脉振频率对脉振模压成型UHMWPE结构与性能的影响

Influence of Pulse Vibration Frequency on Structure and Properties of UHMWPE Molded by Pulse Vibration Molding

现有超高分子量聚乙烯(UHMWPE)静态成型方法普遍存在成型周期长、能耗高、极易出现热分解等问题,其制品的初生相特征结构被彻底消除使其难以同时具有良好的力学性能和耐磨性能。为此,文中采用脉振模压(PVM)成型技术,在低温下高效地制备了UHMWPE样品(PVM-UHMWPE),并研究了熔融热压阶段不同脉振频率对PVM-UHMWPE样品微观结构与宏观性能的影响规律。结果表明:脉振模压作用引起UHMWPE颗粒相互摩擦,能促进UHMWPE颗粒界面熔合,实现低温成型,这能保留UHMWPE初生相高规整度、高结晶度的特征结构,从而提高样品的整体结晶度和晶片厚度;随着熔融热压阶段脉振频率的增大,脉振作用增强,UHMWPE颗粒界面固结质量提高,PVM-UHMWPE的屈服强度、拉伸模量、断裂强度和断裂功均得到改善,但当脉振频率超过3.0 Hz后,脉振作用对UHMWPE初生相高规整度、高结晶度特征结构的破坏程度加剧,使PVM-UHMWPE的整体结晶度和熔点均降低,在未能进一步增强断裂韧性的同时,致使样品的拉伸模量下降;相对于成型周期长一倍、成型温度高40℃的普通模压样品(CM-210℃-60min),成型温度为170℃、熔融热压阶段脉振频率为3.0Hz的PVM-UHMWPE样品(PVM-170℃-3.0 Hz)的屈服强度、拉伸模量分别提升了大约9%和23%,磨损率和磨损指数分别下降了大约24%和22%,即相对于CM-210℃-60 min样品,PVM-170℃-3.0Hz样品具有更高的机械强度和更好的耐磨性能。

The existing static molding methods of ultra-high molecular weight polyethylene(UHMWPE)generally have the problems of long forming cycle,high energy consumption,easy thermal decomposition and so on,and the primary phase characteristic structure of their products has been completely eliminated,leading to failure in keeping good mechanical properties and excellent wear resistance at the same time.Therefore,UHMWPE products(PVM-UHMWPE)were prepared efficiently at low temperature by pulse vibration molding(PVM)technology in this paper,and the influence of pulse vibration frequency during molten hot pressing stage on structure and properties of UHMWPE products were studied.The results show that PVM can promote the interfacial fusion of particles at low molding temperature by friction between UHMWPE particles,and effectively preserve the structure characteristics of high regularity and crystallinity of nascent phase to increase the crystallinity and lamellae thickness.With the increase of pulse vibration frequency during molten hot pressing stage,the effect of pulse vibration increases,and this can improve the quality of particles interface consolidation.The yield strength,tensile modulus,break strength and work to failure of PVM-UHMWPE are all improved.However,when the frequency exceeds 3.0 Hz,the damage degree of such structure characteristics as high regularity and crystallinity of UHMWPE is aggravated by the effect of pulse vibration,and the overall crystallinity and melting temperature are reduced,resulting in the decrease of tensile modulus without further improving fracture toughness.As compared with sample CM-210℃-60 min with double molding cycle and 40℃higher molding temperature,yield strength and tensile modulus of PVM-UHMWPE with a molding temperature of 170℃and a pulsation frequency of 3.0 Hz(PVM-170℃-3.0 Hz)is improved by about 9%and 23%,respectively,and wear rate and wear index decrease by about 24%and 22%,respectively.That is,as compared with sample CM-210℃-60 min,sample PVM-170℃-3.0 Hz has higher mechanical strength and better wear resistance.