Study On The Disentanglement Mechanism Of UHMWPE Molecular Chain With Fluorine-containing Additive Based On The Dynamic Rheological Behavior Of The System

In this paper,ultra high molecular weight polyethylene(UHMWPE)is used as a substrate,and different fluorine-containing additives(PPA)were employed to modify the material.Two different dynamic processing methods including torque rheometer and elongation rheometer were used to prepare the UHMWPE/PPA system.The rheologic test,thermal analysis and mathematic model were performed to study the behaviors of the PPA-modified UHMWPE such as melt modulus,viscosity,melting enthalpy,crystallization temperature,and melting temperature.Eventually,the entanglement mechanism of UHMWPE molecular chains by adding PPA and the effect of different flow fields on the structure and properties of UHMWPE were investigated.It is clear that PPA has a significant impact on the mobility of UHMWPE.Introducing P990 in UHMWPE gives rise to decreasing the melt viscosity and improving the flowability of the system,whereas,adding P960 results in increasing the viscosity and inhibiting the flowability.The UHMWPE/PPA system extruded by elongation rheometer shows higher values both in modulus and in viscosity with comparison of that by the torque rheometer.However,the values of melting point(Tm)or crystallization temperature(Tc)of the system change in little from these prepared by shear flow field.The UHMWPE/PPA system with 0.2 wt%PPA prepared by the torque rheometer has the lowest crystallization temperature Tc and the highest crystallinity.The results indicate that,in the shear flow field,a small amount of PPA acts as an internal lubricant to increase the molecular mobility,molecular chain disentanglement and its crystallinity of the UHMWPE system,leading to the decrement in both storage modulus and viscosity of UHMWPE.On the contrary,the excessive PPA tends to migrate from interior to surface of the melt,causing to the occurrence of phase separation.