Introduction to physical modification of ultra-high molecular weight polyethylene The so-called physical modification refers to the mechanical blending of resin with one or more other materials to achieve certain special requirements, such as reducing the melt viscosity of UHMWPE and shortening the processing. Time, etc., it does not change the molecular configuration, but can give the material new properties. At present, the commonly used physical modification methods mainly include low melting point, low viscosity resin blending modification, flow agent modification, liquid crystal polymer in-situ composite modification, and filler blending composite modification. It is the most effective, easiest and most practical way to improve the flow of UHMWPE melt.
1.1 Blending with low melting point, low viscosity resin
Since HDPE, LDPE, PP, PA, polyester, rubber, etc. are low melting point and low viscosity polymers, it is mixed with UHMWPE to form a blend system. When the blend system is heated above the melting point, UHMWPE resin will be suspended in In the liquid phase of these blends, an extrudable, injectable suspension material is formed. Among them, HDPE and LDPE are used more.
The blending of UHMWPE with LDPE or HDPE can significantly improve the molding processability, but the system after adding the blender will form larger spherulites during the cooling process, and there is a clear interface between the spherulites. There is an internal stress caused by the difference in molecular chain arrangement at the interface, which leads to the generation of cracks, so the tensile strength of the blend often decreases compared with the matrix polymer. When subjected to an external force, the crack will rapidly develop along the spherulitic interface and eventually cause breakage, causing a drop in impact strength. Therefore, when LDPE is blended, the mechanical properties such as tensile strength and flexural elasticity are lowered. When blended with HDPE, it causes a drop in performance such as impact strength and friction resistance.