Continuous process for preparing particulate microporous, open-celled polymer structures in a screw-type extruder

Claim 1

A continuous process for preparing particulate, microporous, open-celled polymer structures comprising i. continuously feeding about 5 to 50 parts by weight of a normally solid organic polymer having a glass transition temperature or a crystalline melting point of at least 293° K., and about 95 to 50 parts by weight of a chlorofluorocarbon or a mixture of chlorofluorocarbons having a boiling point in the range of about 10° C. to 150° C., a melting point in the range of about -40° C. to 125° C., an entropy of fusion of less than 10 calories/°K./mole, a plastic flow index of at least 0.1 g/10 minutes at the reduced temperature of 0.96 to 0.99 and a solubility in water of less than 2 weight percent to a screw-type extruder having first and second temperature zones, ii. nonrandomly milling said polymer and said chlorofluorocarbon in said first zone at a temperature equal to or above the melting point of the highest melting chlorofluorocarbon present to provide a solution of the polymer in the chlorofluorocarbon, iii. passing said solution to said second zone and nonrandomly milling said solution and cooling said solution to a temperature equal to or below the solidification temperature of the lowest melting chlorofluorocarbon present to form a frozen mass, iv. extruding said frozen mass from said second zone as an uncompacted snow-like mass, and v. removing the chlorofluorocarbon from said snow-like mass at a temperature equal to or below the solidification temperature of the lowest melting chlorofluorocarbon present to form said particulate, microporous, open-celled polymer structures.