Particularly preferred for use in the present invention are polyamides, such as the nylons, among which the preferred nylons include polyhexamethylene adipamide, poly-??-caprolactam, polymethylene sebacamide, poly-7-aminoheptanoamide, or polyhexamethylene azeleamide, with polyhexamethylene adipamide (nylon 66) being most preferred.