Pleated filter element microporous membrane stretching method

In the mid-1970s, Calanese developed a new method for preparing microporous membranes, and launched a commercial product of celgrad polypropylene microporous membranes. This method is generally aimed at crystalline polymers. Word. First, a highly oriented crystalline polymer is prepared, and then at a temperature close to the melting point of the polymer, it is extruded into a film with rapid stretching. After the film is cooled, the film is stretched a second time to make the crystal structure of the film. It is damaged, resulting in (200-2500)*10-10m cracks, thereby forming a microfiltration membrane. The basic method of stretching is to extrude the membrane or fiber at a relatively low melting temperature and high stress, and then at a slightly lower Heat treatment at the melting point temperature, the chain segments can move to make the crystal larger and harder, and the polymer chains are folded on the crystallized surface without melting together to eventually form the desired film. This method is suitable for thermoplastic materials such as polypropylene, polyethylene, and polytetrafluoroethylene. The obtained microfiltration membrane has a high porosity, up to 90%, and the pores are elongated and the pore size ranges from 0.1 to 3um. , and the pore structure is a fine-slit network pore structure. Example Polypropylene microporous stretched film material PP solvent No film-making process Polypropylene resin-melt extrusion-hollow forming-cooling-winding-heat treatment-stretching-heat-setting-finished polypropylene hollow fiber membrane. Example Preparation of PET fiber film material by stretching method PET flux Trifluoroacetic acid, dichloromethane. Film making process The film making process includes the following aspects. a Spinning Dissolve the dried ultra-high molecular weight PET sample with a mixed solvent of trifluoroacetic acid/dichloromethane (volume ratio of 7:3) for about 3 days at room temperature, and pour the spinning dope into the prepared spinning solution. In the tube, water is used as coagulant, and dry and wet spinning is carried out at room temperature. The temperature is low, the orientation temperature of the drawn yarn is high, and the crystallization is low. This structure is beneficial to the subsequent secondary drawing, and then the secondary drawing is carried out at a temperature of 230 degrees. Crystallization, therefore, the temperature of the secondary drawing is required to be higher than the crystalline melting temperature of PET to melt the original crystal region, so as to realize the rearrangement of the fiber structure. C. Heat treatment With ethylene glycol as the heat medium, the treatment time is 3min. Appropriate heat treatment can improve the structure of the fiber and improve the thermal properties of the fiber. The heat treatment time has the greatest impact on its mechanical properties, and the performance decreases with time.