Method for preparing poly(phenylene sulfide) membranes

#This invention relates to a method for making separation membranes from poly(phenylene sulfide) resins.

#Poly(phenylene sulfide) (PPS) polymers are known to have excellent thermal stability and chemical resistance. For these reasons, it has been attempted to make membranes from these polymers.

#Membranes are often made by extruding a solution of a polymer in a suitable solvent. With most polymers, this technique is readily applied because the polymers form high viscosity solutions which can be extruded to form membranes having useful properties. However, it has been found to be difficult to prepare membranes in this manner from poly(phenylene sulfide). Unless the polymer concentration is very high, PPS solutions have viscosities so low that they do not maintain their shape as, for example, sheet, tubules or hollow fibers, after they are extruded. These low viscosity solutions are also difficult to feed and convey using the typical screw extrusion equipment since this equipment is designed to use the melt viscosity of the extrudate to provide a pumping action. For these reasons, it is difficult to extrude these solutions into a membrane. As a result, the membrane is either impossible to form, or contains imperfections such as pinholes which destroy the membrane's ability to perform good separations.

#The following examples are provided to illustrate the invention but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

#A commercial grade particulate PPS resin (FORTRON.RTM. 300 BO (polyphenylene sulfide resin, from Hoescht-Celanese) is heated for three hours in air at 280.degree. C. in an air circulating oven. The treated PPS exhibits a solution viscosity in excess of 300 poise.

#Portions of the treated resin are then dissolved in various solvents by heating a mixture of the treated resin and the solvent to about 300.degree. C. with stirring until a clear solution is obtained. The resulting solutions (Sample Nos. 1-5, respectively) are then cooled to allow them to solidify, and granulated. The solvents and proportions of treated PPS and solvent are as described in Table 1 following.