Preparation And Properties Research Of Ultra-high Molecular Weight Polyethylene Microporous Materials

In this thesis,our main task is focused on preparing porous materials of ultra-high molecular weight polyethylene(UHMWPE)and properties research.There are opened-type and closed-type UHMWPE microporous because of the source and form of cell,which can be prepared by different molding methods.We use powder sintering process to prepare opened-type and supercritical CO2 as foaming agent to prepare closed-type UHMWPE microporous materials.The results are as follows:(1)Using powder sintering process to prepare opened-type UHMWPE microporous materials,some defects could be discovered in the traditional static sintering by hot plate heating,such as low molding efficiency,uneven heating,even nonuniform internal structure of the products.1)The specialized electric heating set of molding for our research can effectively solve the first two questions,sintering mold was completely covered and raised the utilization ratio of heat energy.2)In order to solve the nonuniform internal structure of the products,further improvement of the static sintering electric heating set was needed,the sintering mold has been at the stable mechanical vibration during dynamic molding process,which can greatly improve the local closely packed powder of static molding,and increase the chances of the movement in all directions of powder,finally increased the contact point of the materials.Analysis the various performance of dynamic molding products,which showed more uniform microstructure,size and distribution than static molding,besides,higher mechanical properties and vacuum oil absorption rate were obtained,and also had higher molding efficiency.(2)Supercritical CO2 as foaming agent to prepare closed-type UHMWPE microporous materials,optimized the foaming temperature and foaming time of the experimental process after abundant experimental explorations,finally focus on foaming pressure to the influence of different foaming systems.1)For different kinds of PE(LDPE,HDPE,UHMWPE-XM220),with the increase of saturation pressure,the cell density increased and the cell mean-diameter became smaller of three systems.Compared with LDPE and HDPE,smaller cell diameter and more uniform size distribution could be easily obtained in XM220,what's more,the foamed products of XM220 showed more smooth appearance and were not easy to collapse,namely can maintain excellent performance and stable appearance.2)For UHMWPE with different molecular weight(M1,M2,M3,GUR4120),with the increase of molecular weight,higher initial pressure was needed to count complete cell.In the same foaming pressure,the greater molecular weight means the longer molecular chain and the more severe entanglement of the molecular chain,which lead to more difficult growth of cell nuclei because of larger internal resistance.3)For a kind of UHMWPE(XM220),CO2 was in a supersaturated state when the thickness of the matrix material was thin(0.25 mm),directly led to the formation of nonuniform cell in such an unstable system and showed poor foaming performance.On the contrary,CO2 was in an undersaturated state when the thickness of the matrix material was thick(?1 mm),greater resistance need to be overcome for the growth of nuclei,which also showed poor foaming performance.Only in an appropriate thickness of the matrix material can keep stable situation and obtain uniform cell size and distribution,also showed excellent foaming performance.4)For the approximate molecular weight and different original composite state of UHMWPE(PM200 and M1),under a certain saturation pressure,there were more uniform cell size distribution and forming ratio in PM220 than M1.Compared to the M1,which was made of gathered secondary particles,PM200 was directly made of uniform tiny particles in 10 ?m,larger specific surface area can create more nucleation sites at the moment of quickly releasing pressure,which meant more excellent foaming performance in PM200 than M1.