Molecular Movement And Crystallization Behavior Of UHMWPE Under Elongation Flow Field Using Raman Spectrum

Ultra-high molecular weight polyethylene(UHMWPE)are condisered to have extensive application prospects in fields of defense,medical care,and long-distance transportation pipelines due to its excellent properties in wear resistance,impact resistance,corrosion resistance,self-lubricating and so on.In this paper,the confocal Raman spectroscopy was employed to evaluate the aggregation structure of UHMWPE samples under both elongation flow field and shear flow field.The effects of UHMWPE molecular weight and residence time on the UHMWPE aggregate structure were discussed.The research work and the conclusions are as follows.The aggregate structure characteristics of UHMWPE primary powders were investigated and the conditions of confocal Raman spectroscopy for the measurement of UHMWPE aggregate structure were optimized.It is clear that,the microfiber fraction of the UHMWPE primary powder aggregated micro/nanostructures is higher than that of the non-microfiber fractions.The aggregate structure of UHMWPE primary powders is relatively stable in the temperature rang of-120℃-120℃.However,the small particles of UHMWPE powder begin to swell and engulf the microfibrous structure at the temperature over 140 C.The relationship of structure and property of the UHMWPE with a molecular weight of 3.0 × 106 g/mol was studied under the elongation flow field and the shear flow field.The results show that,the molecular weight of UHMWPE is reduced by 40.3%via the shear flow field process at 200 ℃,whereas it is only reduced by 5.0%via the elongation flow field process.This suggests that,the melting fracture of UHMWPE occurred in the elongation flow field process is lower than that in the shear flow field process,leading to the low thermal oxidation degradation.Moreover,the UHMWPE under the elongation flow field gives lower crystallinity but higher orientation than that under the shear flow field.The effects of holding time and UHMWPE molecular weights on the UHMWPE molecular motion and crystallization behavior under the elongation flow field were investigated.The results show that,though the molecular weight of UHMWPE has little effect on the melting and plasticizing behavior under the elongation flow field,the molecular weight decreases significantly,whereas the mobility of molecular chains and the degree of crystallinity increase with increase of UHMWPE molecular weight.It is also clear that,the melting defects of the sample gradually decrease with the holding time,revealing that the mutual diffusion of the molecular chains increase.As a result,the degree of integration is inhenced and the residual stress of the sample is decreased.