超高分子量聚乙烯烧结制品的链缠结调控及其对性能影响

利用新的单中心Ziegler-Natta(Z-N)催化剂,通过干预分子链的生长与聚集行为,可获得低缠结的超高分子量聚乙烯(UHMWPE)初生树脂.本研究利用这类低缠结UHMWPE,通过设置不同的烧结温度(Ts)来改变熔体缠结状态,并探讨了链缠结程度对烧结制品结构与性能的影响.实验结果表明TS=220℃下,UHMWPE样品发生显著的复缠,造成高缠结度;而Ts=170℃下,初始低缠结状态能够得以充分保留,从而获得了缠结度具有明显差别的不同样品.示差扫描量热法(DSC)测试表明,在Ts=170℃下,低缠结度有利于在随后等温及冷却结晶过程中生成高熔点(最高达141℃)晶体与高的结晶度(最高达65%).力学测试表明低缠结度制品的综合力学性能显著提升,其中屈服强度提高72%,拉伸断裂强度提升139%,弹性模量提升162%以及断裂伸长率提升36%,实现了同时增强增韧.这就提供了一种从调节链缠结温度实现UHMWPE烧结制品高性能化的新思路.

Chain Entanglement Regulation of Sintered Ultrahigh Molecular Weight Polyethylene and Its Effect on Properties

Ultrahigh molecular weight polyethylene(UHMWPE)shows outstanding toughness,wear resistance and chemical inertness as a high performance polymer.However,extremely high entanglement degree results in high viscosity and processing difficulties,which greatly limits the applications.To address this issue,the new single-site Z-N catalysts have been used to regulate the growth and cohesion of molecular chains during the polymerization of ethylene in recent years,by which nascent UHMWPE with low entanglement degree and excellent processing capability can be obtained.With such UHMWPE nascent powder,different sintering temperatures(Ts)of 170,190 and 220℃ were set,respectively,then a isothermal crystallization step with precise temperature control was added,and the effect of chain entanglement on the structures and properties of sintered UHMWPE was investigated.Through the tensile tests at 160℃,it was confirmed that UHMWPE chains significantly reentangled when Ts=220℃,resulting in high degree of entanglement;while the initial low entanglement state can be sufficiently reserved when Ts=170℃,Me reached 12.3 kg/mol.Therefore,the samples with distinct different entanglement states can be obtained.DSC results have shown that low entanglement degree was beneficial to the formation of crystal lamellae with higher melting temperature(up to 141℃)and high crystallinity(up to 65%)through isothermal crystallization steps,which was close to the level of nascent UHMWPE powder.Moreover,it proved that the integrated mechanical performance of the product sintered at170℃ was significantly improved.The yield strength was increased by up to 72%,the tensile strength by 139%,the elastic modulus by 162%,and the elongation at break by 36%,realizing simultaneously strengthening and toughening of sintered UHMWPE materials.This provides a new strategy for the high performance UHMWPE sintered products from the perspective of chain entanglement regulation.