A Study On Polymer Microporous Materials Prepared By Blending And Leaching Method

Microporous material is a kind of material whose pore size varies at different application fields,usually less than 10μm. The special structure formed during processing is applicable in separating, permeating and purifying fields. Polymer microporous materials have a structure highly regularized, with open spongy porous structure interweaving each other, and the pore size can be tailored as desired. The maximum porosity accounts for 80% of the total volume. The traditional manufacturing methods include powder-sintering, melt-spinning and cold-stretching, thermally induced phase separation, state track etching, non-solvent induced phase separation, etc.A novel method to prepare polymer open-cell microporous materials is introduced in this paper. It is based on the polymer blending and compatibilizing principle, as well as the leaching method. The polymer matrix was blended with the water soluble polymer and hot-pressed to a sheet or film, and then the water soluble polymer was leached so as to obtain the open-cell microporous materials. Comparing with the traditional leaching method where inorganic salt was used, using water soluble polymer can improve the processing properties, pore shape and pore size, and can avoid the pollution on the environment as well comparing with TIPS which use organic dilute.The polymer matrices used in this paper include the non-polar polymer matrix: polypropylene (PP), high density polyethylene (HDPE), and the polar polymer matrix: Hytrel (Thermoplastic Polyester Elastomer). The water soluble polymers include polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) and starch. It was investigated that the phase separation of the non-polar matrix/water soluble system was so heavy that blends showed poor mechanical properties, and the pore size of the microporous materials which were produced after the leaching process was too large and maldistributed. The molding properties and stability under high temperature of PEO are best among the water soluble polymers used in the paper. The effect of the low molecular compatibilizers such as stearic acid, silane coupler and methacrylic acid on the polyolefin/PEO system is not notable, while the high molecular compatibilizers such as MA-g-PP, EMA, Surlyn can improve the compatibility, and the effect of MA-g-PP is better than the EMA and Surlyn.The polar matrix of Hytrel shows excellent compatibilities with PEO, and the microporous materials are hydrophilic. The pore size varies from 2.1 to 8.6μm with the different recipes, and the porosity varies from 7 to 46%. With the recipe of Hytrel/PEO 50/50, we can get the highly regularized microporous materials with open-cell structure. The plasticizer PEG and filler SiO₂ can optimize the pore size and can improve the mechanical properties to some extent. The microporous products prepared by the method this paper mentioned are expected to be applied in separation as the hydrophilic micro membrane filter.