tLSEVlER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Po!,mer Degradution and S:uhili/.v 61 ( 1998) 9 13 c 1998 Published by Elsevier Science Limited. All rights reserved Printed in Great Britain PII: SOl41-3910(97)00ll8-3 0141-3910/98/$19.00 Thermal degradation of short polyester fiber- polyurethane elastomer composite F. Suhara,” S. K. N. Kutty”* & G. B. Nandobt “Department qf Polymer Science and Rubber Technology, Cochin University qf‘science and Technology, Cochin, India 682 022 hRuhber Technology Centre, Indian Institute of Technology, Kharagpur. India 721 302 (Received 21 April 1997; accepted 17 May 1997) The thermal degradation of short polyester fiber reinforced polyurethane com- posites with and without different bonding agents has been studied by thermo- gravimetric analysis. It was found that degradation of the polyurethane takes place in two steps and that of the composites takes place in three steps. With the incorporation of 30phr of fiber in the matrix, the onset of degradation was shifted from 230 to 238°C. The presence of bonding agents in the virgin elastomer and the composite gave an improved thermal stability. Results of kinetic studies showed that the degradation of polyurethane and the reinforced composites with and without bonding agents follows first-order reaction kinetics. 0 1998 Published by Elsevier Science Limited. All rights reserved 1 INTRODUCTION The reinforcement of elastomers with short fibers results in good strength and stiffness for both the soft and tough elastomer matrices.lm3 Short fiber reinforced elastomer composites have attracted much attention due to their better mechanical properties and economic feasibility.4W.8 Elaborate studies on the various aspects of these reinforced composites have been done earlier.9p’7 In our earl- ier communications, we have reported the cure characteristics, mechanical properties and rheo- logical properties of a short polyester fiber reinforced polyurethane elastomer composite.‘8-~20 Thermal degradation of polyurethanes has also been inves- tigated extensively. The thermal degradation of urethanes based on 4,4’-diphenylmethanediisocyan- ate and 1,Cbutane diol was studied by Yang et a1.2’ who showed that the urethane undergoes degradation at elevated temperature giving rise to isocyanates and alcohol. Schollenberger et a1.‘2 have also reported that the urethane linkages may *To whom correspondence should be addressed. +Present address: Centre for Advanced Materials, Department of Chemistry, University of Massachusetts, Massachusetts 01854, USA. 9 be broken due to the high shear and stress at the elevated processing temperature. The influence of short fibers on the thermal resistance of the matrix, Tg and kinetic parameters of the degradation reac- tion of a thermoplastic polyurethane was studied by Ronald et al. 23 Nando and co-workers24 studied the degradation characteristics of short Kevlar fiber reinforced thermoplastic polyurethane. The present work explores the thermal degradation of short polyester fiber reinforced polyurethane elast- omer composites. 2 EXPERIMENTAL The ether based polyurethane (Adiprene CM) used in this study was obtained from Uniroyal, USA and the polyester short fiber (PET) of length approximately 14 mm and 21 pm diameter was supplied by Madura Coats, India. All the other ingredients were of commercial grade. The formulation of the mixes is given in Table 1. Mixes Al-A3 and mixes Cl-C3 contain 5phr of bonding agents (MD resins) based on poly- propyleneglycol (PPG) and glycerol (GL) with 4,4’- diphenylmethanediisocyanate (MDI). These mixes were prepared on a laboratory two roll mill as per