The effects of gamma-ray irradiation on the oxidation mechanism and free radical reaction of crystalline and amorphous regions of Ultra High Molecular Weight Polyethylene

• Main Authors: Jheng-Ying Jhou, 周政瑩
• Other Authors: Ruey-Yug Tsay
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/26043344285069977745

碩士 === 國立陽明大學 === 醫學工程研究所 === 97 === The wear of UHMWPE is the major cause for the failure of joint artheroplasty. It is known that the oxidation accelerated by residual free radicals induced by gamma irradiation is the main cause for the increase of wear rate. In this work, EPR and FTIR spectroscopy were applied to study the formation and the subsequent reactions of the free radical induced by gamma irradiation for Polyethylene materials with various crystallinity. Theoretical analysis on the dynamic curves of free radical decay obtained by EPR measurements suggests that the reaction kinetics of free radical decay in vacuum or in air for the gamma irradiated PE with different degree of crystallinity can be well described by a parallel second order model proposed in our lab. It also showed that regardless to its crystallinity, the absolute concentrations of various types of free radical all decrease with time. The decay rate increases with the increase of temperature. Also, the percentages of different type of free radicals gradually reach to a constant level. For both of the UHMWPE and HDPE materials, the final equilibrium concentration ratio of the free radicals with unsaturated C=C to radicals without unsaturated C=C, i.e. [allyl+polyenyl radical]/[alkyl radical]3, is higher for PE with higher crystallinity before gamma irradiation. The results of FTIR spectroscopy reveal that after annealing , the residue level of various C=C in order is: trans-vinylene > vinyl > vinyldene > trans-trans-vinylene. Among them, the concentrations of vinyldene and trans-trans- vinylene in GUR1020 (Quench) , GUR1020 and HDPE show no apparent changes with the changes of annealing/aging time and annealing/aging temperature. The formation of trans-vinylene seems to be mainly dominated by gamma ray irradiation and not transformed from the C=C present in the virgin materials. Compared to the other types of C=C, trans-vinylene is rather unstable during the annealing and aging process. The results obtained herein can be implemented to design a cross-linking process which is able to avoid the formation of long-life residue free radical and to ensure better long- term stability.