Thermal Properties, Rheology and Sintering of Ultra High Molecular Weight Polyethylene and Its Composites With Polyethylene Terephthalate Mostafa Rezaei, Nadereh Golshan Ebrahimi Polymer Engineering Group, Chemical Engineering Department, Engineering Faculty, Tarbiat Modarres University (TMU), P.O. Box 14115-4838, Tehran, Iran Marianna Kontopoulou Department of Chemical Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada The addition of polyethylene terephthalate (PET) fibers in ultra high molecular weight polyethylene (UHMWPE) may be a promising approach to achieve improved wear properties in artificial joints. Since UHMWPE/PET com- posites are processed by compression molding, which involves compaction and sintering of polymeric pow- ders, this article investigates their rheology, thermal properties, and sintering behavior to aid in the identifi- cation and selection of optimum processing conditions. Isothermal crystallization kinetics studies have revealed that crystallization of UHMWPE proceeds via heteroge- neous nucleation and is governed by two-dimensional growth. The crystallization rates of the composites were lower than those of the neat material, whereas their ultimate crystallinities were higher. The UHMWPE/PET composites had higher viscosity and elasticity than the neat resin. In the presence of PET fibers the onset of sintering took place at higher temperatures but pro- ceeded at substantially higher rates as compared with pure UHMWPE. A marked discrepancy between the Es- helby-Frenkel model and experimental sintering data suggests that viscous flow is not the prevailing mecha- nism for coalescence but rather that enhanced surface area, attributed to the highly developed internal mor- phology of UHMWPE particles, is the controlling factor. POLYM. ENG. SCI., 45:678 – 686, 2005. © 2005 Society of Plas- tics Engineers INTRODUCTION Ultra high molecular weight polyethylene (UHMWPE) is a thermoplastic material possessing an excellent set of properties such as good wear resistance, the highest impact strength of any plastic at cryogenic temperatures, good corrosion and environmental stress-cracking resistance, low coefficient of friction, noise- and shock-abatement proper- ties, and acceptable biocompatibility. Many applications in different areas—such as mining, foundries, transportation, and medical— have been reported for UHMWPE [1]. UH- MWPE is commonly used for artificial joints in orthopedics because of its high wear resistance. However, in spite of its good performance in short-term applications, wear, creep, and fatigue fracture have been noted in long-term applica- tions [2]. The current clinical practice of using UHMWPE for hip prostheses in younger patients, which translates to an expected implant lifetime of more than 20 years, has led to renewed concerns about the wear and durability of UHM- WPE implants. The major problem related to the long-term clinical performance of these implants is adverse tissue reaction caused by the generation of UHMWPE debris at the articulating surfaces. The resulting particles are trans- ported to the hard and soft tissue surrounding the joint and cause chronic inflammatory reactions and bone resorption [3, 4]. Several attempts have been made to understand the failure mechanisms of UHMWPE in artificial joints [5], and various methods to increase the mechanical and tribological performance of UHMWPE have been suggested. These include optimization of the processing variables, crosslink- ing of UHMWPE, and synthesis of composites. The latter approach is the focus of the present research, in which PET fibers are used to improve the abrasive wear behavior of UHMWPE matrix in total joint replacement. Because of the extremely high molecular weight of UH- MWPE, resulting in poor processability, it is very difficult to prepare UHMWPE composites via conventional melt- mixing technologies. Therefore, powder processing technol- ogies, such as compression molding of powders, which are well established for very high molecular weight polymers such as UHMWPE and polytetrafluoroethylene (PTFE), of- fer a viable alternative [6]. These processes involve com- Correspondence to: M. Kontopoulou; e-mail: kontop@chee.queensu.ca DOI 10.1002/pen.20319 Published online in Wiley InterScience (www.interscience.wiley. com). © 2005 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2005