: Mechanical Testing Data for Unexposed and Exposed Vdcanized Naturai Rubber
Table F. 1 Mechanical Testing Dam for Unexposed Vulcanized Natuml Rubber
THICKNESS GAUGE DISPLACEMENT % LOAD STRESS (mm) LENGTH ATPEAK(rnm) SMAT AT PEAK (-1 AT PEAK (MW PEAK m
Mean Standard
I 1 I 1 were er luded because of their position of fiacture
Table F.2 Mechanical Testing Data for Unexposed Vdcanized Naturai Rubber (continued)
SPECIMEN DISPLACEMENT % STRAIN LOAD AT STRESS AT Yo NUMBER AT BREAK (mm) AT BREAK BREAK (KN) BREAK (MPa) ELONGATION (%) AT BEEAK
3' 123 -90 495 -6 02725 24.5 8 495.6 4* 78-55 3 14.1 0.1228 10.18 3 12.0 5' 121.70 486.8 026 12 23.47 486.8 6 133 -60 534.3 0383 1 26.64 534.4 7' 13 1.90 527.6 0.3085 25.70 527.6 8 132-70 530.8 0.2992 25.80 530.8 9' t 35.00 540.0 0.3389 27.32 530.0 1O 128.80 5 15.2 0.30 16 24.50 5 15.2 1 blean 130.00 520.0 03839 25.20 520.0 Standard 2.97 11.9 0.0 165 1.12 da 1 Deviarion 1 1 1 1 1 *these specirnens were exctuded because of their position of fiacture 139
Table F.3 Mechanical Testing Data for Vuicanized Naturai Rubber afier One Week of Exposure
WIDTH THICKNESS GAUGE DISPLACEhENT (mm) (mm) LENGTH AT PEAK (mm)
Stondard 1 Deviation were excluded of their position fracture
Table F.4 Mechanical Testing Data for Vuicanized Natural Rubber after One Week of Exposure (continued)
SPECIMEN DISPLACEMENT % STRAiN LOAD AT STRESSAT % NUMBER AT BREAK (mm) AT BREAK BREAK (KN) BREAK ELONGATION (%) ! (MW AT BREAK (%) 3 1 130.6 482.4 0.2744 24.65 482.4 -3 1 18.4 473 -6 03630 23.13 473 -6 3* 123 .O 492.0 0.3 10s 25.63 492.0 4 121.8 487.3 0.3024 24.65 487.2 5 113.4 453.6 03862 2 1.32 453 -6 6 114.1 456.4 0.2948 2 1.75 456.4 7 1 10.6 442.4 0.2629 22.02 442.4 8 1 10.8 443 2 03489 2 1.27 443 -2 9 109.1 436.4 0.36 16 30.85 436.4 1O 1 14.6 458.4 03716 2 1.66 458.4 Mean 1 14.8 459.3 03740 22.37 459.3 Standard 4.5 18.1 0.0174 1.44 da 1 Deviation 1 1 1 1 1 1 *these specimens were excluded because of their position of fracture 140
Table F.5 Mechanical Teting Data for Vulcanized Naturai Rubber after One Month of Exposure
SPECIMEN WIDTH THICKNESS GAUGE DISPLACEMENT % LOAD WLBER (mm) (mm) LENGTH ATPEAK(mm) STRAIN AT AT PEAK (mm) AT PEAK uz.( PEAK (KN)
- - L 1 O* 6.000 1.836 25.00 109.8 439.2 0.2332 Mean 6.000 2.084 35.00 106.9 427.4 03541 Standard 0.000 O. 165 0-00 2.1 8.6 0.0289 [ Deviarion 1 1 1 1 1 1 *these specimens were excluded because of their position of fiacture
Table F.6 Mechanical Testing for Vulcanized Natural Rubber afler One Month of Exposure (continued)
SPECIMEN DISPLACEMENT % STRAN LOAD AT STRESS AT % NUMBER AT BREAK (mm) AT BREAK BREAK (KN) BREAK ELONGATION (%) (MW AT BREAK (%) 1 108.5 434.0 0.2703 2 1 -23 431.0 -7 1 08.4 433.6 03747 2 1.48 433.6 3' 103 -6 414.4 02679 19.18 4 14.4 4 105 -9 423 -6 0.25 16 18.57 433 -6 5 102.5 4 10.0 0.2 148 I 18.59 410.0 6 105.4 43 1 -6 0320 1 19.44 421 -6 7 107.5 430.0 03822 20.83 1 430.0 8 107.8 43 1.1 03877 2 1.63 43 1.2 9 108.8 435.1 0.23 1 1 20.57 435.2 1 O* 109.8 439.2 0.2332 21.17 439.2 Mean 106.9 427.4 0.254 1 20.29 427.1 Standard 2.1 8.6 0.0289 1.26 da 1 Deviation ( 1 1 1 *these specimens were excluded because of iheir position of Fracture Table F.7 Mechanical Testing Data for Vulcanized NadRubber after Two Months of Exposure
Table F.8 Mechanical Testing Data for Vulcanized Natural Rubber after Two Months of Exposure (continued)
SPECIMEN DISPLACEMENT % STRAZN LOAD AT STRESS AT ?/a NUMBER AT BREAK (mm) AT BREAK BREAK (KN) BREAK ELONGATlON (%) (MW AT BREAK (%) 1 92.1 O0 368.400 16.010 , 0300 368.4 -7.. 99.170 396.700 17.920 0.23 1 396.7 J 83.720 334.900 13.330 O. 145 334.9 J 97.340 3 89.400 17.100 O. 187 389-4 5 93.580 6 99.350 397.400 19.380 0.23 7 397.4 7 88.750 355.000 15 -560 0.303 355.0 8 94.700 378.800 16.870 0218 378.8 9 94.660 378.600 17.670 O. 199 378.6 1 O 98.850 395.400 18.120 O. 198 395.4 Mean 94.120 376.500 16.870 0.203 378.3 Standard 5.050 20200 1,660 0.025 da Deviation I I I I f I *these specimens were excluded because of their position of fracture Table F.9 Mechanical Testing Data for Vulcanized Naturai Rubber after TZuee Months of Exposure
SPECIMEN WIDTH THICKiWSS GAUGE DISPLACEMENT % LOAD STRESS AT MJMBER (mm) (mm) LENGTH ATPEAK(mm) STRAiN AT I (-1 AT PEAK Wpa) PEAK (KY) I I (%) L 1 6.000 1.843 25 .O0 94.39 377.6 0.1772 16.02 -7" 6.000 1.83 1 25.00 93.1 1 372.4 0.1672 15.14 3 6.000 1 2.139 25 .O0 93.14 372.6 1 0.2035 15.86 4 1 6.000 2.089 25.00 94.9 1 379.6 03083 16.62 5 6.000 1.985 25.00 92.68 370.7 03041 17.14 6 6.000 2.0 1 1 25.00 . 95.45 381.8 . 02116 7 8 9 * 6.000 3.087 25 .O0 92.04 368.2 0.1966 15.7 1O 6.000 2.093' 25.00 9 1.O3 364.1 0.1962 15.6 1 Mean 0.000 2.007 25.00 93 -48 373.9 O. 1973 16.38 Standard 0.000 0.1 13 0.00 1.4 5.9 0.0 165 0.85 Deviation I *these spçcimens were excluded because of their position of fiacnire
Table F. 10 Mechanical Testing Data for Vulcanized Natual Rubber after Three Months of Exposure (continued)
SPECIMEN DISPLACEMENT % STRAM LOAD AT NuMBER AT BREAK (mm) AT BREAK BREAK (KN) STRESSBREAK AT / ELONGATION' 1 (%) (MW AT BREAK (%) t 94.39 377.6 O. 1772 16.02 ! 3 77.6 2 93.11 1 3 72.4 O. 1672 15.14 1 372.4 3 93.14 372.6 0.2035 15.86 3 72.6 4 94.9 1 379.6 0.2083 16.62 379.6 5 91.68 1 370.7 0.204 1 17.14 370.7 6 95.45 381.8 0.21 16 17.54 j 381.8 7 93.1 1 3 72.1 031 06 17-12 3 72.4 8 90.23 360.9 0.1921 16.2 1 360.9 9 92.04 1 3682 0.1966 15.7 368.2 1 O 9 1.O3 1 364.1 0.1962 15.6 t 364.1 Mean 93 -48 3 73 -9 O. 1973 16.3 8 374.1 Standard 1 -4 5.9 0.0 1 65 0.85 nia Deviation 'these specimens were exciuded because of their position of bcture Table F. 11 Mechanicd Testing Data for Vdcanized Natural Rubber after Four Months of Exposure
1 Deviation 1 1 1 1 1 *these specirnens were excluded because of their position of fracture
Table F. 12 Mechanical Testing Data for Vulcanized NadRubber afier Four Months of Esposure (continued)
1 SPECIMEN 1 DISPLACEMENT 1 % STRAM 1 LOAD AT STRESS AT ( % 1 NUMBER AT BREAK (mm) AT BREAK BREAK (KN) BREAK ELONGATION (%) (MW AT BREAK (%) 1 88.00 352.0 O. 1787 12.920 332.0 2 9 1.54 366.2 O. 1865 13 -460 3 66.1 L I 3* 79.94 3 19.8 O. 1448 10.980 3 19.8 4 72.54 290.2 0.1241 9,126 290.2 j* 7 1.83 287.3 O. 1288 9.23 l 287.3 6 77.5 1 3 10.0 0.1419 10.130 3 10.0 7* 72.35 289.4 O. 1306 9.0 18 289.4 8 67.56 270.2 O. 1 076 7.94 1 270.2 9 * 6930 276.8 0.1 126 8.402 276.8 1 O 7 1 -76 287.0 0.1 178 8.504 287.0 bf ean 78-15 3 12.6 0.1428 10.350 3 13.6 Smdard 1 9.60 38.4 0.0329 2.326 1 nia 1 Deviation 1 1 1 1 *these specimens were excluded because of their position of fcacture IMAGE EVALUATION TEST TARGET (QA-3)
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