HOW PLASTICIZER MAKES A DUCTILE POLYMER GLASS BRITTLE? A Thesis Presented to The Graduate Faculty at The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Yue Zhao May, 2016 HOW PLASTICIZER MAKES A DUCTILE POLYMER GLASS BRITTLE? Yue Zhao Thesis Approved: Accepted: _____________________________ _____________________________ Advisor Dean of the College Dr. Shi-Qing Wang Dr. Eric J. Amis _____________________________ _____________________________ Committee Member Dean of the Graduate School Dr. Mesfin Tsige Dr. Chand Midha _____________________________ _____________________________ Department Chair Date Dr. Coleen Pugh ii ABSTRACT During uniaxial extension, a polymer glass of high molecular weight is ductile at high temperatures (still below Tg) and turns brittle when the temperature is sufficiently lowered. Incorporation of small-molecular additives to polymer glasses can speed up segmental relaxation considerably. The effect of such plasticization should be to make the polymers more ductile. We examined the effect of blending a few weight percent of either triphenyl phosphate (TPP) or a mineral oil to commercial-grade PS, PMMA and SAN. Our Instron tests showed that the plasticized PS and SAN were less ductile. Specifically, at 70 oC, the original PS is ductile at an extensional rate of 0.02 min-1 1 whereas the PS with 4 wt. % mineral oil or TPP is brittle. Similarly, at 50 oC, the original SAN is ductile at an extensional rate of 0.02 min-1, but the SAN plasticized by 4 wt. % TPP becomes brittle. No such counterintuitive effect is observed in PMMA. This finding challenges the Eyring type idea2 of activation for flow since the mechanical spectroscopic measurements show that the alpha relaxation time of PS is shortened by more than two orders of magnitude in presence of 4 wt. % TPP. On the other hand, the effect of TPP on PS and SAN can be well anticipated from the recent molecular model 3. iii ACKNOWLEDGEMENTS I am sincerely thankful to my master thesis advisor Dr. Shi-Qing Wang for his patience and guidance throughout my graduate study career. All the achievements on my study and the project research rely on his mentorship. I am so impressed and motivated by his passion for truth in the science field. Especially, he helps me realize the importance of critical thinking. I would also like to thank my thesis reader, Dr. Mesfin Tsige. As a student, I am so lucky to enjoy learning the knowledge about thermodynamics and the algorithm in his classes. Additionally, I am very grateful for his constructive suggestions on my formal seminal. Finally, I want to express my strong gratitude to my group mates. Dr. Panpan Lin, Xiaoxiao Li, and Jianning Liu have provided me so much advice on solving academic and experimental problems. And I want to thank Yexin Zheng and Sirui Ge for their help during my study. iv TABLE OF CONTENTS Page LIST OF TABLES .......................................................................................................vii LIST OF FIGURES ......................................................................................................viii CHAPTER I. BACKGROUND AND INTRODUCTION ............................................................... 1 Plasticizers and Antiplasticization .......................................................................... 1 Traditional interpretations of antiplasticization ...................................................... 2 II. EXPERIMENTAL..................................................................................................... 4 Materials and the Blending Process ........................................................................ 4 Tensile Extension .................................................................................................... 7 Relaxation in Tensile Extension .............................................................................. 7 Small Amplitude Oscillatory Shear (SAOS)........................................................... 8 Dynamic Mechanical Analysis (DMA) .................................................................. 9 Differential Scanning Calorimeter (DSC) ............................................................ 10 Gel Permeation Chromatography (GPC) .............................................................. 11 III. EXPERIMENTAL RESULTS13Solubility of Mineral Oil and TPP in Polymers ...................................................................................................................................... 13 Decrease in Glass Transition Temperature ............................................................ 14 Decrease in Yong’s Modulus and Yield Stress ...................................................... 16 Uniaxial Tensile Extension ................................................................................... 17 SAOS Results and Shift of α Relaxation Time ..................................................... 19 Relaxation in Tensile Extension ............................................................................ 20 IV. DISCUSSION ........................................................................................................ 23 v What Happened at a Breaking Point for a Brittle Polymer in the Molecular Picture? ............................................................................................................................... 23 The Interpretation of Higher Brittleness ............................................................... 25 V. SUMMARY ............................................................................................................. 27 REFERENCES ............................................................................................................ 29 vi LIST OF TABLES Table Page 2.1 Chemical and Rheological Characteristics of Polymers ..................................... 4 2.2 Physical and Chemical Properties of Plasticizers ............................................... 4 vii LIST OF FIGURES Figure Page 1.1 When the concentration of plasticizers was high enough, they not only filled in the voids but diluted the whole chain ................................... 1 2.1 Triphenyl phosphate (TPP) ............................................................................... 5 2.2 Styrene acrylonitrile resin (SAN) with 33% acrylonitrile ................................ 5 2.3 A diagrammatic sketch from the blending process to specimen making .......... 6 2.4 A diagrammatic sketch of uniaxial tensile extension ........................................ 7 2.5 Small amplitude oscillatory shear measurements of (a) polystyrene .................. 9 (b) plasticized polystyrene with 4 wt. % TPP, at a reference temperature Tref = 120 °C ............................................................................... 9 2.6 Schematic of a basic gel permeation chromatograph, including solvent, solvent delivery system, injector of sample, column(s), detector(s), and data system ........................................................................... 12 3.1 Stress strain curves of 4 wt. % TPP/PS blends that underwent different mixing time were compared ............................................................ 14 3.2 Heat flow vs. temperature curves tested by DSC of (a) 0 %, 4% TPP/PS blends ............................................................................ 15 (b) 0 %, 2 % TPP/PMMA blends..................................................................... 15 3.3 Storage modulus (G’) vs. temperature curves tested by DMA for PS and 4 wt. % TPP/PS blends respectively .................................................... 16 3.4 Storage modulus (G’) vs. temperature curves tested by DMA for PMMA and 2 wt. % TPP/PMMA blends ......................................................... 17 3.5 Stress strain curves of (a) PS .......................................................................... 17 (b) PS plasticized by 4 wt. % mineral oil in uniaxial tensile extension at 70 oC and 80 oC respectively, with a strain rate -1 V/L0 = 0.02 min ............................................................................................. 17 viii 3.6 Stress strain curves of 4 wt. % TPP TPP/PS blends in uniaxial tensile extension at 70 oC, 75 oC, and 80 oC respectively, with -1 a strain rate V/L0 = 0.02 min ......................................................................... 18 3.7 Stress strain curves in uniaxial tensile extension of (a) SAN at 30 oC and 50 oC ........................................................................... 19 (b) SAN plasticized by 4 wt. % TPP at 45 oC, 50 oC, and 55 oC, -1 with a strain rate V/L0 = 0.02 min ................................................................. 19 3.8 Stress strain curves in uniaxial tensile extension of PMMA at 55 oC and 2 wt. % TPP/PMMA at 50 oC, 55 oC, and 60 oC, -1 with a strain rate V/L0 = 0.02 min ................................................................. 19 3.9 Comparison of α relaxation time at various temperature between PS and 4 wt. % TPP/PS blends .......................................................... 20 3.10 Relaxation in extension denoting the mobility of polymer chains (b) showed the normalized curve of figure (a) ............................................... 21 3.11 Stress strain curve of stress relaxation at the same stress,19 MPa, of PS at 70 oC, and 4 wt. % TPP/PS blends at 60 oC, 63 oC, and 68 oC ........... 22 4.1 Description of formation of an LBS and the surrounding primary structure. The lac is a length to characterize