The Kinetics of a Methyl Hethacrylate Polymerization Initiated by the Stable Free Radicals in Irradiated Polytetrafluoroethylene and Properties of the Resultant Graft Polymer
A Dissertation Presented to The Faculty of the College of Engineering and Technology Ohio University
In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
Karen Ann Ehnot Donato --. June, 1987
OHJO UNIVERSITY LIBRARY @ 1987
Karen Ann Ehnot Donato
All Rights Reserved This dissertation has been approved
by the Department of Chemical Engineering and the College of Engineering and Technology of Ohio University
Associate Professor of Chemical Engineering
Dean of the College of Engineering and Technology TABLE OF CONTENTS Page List of Figures vi
List of Tables XV List of Appendices xvi ii Acknowledgment ixx I. Introduction 1 11. Polytetrafluoroethylene 3 11.1 Structure and Properties of PTFE 3 11.2 Effects of Radiation on Polytetrafluoroethylene 11.3 Melt Extrudable Fluorocarbon Resins 11.4 Radiation Induced Grafting of PTFE Films with Vinyl Monomers
111. Free Radical Chain Polymerization 111.1 Theory of Free Radical Polymerization 111.2 Inhibition in Free Radical Polymerization 111.3 Hethyl nethacrylate Homopolymerization 111.4 Gel(Trommsdorf) Effect IV. Kinetics node1 for Irradiated PTFE Initiated HM Polymerization IV. 1 Kinetics Model from Earlier Work(69) V. Experimental Procedure for Production of the PTFE-PW Graft Polymer V. 1 Test Tube Runs V. 2 Factorial Design and Reaction Conditions for the Scaled-up Reaction
V. 3 Kinetics Runs in Bulk VI. Results of the Graft Polymerization VI.l Test Tube Factorial VI. 2 Bulk Factorial
VI. 3 Kinetics Data in Test Tubes(68) VI.4 Kinetics Runs in Bulk
VI. 5 Temperature Excursions During Scaled-up Reactions VI. 6 Power Levels for Agitation VII. Discussion of Kinetics Results VII.l Test Tube Factorials VII. 2 Scaled-up Factorial VII. 3 Comparison of Test Tube and Bulk Factorials VII.4 The Mechanics of the Reaction VII. 5 Undesirable Side Reactions VII.6 Determination of Ro VII. 7 Solution of the Conversion Equations VII. 8 Solution of Conversion Equation for Test Tube Runs VII.9 Bulk Reactor Data VII.10 Prediction of Conversion in the Factorial Runs from the Rate Constants in the Kinetics Runs VII.ll Estimation of the Number of PKM Repeat Units per Chain VII.12 Temperature Excursions VII.13 Agitation Excursions VIII. Background for Polymer Characterization VIII.l Rheology VIII.1.a Melt Flow Behavior VIII.1.b Rheology and its Governing Equations VIII.1.c Flow Instabilities VIII.1.d Die Swell VIII.2 Temperature Transitions VIII.2.a Glass Transition Temperature VIII.2.b Melting Temperature VIII.2.c Determination of Glass Transition and Melting Temperatures VIII.3 Resistance of Polymers to Chemical Attack VIII.4 Mechanical Properties of Polymers VIII.4.a Elastic Modulus VIII.4.b Dynamic Mechanical Analysis VIII.4.c Mechanical Properties and Transition Temperatures IX. Equipment used for Product Characterization IX. 1 Melt Rheology 1X.l.a Instron Melt Rheometer 1X.l.b Kayeness Melt Rheometer IX. 2 Temperature Transitions IX. 3 Chemical Resistance IX. 4 Dynamic Mechanical Testing X. Results of Product Characterization 128 X. 1 Melt Rheology 128 X.1.a Instron Melt Rheometer 128 X.1.b Kayeness Melt Rheometer 128 X. 2 Differential Scanning Calorimetry 154
X. 3 Chemical Resistance 175 X. 4 Dynamic Mechanical Analysis 177 XI. Discussion and Interpretation of Product Characterization 185 XI.l Melt Plow Behavior 185 XI.1.a Instron Melt Rheometer 185 XI.1.b Melt Rheology on the Kayeness Rheometer 186 XI. 2 Differential Scanning Calorimetry 201
XI. 3 Chemical Resistance 203 XI.4 Dynamic Mechanical Analysis 205 XII. Applications 210
XIII. Summary 212 XIII.l Conclusions 212 XIII.2 Recommendations 215 v
XIV. Appendices 217
XV. Bibliography 243
XVI. Abstract following page 249 List of Finvres
Page Figure 1: Melt viscosity of irradiated PTFE as a function of dose(l5). 7 Figure 2: Degree of grafting-time curves at various preirradiation doses (Mrad) using acrylic acid and PTFE films. Doses(Mrad): (0) 1; (0) 3; (A) 5; 6)10. Grafting Conditions: AAc conc, 40 wt %; grafting temperature, 308K(35OC); film thickness, 80 m(40).
Figure 3: Degree of grafting-time curves at various acrylic acid concentrations using PTFE films: preirradiation dose, 5 Mrad; grafting temperature, 308K(35OC); film thickness, 80ym(40). Figure 4: Degree of grafting-time curves at various grafting temperatures(K(OC)) using acrylic acid PTFE films. Temperatures: (0) 288(15); (0)298(25); (A) 308(35); (0) 318(45); (0) 333(60). Grafting conditions, except preirradiation dose (5 Mrad), are the same as in Figure 2(40). Figure 5: Degree of grafting-time curves at various PTFE film thicknesses (~m)using acrylic acid. (A) 80; (0) 130; (o) 190. Grafting conditions, except preirradiation dose (5 Wad), are the same as in Figure 2(40). Figure 6: The change of mechanical properties of the irradiated PTFE films grafted with acrylic acid on wetting in distilled water as a function of degree of grafting. Grafting conditions: acrylic acid concentration, 40 wt X; grafting temperature, 308K(35OC); film thickness, 804m(38). Figure 7: Equipment used for scaled up reactions. Figure 8: Log-probability plot of particle size distribution of DLX-6000 as received. List of Figures (Cont.) Figure 9a: ESR scan of DLX-6000 as 5eceived. Conditions: G = 2.0 X 10 ; scan time = 4 minutes! Mod = 2G. For DPPH, G = 2.5 X 10 , Mod = 1G. Figure 9b: ESR scan of particles with a diameter greater than 150 microns in DLX-6000. Conditions are the same as in Figure 9a. DPPH and PTFE curves are slightly displaced compared to Figure 9a.
Figure 9c: ESR scan of particles with a diameter less than 150 microns in DLX-6000. Conditions are the same as in Figure 9a. Figure 10a: Conversion to graft versus time at 333K(60°C) in test tubes with Fluone L-169 in a 1:3 ratio with HMA. The predicted curve from Equation IV.1.9 is shown. Figure lob: Degree of Grafting versus time at 333K(60°C) in test tubes with Fluone L-169 in a 1:3 ratio with MU. The predicted curve from Equation IV.l.ll is shown. Figure lla: Conversion versus time at 353K(80°C) in test tubes with 1 gram Fluone L-169 to 3 milliliters IMA. The predicted relationship from Equation IV.1.9 is shown. Figure llb: Degree of Grafting versus time at 353K(80°C) in test tubes with 1 gram Fluone L-169 to 3 milliliters !MA. The predicted relationship from Equation IV.l.ll is shown. Figure 12a: Conversion to graft versus time at 343K(70°C) in test tubes with 2 grams of Polymiste F-5A to 5 milliliters H)IA. The predicted relationship from Equation IV.1.9 is shown. Figure 12b: Degree of Grafting versus time at 343K(70°C) in test tubes with 2 grams of PolymisteF-5A to 5 milliliters M. The predicted relationship from Equation IV.l.ll is shown. 54 List of Figures (Cont.) Figure 13a: Per cent conversion to graft versus time at 343K(70°C) in the bulk reactor. The predicted relationship from equation IV.1.9 is shown. Figure 13b: Degree of grafting versus time at 343K(70°C) in bulk reactor. The predicted relationship from equation IV.l.ll is shown.
Figure 14a: Per cent conversion to graft versus time at 353K(80°C) in the bulk reactor. The predicted relationship from equation IV.1.9 is shown. Figure 14b: Degree of grafting versus time at 353K(80°C) in bulk reactor. The predicted relationship from equation IV.l.ll is shown. Figure 15: Total conversion from scaled-up reactor for one hour reaction times as a function of temperature.
Figure 16: Conversion to graft from scaled-up reactor for one hour reaction times as a function of temperature. Figure 17: Conversion to homopolymer from scaled-up reactor for one hour reaction times as a function of temperature. Figure 18: Degree of Grafting for scaled-up reactor for one hour reaction times as a function of temperature.
Figure 19: Reactor temperature as a function of time for a bulk reaction at 333K(60°C) for one hour.
Figure 20a: Reactor temperature as a function of time for bulk reactions at 343K(70°C) for one hour. Figure 20b: Power level as a function of time for bulk a reaction at 343K(70°C) for one hour. Figure 21a: Reactor temperature as a function of time for bulk a reaction at 353K(80°C) for three hours. List of Figures (Cont.)
Figure 21b: Power level as a function of time for a bulk reaction at 353K(80°C) for three hours. Figure 22: ESR scan of LX 6000. For PTFE: G = 2.0 X 109. Mod- = 2.06. For DPPH: G = 2.5 X 10'; Mod = 1.06. Figure 23: ESR scan of Polymist" F5A. Curve 1 is at the same conditions use9 in Figure 22. Curve 2 is at G = 4.0 X 10 . Figure 24: ESR scan of ljluona L-169. For PTFE: G = 2.0 X 10 Mod = 2.06. For DPPH: G = 2.5 X loo: Mod = 1.W. Figure 25: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 333K(60°C) using Fluon* L-169 in a ratio of 1 gram PTFE to 3 milliliters HHA. A line with a slope equal to 1 is shown. Figure 26: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 353K(80°C) using Fluon* L-169 in a ratio of 1 gram PTFE to 3 milliliters HHA. A line with a slope equal to 1 is shown. Figure 27: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 343K(70°C) using Polymist' F-5A in a ratio of 2 gram PTFE to 5 milliliters W. A line with a slope equal to 1 is shown. Figure 28: Parity Plot of graft conversion values predicted from equation VII.7.1 versus experimental values for the bulk reactions at 343K(70°C) using DLX-6000 in a ratio of 1 gram PTFE to 3 milliliters H)IA. A line with a slope equal to 1 is shown. List of Figures (Cont.) Figure 29: Parity Plot of graft conversion values predicted from equation VII.7.1 versus experimental values for the bulk reactions at 353K(80°C) using DLX-6000 in a ratio of 1 gram PTFE to 3 milliliters MMA. A line with a slope equal to 1 is shown. Figure 30: Conversion profile for methyl methacrylate polymerization depicting different phases of reaction(76,77). Figure 31: Schematic of the shear stress and shear rate when a polymer melt is confined by two parallel plates(78). Plate A moves with velocity, v, caused by the force, F; plate B is stationary. The shear rate, du/dr, is defined as the rate of change of the liquid velocity across the plate separation, r. Figure 32: Description of materials by the response of their viscosity to shear rate(78-80). Figure 33: Specific volume of a polymer as a function of temperature. T is the glass transition temperature of th6 amorphous regions. T is the me1 t ing of the crystalline domainsy42). 112 Figure 34: Response of elastic and viscoelastic materials to a sinusoidal stress(ll4). 117 Figure 35: The regions of viscoelastic behavior of amorphous polymers(75). Figure 36: Schematic of sample deformation in a DW(115). 126 Figure 37: Explanation of the equations used to calculate the elastic and shear moduli using a DHA(114). 127
Figure 38a: Shear stress of PHHA homopolymer (Elvaciteb 2051) as a function of shear rate at 473K(200°C) and 488K(215OC). Figure 38b: Apparent viscosity of PWhomopolymer (Elvaciteb 2051) as a function of shear rate at 473K(200°C) and 488K(21S°C). List of Figures (Cont.) Figure 39: Photograph of PHNA (Elvacitee 2051) extruded at 488K(215OC). Figure 40a: Shear stress of PTFE micropowder (DLX-6000) as a function of shear rate at 488K(215OC) and 543K(270°C). Figure 40b: Apparent viscosity of PTFE micropowder (DLX-6000) as a function of shear rate at 488K(215OC) and 543K(270°C). Figure 41: Photograph of PTFE micropowder (DLX-6000) extruded at 543K(270°C). Figure 42: Shear stress and apparent viscosity as a function of shear rate for the graft polymer extruded at 473K(200°C). Figure 43: Shear stress and apparent viscosity as a function of shear rate for the graft polymer extruded at 488K(215OC).
Figure 44a: Shear stress as a function of shear rate for the graft polymer extruded at 513K(240°C). Also included are data for material re-extruded at this temperature. 144 Figure 44b: Apparent viscosity as a function of shear rate for the graft polymer extruded at 513K(240°C). Also included are data for material re-extruded at this temperature. 145 Pigure 45a: Shear stress as a function of shear rate for the graft polymer extruded at 543K(270°C). Also included are data for the re-extrusion of this material at 513K(240°C). Figure 45b: Apparent viscosity as a function of shear rate for the graft polymer extruded at 543K(270°C). Also included are data for the re-extrusion of this material at 513K(240°C). Figure 46: Photograph of graft polymer extruded at 513K(24OoC). List of Figures (Cont.) Figure 47a: Shear stress as a function of shear rate for a mixture of DLX-6000 micropowder and Elvaciteg 2051 at a ratio or 4:l and extruded at 488K(215OC). Also included are data for the re-extrusion at the same temperature. Figure 47b: Apparent viscosity as a function shear rate for a mixture of DLX-6000 micropowder and Elvacitee 2051 at a ratio or 4:l and extruded at 488K(215OC). Also included are data for the re-extrusion at the same temperature. Figure 48a: DSC run of Elvacitee 2051. Figure 48b: DSC rerun of sample from Figure 48a. Figure 49a: First DSC run of DLX-6000. Figure 49b: Integration of DSC run of Figure 49a. Figure 50a: Second heating DSC run of material in Figure 49a. Figure 50b: Integration of DSC run from Figure 50a. Figure 51a: First DSC heating cycle for extruded DLX-6000. Figure 51b: Integration of the PTFE melting peak in Figure 51a.
Figure 52a: Second DSC heating cycle for the sample used in Figure 51a. Figure 52b: Integration of the PTFE melting peak in Figure 52a. Figure 53a: First DSC heating cycle for virgin graft polymer. Figure 53b: Integration of the PTFE melting peak in Figure 53a. List of Figures (Cont.) Figure 54a: Second DSC heating cycle for the sample used in Figure 53a. Figure 54b: Integration of the PTFE melting peak in Figure 54a. Figure 55a: First DSC heating cycle for extruded graft polymer. Figure 55b: Integration of the PTFE melting peak in Figure 55a. Figure 56a: Second DSC heating cycle for the sample used in Figure 55a. Figure 56b: Integration of the PTFE melting peak in Figure 56a. Figure 57: Oscillation frequency of a sample bar of graft polymer subjected to a strain with an amplitude of 0.2 millimeters as a function of temperature. Figure 58a: Elastic storage modulus(l3') as a function of temperature for the graft polymer. Figure 58b: Tan delta as a function of temperature for the graft polymer. Figure 58c: Elastic loss modulus(Ew) as a function of temperature for the graft polymer. Figure 59a: Shear storage modulus(G') as a function of temperature for the graft polymer. Figure 59b: Shear loss modulus(Gw) as a function of temperature for the graft polymer. Figure 60: Natural logarithm of viscosity as a function of 1/T for various shear rates for PlIHA (Elvacitee 2051) extrusion. List of Figures (Concluded) Figure 61: Activation energy for flow of PWA (Elvacitee 2051) as a function of shear rate, taken from extrusion runs at 473K(200°C) and 488K(21S°C).
Figure 62: Viscosity of DLX-6000 micropowder as a function of temperature for several shear rates. Figure 63: Activation energy for flow of DLX-6000 as a function of shear rate. Pigure 64a: Viscosity of the graft polymer as a funcfion of temperature at a shear rate of 1 sec- . Figure 64b: Viscosity of the graft polymer as a funcfion of temperature at a shear rate of 5 sec- . Pigure 64c: Viscosity of the graft polymer as a funct'on - 1 of temperature at a shear rate of 13 sec . Pigure 64d: Viscosity of the graft polymer as a funct'on of temperature at a shear rate of 26 sec- 1 . Figure 64e: Viscosity of the graft polymer as a function of temperature at a shear rate of 33 sec- . Figure 65: Activation energies for the flow of the graft polymer as a function of shear rate.
Figure 66: Complex viscosity as a function of temperature for the graft polymer(viscosityt is the lower curve; viscosity" is the upper curve)
Figure 67: Logarithm of the elastic modulus as a function of temperature. Figure 68: Logarithm of the shear modulus as a function of temperature. List of Tables Page Table 1 Properties of Fluoroplastics(l3) 8 Table 2 Structure of commercially available fluoroplastics Table 3 Conversion Results for One Quarter of a Two Level Five Variable Factorial in Test Tubes Table 4 Conversion Results for a Two Level Three Variable Factorial in Bulk Table 5 Mass Fractions for the Test Tube Factorial (Levels are Describe in Table 3) Table 6 Coefficients for Equations for Test Tube Factorial: Y = Bo + (Bl*Time) + (B2*Temp.) + (B3*Grade) + (B4*Conc.) + (B5*N2) Table 7 Relative Effects for Factorial in Test Tubes Table 8 Mass Fraction for the Bulk Factorial (Levels are Described in Table 4) Table 9 Coefficients for Equations for Bulk Factorial: Y = Bo + (Bl*Time) + (B2*Ratio) + (B3*Agit.) + B12(Time*Ratio) + B13(Time*Agit.) + B23(Ratio*Agit.) + B123(Time*Ratio*Agit.) 43 Table 10 Relative Effects for Reactions in Bulk Fac torial Table 11 Reaction Data at 333K(60°C) with 1 gram PTFE(L-169) :: 3 milliliters MA in Test Tubes 46 Table 12 Reaction Data at 353K(80°C) with 1 gram PTPE(L-169) :: 3 milliliters MU(DuPont) in Test Tubes 47 Table 13 Reaction Data at 343K(70°C) with 2 grams PTFE(Polymist* F-5A) :: 5 milliliters W(DuPont) at 273.2(0.2OC) 48 Table 14 Reactions at 343K(70°C) in Bulk 56 List of Tables (Cont.) Table 15 Reactions at 353K(80°C) in Bulk 59 Table 16 Conversion Data for Reaction in Bulk at 333K(60°C) at 1:3 PTFE:W, 500 rpm, using DLX-6000. 62 Table 17 Relative Effects of Time and initial Concentration in Both the Bulk and Test Tube Systems 76 Table 18 Free Radical Concentration and Irradiation Dose in Micropowders as Determined by Equation VII.6.1 Table 19 Rate Constants for the Test Tube Reactions as Calculated from Equation VII.7.1 Table 20 Comparison of Rate Constants and Activation Energies at 333K(60°C) for Graft Polymerization of MHA to PTFE (L-169) in Test Tubes and Homopolymerization of iUlA(42) Table 21 Rate Constants for the Bulk Reaction as Calculated from Equation VII.7.1 using DLX-6000 Table 22 Activation Engergies and Frequency Factors for the Bulk Reaction using DLX-6000 Table 23 Experimental and Predicted Conversion to Graft for the Test Tube Factorial Based on the Rate Constants from the Kinetics Runs Table 24 Experimental and Predicted Conversion to Graft for the Bulk Factorial Based on the Rate Constants from the Kinetics Runs in Bulk Table 25 Rheology of PMHA (Elvacitee 2051) at 473K(2OO0C). Table 26 Rheology of PMHA (Elvacitee 2051) at 488K(215"C).
Table 27 Rheology of PTFE Hicropowder (DLX-6000) at 488K(215OC). List of Tables (Concluded) Table 28 Rheology of PTFE Hicropowder (DLX-6000) at 543K(27OoC). Table 29 Rheology of Graft Polymer at 473K(200°C). Table 30 Rheology of Graft Polymer at 488K(215OC). Table 31 Rheology of Graft Polymer at 513K(240°C). Table 32 Rheology of Graft Polymer at 545K(270°C). Table 33 Rheology of Graft Polymer Extruded at 513K(240°C) and Re-extruded at 513K(240°C). Table 34 Rheology of Graft Polymer Extruded at 543K(270°C) and Re-extruded at 513K(240°C). Table 35 Rheology of DLX-6000 and Elvacitee 2051 Physically Hixed in a 4:l Ratio Extruded at 488K(215"C). Table 36 Rheology of DLX-6000 and Elvacitee 2051 Physically Nixed in a 4:l Ratio Extruded and Re-extruded at 488K(215OC). Table 37 Results from DSC Scans of DLX-6000 Hicropowder Table 38 Results from DSC Scans of Graft Polymer Table 39 Solubility Parameters of Solvents(ll8) used to Study Chemical Resistance of the Extruded Graft List of Appendices Appendix A Sample Calculations for the Determination of Homopolymer and Graft Appendix B1 General Linear Method SAS Procedure for the Determination of the Effects of Reaction Conditions on Total Product in the Test Tube Factorial Appendix B2 Reproducibility of Graft and Homopolymer in Experiments 2A and 2B in the Test Tube Factorial Appendix B3 Reproducibility of Graft and Homopolymer in Experiments 6A and 6B in the Test Tube Factorial Appendix C1 STEPWISE SAS Procedure for the Bulk Factorial with Total Product as the Dependent Variable
Appendix C2 Reproducibility of Conversion to Graft and Homopolymer in Experiments at 353K(80°C) in the Bulk Reactor for One Hour 232
Appendix D NLIN SAS Output for a Kinetics Run in Test Tubes using Fluon" L-169 at 333K(60°C) at lg ETFE/3ml W 234
Appendix E NLIN SAS Output for a Kinetics Run in Test Tubes using Fluone L-169 at 353K(80°C) at lg PTFE/3m1 MHA 236
Appendix F NLIN SAS Output for a Kinetics Run in Test Tubes using Polymiste F5A at 343K(70°C) at 2g PTPE/5ml W 238
Appendix G NLIN SAS Output for a Kinetics Run in the Bulk Reactor Using DLX-6000 at 343K(70°C) at lg PTFE/3ml
Appendix H NLIN SAS Output for a Kinetics Run in the Bulk Reactor Using DLX-6000 at 353K(80°C) at lg PTFE/3m1 KW xix ACKNOWLEDGHENT
No piece of work stands on the merits of just one person. nay people have provided guidance, encouragement, and materials over the course of my research. I would like to thank Professors J. R. Collier and J. H. Day for serving on both my masters1 and doctorate committees. The help provided by Dr. M. E. Prudich in serving as the head of my committee and his aid in developing my kinetics model is greatly appreciated.
W. A. Galloway, who witnessed my notebook many times, and R. Rabe provided help in setting up equipment. Professor C. C. Houk provided laboratory space for the initial kinetics runs. Over the course of three years, Professor P. D. Sullivan ran numerous ESR scans and helped interpret them.
For supplying micropowders, I would like to thank A. Hatthews of ICI Americas for Fluone; P. Pifoot of Allied for PolymistQ; and W. C. Morris, C. A. Dykes, and D. W. Boothe of DuPont for DLX-6000. I would like to thank several people from DuPont who provided guidance on special topics: D. W. Johnson, W. L. Eppelheimer, and C. W. Jones for their comments on extrusion; A. J. Playtis and
R. L. Johnson, for their help in interpreting DSC scans; B. I4. Harks, for helping set up rheology experiments; H. S. Hahn for providing information on poly(methy1 methacrylate) and free radical polymerization; H. J. Tribo, for help both to set up and interpret DSC and DM experiments; F. W. Yeager, for general comments on polymer properties and the equipment to study them; and C. E. Steiner, for for witnessing my notebook and providing insight into mechanical design. Special thanks are extended to C. A. Sperati who has served on both my thesis and dissertation committees and has provided both professional and personal guidance.
Lastly, I would like to thank two very special people in my life: my son, Adam, for helping me keep my priorities straight, and my husband, Bruce, for reading, typing, and proofreading my dissertation, assisting in running experiments, and for supporting me
throughout the course of my studies. PART I Introduction
Polytetrafluoroethylene(PTFE) is a chemically stable polymer which degrades upon exposure to ionizing radiation. The resulting free radicals have very long lives due to being trapped within the crystalline matrix of the polymer. Irradiation of PTFE on a commercial basis produces micropowders which are used as lubricants and thickeners. Methyl methacrylate readily undergoes free radical initiated polymerization to poly(methy1 methacrylate). The amorphous polymer is well known for its glass - like properties. In the research presented here, the free radicals in irradiated PTFE micropowder were used to initiate a methyl methacrylate polymerization, resulting in a graft polymer of PTFE and PW. Experiments on a test tube scale proved the feasibility of the reaction. A factorial design was used for runs in both test tubes and a scaled-up reactor to determine appropriate conditions for high conversion of W to graft. A nitrogen purge was necessary in the scaled-up system to limit the inhibiting effects of oxygen. A kinetics model was derived to relate conversion of KM to graft to the time of reaction and initial quantities of PTPE free radicals and
PlU monomer. The rheology and stability properties of the graft polymer were studied. From the rheology experiments, the viscosity was found to be between that of PMMA homopolymer and the PTFE micropowder, but closer to that of the PMMA, implying that the PHHA domains "dragw along the micropowder. Differential Scanning Calorimetry thermograms related the heat of transition of the PTFE melting peak to the quantity of micropowder in the graft sample. Chemical stability studies in solvents detrimental to PIMA caused degradation of the graft unless prior heat treatment had been done. A dynamic mechanical analysis of the graft placed its mechanical properties between those of PTFE and PHHA, but closer to those of PTFE, implying that the PTFE controls the graft's mechanical behavior. Possible uses of the graft polymer include extrusion of fibers or injection molding which utilizes the properties of the PTFE. PART I1 Polytetrafluoroethylene
11.1 Structure and Properties of PTFE
Polytetrafluoroethylene is a homopolymer of tetrafluoroethylene with a repeat unit of -[CP2-CF2J-. PTPE is one of the most stable organic compounds; it is insoluble in all common solvents and highly resistant to chemical attack(l,2). For this reason, the molecular weight of this polymer cannot be determined by typical means. Specialized methods, such as end group analysis(3,4,5), a standard specific gravity test(6) and differential scanning calorimetry measurements(7), set the molecular weight of commercial PTFE at 106 - 107(1,2,7). PTFE has a very high melting point of 600K(327°C) for sintered
material and 613K(340°C) for virgin resin. Two first order room temperature transitions at 292K(19°C) and 303K(30°C) account for about a one per cent increase in density(2). Second order transitions are at 193K(-80°C) and 393K(120°C)(8). The very high, sharp melting point is related to the linear, unbranched crystalline structure(1,Z). The PTPE matrix can be up to 98% crystalline, as produced; this has been verified by infrared spectroscopy(9), multiple pulse nuclear magnetic resonance
spectroscopy(lO), X-ray analysis, and electron microscopy(7,11). The 3 3 density of the crystalline regions is 2.3Hg/m (2.3g/cm ); that of the amorphous regions is 2.0Mg/m 3 (2.0g/cm 3 )(I). The very high molecular weight and highly ordered crystalline morphology cause the melt viscosity of PTFE to be extremely high: 107 kilopascal-seconds(lO1l poise) at 653K(380°C)(11,12) This high melt viscosity prevents the use of typical polymer processing methods for PTFE; instead, metal processing techniques such as compression molding and ram extrusion are used(l,l3). Solid state extrusion techniques have been used on a laboratory scale(l4).
Material with a melt viscosity of 0.1 - 10 kilopascal-seconds (103 -105 poise) can be made, but this material crystallizes so fast from the melt that any molding becomes highly crystalline and very brittle. In order to have adequate strength, it is necessary to use high molecular weight highly crystalline PTFE or to disrupt the crystalline order by the use of comonomers(l2).
11.2 Effects of Radiation on Polytetrafluoroethylene Despite its chemical stability, polytetrafluoroethylene degrades readily when exposed to ionizing radiation(l6). Random scissions result in the production of a propagating radical, -[CF2-CE2'], and a chain radical, -[CF2-FF-CP2], in a ratio of 1:10(17,20). Both radicals will react with oxygen to form peroxy radicals which hinder recombination reactions, thus increasing the extent of degradation(l5,17-21). The number of free radicals produced is directly proportional to the dose of ionizing radiation and decays with time and increases with temperature(l6). The free radicals have an extremely long lifetime of up to years(16,22) since they become trapped within the crystalline
matrix(18,19,23). Severed ends at a broken C-C or C-F bond recombine if they remain with a "recombination cagen; if the fragments diffuse away from each other, recombination is impossible. The production of lower molecular weight fragments resulting from scissions occur more often in the amorphous regions, relieving stresses and allowing subsequent radiation induced crystallization(l5); therefore,
radiation exposure produces an increase in the samplers crystallinity(l9,24). Upon radiation exposure, the molecular weight of the PTFE decreases as a result of chain breaks(25), the first order transition temperatures decrease due to a drop in molecular weight(26), and the density increases with the rise of the denser packing in the regions which have been induced to crystallize by the radiation(27). Radiation degradation causes significant changes in the mechanical properties of PTFE. The tensile strength of PTPE begins to decrease after exposure to a dosage of greater than 5 megarads(27). Wall and Florin(28) have shown that a radiation dose in air which causes a 100 per cent loss in tensile strength causes only a 50 per cent loss in a system under vacuum(28). The increase in impact strength at low doses is attributed to internal plasticization caused by low molecular weight degradation products(27); at higher doses, the impact strength decreases rapidly to zero(22). Due to a significant decrease in molecular weight after even a few scissions, the melt viscosity of the irradiated PTFE decreases proportionally to the dose received(29-31). As shown in Figure 1(15), an initial rapid decrease from about 107 to 102 kilopascal-seconds(lO1l to 10 6 poise) occurs at doses of about 2 megarads due to chain scissions. A slight increase at about 2.5-5 megarads is due to an increase in the number of molecules at the high end of the molecular weight distribution which results in more entanglements and a higher viscosity. Above 5 megarads, the viscosity decreases rapidly because of further induced radiation scissions(l5). Melt extrusion of irradiated polytetrafluoroethylene can be used as a "go-no gow test to guarantee that an adequate dose has been received(31).
11.3 Melt Extrudable Fluorocarbon Resins Several copolymers of tetrafluoroethylene are melt extrudable. The ability to process by conventional thermoplastic techniques usually is accompanied by a decrease in the melting and end use temperatures. Crystallinity of these materials is controlled by molecular structure and is relatively insensitive to processing conditions. Table l(13) contains a list of some of the co~nmercially available fluoropolymers and melt extrudable fluoroplastics and their properties(l3). Table 2 gives the chemical structure of these materials(32).
11.4 Radiation Induced Grafting of PTPE Films with Vinyl Monomers Work has been done using PTPE films as a template upon which vinyl polymerization can occur. Either simultaneous irradiation(33-36) of both the film and monomer or preirradiation of
I I 1 I I 0 5 0 15 20 25 Dose (MRod)
Figure 1: Melt viscosity of irradiated PTFE as a function of dose(l5). Table 1
Properties of Pluoroplastics(l3) Table 2 Structure of commercially available fluoroplastics
Polytetrafluoroethylene PTPE -[-CP 22nCP -1 -
Fluorinated ethylene- PEP - [ (CF2CF2 )nCP2CFlm- propylene copolymer I CF3
Perfluoroalkoxy resin PPA - 1 (CF2CF2)nCP2CP],- I 0 Rf
Polyvinylidene fluoride PVDF
Polychlorotrifluoro- PCrPE ethylene
*Rf = hydrocarbon chain the film(37-41) is used. Monomers used for these studies include styrene(33,34,36,37,41), acrylic acid(34,38,40), 4-vinylpyridine(34), n-vinylpyrolidone(34,39),vinyl acetate(33,35) and methyl methacrylate(33). The degree of grafting in these systems is defined as the weight gain in the film (W -W ) divided by the original weight (Wf) times g f 100(39,40):
wg - wf x 100 = degree of grafting (11.4.1) Wf
The course of grafting, as shown in Figure Z(40) for an acrylic acid system, is similar for each monomer. The rate of grafting is initially linear but approaches a limiting conversion at longer times(37,39). Initiation corresponds to the addition of the first monomer unit and the rate determining step is diffusion of monomer into the ungrafted parts of the film(37,41). Propagation is rapid and termination is bimolecular(37). The irradiation dose received by the system determines the amount of free radicals(l6) produced and has a direct effect on polymerization. Figure 2(40) shows that there is an increase in the limiting value of graft as the dose is increased. In general, higher doses will result in more grafting for the same reaction times(34,39). The effect of the weight fraction of the monomer on the grafting rate and final per cent grafting is given in Figure 3 for an aqueous Figure 2: Degree of grafting-time curves at various preirradiation doses (Hrad) using acrylic acid and PTFE films. Doses(Hrad): (0) 1; (0) 3; (A) 5; (a) 10. Grafting Conditions: AAc conc., 40 wt. X; grafting temperature, 308K(35OC); film thickness, 80xm(40). acrylic acid system(40). A similar graph is obtained for other sys tems . Temperature effects are shown in Figure 4 for the acrylic acid system(40). Since the decay of trapped free radicals is enhanced at higher temperatures, the grafting reaches its final per cent faster. This decay effect overwhelms the enhancement of the diffusibility of the monomer into the film at higher temperatures(39). The overall activation energies for this system are 63.6 k.J/mole and 20.1 W/mole below and above the 308K(35OC) transitions, respectively(40). The final degree of grafting decreases with increasing film thickness as shown in Figure 5(40). The initial weight increase per unit surface area of the film is constant, irrespective of thickness. The reaction proceeds from the surface and proceeds gradually into the film center with progressive monomer diffusion though the grafted
Figure 3: Degree of grafting-time curves at various acrylic acid concentrations using PTFE films: preirradiation dose, 5 Hrad; grafting temperature, 308K(35OC); film thickness, 80~m(40). layer. Grafting is controlled mainly by monomer diffusion(40). Partial destruction of the crystalline region occurs at a high degree of grafting. Dobo and Hedwig(41) show that at the limiting conversion, the crystallinity of the PTFE film drops from 65 per cent to 30 per cent at 353K(80°C) and 40 per cent at 323K(50°C). An autoacceleration was noted in a study of simultaneously irradiated vinyl acetate and PTFE film. This increase in rate was attributed to the greater efficiency of poly(viny1 acetate) free radicals over PTPE free radicals for promoting polyrer
40
Figure 4: Degree of grafting-time curves at various grafting temperatures(K(OC)) using acrylic acid PTFE films. Temperatures: (o) 288(15); (0)298(25); (A) 308(35); (a) 318(45); (e) 333(60). Grafting conditions, except preirradiation dose (5 Hrad), are the same as in Figure 2(40). The mechanical properties of PTPE-poly(acry1ic acid) the graft are better than those of the irradiated PTFE, as shown in Figure 6(39). Material which has received a lower dose shows better tensile strength and elongation(38). Using various monomers, Chapiro and Jendrychowska- Bonomour(34) have shown that these grafted films have high mechanical strength, can withstand strain, and do no compact under pressure. They proposed that these materials may be suitable for use under harsh conditions. Graftlng Time (hr)
Figure 5: Degree of grafting-time curves at various PTFE film thicknesses (Am) using acrylic acid. (A) 80; (0) 130; (u) 190. Grafting conditions, except preirradiation dose (5 Hrad), are the same as in Figure 2(40). Figure 6: The change of mechanical properties of the irradiated PTFE films grafted with acrylic acid on wetting in distilled water as a function of degree of grafting. Grafting conditions: acrylic acid concentration, 40 wt. X; grafting temperature, 308K(35OC); film thickness, 80~m(38). PART I11 Pree Radical Chain Polymerization
111.1 Theory of Free Radical Polymerization Classical free radical chain polymerization involves three steps: initiation, propagation, and termination(42-45). The initiation step consists of two reactions: the dissociation of the initiator, I, to yield a pair of free radicals, R', and the subsequent addition of a monomer molecule to the free radical to produce the chain initiating species H'; these reactions are shown in equations 111.1.1 and 111.1.2, respectively:
Equation 111.1.2 is so fast that it cannot be rate controlling(42). The "kW values are rate constants for the reactions. Propagation consists of the successive addition of other monomer molecules to the growing polymer chain: The propagation terminates by a bimolecular reaction of coupling
which adds two molecules together by production of a saturated bond between them, or by a disproportionation reaction, resulting in the formation of one saturated and one unsaturated bond:
A combination of coupling and disproportionation can occur, with one being favored over the other under certain reaction conditions. To simplify the kinetics, three assumptions are made: (1) The radical reactivity is independent of the radical size.
(2) Consumption of monomer in the initiation step is negligible relative to the amount used in the propagation step.
(3) A steady state concentration of free radicals is reached. In other words, the rate of production of free radicals is equal to their rate of termination. Solution of the kinetics equations 111.1.1 - 111.1.5 for the rate of disappearance of monomer, or the rate of propagation, R P ' gives Equation 111.1.6:
in which f is the initiator efficiency with a value between 0 and 1, dependent upon the reactions conditions(42,47), and the brackets signify concentration.
111.2 Inhibition in Free Radical Polymerization An additional step can be added to the sequence for free radical polymerization to account for inhibition and retardation of the propagation reaction:
in which Z is the inhibitor or retarder. The Z' radicals are assumed to terminate without regeneration of the original Z molecule. The inhibition constant, z, is defined as the ratio of the rate constants for inhibition and propagation: Oxygen is a powerful inhibitor with the largest z values known: 33,000 for methyl methacrylate and 14,600 for styrene(42). It is believed that oxygen reacts with free radicals to form a relatively unreactive peroxy radical
which reacts with itself or with other radicals to form inactive species(42,48,49).
111.3 Methyl Methacrylate Homopolymerization Methyl methacrylate(M4A) polymerizes by a chain radical mechanism to form poly(methy1 methacrylate)(PM4A):
Thermal polymerization can occur to some degree(45), but nitriles(47,50-55) and peroxides(56) are typically used for initiation of the HMA(57,58). Host experiments are done under nitrogen(50) or under vacuum to limit the inhibitory effects of oxygen(42). Hayden and Helville(59) divide HHA polymerization into initial, intermediate, and final stages. In the initial stage of up to 10 per cent conversion, the reaction medium increases in viscosity from a mobile liquid to a viscous syrup(60). The intermediate stage occurs between 10 and 50 per cent conversion when both the conversion rate and the lifetime of the chain increase. The rate constant for
termination drops due to the effects of diffusion of growing chains through the viscous reacting mixture and the gel (Trommsdorf) effect occurs(59). In the final stage, there is a reduction in monomer mobility due to the system viscosity(60) and the energy required for both propagation and termination increases(59). Termination is assumed to be diffusion controlled due to its dependence on mobility and system viscosity(61-63).
111.4 Gel (Trommsdorf) Effect
In their studies on methyl methacrylate polymerization initiated by benzoyl peroxide, Norrish and Smith(64), and later Tromsdorf(65), found an acceleration in propagation rate at 12 - 26 per cent conversion, which they attributed to an increase in bulk viscosity. This reduced the mobility of the growing free radicals and produced a drop in the termination rate(64). The viscosity increase (66,67) is a result of high molecular weight dead polymer and propagating polymer radicals that have become entangled(68); therefore, steric hindrances prevent active chain ends from coming within the 3-4 angstrom cage in which termination can occur(61-63). PART IV Kinetics Model for-IrradiatedE'TFE Initiated HHA Polymerization
IV. 1 Kinetics Model from Earlier Vork(69) A kinetics model has been derived in earlier work to account for the irradiated PTFE initiated polymerization of methyl methacrylate, to produce a PTFE-PHHA graft polymer. The kinetics of the reacting system involved three steps:
INITIATION:
PTFE02 ' > E'TFE' (IV.1.1) ki (IV. 1.2)
PROPAGATION:
Ir P HHA*~+ m ' -'n+l
Irt HHA', + W', > dead or occluded polymer (IV.1.4) The initiation step is assumed to be so fast that it is not considered rate controlling. The stability of the graft polymer upon heat treatment suggests that the oxygen is removed from the PTFE-peroxy free radical in equation IV.l.l by a currently undefined mechanism before reaction with the UHA. Equations for disappearance of monomer and the free radical with time, based on concentration, have the forms:
(IV. 1.5)
(IV. 1.6) in which the brackets, ([I), signify concentration, H is the monomer, H' is the free radical, and k and kt are the rate constants for P propagation and termination. By setting the concentration of free radicals at t=O as the initial concentration of PTFE free radicals,
[PTFElo, solution of equation IV.1.5 gives
[U'] = [PTFE]o/(ktt[PTFE]o + 1) (IV. 1.7)
Substitution of IV.1.6 into equation IV.1.4 with integration and subsequent rearrangement yields
(IV. 1.8) Conversion given as x = (1 - [M]o/[M]) is defined in Equations IV.1.9 and IV.l.lO:
(IV. 1.9)
(IV. 1.10)
Conversion increases with the quantity of PTPE and approaches a limiting value with respect to time. The degree of grafting(29) is given by equation IV.l.ll: degree of ={l-(l/exp((k /k )ln(ktt[PTPE]o+l))J(Mo/PTPE)*lOO (IV.l.ll) grafting P t in which no and PTPE are the initial masses of HHA and PTFE in grams. PART V Experimental Procedure for Production of the PTFE-PW Graft Polymer
V. 1 Test Tube Runs
In earlier work(69), reactions between irradiated PTFE and IMA monomer were carried out in test tubes at various PTFE/IMA ratios and temperatures to determine the effects of time, component ratio, and temperature on the conversion of monomer to graft. In the work presented here, initial runs in test tubes were done to quantify the effects of time, component ratio, temperature, initial starting material, and the exclusion of oxygen. One quarter of a two-level five variable factorial consisting of eight runs was made. Fisher laboratory grade methyl methacrylate containing 98 per cent HHA by weight was washed with 5 weight per cent aqueous sodium hydroxide to remove the inhibiting hydroquinone and was preheated before measurement. An appropriate quantity of PTPE, either 6 or 10 grams, was weighed into the test tubes to obtain the ratios of 1 gram of PTPE to 3 milliliters of W or 1 gram to 5 milliliters. Temperatures were maintained by use of a constant temperature water bath. All runs at the same temperature were made at the same time. Two grades of irradiated PTFE were used: DLX-6000 from DuPont and Polymiste F-5A from Allied. Reactions were made at either 332K(5g°C) or 341K(68OC) and the time of the reaction was measured from the time the two components were mixed. Half of the runs were made under a nitrogen blanket. After one half or two hours, the reactions were inhibited with half of a gram of hydroquinone. All samples were extracted with acetone in a soxhlet extraction column for three hours. The acetone used for extraction was evaporated, and the amount of residue was set equal to the quantity of hydroquinone used plus the amount of poly(methy1 methacrylate) homopolymer produced. No solid residue was obtained from the evaporation of the acetone as received. The weight gain in the amount of solids was set equal to the quantity of PMthat grafted onto the PTPE. A summary of reaction conditions and grafts and homopolymer produced is given in Table 3.
V. 2 Factorial Design and Reaction Conditions for the Scaled-Up Reaction
A complete two level factorial design using time, initial component ratio (grams of PTFE/milliliters of M),and agitation was made to determine the effects and interactions of these variables on the conversion of M4A to graft and, therefore, to determine appropriate conditions for kinetics runs. These reactions were made in the system shown in Figure 7. A 10.2 centimeter diameter-500 milliliter glass reactor was used. A four port dome allowed an agitator, thermometer, nitrogen inlet and outlet, and a monomer inlet. Table 4 summarizes the reaction conditions and conversion results . TABLE 3 Conversion Results for One Quarter of a Two Level Five Variable Factorial in Test Tubes
PTFE/MMA -RUN TIME -TEMP GRADE Ratio PMMA ( y ) GRAFT ( g ) 1 - 1 - 1 - 1 1 0.0921 3.0254 2 1 - 1 - 1 - 1 0.0000 1.8596 2 B 1 - 1 - 1 - 1 0.4332 2.1452 3 - 1 1 - 1 - 1 0.2442 1.5864 4 1 1 - 1 1 0.3806 5.8525 5 - 1 - 1 1 1 0.1879 2.5913 6 1 - 1 1 - 1 0.5688 2.5578 6 B 1 - 1 1 - 1 0 .oooo 6.4613 7 - 1 1 1 - 1 0.3556 1.9281 8 1 1 1 1 1.5331 11.3643
Levels Confounding Pattern
+ - Tine(hr) 2 1/ 2 Temp ( K 341~(68O~) 332~(59O~) Grade DLX-6 0 0 0 Polyrist* F-5 Ratio 1:3 1:5
Yes N 0 2
A Lightnin variable speed controller(TS1515) was used with a three bladed 45' pitched turbine impeller. Experiments with several agitators showed this to be the optimum system to mix the irradiated PTFE with an organic solvent uniformly. The agitator was set one inch from the bottom of the reactor, corresponding to two thirds of the liquid depth(70).
Figure 7: Equipment used for scaled up reactions.
DLX-6000, drum # 5621, was used for all runs. Results from a dry sieve analysis to determine the particle size distribution of the material as received is shown in Figure 8. After the appropriate time, the reactions were inhibited with hydroquinone and agitated for two more minutes to distribute the inhibitor. Figure 8: Log-probability plot of particle size distribution of DLX-6000 as received. Most of the residual monomer was evaporated from the product at room temperature, and the resulting solids were weighed(gross weight) and then ground in either a Waring blender or a Wiley mill with a two millimeter screen. A sample of 10 to 12 grams was extracted in acetone in a Soxhlet extraction column. The acetone was evaporated and the residual solids were set equal tn the amount of poly (methyl methacrylate) homopolymer and hydroquino~ie in the extracted sample.
The weight loss of the PTFE-PW graft sample was equal to the amount of homopolymer, hydroquinone, and residual monomer in the original sample. By assuming a homogeneous distribution of components both in the sample and in the total quantity produced in the reactor, the amount of graft could be determined by use of the following relationships:
HQ in sample - EQ in total Sample Weight Gross Weight
Residue after PHllA homopolymer evaporation of - HQ in sample = in sample (V.2.2) acetone
PWhomopolymer PWhomopolymer - in total in sample (V.2.3) Sample Weight Gross Weight Weight Residue after Residual loss of - evaporation of = Monomer PTFE-PHHA graft acetone in sample
Residual Monomer Residual Monomer in sample - in total (V.2.5) Sample Weight Gross Weight
(HQ in total + PMMA in Gross - total + Residual Monomer = Graft Weight in total + PTFE in total) Polymer
Total product = PElllA + PTFE + weight :raft Polymer A sample calculation is given in Appendix A.
V. 3 Kinetics Runs in Bulk Kinetics runs were made at 333K(60°C), 343K(70°C), and 353K(80°C) for several different times. All reactions were carried out at a ratio of 1 gram of PTFE to 3 milliliters of prewashed uninhibited laboratory grade W4A (98 weight per cent IMA) at an agitation speed of 500 revolutions per minute. The W4A was heated after the volume measurement of the sample. Nitrogen at a flow rate of 1.5 cubic centimeters per minute was purged over the system. In order to remove oversized particles that might cause heterogeneities in the finished product, the irradiated PTFE was chilled and then screened through 300, 150, and 38 micron screens. The material on the 38 micron screen with a particle size between 38 and 150 microns was used for all runs. A Varian E-15 EPR Spectrometer was used to determine the relative quantities of free radicals in each of the screened cuts(Figure 9).
1,l-Diphenyl(-2picrylhydrazl) (DPPH) was used as a reference marker for all scans. The electron spin resonance(ESR) scans showed no decrease in the relative amounts of free radicals in any of the screened cuts (Figures 9a - 9c), confirming that the free radicals are homogeneous throughout the irradiated PTFE and their number is not related to the outside surface area of the micropowder.
DPPH
Figure 9a: ES4 scan of DLX-6000 as received. Conditions G = 2.0 X ; scan time = 4 minutes; Hod = 26. For DPPH, G = 2.5 X
The procedure used in the scaled-up factorial, as described in equations V.2.1 - V.2.7, was used for determination of the conversion. DPPH
Figure 9b: ESR scan of particles with a diameter greater than 150 microns in Dm-6000. Conditions are the same as in Figure 9a. DPPH and PTFE curves are slightly displaced compared to Figure 9a.
DPPH Figure 9c: ESR scan of particles with a diameter less than 150 microns in DLX-6000. Conditions are the same as in Figure 9a. PART VI
Results of the Graft Polymerization
VI.l Test Tube Factorial The conversion results from the test tube factorial are shown in Table 3. These results are given on a mass fraction basis in Table 5. Effects were determined from the factorial using the
General Linear Hodels(GLl4) Procedure in the Statistical Analysis Systems(SAS) Package to fit a line of the following form to the experimental data:
The SAS output for the GLH procedure using total product as the dependent variable is given in Appendix B1. Only one quarter of the full factorial was run; therefore, no interaction effects were able to be determined. The PTFE/)OIA ratio and nitrogen were the confounded variables. The coefficients for equation VI. 1.1 are given in Table 6, along with the r2 correlation which is defined as the sum of the squares of the predicted values divided by the sum of the squares of the experimental values. The single order effects account for most of the variability of the data, except in those relationships involving the amount of homopolymer. TABLE 5 Mass Fractions for the Test Tube Factorial (Levols are Described in Table 3)
PTPE/MMA PHHA GRAFT TOTAL PMMA GRAFT PMMA+GRAFT RUN TIME TEMP GRADE RATIO N2 GRAFT PTFE PROD. TOTAL TOTAL TOTAL
Runs 2A and 2B were replicates as were 6A and 6B. The means and standard deviations of the results from these experiments are given in Appendices B2 and B3. Poor reproducibility of the PWcontent is due to the small quantities of homopolymer produced. Relative effects obtained by dividing the coefficients by the value of the smallest are given in Table 7. In general, use of nitrogen has the smallest effect on conversion to either graft of homopolymer. The effects of time are usually two to three times the effects of nitrogen. Temperature, grade, and initial ratio effects are all the same order of magnitude, except in those relationships involving poly(methy1 methacrylate) homopolymer.
TABLE 7 Relative Effects for Factorial in Test Tubes Initial PTm/m Variable -Time Temp Grade Ratio _N2- PW GRAFT PHHA/GRAFT GRAFT/PTF'E TOTAL PROD. PW/TOTAL GRAFT/TOTAL PW+GRAPT TOTAL
VI.2 Bulk Factorial Data from the test tube factorial were used to determine the conditions for the bulk factorial. Although a nitrogen atmosphere was not important in the test tube factorial, it was necessary to get any conversion in the bulk system. In the bulk reactor, the exposed surface area to volume ratio is higher than that of the test tube and the diffusion of oxygen across the surface area is enhanced by the pumping action of agitation. Use of a nitrogen purge significantly reduces the oxygen available and enhances the conversion rate. Conversion data are given in Table 4. Mass fraction data are given in Table 8. The STEPWISE SAS procedure was used to determine coefficients for the equation:
The STEPWISE procedure adds or subtracts independent variables and cross terms from the model in order to maximize the r2 correlation coefficient. Only first order relationships in each variable are considered. According to J. S. Hunter(71), third order interactions are not realistic for modeling; therefore, the model chosen to represent the data was the last one developed by the STEPVISE procedure before the time*ratio*agitation term was added to maximize r2 . The coefficients from the bulk factorial are given in Table 9; for only PIMA homopolymer are two interactions significant for modeling; for all other dependent variables, only one interaction is significant. single order effects are significant for all dependent variables. Relative effects are given in Table 10. The SAS output for the STEPWISE procedure for total product as the dependent variable is given in Appendix C1. The mean and standard deviation for conversion to both graft and homopolymer in runs 8a-8e are at the same reaction conditions are given in Appendix C2. For the observed quantities of PW,PW/total, and graft + PW/total, one of the single order independent variables is least important. For all other cases considered, the least important effect in the linear model is an interaction term. In general, interaction terms are less significant than main effects. Time*PTFE/lMA ratio and agitation*PTPE/lMA ratio interactions are more significant than time*agitation interactions. Prom a mechanistic viewpoint, time and PTFE/lMA ratio or agitation and PTPE/IMA ratio are related due to conversion and diffusional effects, respectively; whereas, agitation speed has no relationship to time.
TI. 3 Kinetics Data in Test Tubes(69) Kinetics runs in test tubes were made in earlier work(69). Reactions using ICI1s Fluone L-169 were done at 333K(60°C) and
353K(80°C). Both products were used at a ratio of 1 gram of PTFE to 3 milliliters of preheated MMA. Runs using Allied's Polymiste F-5A were made at 343K(70°C) and a ratio of 2:5. Conversion to graft and degree of grafting as functions of time are given in Tables 11-13 and
Figures 10-12. The change in density of MXA with temperature was 3 3 assumed to be linear, based upon values of 0.9440 Hg/m (g/cm ) at 293K(20°C) and 0.9400 Mglm 3(g/cm3) at 298K(25OC) (72). The quantity of homopolymer formed in these reactions was measured for only one run and accounted for less than ten per cent of the total conversion. Since only small quantities of the reactants were used in test tubes, homopolymer measurements would not be reproducible and were not not made for subsequent test tube reactions.
For L-169, more conversion occurs at the higher temperatures. Higher conversions for the Polymiste are due to the larger number of free radicals contained in the Polymist@(Pigure 12). wem r-... mr- 4 4 d I I
Reaction Data at 353K(80°c) with 1 gram PTPE(L-169) : 3 milliliters MHA in Test Tubes
PTFE MHA Graft Conv. to Graft Degree of (nl) (temp -K) O (%) Grafting 9 353. 7.9027 0.4682 1.2392 9 355. 7.8886 0.4209 1.1621 9 353.75 7.8974 0.3596 0.9279 9 354.5 7.8921 0 -4118 1.0506 9 352.5 7.9062 2.6157 6.9468 9 353. 7.9027 5.8018 15.6309 9 352.5 7.9062 5.6955 14.2437 9 352.5 7.9062 8 -9208 23.6107 9 352.5 7.9062 8.4149 21.7177 9 353. 7.9027 8.9501 23.0887 Table 13 Reaction Data at 343K(70°c) with 2 grams PTPE(Po1ynist' F-5A) : 5 milliliters MHA
Tire PTFE HHA Graft Conversion Degree of (nin) 0 (m1) (temp K) Grating Figure 10a: Per cent conversion to graft versus time at 333K(60°C) in test tubes with Fluone L-169 in a 1:3 ratio with MMA. The predicted curve from equation IV.1.9 is shown. Figure lob: Degree of grafting(29) versus time at 333K(60°C) in test tubes with Fluone L-169 in a 1:3 ratio with W. The predicted curve from equation IV.l.ll is shown. Figure 11s: Per cent conversion to graft versus time at 353K(80°C) in test tubes with 1 gram Fluone 6169 to 3 milliliters W4A. The predicted relationship from equation IV.1.9 is shown. Figure llb: Degree of grafting(29) versus time at 353K(80°C) in test tubes with 1 gram Fluone L-169 to 3 milliliters MA. The predicted relationship from equation IV.l.ll is shown. Figure 12a: Per cent conversion to graft versus time at 343K(70°C) in test tubes with 2 grams of Poly.ist@F-5A to 5 milliliters HHA. The predicted relationship from equation IV.1.9 is shown. Figure 12b: Degree of grafting(29) versus time at 343K(70°C) in test tubes with 2 grams of PolymisteF-5A to 5 milliliters MA. The predicted relationship from equation IV.l.ll is shown. VI.4 Kinetics Runs in Bulk From the factorial in bulk and in test tubes, appropriate conditions were chosen for kinetics runs: higher temperatures of 343K(70°C) and 353K(80°C), and the higher ratio of one gram of PTFE to three milliliters of HHA. The higher agitation speed of 500 revolutions per minute was chosen, despite its conversion reducing effect, since the agitator bound at 250 revolutions per minute at longer reaction times. DLX-6000 was chosen as starting material because of its availability. Conversion and degree of grafting(29) as a function of time at 343K(70°C) are given in Table 14 and Figures 13a and 13b. The conversion approaches a limiting value at longer times. Data from runs at 353K(80°C) under the same reaction conditions are shown in Table 15 and Figues 14a and 14b. As for the data at 343K(70°C), the results at this temperature show conversion approaching a limiting value with time. Slightly lower conversions are seen at 353K(80°C) than 343K(70°C). One run was made at the above conditions and a temperature of 333K(60°C) and the results are given in Table 16. Figures 15-18 give the appropriate conversions as a function of temperature for a one hour run. Conversions decrease slightly with temperature using DLX-6000.
Figure 13a: Per cent conversion to graft versus time at 343R(70°C) in the bulk reactor. The predicted relationship from equation IV.1.9 is shovn. Figure 13b: Degree of grafting(29) versus time at 343R(70°C)in the bulk reactor. The predicted relationship from equation IV.l.ll is shown.
Figure 14a: Per cent conversion to graft versus time at 353K(80°C) in the bulk reactor. The predicted relationship from equation IV.1.9 is shown. Figure 14b: Degree of grafting(29) versus time at 353K(80°C) in bulk reactor. The predicted relationship from equation IV.l.ll is shown. Table 16
Conversion Data for a Reaction in Bulk at 333K(60°C) at 1:3 PTFE:HNA, 500 rpm, using DLX-6000.
Time,min 60.
l'TI7E 7 g 103.7427
M?iJ 277.536 I'm, I'm, g 3.6192
HQ,g 0.1095
graf t,g 38.7054 PM/graft 0.0935
Degree of Grafting 37.3090
total product,g 146.0673 PW/total 0.0248 graft/total 0.2650
PMA+graft/total 0.2898 total conversion,% 15.2501
conversion to graft,% 13.9461 conversion to PM,% 1.3040 Figure 15: Total conversion from scaled-up reactor for one hour reaction times as a function of temperature. Figure 16: Conversion to graft from scaled-up reactor for one hour reaction times as a function of temperature. Figure 17: Conversion to homopolymer from scaled-up reactor for one hour reaction times as a function of temperature. Figure 18: Degree of grafting(29) from scaled-up reactor for one hour reaction times as a function of temperature. VI. 5 Temperature Excursions during Scaled-up Reactions The temperature of the reactor contents varied with time. After a short time during which the reactor contents reached the temperature of the water bath, the temperature continued to rise sharply to a peak six to eight degrees above that of the bath. The subsequent decrease in temperature was much slower than the increase; however, slight increases in temperature were seen after about a one hour reaction time. Temperature versus time curves are shown for reactions at 333K(60°C), 343K(70°C), and 353K(80°C), in Figures 19, 20a, and 21a.
VI.6 Power Levels for Agitation The power drawn by the agitator controller to maintain agitation speed could be obtained directly and was measured to the hundredth of a watt. For most of the course of the reactions, less than 0.01 watt was necessary to maintain agitation speed. Later in the course of the polymerization, the power required was higher due to the increase in viscosity. Some power levels showed a subsequent decrease afterward due to increased stagnation and vortices. Power levels are shown along with the temperature-time relationships in Figures 20b and 21b. Figure 19: Reactor temperature as a function of time for a bulk reaction at 333K(60°C) for one hour. Figure 20a: Reactor temperature as a function of time for a bulk reaction at 343K(70°C) for one hour. Figure 20b: Power level as a function of time for a bulk reaction at 343K(70°C) for one hour. Data from earlier than 40 minutes are not available. Figure 21a: Reactor temperature as a function of time for bulk reactions at 353K(80°C) for three hours. Figure 21b: Power level as a function of time for bulk reactions at 353K(80°C) for three hours. PART VII Discussion of Kinetics Results
VII.l Test Tube Factorials
The test tube factorial shows little effect of a nitrogen atmosphere on conversion, despite the great inhibiting effect of oxygen on methyl methacrylate polymerization. Oxygen is entrained in both the micropowder and the monomer and additional oxygen enters the system by diffusion across the small exposed surface area. The surface area to volume ratio is so small that the inhibiting effects of oxygen are not observed. Grade and ratio effects are significant since these independent variables determine the amount of reactive PTFE sites present. In a given ratio of PTFE to MHA, the grade, or dose, of PTFE determines the number of free radicals available. The higher the dose, the higher the number of reactive sites(l6) at which more grafting and higher conversion can occur. This is demonstrated also for PTFE films in Figure 2(40).
The relative effects of time are of the same magnitude for all dependent variables considered. No limiting effects are seen from the factorial. The ratio of PW/graft shows a decrease with time; this is a result of the shorter homopolymer chains becoming involved in adventitious termination of the graft chains. The relative effects of temperature show an increase in conversion with an increase in temperature, implying that kinetic control is present over the range of independent variables studied.
VII.2 Scaled-up Factorial The complete two level three variable factorial was run for the
scaled-up system by varying time, initial ratio(grams of
PTFE/milliliters of MMA), and agitation. This allowed for calculation of interaction terms. As mentioned in the results section, the model chosen from the SAS STEPWISE procedure had the maximu. r2 before the third order interaction effect was incorporated. The purpose of the test tube factorial was to determine the necessity of using a nitrogen purge to obtain a measurable conversion. Since the use of nitrogen had little effect on the test tube results, it was not used at first for the bulk system. Repeated experimentation resulted in very little (less than one per cent) to no conversion. The nitrogen purge was necessary to get the reaction to run in the 10.2 centimeter reaction flask.
Agitation speed increases result in a decrease in the conversion to both graft and homopolymer. This is postulated to be an inhibiting effect of oxygen; the agitation makes the residual oxygen in the PTPE and MHA more accessible to the entire reactor contents. Increasing the ratio of PTFE to increases conversion to graft. Since HnB is in a very large excess, it does not limit the reaction. The number of PTFE free radicals is equal to the number of reactive sites from which graft growth can occur, thus limiting the number of chains which may grow. The amount of homopolymer decreases with time, due to increased use of growing homopolymer free radicals for adventitious termination reactions with the graft. No limiting effects of time were seen for graft production.
VII.3 Comparison of Test Tube and Bulk Factorials Despite the slightly different conditions under which the test tube and scaled-up factorials were run, several comparisons can be made. Already mentioned is the necessity of a nitrogen purge for the agitated system. The inhibiting effects of oxygen are less important for the test tube systems due to the relatively small surface area exposed to the oxygen. All large scale reactions were done at 353K(80°C) with only one grade of PTFE: DLX-6000. Agitation was used in this system; whereas the test tube system was quiescent. Time and initial concentration were varied over different ranges in both systems, but the effects were fairly consistent. Table 17 shows the r2 when only time and initial concentration are used to model the conversion in both systems. For the bulk system's dependent variables, over one third of the TABLE 17
Relative Effects of Time and Initial Concentration in Both the Bulk and Test Tube Systems
Relative Effects
Dependent Bulk Test Tube Variables
PTPE/W PTPE/m Time Ratio Ratio
Prn -1.00 GRAFT 1.00 Prn/GR.A.Fr -1.02 GRAFT/PTPE 2.71 TOTAL PROD. 1.00
Prn/TOTAL -1.00
GRAFT/TOTAL 2.20
PW+GRAFT 2.76 1.00 0.3930 2.71 1.00 0.4581 TOTAL variability can be accounted for by modeling with just these two independent variables. Total product can be predicted with over 98 per cent of the variability determined from these two independent variables. For the test tube system, less of the variability is determined by these two independent variables; however, an r2 of 0.7587 is obtained for the model for total product formed. The importance of time and the quantity of PTFE and HHA in describing the kinetics of the reacting systems is shown in section IV.l in which the mechanism of the reaction is modeled.
VII .4 The Mechanics of the Reaction In the heterogeneous system considered, PTFE and the graft are in the solid phase and adventitious homopolymer, monomer, and impurities are in the liquid phase. Graft polymerization occurs at the solid-liquid interface and undesirable homopolymerization occurs entirely in the liquid phase.
VII.5 Undesirable Side Reactions Impurities in the HWA promote the thermally initiated homopolymerization of HWA(42,73). In addition, some of these impurities, such as ethyl acrylate, can undergo polymerization also.
Adventitious thermal polymerization of IU4A has the following kinetics scheme: ki~ MMA' + HHA > MMA-MMA'
kt~ MMA', + WA', > dead polymer (VII. 5.4)
The krsare the rate constants for the homopolymerization. The exact mechanism by which step VII.5.1 occurs is unknown(73). In addition, the homopolymer free radical can react with the graft free radicals during termination:
kte~ IiMA', + PTPE-MMA'm > dead or occuled polymer (VII.5.5)
Some homopolymerization occured in the systems studied here.
Since homopolymerization can be avoided by ultrapurification(42,73) and accounts for only a very slight conversion (0-2 per cent) of the monomer available, its effects on causing a decrease in monomer concentration are not considered and equation IV.4.9 is used to correlate the conversion data based upon conversion only to graft.
VII. 6 Determination of [PTFEIo Judekis and Hedgpeth(l6) have developed an expression for the molar quantity of free radicals in micropowder as a function of the irradiation dose in air:
in which Q* has the units of micromoles of free radicals per kilogram of PTFE and D is the irradiation dose in rads. The quantity of free radicals in the PTFE micropowder, Ro, is defined as
Ro = Q(mass of PTFE) (VII.6.2)
in which Q has been converted from micromoles of free radicals per kilogram of PTFE to Q with units of moles per gram and the mass of PTFE is given in grams. The initial concentration of PTFE free radicals is defined by the initial molar quantity of PTFE free radicals divided by the initial liquid volume at the temperature of the reaction: [PTFE'Jo = Ro/Volume of liquid at reaction temperature (VII. 6.3)
Electron Spin Resonance(ESR) scans of the PTFE micropowders used are given in Figures 22-24. The irradiation dose of the DLX-6000 is known; substitution of the value of the dose into equation VII.6.1 gives the free radical content of the micropowder assuming that no decay has occurred since irradiation. Cutting and weighing the other curves and accounting for the different masses and sensitivities
DPPH
Figure 22: ESR scan of DLX-6000. For PTF : G = 2.0 X lo2; Mod = 2.06. For DPPH: G = 2.5 X 10b ; Mod = 1.OG. DPPH Figure 23: ESR scan of Polymist* F5A. Curve 1 is at the same 2 conditions used in Figure 20. Curve 2 is at G = 4.0 X 10 .
DPPH 3 For PTFE: G = 2.0 X 10 ; Mod = Figure 24: ESR scan of Fluone L-169. 0 2.06. For DPPH: G = 2.5 X 10 ; Hod = 1.OG. allows for determination of the quantity of free radicals in the other micropowders. It is important to note that all ESR scans were made at the same time, although reactions with Polymiste and Fluone were made eighteen months prior to the scaled-up reactions. It is expected that Polymist" and Pluone grades have received higher irradiation doses than the DLX-6000, and that decay of the free radicals has occurred over the four to eight years that have elapsed since their treatment.
Table 18 gives the calculated concentration of free radicals in each sample.
TABLE 18 Free Radical Concentration and Irradiation Dose in Ilicropowders as Determined by Equation VII.6.1
Moles of Corresponding
Ilicropowder free radicals/gram Dose (Mrad)
DuPontrs DLX-6000 Allied's Polymiste P-5A ICIrs Fluone L-169 VII.7 Solution of Conversion Equation The kinetic model for graft polymerization has been derived in section IV.1(69). The NLIN procedure in SAS, which uses a nonlinear regression technique to maximize the r2 and minimize the residual due to error, was used to solve for the rate constants k and k P t'
ln([H]o/[H]) = ln(l/(l-x)) = = (k /k )ln(ktt[PTPE]o +1) (IV. 1.7) P t
in which
The units on the rate constants are liters/mole-second.
VII. 8 Solution of Conversion Equation for Test Tube Runs Data from runs in test tubes at 333K(60°C) and 353K(80°C) for Pluone 6169 have been given in Tables 11 and 12; data for Polymiste P5A at 343K(70°C) have been given in Table 13. The NLIN SAS procedure was used to solve for the curves shown in
Figures 10 - 12 as solutions to Equations VII.7.1, VI.1.9, and VI.l.ll. Table 19 gives a summary of the rate constants obtained by solution of VII.7.1, accounting for the conversion of units from time in minutes to time in second. Appendicies D - F give computer output for the NLIN procedure used for the test tube runs. Parity plots of actual versus predicted values are given in Figures 25 - 27.
Table 19 Rate Constants for Test Tube Reactions Calculated from Equation VII.7.1
Ratio Temperature g PTFE/ [PTPEJo k kt Grade K( OC) ml HHA moledl l/mgle-s l/mole-s R~
The degree of conversion in test tubes using L-169 is enhanced at the higher temperatures, and this effect is not overcome by that of the increased decay of free radicals with temperature as seen in work with PTFE films(39,40). Although reactions at both temperatures show a limiting tendency of conversion with time, the higher temperature results in higher conversion for the time ranges studied. The rate constant for termination of the Polpist@ reaction at 343K(70°C) is between those for L-169 at 333K(60°C) and 353K(80°C); the propagation rate constant is much higher than the values for L-169. The reactions with Polymist* were made eighteen months before the bulk reactor experiments, although the measurement of radicals by 0 2 4 6 8 10 ACTUAL X CONVERSION
Figure 25: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 333K(60°C) using Fluon' L-169 in a ratio of 1 gram PTPE to 3 milliliters M. A line with a slope equal to 1 is shown. ACTUAL X CONVERSION
Figure 26: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 353K(80°C) using Fluon* L-169 in a ratio of 1 gram PTFE to 3 milliliters !MA. A line with a slope equal to 1 is shown. 20 40 ACTUAL X CONVERSION
Figure 27: Parity plot of conversion values predicted from equation VII.7.1 versus experimental values for reactions in test tubes at 343K(70°C) using Polymiste F-5A in a ratio of 2 gram PTFE to 5 milliliters MU. A line with a slope equal to 1 is shown. electron spin resonance was made at the same time as the DLX-6000 runs. A decay in free radicals would have occurred over this time and affected the calculations of the amount of free radicals from the ESR scans, and therefore, the calculation of the rate constants.
In addition, the conversion to graft was significantly higher for the Polymiste than for the Pluone. The anomalous behavior of the
Polymiste F5A may be a result of structural changes(l5,19,24-27) that occured at its higher irradiation dose, implying that not only the concentration of free radicals relative to monomer is important in determining conversion, but also that the structural conformation affects the ease with which the reaction can occur. The rate constants obtained would then be not only functions of temperature, but also related to irradiation dose. The calculated activation energies and frequency factors are compared with values in the literature for poly(methy1 methacrylate) homopolymerization in Table 20. Overall, comparison of the graft polymerization values with
those in the literature for WlIA homopolymerization shows differences which are related to the mechanisms of homogeneous versus heterogeneous polymerization, such as interfacial effects, diffusional restraints, and steric hindrances. The activtion energies for both are within the same range; however, the rate constants are much smaller for graft polymerization. This implies that, in separate systems, the homopolymerization of methyl methacrylate initiated by nitriles or peroxides will occur to a greater extent than graft polymerization initiated by PTFE free radicals. Table 20 Comparison of Rate Constants and Activation Energies at 333K(60°C) for Graft Polymerization of HHA to PTFE (L-169) and Homopolymerization of W(42) Li tera ture values for Graft Polymerization Homopolymerization
Higher conversion to graft was seen for the micropowder-W system than for the aqueous acrylic acid-PTPE film system shown in Figure 2. The quantity of free radicals in Fluon. L-169 at 333K(60°C) corresponds to a dose of 500,000 rads, as determined by ESR scans, and at one hour reaction times, to a graft to micropowder ratio of about 0.16. The film system, at 308K(3S°C), shows a graft/PTFE ratio of less than 0.05 for a 1 megarad dose. The difference is accounted for by the higher temperature of the micropowder system, different monomer reactivities, or a difference in activity of the film and micropowder for initiation. Figure 4 gives grafting as a function of temperature in a film system for a 5 megarad preirradiation dose. The Polymist* data, which corresponds to this dose, show a much higher graftlPTFE ratio of about 1:l versus 0.20 for the film system. This difference may be due to the system temperature-333K(60°C) for the film system and 343(70°C) for the micropowder system; however the Polymiste data seem anomalous due to their very high values when compared to either the DLX-6000 or L-169 data.
VII.9 Bulk Reactor Data
Data from 333K(60°C) - 353K(80°C) have already been given in
Tables 14-16 and Figures 13 - 18. The rate constants obtained from the NLIN procedure are given in Table 21. Computer outputs of NLIN are given in Appendices G and 8. The units of the rate constants on the computer outputs are for time in minutes. The rate constants are of the same magnitude as those obtained in the test tube reactions.
Table 21 Rate Constants for the Bulk Reactor as Calculated from Equation VII.7.1 using DLX-6000
Temperature Ratio [PTFEJo k k K( OC) g PTPElml W molell l/mo!e-see llmofe-sec R~ Parity plots of actual and predicted values are given in Figures
28 and 29. The calculated activation energies and frequency factors for the DLX-6000 reactions are given in Table 22.
Table 22 Activation Energies and Frequency Factors for the Bulk Reaction using DLX-6000
A slight decrease in conversion with an increase in temperature is shown in Figures 15 - 17, suggesting that the graft polymerization is effectively endothermic in the bulk reactor, as shown in Table 22. Although the polymerization itself is exothermic, its expected increase with temperature is postulated to be counteracted by a decay of free radicals. The work of Hegazy et.a1.(39,40) with acrylic acid and PTPE films confirms these effects of free radical decay with temperature (Figure 4). Since fewer free radicals are available at the higher temperature, less growth sites are available and the conversion is lower compared to that at lower temperatures, thus 0 0.04 0.08 0.1 2 0.1 6 0.2 0.24 ACTUAL CONVERSION
Figure 28: Parity Plot of graft conversion values predicted from equation VII.7.1 versus experimental values for the bulk reactions at 343K(70°C) using DLX-6000 in a ratio of 1 gram PTFE to 3 milliliters IUIA. A line with a slope equal to 1 is shown. ACTUAL CONVERSION
Figure 29: Parity Plot of graft conversion values predicted from equation VII.7.1 versus experimental values for the bulk reactions at 353K(80°C) using DLX-6000 in a ratio of 1 gram PTFE to 3 milliliters W. A line with a slope equal to 1 is shown. making the activation engeries effectively endothermic.
The decay of free radicals with temperature was not seen in the test tube runs with Pluone L-169. The Fluone was several years old and most expected recombination reactions would have occurred within that time(l6). The DLX-6000 was irradiated several weeks before use, and many recombinations would not have occurred until mobility and diffusion were enhanced by the increase in temperature. From the activation energies in Table 22, the rate constants at 333K(60°C) can be predicted as
for a conversion of 7.4053 per cent from equation IV.1.9, versus the actual conversion of 13.9461 per cent. The activation energies and frequency factors obtained from the data at 343K(70°C) and 353K(80°C) predict a decrease in conversion at 333K(60°C) relative to the higher temperatures, vhich is not seen in experiments. Conversion in test tubes using Fluone L-169 and in the bulk reactor using DLX-6000 was similar over the same time range. This confirms the concept of a reacting front vhich begins at the solid-liquid interface. The HHA reacts with those free radicals that are easily accessible close to the interface. Diffusion of monomer through the already grafted portions must continue for further reaction to occur. If the free radicals are homogeneous throughout the sample, the DLX-6000 will have more of them at the solid-liquid interface. Initiation of the graft will be immediate with reaction between the PTPE' and the monomer; a tangled web of graft will form rapidly at the surface and diffusion of monomer through this web will sustain the reaction. The Pluone L-169 has a fewer number of free radicals at the surface, so monomer can diffuse into the micropowder further before the pores are blocked by graft. This assumes that the rate of diffusion and the rate of reaction are balanced. The agitation in the DLX-6000 system provides a means of maintaining temperature control and homogeneity of the reacting mixture, but does not control the reaction rate if oxygen is excluded.
For the same period of time, conversion of !U4A to graft at 333K(60°C) was slightly higher for a micropowder system which received a dose of 9 megarads, than it was in the irradiated film systems which received a 5 megarad dose(40) as shown in Figure 4. This may be due to a difference in the reactivity of the monomers(!U4A versus an aqueous acrylic acid system), or dose. In addition, the geometry of the micropowder may allow easier access to the free radical sites. As shown in Figure 5(40), film thicknesses approximately equal to the average particle size of 100 microns, as used in the kinetic runs, and dose of 5 megarads show about the same per cent increase in weight as does the micropowder at a 9 megarad dose for the same time period. If both samples were used immediately after irradiation, the micropowder which received the 9 megarad dose would be expected to have a higher number of free radicals and, therefore, initiate a higher conversion to graft than the PTPE film. Decay of free radicals in this sample would account for the lower than expected conversion. VII.10 Prediction of Conversion in the Factorial Runs from the Rate Constants in the Kinetics Runs Rate constants as obtained from.the kinetics runs were used to predict the conversion for the factorials in both test tubes (Table 23) and in bulk (Table 24).
Table 23
Experimental and Predicted Conversion to Graft for the Test Tube Factorial Based on the Rate Constants from the Kinetics Runs
Test Tube Actual Predicted Factorial Run Conversion Conversion Table 24 Experimental and Predicted Conversion to Graft for the Bulk Factorial Based on the Rate Constants from the Kinetics Runs in Bulk
Bulk Actual Predicted Factorial Run Conversion Conversion
For the test tube factorial, no values were obtained for those experiments using PolymistQ at 331(5g°C), since Polymiste runs were made only at 343(70°C) and rate constants cannot be estimated at the other temperatures. For those runs at 341K(68OC), the rate constants at 343K(70°C) were used. Poor correlation between the actual and predicted values was obtained, since the rate constants were found using the very high conversion values from several year before the measurement of free radicals(refer to section VII.8). Correlation of predicted values using DLX-6000 and predicted rate constants from the bulk reactions is slightly better. Correlation of the predicted and actual values for the bulk factorial data using Dm-6000 at 353K(80°C) was very good since these values interpolate between those in the kinetics runs used to determine the rate constants.
VII.ll Estimation of the Number of PHHA Repeat Units per Chain Since the PHHA graft is chemically combined to the PTFE matrix, and the PTFE domains do not dissolve readily in common solvents,typical methods of molecular weight determination cannot be used. An estimation of the average number of PlUU repeat units in each chain is made here, based on the quantity of PTFE free radicals, assuming that each chain is the same length and each PTFE free radical is the site of chain growth. For the DLX-6000 micropowder, there are 1.1462 X moles of free radicals per gram as determined by equation VII.6.1. By assuming that each free radical is a site of PHHA chain growth, then (1.1462 X moles (1.1462 X moles of free radicals ) - of chains 1 (VII. 11.1) gram PTFE gram PTFE
For a sixty minute conversion time at 353K(80°C), the ratio of graft to PTFE is approximately 0.25(Table 15); therefore,
0.25 g graft I g PTFE 1 mole of chains X 1 g PTFE (1.1461 X 6.02 X chains moles of chains)
1 mole of graft 6.02 X repeat uni ts X - 100.13 g graft mole of graft
2178 repeat units of HHA chain of graft Since the carbon-carbon bond distance is about 1.54 angstroms(75), this would correspond to a totally extended length of 3354 angstroms. The molecular weight of a chain with 2178 repeat units is 218,100.
Since the critical entanglement weight of PHHA is 30,000(75), the chains produced here are long enough to be flexible and to entangle.
VII.12 Temperature Excursions As shown in Figures 19-21 the temperature of the reacting mixture peaks after about fifteen minutes: at 353K(80°C), the temperature rise was six degrees; at 343K(70°C), the rise was five degrees, and at 333K(60°C), the temperature did not rise until 30 minutes into the reaction at which time it rose four degrees and stayed at approximately this temperature. In test tubes, the temperature rise was much higher, at ten to twelve degrees, using a 343K(70°C) water bath. In this case also, the maximum was seen about fifteen minutes into the reaction. For all times studied, measurable conversion occurred. In test tube runs(69), conversions at one minute were obtained as long as the temperature was 333K(60°C) or higher. Reactions at 313K(40°C) and 293(20°C) showed no conversion. The temperature peak is not related to a gel effect since there is no inflection point in the conversion rate curves in
Figures 10a - 14a to mark the beginning of a gel effect as seen in Figure 30(76,77) for homopolymerization of M. In addition, the conversion at this time is lower than that at which the gel effect typically is seen. Billmeyer(73) attributes induction times to consumption of inhibiting or retarding species, such as residual oxygen in the monomer or PTFE. The higher temperature rise seen in test tubes is due to the heterogeneity of the reaction medium. Since the contents are not mixed, heat exchange with the environment is poor and localized hot spots can occur easily. The "hot spotw effect is not seen in the agitated bulk systems due to their homogeneity and improved heat transfer with the constant temperature water bath that is aided by mixing. There are three reasons why no temperature rise is reported in the literature for PTFE films(33-41): (1) the temperature of the reacting medium was not measured; (2) the temperature was measured, but no rise was observed; (3) the mechanism of reaction of the film
Phase E!
Phosc III ik
00 10 2 0 30 TIME (rnin)
Figure 30: Conversion profile for methyl methacrylate polymerization depicting different phases of reaction(76,77). versus that of the micropowder is different enough that the temperature rise is seen only when using micropowders. Of these, reason (1) is most likely since no mention is made of the system temperature. The subsequent rise in temperature seen after about fifty minutes of reaction time is due to the addition of mechanical energy. At that time, very little free liquid is present in the reactor and the polymer has the consistency of very sticky dough. Increased vortexing and mixing energy requirements accompany this change in the system appearance.
VII.13 Agitation Excursions. The Lightnin controller TS1515 was oversized for this reaction system. Power readings were obtained only after the reaction had proceeded for a significant amount of time. In addition, power readings were not always reproducible from one run to the next. In general, the agitation power readings show an increase corresponding to a visible increase in system viscosity. In most cases, the agitation power decreased or fluctuated at the second temperature increase seen at about fifty minutes. A power decrease was seen when swollen polymer rolled into a ball or flattened against the reactor wall and did not undergo any mixing. Occasionally, chunks of polymer were pulled into the paddle blades and the power would surge. PART VIII Background for Polymer Characterization
VIII. 1 Rheology
VIII.l.a Melt Flow Behavior
When a material is subjected to a force, or stress, it responds by deforming, or undergoing strain. Elastic materials recover the strain completely upon removal of the stress; viscous materials have no recovery at all(78). For viscoelastic materials, such as most polymers, the application of stress results in an instantaneous deformation due to bending and stretching of primary valence bonds.
This deformation has two parts - a retarded and recoverable elastic deformation due to moving to a new equilibrium position associated with the reoriented state and an irrecoverable deformation due to polymer chains slipping past each other(79). A classical explanation of shear stress is given in
Figure 31(78). A and B are parallel plates; B is stationary while A moves at a control velocity, v, as a result of the force, F. The
fluid layer next to B does not move, while the fluid layer next to A moves with the same velocity as A. The rate of change of the liquid velocity across the plate separation, r, is called the shear rate, du/dr, while the force, P, is called the shear stress(78-81).
A fluid is said to be Newtonian if its shear stress and shear rate are related linearly by(78,80)
in which
1 = shear stress
d/ = shear rate
% = viscosity
Figure 31: Schematic of the shear stress and shear rate when a polymer melt is confined by two parallel plates(78). Plate A moves with velocity, v, caused by the force, F; plate B is stationary. The shear rate, du/dr, is defined as the rate of change of the liquid velocity across the plate separation, r.
The viscosity of Newtonian fluids is not a function of either the shear rate or shear stress. A material whose viscosity increases with shear rate is called dilatant or shear thickening; a polymer whose viscosity decreases with shear rate is called pseudoplastic or shear thinning(81). This difference is shown in Figure 32(78,80). Most polymers are shear thinning and show a plateau of Newtonian behavior before entering into the pseudoplastic regime. "Constitutive" equations of varying degrees of complexity(79-81) have been derived to explain polymer melt behavior in the shear thinning regime.
7 - Newtonian
-
Figure 32: Description of materials by the response of their viscosity to shear rate(78-80).
VIII.1.b Rheology and its Governing Equations. The purpose of melt rheology is to study the flow of polymers under variations of stress or strain (78,82). Use of a melt rheometer assumes that there is no slip at the walls and that the flow is isothermal and incompressible(80). Polymer is contained within a heated barrel and a piston or ram is used to force the molten material through a die with a given length to diameter ratio. From the force required to extrude the polymer at a set ram speed, the shear stress and shear strain can be determined. Since both the shear stress and shear strain have maximum values at the wall due to the no slip condition, it is usually these values which are used for study(78,82):
(VIII. 1.3)
(VIII. 1.4) in which
F = load on the ram
r = die radius
R = barrel radius
L = capillary(die) length
VR = ram speed
'Ia = apparent viscosity
$a is called the apparent viscosity because the equations used to define it assume Newtonian behavior(78).
An Arrhenius relationship can be used to describe the effect of temperature on viscosity: in which K is a pre-exponential factor unique to the polymer, b E is the activation energy for flow, and T is the absolute temperature(83). This equation can be used for either constant shear stress or constant shear rate conditions(78-80,83).
VIII.1.c Flow Instabilities In extrusion, the rate of production is limited by the onset of flow instabilities(84-86); this is noted by variations in pressure and force(87,88) and a decrease in the quality of the extrudate. The occurrence of instabilities was named melt fracture by Tordella(89) because of audible tearing and popping noises that sometimes accompany the distortion of the extrudate. The onset of melt 6 fracture occurs at a shear stress of about lo5 - 10 newtons per square meter(88,gO-92). Several types of extrudate distortion occur. "Mattew, a small scale roughness resulting in a surface vithout specular gloss, is not a shear stress initiated phenomenon. "Ripple", an increasing degree of roughness from matte, consists of a series of peaks and valleys and resembles ripples on the surface of water. The roughness is one fifth to one tenth that of the overall specimen diameter. "Sharkskin" is a form of the ripple distortion in which the surface of the extrudate resembles that of fish scales. "Wavinessw, a more severe form of surface irregularity, may take the form of zig-zags, single or double helicies, or irregular waves, and in its most extreme form, fragmentation of the extrudate results(92). Ripple and waviness are believed to initiate at different sites within the capillary, but there is not agreement on the mechanisms involved for each(85,92). Ripple has only been seen for high density linear polyethylene and a copolymer of tetrafluoroethylene and hexafluoropropylene(TPE-HFP), while waviness is associated with all other polymers(92). The degree of distortion decreases with capillary length for branched polymers, perhaps due to a relaxation in the polymer during transit through the capillary(91-93). For linear polymers, distortion increases with die length(88,94-96). "Streamlinedn dies reduce the degree of distortion, due to a lower increase in shear rate near the capillary. The critical shear stress at which the distortion occurs, however, does not change with streamlining(92,95,97). Tordella(92) gives a summary of the proposed mechanisms by which melt fracture occurs. Tordella discounts Reynolds number dependence, die swelling resulting in a difference in strain between the material on both sides of die exit, viscous heating which causes thermal gradients in the melt, and cavitation phenomena in which the stored energy of the sheared polymer exceeds that required to form a new surface. The theory that Tordella(92) supports is related to elastic strain: distortion of coiled molecules from equilibrium occurs during shear and results in elastic strain. Helt fracture is then a consequence of the inability of the polymer structure to support further elastic deformation beyond a critical elastic strain(92,98-101). The failure involves large scale elastic deformations on a time scale faster than the natural time scale of relaxation of the molecules(92).
VIII.1.d Die Swell. Swelling of an extrudate as it exits from a capillary is typical of Non-Newtonian viscoelastic liquids and is believed to be related to their elastic properties. Prom a molecular viewpoint, die swell is a result of disorientation, upon exit from the die, of the macromolecules which have been oriented within the capillary by the high shear field; while from a rheological viewpoint, die swell is a result of non-instantaneous recovery of elastic deformation imposed in the capillary(98). The swell ratio, defined as the ratio of the extrudate diameter to that of the die orifice, decreases as the ratio of the length to diameter(L/D) of the capillary increases, implying memory effects(l02). The swell ratio is about 1.1 for Newtonian liquids(l02) and significantly higher for viscoelastic materials. The mechanism by which die swell occurs is under debate. Some researchers believe that it is related to the relaxation of axial normal stress upon exit from the die(103-105), while other explain it by relaxation of radial normal stress(106,107).
VIII.2 Temperature Transitions.
The glass transition(T ) and melting(Tm) temperatures are useful in characterizing and determining end use behavior of a polymeric material.
VIII.2.a Glass Transition Temperature. The glass transition temperature is that temperature below which the amorphous domains of a polymer assume the characteristics of the glassy state and become brittle, stiff, and rigid(42). Above that temperature, the chain ends, being more mobile than segments within the polymer molecule, have more flexibility and generate a larger free volume into the space they occupy, thus providing more empty space and greater flexibility for the rest of the molecule(108). The glass transition temperature, as shown in Figure 33, is defined as the temperature at which the specific volume versus temperature curve shows a change of slope(42). Chain rigidity and asymmetry cause the chains to be more polar and pack more tightly, resulting in higher T values(42). Impact g strength decreases below the T due to increased brittleness. g ' Softening that occurs around the T generally limits the upper end g use temperature(l08). I
L 1 I I TP Tm Temperature Figure 33: Specific volume of a polymer as a function of temperature. T is the glass transition temperature of the amorphous rkions. Tm is the melting of the crystalline domains(42).
VIII.2. b Melting Temperature The melting temperature(Tm) is that temperature at which the crystalline domains of a polymer melt. From a thermodynamic viewpoint, melting is an equilibrium process and the change in free energy(AG) is equal to zero:
in whichAH is the enthalpy of fusion, AS is the entropy of fusion, and T is the absolute temperature. The melting temperature can then be defined as(80) In Figure 33(42), the specific volume versus temperature curve shows a discontinuity at the melting temperature. A first order transition occurs at the crystalline melting temperature, whereas a second order transition occurs at the glass transition temperature. A semicrystalline polymer having both amorphous and crystalline domains would show both a T and Tm(42). Polymers with high T Is g g generally have high Tmrs; the reverse is seen for low transition temperatures(42).
VIII.2.c Determination of Glass Transition and Uelting Temperatures Glass transition and melting temperatures can be determined easily by use of a differential scanning calorimeter(DSC). DSC measures the heat flow required to maintain a sample and a reference system at the same temperature as this temperature is either kept constant or varied linearly with time. Vhen the sample undergoes a thermal transition, a signal proportional to the power difference between the samplers heater and that of the reference is plotted on the y-axis of the recorder with temperature recorded on the x-axis(l09). The area under the curve is proportional to the heat of transition; the displacement of the sample curve from that of the reference is proportional to the specific heat. The curves show peaks at the melting temperature and a change in slope at the glass transition temperature(ll0).
VIII.3 Resistance of Polymers to Chemical Attack Solubility or swelling of a polymer in a solvent depends upon competitive intermolecular attraction between (a) solvent and polymer molecules and (b) adjacent polymer molecules. Although adjacent molecules will exert maximum attraction for each other, a solvent molecule can intercept this intermolecular attraction either to dissolve the polymer or else to cause it to swell(l08). The solubility and swelling of polymers in solvents is related to the solubility parameter, 6, which is defined in terms of the cohesive energy, %oh' necessary to break all intermolecular contacts:
e /V (at 298K) coh = Ecoh
1/2 d = (Ecoh/V) = e coh 1/2 in which ecoh is the cohesive energy density and V is the volume at 298 kelvins. The cohesive energy density of a polymer can be determined from contributions by the various functional groups. The solubility parameter of a solvent can be found from the energy required for vaporization(4 E )(75) : vap
(VIII. 3.4)
In general, solubility parameters of a polymer should be within one to two units away from that of the solvent in order to dissolve or swell in it(73).
ASTH has provided a test method for resistance of plastics to chemical attack. In this method, procedures are given for preparing test specimens and specific solvents are listed(ll1).
VIII.4 Mechanical Properties of Polymers.
VIII.4.a Elastic Hodulus When a force(stress) is applied to a polymer, the polymer deforms(strain). If the force is a tensile stress, the relationship between tensile stress(c) and tensile strain(4 ) defines the tensile(Youngfs) modulus, E: in which D is the tensile compliance. If the force is a shear stress, the relationship between shear stress(T;) and shear strain($) defines the shear modulus,G:
in which J is the shear compliance.
If the polymer is assumed to isotropic, then
in which L,, Poisson's ratio, is given by
with V as the volume. For most polymers is in the range of 0.2 to 0.5(112).
VIII.4.b Dynamic Mechanical Analysis In a dynamic mechanical test, a polymer is subjected to a sinusoidal stress or strain, as compared to a step function in the static experiments(ll3). The response of a perfect elastic material undergoing shear is given in Figure 34(114,115). Stress and strain rate are in phase. /
STRESSISTRAIN RESPONSE OF ELASllC MATERIALS 6 = 0
STRESSISTRAIN RESPONSE OF IDMA/ VlSCOELASTlC MATERIAL 6 2 0
Figure 34: Response of elastic and viscoelastic materials to a sinusoidal stress(ll4). For a perfectly viscous material, the strain rate exhibits a maximum while the stress is at a minimum, and vice versa. Since the sine wave has its maximum rate of change at zero amplitude and its minimum rate of change at maximum amplitude, and the stress is sinusoidal, and stress and strain are 90° out of phase. For a viscoelastic material which exhibits some of the characteristics of both viscous and elastic materials, the phase lag is between 0 and 90° and is call the loss angle. This is shown in Figure 34(114). The absolute shear modulus((;) is defined as the ratio of the magnitude of the shear stress vector to the magnitude of the strain vector. The absolute shear compliance is the reciprocal of the modulus. The viscoelastic response is separated into "in-phase" and
2- "out of phasew components; the projection of the stress vector,t , 2 onto the strain vector, a', yields I, the component in phase with
2 the strain, while the projection of i5 onto an axis perpendicular to
'ZT gives Zw,the component 90° out of phase with the strain. The shear moduli and shear compliances are given by the magnitude of the vectors as: The tangent of the loss angle gives the relationship between the primed('), or storage functions, and the double primed("), or loss functions, as
Storage and loss viscosities are define by
in whichdis the angular frequency of the sinusoidal stress. Dynamic and static properties can be related by the following equations(ll6):
in which
G = shear modulus
A = %/G )2. = viscosity The value of the tensile modulus can be obtained from equation VIII.4.3. In terms of complex numbers,
The complex numbers are useful for describing the geometry of the in-phase and out-of-phase vectors.
VIII.4.c Mechanical Properties and Transition Temperatures. The dynamic properties are sensitive to transitions, relaxation processes, structural heterogeneities, and the morphology of multiphase systems. The loss angle is used to study molecular weight, composition of copolymers, cross-linking, etc. The modulus, as calculated from equations VIII.4.12 and VIII.4.13 or equation VIII.4.14, is shown as a function of temperature in Figure 35(75). Near the glass transition region, some molecules have more mobility than others. If the stress is applied a wfrozenw segment which later becomes mobile while still under stress, part of the segment will move to reduce the stress, dissipating the energy as heat and reducing its available stored energy(ll3). log 0
Muhan~cal Glossy Leathery Rubbery- Rubbery Llquld Behavlour elast~c tLow flow
Moluulor Only v~bmbons Short-mnge Rap~dshort- Sl~ppoged Long-mnge Behovlour of otomlc dtff us~onai mnge dt tfuu - long-range confqurobonat groups motton onal mot~ons entang~emtschanges (whda (cham Retamed bng- md.Culas) wgmnts) rongrmohons
Figure 35: The regions of viscoelastic behavior of amorphous polymers(75). PART IX Equipment Used for Product Characterization
The graft polymer chosen for characterization was material made at 353K(80°C) for 1 hour. It was a mixture of two runs, which when combined, had 0.2836 grams of graft to 1 gram of micropowder. Since this material was not extracted, there was also 0.0549 gram of homopolymer per gram of micropowder.
IX. 1 Melt Rheology.
1X.l.a Instron Melt Rheometer. Several experiments were made using the Instron MCR capillary Rheometer mounted in an Instron universal testing machine with a capillary die of 0.0762 centimeter diameter and 10.15 centimeters land length. The barrel diameter of the rheometer was 0.9525 centimeters. Runs were made at ram speeds less than 2.5 centimeters per minute at a temperature of 433K(160°C).
1X.l.b Kayeness Helt Rheometer. A Kayeness, Inc., Computer controlled melt rheometer, model 2052, was used for the majority of the melt extrusion runs. This machine, which was used in the constant shear rate mode, can also be used in a constant stress mode. The controller is programmed to step through various ram speeds. Output from the host computer tie-in includes forces, ram speeds, and shear rates and shear stresses calculated from equations VIII.1.2 - VIII.1.4. A "streamlined" capillary with an entrance angle of 120°, a diameter of 0.2093 centimeters, and a land length of 2.33 centimeters was used. The barrel diameter was 0.9525 centimeters. Ram speeds from 0.10 to 30.5 centimeters per second were used. PHiU homopolymer(nominal1y 10 grams per run of Elvacitee 2051 supplied by DuPont), graft material(nominal1y 12 grams per run), irradiated PTFE micropowder(nominal1y 15 grams per run of DLX-6000 supplied by DuPont), and a 4:l mixture of the micropowder and the PHHA were extruded at various rates and temperatures.
IX. 2 Temperature Transitions A Mettler TA3000 system with a DSC 30 cell was used to determine temperature transitions in the PHHA, graft material, and the PTFE micropowder. Also checked for temperature transitions were the extruded graft(extruded at 513 kelvins) and extruded micropowder (extruded at 543 kelvins). A heating rate of 10 kelvins per minute over a range of 368K(95"C) to 623K(350°C) was run.
IX. 3 Chemical Resistance
Graft extrudate (extruded at 513 kelvins) was subjected to exposure in test tubes in 25 milliliters of the following chemical reagents: benzene, methanol, methyl methacrylate, acetone, and distilled water. Exposure times were one hour, three hours, and 3 days. The extrudate was also exposed to boiling spring water for
three hours. Extrudate baked in a conventional oven for twenty minutes at greater than 533 kelvins(500°F) was subjected to an acetone environment, the most hostile reagent for the graft. Changes in mechanical integrity were noted.
IX. 4 Dynamic Mechanical Testing
A Dupont Instruments 983 Dynamic Mechanical Analyzer was used to obtain the storage and loss elastic and shear moduli over a temperature range of 298K(25OC) - 473K(200°C). The same material used for extrusion was used to mold a bar 11.53 x 14.08 x 4.24 millimeters using a platen press at 69,000 kilopascals(10,000 psi) and 543K(270°C). The sample was clamped to driver arms in the DM as shown in Figure 36(114,115). The DHA was used in the resonant mode in which the arms and sample are displaced 0.2 millimeters by an electromagnetic driver, subjecting the sample to a fixed deformation and setting the system in resonant oscillation. The amplitude and frequency of the oscillation, together with the amount of energy sent to the driver, is used to calculate the viscoelastic properties. The modulus
equation used for calculation is defined in Figure 37(114). A Poisson's ratio is assumed in order to calculate the shear modulus. The tan d term can be defined as
2 2 tan delta = (Cfla)([V-Vl(f,a)]/f -fo ) in which
C' = amplitude independent damping function a = oscillation amplitude
V = measured damping voltage
V1 = instrument damping voltage as a function of f and a
= instrument resonant frequency £0 f = measurement frequency The tan term relates the loss and storage moduli:
tan delta = En/Ef = Gw/Gr Figure 36: Schematic of sample deformation in a DHA(114,115). MODULUS EQUATION
84b-K (L A L) E' = 2((+0) 77 [a + 2*==] ~(9
and E' = 2C' (4 +o) #.n:o = Coluon'r Rallo A = kmpb CIOII-mctlonol om k = kmpc. croar-mctlonal rodlur of gyrotlon (k = ~firdr not wmmor, t = 1112 lor eyl~nertcol wmwa)
B = Am Spacing (Dlrtanca 8ohvo.n hot Canten) I(f)= Inrtrument compliance conutlon a = Shoor dlrtomon toctor J = Momant of IMma K = Ptvot Ipdng conrtont L = Samplo ungm AL = Sample length comctlon T Sampc. mkk~8~ E' = m8tk Modulw G' = Shoat MOduIua f = Remnant Freawncy
Figure 37: Explanation of the equations used to calculate the elastic and shear moduli using a DHA(114). PART X Results of Product Characterization
X. 1 Melt Rheology
X.1.a Instron Melt Rheometer
No acceptable data was obtained from running the Instron melt rheometer. Problems with this equipment are discussed in Part XI.
X.1.b Kayeness Melt Rheometer
o PMMA homopolymer Elvacite* 2051, lot number 16041-639, was supplied by DuPont. This material is a homopolymer of poly(methy1 methacrylate) with several trace additives for increased stability. The Elvacitee was extruded in the Kayeness rheometer at
473K(200°C) and 488K(215OC) at several ram speeds. The corresponding force and calculated shear rate, shear stress, and apparent viscosity are given in Tables 25 and 26. A graph of shear stress and apparent viscosity as a function of shear rate at these two temperatures is shown in Figures 38a - 38b. Viscosity decreases with increasing shear rate; whereas, shear stress shows a slight increase over the range of shear rates. For Table 25 Rheology of PW(ElvaciteQ 2051) at 473K(2W°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) ( l/sec) (kPa) (k Pa-sec)
0.04 279.2 1 392.0 291.7 0.16 383.1 5 537.9 100.0 0.40 396.4 13 556.6 41.4 0.80 389.1 26 546.3 20.3 1.00 337.2 33 473.5 14.0
most shear rates, the shear stress and viscosity are higher at the lower temperature. Extrudates were poor at both temperatures with a very irregular surface, resembling a strand of mismatched pearls. The extrudate ranged from transparent to translucent. A photograph of the material extruded at 488K(215OC) is shown in Figure 39.
o PTFE micropowder. The micropowder was extruded-through the Kayeness rheometer at 488K(215OC) and 543K(270°C). Results of these runs are given in Tables 27 and 28. These data are graphed in Figures 40a and 40b. Table 26
Rheology of PM4A (Elvacitee 2051) at 488K(215OC).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( k Pa ) (k pa-sec) 0.04 155.5 1 218.3 162.5 LOG SHEAR RATE(l/SEC) 0 473K 4 488K
Figure 38a: Shear stress of PHHA homopolymer (Elvacitee 2051) as a function of shear rate at 473K(200°C) and 488K(215OC). LOG SHEAR RATE(1 /SEC) t 473K A 488K
Figure 38b: Apparent viscosity of PWhomopolymer (Elvacite* 2051) as a function of shear rate at 473K(200°C) and 488K(215OC). Figure 39: Photograph of PW(Elvacitee 2051) extruded at 488K(215OC). Table 27
Rheology of PTPE Hicropowder (DLX-6000) at 488K(215OC).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( KPa) (k Pa-see)
Table 28
Rheology of PTPE Hicropowder (DLX-6000) at 543K(270°C).
Ram Shear Shear Apparent Speed Porce Rate Stress Viscosity (in/min) (lbs.) (l/sec) (KPa) (k Pa-sec) Figure 40a: Shear stress of PTPE micropowder (DLX-6000) as a function of shear rate at 488K(215°C) and 543K(270°C). LOG SHEAR RATE(I/SEC) t 488K A 543K
Figure 40b: Apparent viscosity of PTPE micropowder (DLX-6000) as a function of shear rate at 488K(21S°C) and 543K(270°C).
Viscosity decreases over the shear rate range; whereas, shear stress remains approximately constant to slightly increasing. Only a slight decrease in shear stress and viscosity over these shear rates is seen as the temperature increases from 488K(215OC) to 545K(270°C). The micropowder extrudate was very fragmented with lengths of about one to two centimeters at the lower temperature. At higher temperatures, the fragments ranged from 4 centimeters at lower shear rates up to 15 centimeters at higher shear rates. The extrudate at 545K(270°C) broke at about 15 centimeters upon contact with the lab bench due its brittleness. The diameter of the extrudate was constant and the surface was smooth. The interior of the extrudate was granular, and did not appear to have coalesced. A photograph of the micropowder that was extruded at 545K(270°C) is shown in Figure 41.
o Graft The graft sample from a mixture of two runs at 353K(80°C) for one hour reaction times was extruded in the Kayeness rheometer at 473K(200°C), 488K(215OC), 513K(240°C), and 545K(270°C). Tables 29 to 32 summarize these runs. These data are graphed separately in Figures 42 to 45. Table 29
Rheology of Graft Polymer at 473K(200°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-sec)
Table 30
Rheology of Graft Polymer at 488K(215OC).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-sec) Table 31
Rheology of Graft Polymer at 513K(240°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity ( in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-see) 0.04 196.1 1 275.3 204.9 Table 32
Rheology of Graft Polymer at 545K(270°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( k Pa ) (k pa-sec) 0.04 126.9 1 178.1 132.6 LOG SHEAR RATE(1 /SEC n SHEAR STFiESS + VI 4COSllY
Figure 42: Shear stress and apparent viscosity as a function of shear rate for the graft polymer extruded at 473K(200°C). LOG SHIM ARE(I/SEC) 0 SHEAR SRESS + VI,COSFIY
Figure 43: Shear stress and apparent viscosity as a function of shear rate for the graft polymer extruded at 488K(21S°C). LOG SHEAR RATE(I /SEC) o lNWEXTFlUSION O RE-EXTRUDED
Figure 44a: Shear stress as a function of shear rate for the graft polymer extruded at 513K(240°C). Also included are data for material reextruded at this temperature. LOG SHEAR RATE(1 /SEC t INlW U(TRUSI0N A A E-MTRUSION
Figure 44b: Apparent viscosity as a function of shear rate for the graft polymer extruded at 513K(240°C). Also included are data for material reextruded at this temperature. LOG SHEAR RATE(1 /SEC) a 543K 0 513K
Figure 45a: Shear stress as a function of shear rate for the graft polymer extruded at 543K(270°C). Also included are data for the re-extrusion of this material at 513K(240°C). LOG SHEAR RATE(l/SEC) t 543K A 513K
Figure 45b: Apparent viscosity as a function of shear rate for the graft polymer extruded at 543K(270°C). Also included are data for the re-extrusion of this material at 513K(240°C). At all temperatures, the viscosity decreases rapidly with shear rate. The shear stresses are approximately constant, showing a decrease at 473K(200°C) and slight increases with shear rates at the other temperatures. Extrudates from 473K(200°C) and 488K(215OC) looked slightly less coalesced than material extruded at 513K(240°C). The best quality extrudate was made at 513K(240°C), with the smoothest surface. Extrudate made at 543K(270°C) was much rougher and of poorer quality. The extrudates came out of the rheometer in continuous lengths and could be bent while still hot. A photograph of material extruded at 513K(240°C) is shown in Figure 46. Material extruded at 513K(240°C) was re-extruded at the same temperature. The data are shown in Table 33 and graphed along with the other data at 513K(240°C). No change in physical condition or rheological properties was seen as a result of the repeated extrusion. Graft extrudate from 545K(270°C) was re-extruded at 513K(240°C). Data are given in Table 34 and graphed along with the initial run at 545K(270°C). A significant increase in the viscosity and shear stress is seen for this re-extrusion. The material obtained from this re-extrusion resembled the extrudate obtained at 513K(240°C). Figure 46: Photograph of graft polymer extruded at 513K(240°C). Table 33 Rheology of Graft Polymer Extruded at 513K(240°C) and Re-extruded at 513K(240°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity (in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-sec)
Table 34 Rheology of Graft Polymer Extruded at 543K(270°C) and Re-extruded at 513K(240°C).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity ( in/min) (lbs. ) (l/sec) (kPa) (k Pa-sec) o 4:1 Ratio of Irradiated PTFE and PMMA Hicropowder and PMMA homopolymer were mixed together and extruded at 488K(215OC). A poor quality extrudate with a small scale surface roughness consisting of transparent powder was obtained. re-extrusion of this material at the same temperature had no effect on extrudate quality. the results of these extrusions are shown in Tables 35 and 36 and in Figure 47a and 4b.
Table 35
Rheology of DLX-6000 and Elvacitee 2051 Physically Mixed in a 4:l Ratio Extruded at 488K(215OC).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity ( in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-sec) LOG SHEAR RATE(l/SEC) O lNWEXTRUSION 0 RE-EXTRUSION
Figure 47a: Shear stress as a function of shear rate for a mixture of Dm-6000 micropowder and Elvacite* 2051 at a ratio or 4:l
and-- - extruded at 488R(215OC). Also included are data for the re-extrusion at the same temperature. LOG SHEARRATE(I/SEC) t INlTlAL MTRUSION A RE-EXTRUSION
Figure 47b: Apparent viscosity as a function log shear rate for a mixture of DLX-6000 micropowder and Elvacite* 2051 at a ratio or 4:l and extruded at 488K(215OC). Also included are data for the re-extrusion at the same temperature. Table 36
Rheology of DLX-6000 and Elvacite* 2051 Physically Mixed in a 4:l Ratio Extruded and Re-extruded at 488K(215OC).
Ram Shear Shear Apparent Speed Force Rate Stress Viscosity ( in/min) (lbs. ) (l/sec) ( k Pa ) (k Pa-sec)
X. 2 Differential Scanning Calorimetry A DSC analysis of Elvacitee 2051, micropowder, extruded DLX-6000, and virgin and extruded graft polymer was done.
0 PmA
Figure 48a shows a DSC scan for Elvacitee 2051 over a
temperature range of 313 - 633K(40 - 360°C). Boles were punched in the sample pan to allow escape of any volatiles. Molecular
transitions are occurring over the range of 373 - 413K(100 - 140°C). Beyond approximately 533K(260°C), degradation begins to occur. A subsequent DSC run, shown in Figure 48b, shows that total degradation of the Elvacitee 2051 has occurred over this temperature range. < --TWUH3HLOX3 mO1.d IW3H .3o 38Il lWM3dW31 Figure 48a: DSC run of Elvacitee 2051. Figure 48b: DSC rerun of sample from Figure 48a. o PTFE Figure 49a and 49b show the first DSC heating cycle of DM-6000 micropowder and integration of the melting peak. The scan is fairly flat, except for the melting peak at 600.8K(327.8°C). Figures 50a and 50b show the rerun of the heating cycle for the same micropowder samples. The melting peak curves are almost identical and similar values are obtained for both the melting temperature and heats of fusion. Extruded micropowder DSC scans are shown in Figures 51 and 52. Figure 51a and 51b are for the first heating cycle and integration; Figures 52a and 52b are for the second cycle. Melting points and heats of transition are slightly higher for the extruded material. Results of the PTFE DSC scans are given in Table 37.
Table 37
Results from DSC Scans of DLX-6000 Micropowder First heating Second heating
Me1 t ing Me1 t ing Temperature Temperature 4H K(OC) K( OC) f~7A9" Virgin Micropowder 600.8(327.8) 63.615 601.3(328.3) 58.040 Extruded Micropowder 604.0(331.0) 64.283 604.4(331.4) 61.357 Figure 49a: First DSC run of DLX-6000. Figure 49b: Integration of DSC run of Figure 49a. Figure 50a: Second heating DSC run of material in Figure 49a. Q IIJ
Figure Sob: Integration of DSC run from Figure 50a. Figure 51a: First DSC heating cycle for extruded DLX-6000. ems ~rnI
Figure 51b: Integration of the PTPE melting peak in Figure 51a. Figure 52a: Second DSC heating cycle for the sample used in Figure 51a.
o Graft Polymer Figure 53a and 53b give the first heating cycle and integration of the PTFE peak for unextruded graft polymer. A reproducible peak is seen on the low temperature side of the PTFE melting curve. The scan is flat up to this shoulder. A subsequent heating cycle with integration is given in Figures 54a and 54b. The low temperature shoulder of the PTFE peak disappears upon cooling and reheating. Melting temperatures and heats of fusion show only a slight decrease. The first heating curve is slightly broader than the second. The heats of transition for the PTFE peak are significantly less than those obtained for the micropowder alone. Figures 55a and 55b give the first heating cycle and integration for the PTFE peak for extruded graft; the second heating cycle and integration is given in Figures 56a and 56b. Extruded graft does not show the low temperature shoulder seen in the virgin material. Almost identical curves are obtained for each scan, while the heat of fusion is slightly higher for the first heating cycle than for the second. Results of the DSC scans for the graft polymer are summarized in Table 38. Figure 53a: First DSC heating cycle for virgin graft polymer. Figure 53b: Integration of the PTFE melting peak in Figure 55a. Figure 54a: Second DSC heating cycle for the swple used in Figure 53a. Figure 54b: Integration of the PTPE melting peak in Figure 56a. Figure 55a: First DSC heating cycle for extruded graft polymer. Figure 55b: Integration of the PTPE melting peak in Figure 55a. Figure 56a: Second DSC heating cycle for the sample used in Figure 55a. Figure 56b: Integration of the PTFE melting peak in Figure 56a. Table 38 Results from DSC Scans of Graft Polymer
First heating Second heating
Me1 ting Me1 t ing Temperature AHfusion Temperature AHfus ion
K( OC) (Jig) K( OC) (J/g)
Virgin Micropowder 600.6(327.6) 44.432 600.4327.4) 42.040
Extruded Micropowder 602.3(329.3) 38.824 601.8(328.8) 34.677
X. 3 Chemical Resistance Extrudate samples were exposed to various solvents to determine their chemical resistance; these solvents included benzene, methanol, methyl methacrylate, acetone, and boiling and distilled water. Samples kept in benzene showed no change after one hour. At about seventy five minutes exposure time, the sample started to look slightly furry, with a well defined core. After two and a half hours, the surface looked blistered. A slight weight gain(< 4 per cent) occurred at a three hour exposure. After three days in benzene, the sample was crumbly in the bottom of the test tube. Samples exposed to methanol showed no change in structural integrity and about a four per cent weight gain over three days. Exposure to methyl methacrylate monomer was detrimental. After twenty minutes exposure, bubbles formed on the surface and hairy tendrils grew out from the sample. At one hour, the sample surface was roughened and sticky, but quickly hardened on evaporation of the monomer. After about two hours, an expanded tendril formation covered the entire surface and broke off in patches. Loss of structural integrity occurred at three and a half hours of exposure. After three days, the sample was a fibrous mass at the bottom of the test tube. Acetone was the most destructive solvent for the graft polymer. After ten minutes, tendrils began to form and to break off shortly thereafter. Collapse of the extrudate occurred at about one hour. At two and a half hours, the sample was a gelatinous mass in the bottom of the test tube. Neither distilled water at room temperature for exposure times of up to three days nor boiling water for three hours had any effects on the graft polymer. A sample of extrudate was sintered in a conventional oven at greater than 519K(500°P) for twenty minutes. The surface showed slight blistering and a decrease of 6.7 per cent in weight was noted. Part of this weight loss may have been due to polymer stuck to the baking pan. There was no change in structural integrity on exposure to acetone for greater than four weeks, but a 4.2 per cent weight increase was observed. A graft sample that was extracted with acetone before extrusion at 513K(240°C) was exposed to acetone. It showed increased resistance over the unextracted sample but significantly reduced resistance in comparison to the heat treated extrudate sample.
X. 4 Dynamic Mechanical Analysis. The dynamic mechanical analysis was done in the resonant mode, using the resonant oscillation of the sample bar after removal of a fixed stress. Figure 57 shows this frequency as a function of temperature, varying from 25 to 5 hertz over 293 - 473K(20-200°C). An inflection point in this curve is seen at approximately 413K(14OoC). The elastic storage modulus is calculated from the equation shown in Figure 37. Figures 58a, 58b, and 58c show the elastic storage modulus, tan delta, and elastic loss modulus respectively. An inflection point is seen in the storage modulus at about 403K(130°C) and 310.5 kilopascals(45 k psi). The loss modulus shows a flat region over the temperature range of 393 - 403K(120 - 130°C); beyond this point the curve approaches a limiting value at 0. The tan delta curve has a maximum value of 0.53 at about 425K(153OC) Prom an assumed value of Poisson's ratio of 0.44, the shear modulus and shear loss modulus can be calculated from equations VIII.4.3 and VII.4.9 and are graphed in Figures 59a and 59b. The shapes of the shear storage and shear loss curves are identical to that of the elastic storage and loss values over the same temperature range. During the course of the analysis the sample bar cracked through approximately 80 per cent of its thickness. Figure 57: Oscillation frequency of a sample bar of graft polymer subjected to a.strain with an amplitude of 0.2 millimeters as a function of temperature. Figure 58a: Elastic storage modulus(Et) as a function of temperature for the graft polymer. Figure 58b: Tan delta as a function of temperature for the graft polymer. Figure 58c: Elastic loss modulus(EW) as a function of temperature for the graft polymer. Figure 59a: Shear storage modulus(Gt) as a function of temperature for the graft polymer. Figure 59b: Shear loss modulus(GW) as a function of temperature for the graft polymer. PART XI Discussion and Interpretation of Product Characterization
XI.l Helt Flow Behavior
XI.1.a Instron Helt Rheometer Difficulties in using the Instron melt rheometer were due to the die available, temperature limitations and control, and the quantity of material required to make a run. The available die had a diameter of 0.0762 centimeter and a land length of 10.15 centimeters, for an L/D ratio of 133. The shear stress for this die, approximated from attempts to run and equation
VIII.1.2, was about 1.2 - 5.9 X 106 Newtons per square meter, well within the range at which melt fracture occurs(87-91). Extrudate of micropowder was highly fragmented; poly(methy1 methacrylate), which was very difficult to push out of the rheometer, resembled a strand of mismatched beads placed an unequal distance apart. Tearing and popping noises associated with melt fracture(87) were also heard. The heaters on the rheometer barrel would not heat the barrel contents higher than about 433K(160°C) - 453K(180°C). This temperature, as will be demonstrated in the next section, was not high enough to obtain a good quality extrudate. In addition, this rheometer requires relatively large samples (20-30 grams) of material per run. Since reactor batches were on the order of 120 - 150 grams of product, this would severely limit the number of runs that could be made.
XI.1.b Melt Rheology on the Kayeness Rheometer
The Kayeness melt rheometer is a "desk-top" model, easier to run and requiring about one half to one third of the material required by the Instron. The die available, with an L/D of 20 and an included angle of 120°, was much better suited for extrusion of the materials involved. The rheometer used was not equipped to reach the melting point of the micropowder and, thus, the maximum extrusion temperature studied was 543K(270°C)
0 PW Tables 25 and 26 and Figures 38a and 38b summarize the extrusion data on PHHA. The photograph of the extrudate in Figure 39 shows a high degree of melt fracture; this is substantiated by the high shear 5 stresses of about 4-6 X 10 Newtons per square meter. Materials for commercial extrusions have a viscosity in the 4 6 range of 1 - 100 kilopascal-seconds (10 -10 Poise); the viscosity of PHWA (Elvacitee 2051) at the temperatures studied is well within this range. The natural logarithm of viscosity as a function of inverse temperature is shown for various shear rates in Figure 60. The viscosity shows a decrease with increasing temperature(75) for all Figure 60: Natural logarithm of viscosity as a function of 1/T for various shear rates for PH)1A (Elvacitee 2051) extrusion. Figure 61: Activation energy for flow of PMA (Elvacitee 2051) as a function of shear rate, taken from extrusion runs at 473K(200°C) and 488K(21S°C). shear rates, as predicted by equation VIII.1.5. The activation energy for flow can be predicted by this equation, and is shown as a function of shear rate in Figure 61. The activation energy shows a decrease with an increase in shear rate. The data at a shear rate of 33 inverse seconds gave a slightly higher viscosity at the higher temperature due to insufficient material in the barrel and is not included in the graph. The values of the activation energy are fairly low, compared to values of 20 - 100 kilojoules/mole for other polymers(ll6), implying that the melt flow of PHWA has only a slight dependence on temperature over the given temperature range. Longer lengths of PWA extrudate were obtained by using the shorter die in the Kayeness rheometer than the longer die in the Instron; this agree with the observation of Tordella(87) and others(88,94-96) for unbranched polymers. The included die angle in the Kayeness die improved streamlines(92,95,97). Since the diameter of the PWA extrudate varied so greatly, no comments about the effect of die swell can be made.
o PTFE The viscosity of the DLX-6000 micropowder at 488K(21S°C) is about two to three times that of the PHWA at the same temperature. The viscosity of the micropowder is at the upper range of melt processibility. An increase in the temperature of 55 kelvins has very little effect on the viscosity of the micropowder, since the micropowder is not above its melting temperature, and the crystalline chains do not have enough mobility to slide past each other easily. The viscosity values are similar to those obtained by Fisher and Corelli(Figure 1)(15) for melted irradiated PTFE exposed to a dose of 9 megarads, the dose received by DLX-6000, even though the extrusion temperature is lower and below the melting temperature 543K(27O0C) versus 623K(350°C). Application of equation VIII.1.5 to this data to express the viscosity as a function of temperature and to determine activation energies is shown in Figures 62 and 63. Since only a slight decrease in viscosity occurs over this temperature range, only a slight increase in mobility occurs and the activation energies for flow are correspondingly small. The activation energy for PTPE flow is much lower than that for the PHHA flow. This is due to the low mobility of the PTPE molecules below their melting temperature compared to the higher mobility of poly(methy1 methacrylate) molecules above their glass transition temperature. The severe fragmentation of PTFE extrudate, shown in Figure 41, and the high shear stresses show that the extrusion of the micropowder was in a region of melt fracture(87-92). The extrudate was not coalesced at either temperature since it was far below its melting point . Figure 62: Viscosity of DLX-6000 micropowder as a function of temperature for several shear rates. Figure 63: Activation energy for flow of DLX-6000 as a function of shear rate. As for the PEMA, longer pieces were made using the Kayeness than the Instron rheometer due the shorter die length(86,92-94) and the included entrance angle(90,93,95).
o Graft Polymer Data from graft polymer extrusions are summarized in Tables 29-34 and Figures 42-45. The viscosity of the graft polymer at 488K(215OC) is approximately equal to that of the homopolymer at the same temperature, implying that the homopolymer block is "draggingw along the micropowder through the extrusion and that the micropowder is providing little resistance to the flow. The viscosity of the graft is in the melt processable range. The graft polymer viscosity shows a dependence on temperature of about the same order of magnitude as the PMHA homopolymer. Viscosity data as a function of temperature and shear rate are shown in Figures 64a - 64e. The dependence of viscosity on temperature shows that the PHIU block of the graft exerts a strong influence on the flow behavior. In addition, the activation energies for flow, as shown in Figure 64,
are between those of the PUMA and PTPE, but closer in value to those of the PHIU. The re-extrusion at 513K(240°C) of material initially extruded at 513K(240°C) shows that the graft polymer is thermally stable and melt processable at those temperatures. Re-extrusion at 513K(240°C) Figure 64a: Viscosity of the graft polymer as a -Yf nction of temperature at a shear rate of 1 sec . Pigure 64b: Viscosity of the graft polymer as a fynction of temperature at a shear rate of 5 sec- . Figure 64c: Viscosity of the graft polymer as a fyction of temperature at a shear rate of 13 sec- . Figure 64d: Viscosity of the graft polymer as a fu ction of temperature at a shear rate of 26 sec- f . Figure 64e: Viscosity of the graft polymer as a fupction of temperature at a shear rate of 33 sec- . Figure 65: Activation energies for the flow of the graft polymer as a function of shear rate. of material initially extruded at 545K(270°C) improves the extrudate quality, showing that temperature has a significant effect on processing. A physically combined mixture of micropowder (DLX-6000) and Elvacitem 2051 was extruded twice, with no decrease in the roughness of the sample. Quality of the extrudate surface was poor in both runs and there was no coalescence of the extrudate. The PWacted only as a lubricant for the micropowder extrusion. Grafting of the
PTFE and PERIA yields a much better product than physical combination. The shear stresses for the graft extrudate are slightly less that those for either the Elvacitee or DLX-6000, but are still above the range for melt fracture. The only evidence of melt fracture, however, is a very slight roughness of the surface. The surface roughness does not approach "ripple" distortion(92), but is rougher than a "matte" finish(92). The roughness may be decreased possibly by extruding with capillaries of different L/D ratios or at different ram speeds. The diameter of the extrudate is fairly constant, with values ranging from 0.208 to 0.211 centimeters, compared to a die diameter of 0.209. Very little die swell occurred upon exit from the capillary, implying only a slight elastic response(98,102). XI.2 Differential Scanning Calorimetry
0 PW
Transition activity observed in Figure 48a in the range of 373 -
413K(100 - 140°C) is seen in commercial grades of PMU produced by DuPont and is due to the melting of trace components. This peak overlaps the region in which the glass transition temperature of the ElvaciteQ is expected to occur. At about 493K(220°C), the slope of the scan begins to decrease. This temperature corresponds to the ceiling temperature of PM, the temperature at which depropagation of the chain occurs(42,75). Unzipping of the Elvacitee from both the chain ends and the weak links(75) continues to occur as the temperature is raised. This degradation of the PWchain is substantiated by the flat scan in the repeated thermogram shown in Figure 48b.
0 PTFE Extrusion of the PTPE micropowder resulted in a small increase in the heat of fusion and the peak temperature, indicating that a slight degree of extrusion induced orientation occured. The heat of fusion for unirradiated PTFE is 75.31 joules per gram. The heat of fusion for the micropowder, as calculated from the DSC scans, is twenty to thirty per cent lower due to its lower molecular weight(25). The micropowder was not sintered before irradiation; therefore, its melting point was lowered(26) from that of virgin PTFE and, by coincidence, or by a similar molecular rearrangement that occurs both upon sintering and upon irradiation, is approximately equal to that of sintered PTFE.
o Graft Polymer A shoulder on the low temperature side of the PTFE melting peaks was seen by Fisher and Corelli(l5) for irradiated PTFE. They attributed this shoulder to the presence of imperfect crystallites in the PTFE. A low temperature shoulder is seen in the graft polymer thermograms in Figure 53a, but not in the micropowder scan in Figure 49a, and therefore, is not related to the micropowder. This shoulder corresponds to the temperature range seen in the scan for the degradation of PWhomopolymer in Figure 48a. Since the shoulder is not seen in a second heating cycle or in material extruded above the ceiling temperature of PIUlA(42,75), its presence may be related to the homopolymer in the original sample. The scans give no indication of thermal degradation of the grafted PIIWA. The heats of fusion for the grafted polymer decrease from those of the micropowder by a factor equivalent to the mass fraction of PTFE in the graft; however, melting temperatures are the same. Extrusion causes a slight increase in the melting temperature, but a decrease in the heats of transition, indicating that a slight degree of orientation may have occurred. XI.3 Chemical Resistance Contact of acrylics with chlorinated or aromatic hydrocarbons, esters, and ketones is not recommended(ll7); polytetrafluoroethylene, on the other hand, is resistant to hostile chemical environments(32). Poly(methy1 methacrylate) has a solubility parameter of 9.1 - 12.8 cal1/2cm3/2; that of polytetraf luoroethylene is calculated to be 6.2(72). The solubility parameters for the solvents used to study chemical resistance are given in Table 39.
Table 39 Solubility Parameters of Solvents(ll8) used to Study Chemical Resistance of the Extruded Graft
Resistance of the (cal 11Zcm3/2) Graft Extrudate
He thy He thacrylate 8.8 Very poor Benzene 9.2 Poor Ace tone 10.3 Very poor
He thanol 14.5 Very good Water 23.4 Excellent Boiling Water 23.4 Excellent Good solvents for poly(methy1 methacrylate) cause extensive damage to the graft extrudate, implying that untreated graft would not be suitable in environments hostile to PMA. A sample heat-treated for twenty minutes at 519K(500°P) lost 6.7 per cent of its weight, some of which was due to sticking to the baking pan. This sample had excellent resistance to acetone, suggesting that degradation and loss of homopolymer upon heat treatment increased the chemical resistance of the graft. A sample extracted in acetone for three hours before extrusion to remove homopolymer had an improved resistance to acetone over the unextracted sample, but did degrade at longer exposure times. The presence of the PMA homopolymer reduces the chemical stability of the graft extrudate. Either all the PHHA homopolymer was not removed from the extracted sample or else its removal alone does not account for the increased resistance of the heat treated sample. Some kind of molecular rearrangement, which may include a change in the domain structure or endcapping of the graft chains, may occur upon heating to very high temperatures and improves the chemical stability of the graft polymer. Higration of the PTFE to the surface as seen in stratified coatings(ll9) would provide a protective layer against chemical attack. XI. 4 Dynamic Mechanical Analysis The resonant frequency and storage and eleastic moduli of the graft polymer bar have been given in Figures 57 - 59. The higher values of the elastic storage modulus desginate the polymer as thermoplastic or thermoset rather than rigid or elastomeric(ll4). The complex viscosity can be calculated from equations VIII.4.14 and VIII.4.15 and is graphed as a function of temperature in Figure 66. The slight peak in the curve at 383K(110°C) may be due to the sample cracking at that point. The shear and elastic moduli can be calculated from the complex viscosities in equations VIII.4.16 and VIII.4.17. The moduli are graphed as functions of temperature in Figures 67 and 68 and compared to Figure 35(75). The shape of each of these curves show a glassy plateau region up to about 373K(100°C), a transition or "leathery" region between 373 - 433K(100 - 160°C) and a rubber elastic region beyond 433K(160°C). High enough temperatures were not reached for rubbery or liquid flow to occur. The glass transition temperature can be determined by the method given by Von Krevelen(75) in Figure 35 and is approximately 398 - 403K(105 - llO°C). The DSC thermogram of the graft given in Figure 53a shows no activity at this temperature. The calorimeter used is probably not sensitive enough to discern the slope change which designates the T 8' The elastic modulus for PTFE at 293K(80°C) is 350,000 to 700,000 kilopascals(50 - 100 k psi), while that of PHHA is 3.5 X 106 kilopascals(500 k psi)(l20). The value obtained for the graft polymer's elastic modulus at 298K(80°C) is about 815,000 kilopascals (118 k psi), implying that the presence of the PTFE dominates the mechanical properties of the graft polymer. Figure 66: Complex viscosity as a function of temperature for the graft polymer(viscosity' is the lower curve; viscosityn is the upper curve) Figure 67: Logarithm of the elastic modulus as a function of temperature. Figure 68: Logarithm of the shear modulus as a function of temperature. PART XI1 Applications
A graft polymer of PTFE and PHHA may prove useful in applications which require the stability and low friction properties of the PTFE and easy processability provided by the PWgraft. Heat treatment, as described in the chemical stability section, may be required to guarantee resistance to hostile environments.
o Paints and Finishes Poly(methy1 methacrylate) has been used in paints and finishes because of its durability and good pigment uptake. Addition of PTFE would provide a non-wetting, low friction surface which would reduce the build-up of dirt or other contaminants. This would be especially useful in household applications to reduce clean-up and in marine applications to increase environmental resistance to reduce barnacle growth which results in increased drag and fuel consumption.
o Fibers and Filaments Extrusion of the graft polymer was demonstrated in the rheology experiment. Approriate conditions of spinning can be used to produce a filament with excellent thermal and chemical properties. o Molding
Injection molding of the graft would take advantage of the lubricating properties of the PTFE and the easy processing of the
PHWA. The PTFE would allow quick release from molds. Viscosity and strength requirements could be tailored by modifying the quantities of PTFE and PMMA in the graft. PART XI11 Summary
XIII.l Conclusions Initial reactions in test tubes using PTFE micropowders, ICI's
FluonQ L-169 and Allied's Polymiste F-5A, and MMA monomer proved the feasibility of the reaction of irradiated PTFE free radicals and HIU monomer above a minimum activation temperature. Experiments with a factorial design showed that conversion of MMA to graft was improved with higher ratios of PTFE to MMA and higher temperatures of reaction. A nitrogen purge did not improve the conversion to graft, but slightly reduced the adventitious homopolymerization to poly(methy1 methacrylate). A factorial experiment in a scaled-up reaction was made to determine effects of agitation. A different grade of PTFE micropowder, DuPont's DLX-6000, was used because of its availability. Since the agitator continually pumped oxygen into an open system and inhibited the reaction, a closed system with a nitrogen purge was necessary to obtain measurable conversion. Kinetics runs over several temperatures showed that the conversion using DLX-6000 was affected by temperature only slightly,
implying diffusion control for the reactions using DLX-6000. Temperature peaks seen a few minutes after combination of the micropowder and monomer were related to an activation time necessary to consume inhibitors or retarders.
Since the PTFE free radicals were produced independent of the polymerization scheme, the steady state assumption of free radical polymerization did not apply. The derived kinetics model related conversion as a function of the time of reaction and initial quantities of PTFE free radicals and monomer. A nonlinear regression technique in the Statistical Analysis System was used to calculate the rate constants from this model. Discrepancies with using the model may be related to an inability of determining the exact quantity of free radicals in the micropowder and their decay with time and temperature. The predictive nature of the model can be improved by knowledge of the time - temperature decay and rate of consumption of the PTFE free radicals. A more detailed analysis of the effects of agitation and diffusion would be necessary before a very large scale-up could be made. Graft material from several runs was combined and subjected to property tests. This material contained PTFE, PWA graft and PW homopolymer in a ratio of 18:5:1. The rheology of the material gave a melt viscosity of the graft polymer between that of the micropowder and PH)LA homopolymer, but closer to that of the PWhomopolymer, implying that the PW dragged along the micropowder. Conditions which resulted in severe melt fracture for the PTFE micropowder and PWhomopolymer caused only a matte finish on the surface of the graft polymer extrudate. Graft polymer which was re-extruded was stable. A physical comibination of PTFE and PHHA in the same ratio as the graft polymer resulted in a poor quality extrudate. Differential scanning calorimetry showed the thermal stability of the graft. The heat of transition of the PTFE melting peak, on a gram basis, was proportional to the quantity of PTFE in the graft, and, therefore, can be used to determine conversion. The melting point of the PTFE was lowered by the irradiation from 613K(340°C) to about 600K(327OC). The PTFE was not sintered before irradiation. Chemical stability of the graft polymer, as polymerized, was equal to that of the poly(methy1 methacrylate) homopolymer. Aromatics, ketones, and HHA monomer were detrimental to the graft; whereas, methanol and water are not. Heat treatment of the graft reduced its weight by approximately the quantity of the homopolymer and improved the chemical stability, possibly due to removal of all the homopolymer from the sample. The shear and elastic moduli of the graft as determined by dynamic mechanical analysis were between those of PTFE and PIMA, but closer to the values of PTFE, implying that the PTFE controls the mechanical behavior. From the moduli, the graft was described as "stiff", rather than elastomeric or rigid. From a curve of the modulus versus temperature, the glass transition temperature of the
PWdomains was determined as 378 - 383K(105 - llO°C). Experiments with irradiated PTPE films showed approximately the same degree of grafting(33-41) for the same time of reaction as the micropowder; however, grafted material in the form of an easily processed powder lends itself to more applications than does an already pre-processed film.
XIII.2 Recommendations o Free radicals in the micropowder decay with time and temperature. A study of freshly irradiated material and the decrease of free radicals with time and temperature would improve the accuracy of the determination of the concentration of free radicals, and more suitably model the reacting system. In addition, experiments can be run with the same material at different times after irradiation to determine the decrease in conversion as related to a decay of free radicals in the micropowder. o An electron spin resonance study of the reaction would indicate both the species and quantities of free radicals involved in the reaction, and would provide a numerical analysis that would be used to improve the kinetics model. o Various irradiated fluorocarbons(PTFE, FBP, etc.) can be used to initiate other vinyl polymerizations. Ultrapurification of the monomers should be done to minimize the extent of
thermally initiated homop&eriza t ion. The resulting graft polymers can be tailored for appropriate applications. o The derived kinetics model can be used to describe the
polymerization using other grades of PTFE. The rate constants determined may be related to the irradiation dose or starting material before irradiation. In addition, the suitability of this model for other systems can be determined. o Modification to the kinetics model to account for diffusional
resistances, which may have been important with particular grades of PTFE, can be made. o The viscosity and mechanical properties of the graft can be determined as a function of the vinyl monomer content. This may affect the suitability of the graft material for certain processing techniques or final applications. o A study of the domain formation in the fluorocarbon - vinyl graft system and any phase inversions as a function of temperature would help explain various properties and determine the temperature range of end uses. o The exact mechanism of improving the chemical resistance of the graft polylner upon heat treatment would determine the
time and temperature required to guarantee adequate stability. o The feasibility of injection molding such a graft material can be studied. Appendix A
Sample Calculations for the Determination
of Homopolymer and Graft Appendix A Appendix A Appendix B1 General Linear Method SAS Procedure for the Determination of the Effects of Reaction Conditions on Total Product in the Test Tube Factorial
CEY'iSAL L INtA* NODELS PROCEDURE
DEPENOENT VARIABLE: 164
SOURC t OF SUM OF SQUARES MEAN SQUARt' F VALUE MODtL 5 195.d5824784 39.171 64957 13.45 ERQOR 4 11.65196912 2.01296728
CORRECTED TOTAL 9 207.5101 1696
SOURCE JF TYPE I SS F VALUE r1"E TEqP GRA OE COYC N 2
7 FOR YO: PR > lrl ST0 ERROR JF ESTIMATE PARAYETCR-0 ESTIMATF INTERCEPT TIrE Tt*P GRL DE COY L v.2
PR > F R-SOUARF C.V. 14.2936 0.0130 0.943849 IGW *€AN ROOT nsE 11.94058000 1.10674171
TYPE 111 $5 F VALUE PR > F Appendix B1
OSSERVEO PREJICTED RESIDUAL VALUE V4LJF
SUM OF RESIDUALS SUM OF SPUAREO RESIDUALS SUM OF S4UARED RESIDUALS - ERROR SS PRESS STATISTIC FIRST ORDER AUTOCORRELATION OURRIN-MATSO'4 0
LOYFR 95% CL UPPER 95% CL INDIVlWAL INDIVIWAL Appendix B2
Reproducibility of Graft and Homopolymer in
Experiments 2A and 2B in the Test Tube Factorial
I 1 0.596 2 2.1452 STD DW FOR GRAMS GRAFT IN TT FACTORIAL FCR EXPERI MENTS 21 AN0 28
VARIABLE MEAN STANDARD MINI MUM MAXI MUM STD ERROR DEV IATION VALUE VALUE ff WEAN
GGRAR 2.00~~0000 O. n~m70 I. essaoooo 2. r4szoooo o. 14zsoooo
C.V. sum VARIANCE
1 0 ..wo 2 0.4332 ST0 DN FOR CRAWS PMMA IN TT FACTWlrL FOR EXPERILYNTS 2A AND 28 I VARI ABLE N MEAN STA hOAR0 MINXMU MAXIMUM STD ERROR DEVIATICN VUUE VUUE OF MEAN
SUM VARI ANCE C.V.
0.41320.00 0.093031 12 141.421 Appendix B3
Reproducibility of Graft and Homopolymer in
Experiments 6A and 6B in the Test Tube Factorial
OBS GGRKT
1 2.SS78 2 6.4613 STD DEV FaR GRAMS CRAFT IN TT FACTORIAL FOR EXPERIMENlS 64 WD 68
VARIABLE N =AN STANDARD MIHIJ4UY MAXIYUM ST0 ERROR DEVIATIOJ VALUE VALUE OF MEAN
GCRAFT 2 4.SOS55000 2.760191 32 2.58789000 6.46130000 1.9517SO00
SW VARIANCE C. V.
1 0.WI 2 0.0000 ST0 OW FOIl GRAMS N)WP IN TT FACTORIAL FOR EXPERIMENTS 6A AN0 60
VARIABLE N ME AN STAWO MI NlMUM MAXIMUM STOERRW OW EAT ION VALUE VAL- ff =AN
SUM VAR IMCE C. V-
0.56110000 0.16178672 141.421 Appendix C1
STEPWISE SAS Procedure for the Bulk Factorial with Total Product as the Dependent Variable
4. J W n>> 1 CI U M .?in@ d NNI dm* UCU C &I u do* 0 GOI NN* - w 3- w 01 e* -3-4 (L mml m c -. a a @a% Q
& 0 u a C u -om a C > a 0 3 > 0 w. 0 I- C z z .< WQW 0 I Yz 0
;E: 3?1 L U VI rlddrl PPl* U mmmm - .3 I U.L. LI d..#.-. CC I C-Q 4 amwm 7 "-PI501 c 3 CCCC 0 4999 ern1 A "1 NNNN irNl U C700 ..I '3 V. u .*.I ..I --I u hi C NON lam ram I N X 9 C 12-3 In H IC3PLn N N I-* 16.7 IU. lL.0 f 2 I u If "C I 10 3060.3 =dl - OOOOC I 3 Z lh000.n Chl a a NNOOC -01 4 3 +HIYNLn ,191 3 3 m9InC19 .Cbl'ndF a:! s " LL ~NNCN ..I LL u O ..a*. T* 1 $+@*N +I I
Appendix C1
I I .Eel COQ 1 VC I f-C urn 1 -*z: -m l *me 1 VIN I mmm I db 1 wma I rnf- I 0.)-0 l rnm I NWd I ..I *..I cr I I-N* I em I erne I 9- I cecl I * I N I N I N I I I I I uYi0. -corn 000 1 *oa NN+ Inmu7 I 40- mm- 6a9 I POW N'arn 000 1 clme -r m + 094 1 &MF- WNC YIHR 1 omin O'nIn mmm I omul mN(n NNN I *..I vt :,' Hdcl I -r cl m I a++ m cn N N
I 000 1 000 1 WOO 1 -4-7-11 adN I *ern I 4-4 I -9- I *..I mb~I muI I Appendix C1 f Il L: TIF, t 4 VW/SP CDNVERSATIONAL WITOR SYSTEM PAG' 007 F ATC -0.72770bOO 1.188@&210 4.7659?56 1 0 -39 0.5608 , - - - - - SA5 - nAxlnun R-SOUARE IMPROYE~E~TFOR OFPENDENT VARIAHLF ILW
THC LJrlVF *OlltL IS TI1€ t)r\T b VARIARLE MODEL FOUNO.
511 P 7 VAQiAhLr- iC FNTEREO R SQUARE = 0.99765470 C(P) = 8.OI)OOOOFO
OF SUN OF SQUARES MEAN SQUARE F PROB>F
HrLRtS\ION 7 25612.20699757 3667.458 1425 1 743.0d 0.0001 t RRflR 4 60.350+8392 15.08762098 TOTAL 11 75732.55748149 a* a 0 VALUE ST0 ERROR TYPE I1 SS F PROB>F L! INTFRCEPT 1 In1 CONC 4GlT TC I4 A[: Arc ------Appendix C2
Reproducibility of Conversion to Graft and
Homopolymerin Experiments at 353K(80°C)
in the Bulk Reactor for One Hour
VARIABLE N MAN STANDARD MIWIW MAXIWn ST0 ERROR SVIATION VALUE VALUE OF MEAN
GRAFT 5 0.109676b0 0001798559 0.09280100 0.13718@00 0.00804340 H Ow OP 5 0.01662500 0-00535071 0-00878400 0.02180200 0.00239291
sun VARIANCE C.V.
16.399 0.5+838300 0.00032348 32.185 0.08312500 0.00002863 - -- - Appendix D
NLIN SAS Output for a Kinetics Run in Test Tubes using Fluone 6169 at 333K(60°C) at lg PTPE/3m1 llWB
UJ 0 * wow 9 $! 5:; ; 3 *NO 9 VI 0 NNLm Q u v, 40-4 C) n 000 L- , *** ? vl- 0 000 0
r 3 -1 a C '? 0 2 C 0 C C kl 0 zwo u, OCLO d 340 C b3aw U a w *>a w a u LO* a w e en0 a
-1 Appendix D
i 15:88289"+ ,5$3X&3ltf 0and)rOa.~aewrnrrdm I- @ggO0009 *& a a.. 000 Appendix E
KLlN SAS Output for a Kinetics Run in Test Tubes using Fluone L-169 at 353K(80°C) at lg PTPE/3m1 WIU
eFQ +*w d0N wmm CNO ONm mom 0**. 0 0 OCO
Mu- vi M N 4 M 0 Or- * # 6 9 C N6-l N'h ..I
Appendix F
NLIN SAS Output for a Kinetics Run in Test Tubes using PolymistQ F5A at 343K(70°C) at 2g PTFE/5ml MMA
-. 4 ou 6 LO:i5 t YIU.- 4 z oa(ob uwr-g =NN ome A90 N N
a x X U. wmo O. 3 0 ..( II)
Appendix G
NLIN SAS Output for a Kinetics Run in the Bulk
Reactor Using DLX-6000 at 343K(70°C) at lg PTFE/3rnl HHA
a+* wmn 4rdNrre eacw *+ 0) w mm :: ?? umz 02 C' A 1~ mm C W '- 0 u W P; 2: aC 2 d 3 ,"," aw ul 00 r L.l I rn 0 (I) Y
P: = 77 iT;O(-m, > g 00 ULYrn I- 8 3 .? om- u LU dmm c 0 N* W OW Wz om 0 .* : ON aW * 2 * 9m0, N w mmm a *Q~ a*+ 3 ~nea ul a-w u 2 000 I -0- C 8 ddd I C z 3 ul cnC
CONVERSION AS A FUNCTION OF TINE AT EIGHTY OEGREES AND DATA FIT TO KINETIC EWATIONS IN BULK REACTOR
OBS TIRE PT FE MIU L CONV VHAT YRESIO
1 10 100.B19 0.3150 0.044020 0.023599 0.020421 2 30 99.911 0.3141 0.080151 OoO6bOM 0.014141 3 60 99.940 0.3155 0.113159 0.120611 -0.007+85 4 60 101.53b 0.3142 0.121891 0.122673 -0.000176 5 60 100.091 0.3138 0.148254 0.121343 0.026911 6 60 102.1% 0.3131 0.100967 00123657 -0.022690 7 60 99.929 0.3131 0.091399 0*121+05 -0.024006 8 90 99.396 0.3157 0.1506M 0.166738 -0.016094 9 1U) 101.296 0.3155 0.241109 0.210610 0.036499 * 10 180 99.180 0.3141 0.261191 0.2718bl -0*010676 'u 11 0 100.000 0.3150 0*000000 0~00009<) 0.000000 P CONVERSION AS A FUNCTION OF TIME AT EIGHTY DEGREES AN0 OATA FIT TO KINETIC EWATIONS IN WLK REACTOR 3
eX OE? VARI&BLE: VHI1 SUM OF MAW SOURCE OF S WARES SWARE F VALUE ?ROI)>F llOO€L 1 0*051141 0~05~r41 ltb.93b 0.0001 EMOR 9 0-00409+316 0.0804H9307 C TOTAL 18 0.061@41 ROOT MSE 0.021329 I-SW4RE 0*933@ OEP WEAN OI1231*0 AOJ (1-59 0.9264 C.V. 17.32104 BIBLIOGRAPHY
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Test tube runs using different ratios of mA to PTFE were made to determine the feasibility of the reaction and optimum reaction conditions. The amount of graft produced was equal to the weight gain of the solids after removal of the adventitious homopolymer by extraction in acetone. Test quantities of material were produced in a 500 milliliter agitated reactor. A higher ratio of PTFE to excess M4A and longer reaction times result in higher conversion in test tubes. Higher temperatures decrease conversion if freshly irradiated PTFE is used, due to the thermally induced decay of free radicals. In a scaled-up reactor, the inhibiting effects of oxygen, which are exacerbated by the agitation, require that a nitrogen purge be used. A kinetics model relates the original concentration of PTPE free radicals. Graft polymer containing PTFE micropowder, PHHA graft, and PM4A homopolymer in a ratio of 18:5:1 was used for property characterization. Rheoloe experiments using a die with an L/D of 20 and included angle of 120' were made with the graft, PHHA homopolymer, and PTFE micropowder. Differential Scanning Calorimetry was used to study themal transitions. Exposure of the graft to solvents detrimental to PIUlA was done to determine the graft's chemical resistance. Dynamic mechanical analysis was used to obtain the tensile and shear moduli.
The graft material extrudes well at 513K and has a viscosity comparable to that of PMW homopolymer. The material is stable upon re-extrusion. DSC thermagrams show that the heat of transition of the PTFE melting peak is proportional to the amount of PTFE in the sample. Good solvents for PHHA are detrimental to the structural integrity of the graft extrudate; heat treatment improves the chemical resistance. The PTFE block controls the mechanical properties of the graft.
Approved :