Examples of a polymer include homopolymers and copolymers of acrylonitrile, sulfone, vinylidene chloride, vinyl chloride, vinyl acetate, methyl methacrylate, urethane, styrene and vinyl alcohol; polytrifluorochloroethylene; polytetrafluoroethylene; polyolefins such as polyethylene and polypropylene; polyamides; polyesters; cellulose acetate, cellulose nitrate, cellulose butyrate and cellulose acet