超高分子量聚乙烯/石蜡油体系的热力学相图及微孔膜的结构

Thermodynamic Phase Diagram of Ultra-High-Molecular-Weight-Polyethylene/Liquid Paraffin Blend and Structure of Microporous Membranes

在制备超高分子量聚乙烯(UHMWPE)微孔膜的过程中需要加入大量的稀释剂如液体石蜡(LP),以降低聚乙烯的熔体黏度,同时作为微孔膜的造孔剂。文中首先通过热力学理论分析了UHMWPE/LP体系是属于强相互作用体系,然后通过热台-显微镜装置在慢速的升温和降温过程中获得了相平衡温度曲线,再通过差示扫描量热测试获得了结晶温度曲线,发现相平衡温度与结晶温度均与聚乙烯含量成正相关性,分别组成了UHMWPE/LP体系的热力学相图中的相变开始和相变结束时的温度曲线。该相分离发生在100～130℃的温度范围内,是由于该体系中聚乙烯结晶引发了固-液相分离,该体系的相分离过程可以认为是晶相与非晶相之间的物质交换的过程。最后扫描电镜照片也表明UHMWPE/LP体系中的液体石蜡会削弱聚乙烯的结晶能力,影响冷却后非晶相的尺寸,从而改变萃取后微孔膜的微观结构。

During the preparation of ultra-high-molecular-weight polyethylene (UHMWPE) microporous membranes,a large number of low-molecular-weight diluents such as liquid paraffin (LP) were added to reduce the viscosity of polyethylene melts,and it was used as pore-forming agent for polyethylene microporous membranes.This paper firstly proved that UHMWPE / LP blend belongs to the strong interaction system through the analysis of thermodynamics theory.Then the phase equilibrium temperature curve was obtained in slow heating and slow cooling process through high precision hot stage microscope device,while the melting curve and crystallization temperature curve were obtained by differential scanning calorimetry (DSC).It is found that the phase equilibrium temperature curve and crystallization temperature curve are proportional to the content of polyethylene,which are regard as the curves of the beginning temperature and the end temperature of phase transition in the thermodynamic phase diagram of UHMWPE / LP blends,respectively.The phase separation process occurs in the temperature range of 100~130℃.The solid-liquid (S-L) phase separation of UHMWPE / LP blends is resulted from the crystallization of polyethylene,and the phase separation process of UHMWPE / LP blends is considered as the process of material exchange between crystalline phase and amorphous phase.Finally,through the SEM pictures of microporous membranes prepared by adding different content of paraffin oil,it is found that liquid paraffin in UHMWPE / LP blends could weaken the crystallization ability of polyethylene and affect the size of the amorphous phase,which could change the microstructure of polyethylene microporous membranes.