Research On Factors Affecting The Cryogenic Performance Of UHMWPE

Cryogenic engineering puts forward higher requirements for the toughness and strength of materials in low-temperature environments due to the development of largescale cryogenic industries such as liquefied natural gas(LNG)transportation.Ultra-high molecular weight polyethylene(UHMWPE)can maintain high impact resistance and tensile strength at low temperatures,so it can become a promising candidate for the next generation of cryogenic materials..UHMWPE has extremely long molecular chains and large chain entanglement,so it has both good toughness and stiffness.At the same time,changing the molecular weight and molding temperature can control the chain entanglement degree of UHMWPE products.Therefore,this paper mainly explores the relationship between UHMWPE chain entanglement degree and low temperature performance by changing the molecular weight and molding temperature.(1)Study the low temperature impact strength of UHMWPE original particles and products of different brands to explore the influence of the macro and micro states of raw materials on the low temperature performance of products.The particle morphology,thermal stability and crystallization behavior of the raw materials were studied,and the results showed that the low temperature properties of UHMWPE with similar molecular weights synthesized by different catalytic processes were quite different;the low temperature properties of conventional UHMWPE increased with the increase of molecular weight.In addition,the low temperature impact strength of UHMWPE is much higher than the currently recognized low temperature plastic polychlorotrifluoroethylene(PCTFE).(2)Study the low temperature properties of UHMWPE products synthesized by different catalytic processes to analyze the factors affecting the low temperature properties of UHMWPE.By analyzing the low temperature impact section,crystallization and chain entanglement degree of the two products,it is found that the crystallinity of400 Fine(low initial entanglement degree)is higher than that of 4012,and the chain entanglement degree of the product is much lower than the latter.The difference in low temperature impact strength come from the difference in crystallinity and chain entanglement.(3)The influence of molecular weight on the low temperature performance of the product was explored to analyze the relationship between the degree of chain entanglement and the low temperature performance of UHMWPE.The results show that the increase in molecular weight only increases the chain entanglement degree of the product without affecting the crystallinity,and the chain entanglement degree has the same trend as the low temperature impact strength.(4)To further explore the relationship between chain entanglement and the low temperature performance of UHMWPE,only the molding temperature of GUR 4130 was changed to regulate the chain entanglement.Increasing the molding temperature has no effect on the crystallinity and crystal form of the product,but significantly increases the degree of chain entanglement and the low-temperature impact strength of the product.In addition,the contribution mechanism of chain entanglement degree to low temperature toughness was revealed by means of DSC,DMA,PALS and other characterization methods.In conclusion,this paper studies the effects of particle microstructure and molding temperature on the low-temperature properties of UHMWPE products.Through DSC,XRD,SEM,DMA,PALS and high-temperature stretching methods,the crystallization behavior and chain entanglement degree of the products are analyzed,revealing the excellent low-temperature properties of UHMWPE.The resilience is largely due to the dense network of entanglements.At the same time,appropriately increasing the molding temperature is beneficial to improve the low temperature toughness of the product.This has important guiding significance for the low temperature application of UHMWPE.