Stabilized gamma-irradiatable polypropylene fibers and sterilizable

Abstract

Excellent stabilization of polypropylene (PP) fibers exposed to sterilization levels of gamma radiation, is obtained with a hybrid stabilizer having a N-(substituted)-1-(piperazin-2-one alkyl) group at one end and a (3,5-dialkyl-4-hydroxyphenyl)-.alpha.,.alpha.-disubstituted acetamide at the other. When this hybrid of a hindered amine with a hindered phenol is combined through a disubstituted alpha carbon atom of the acetamide in a single molecule, it affords the advantages of each group with respect to its stabilization against oxidation, but without the known inherent disadvantages of either group. This molecule is N-(substituted)-1-(piperazin-2-one alkyl)-.alpha.-(3,5-dialkyl-4-hydroxyphenyl)-.alpha.,.alpha.-substituted acetamide molecule ('3,5-DHPZNA' for brevity). When the hybrid stabilizer is incorporated into PP fibers which are exposed to gamma irradiation, the PP fibers exhibit only a barely noticeable discoloration, yet are inculcated with a unique property: though exposed to 4 Mrad of gamma radiation, the PP fibers suffer essentially no loss of their original, pre-irradiated tensile strength after about seven months at 60.degree. C. in an oven. This property is atypical of PP fibers stabilized with several other hindered phenols and hindered amines tested. The unexpected retention of tensile strength in 3,5-DHPZNA stabilized PP fibers used in articles exposed to a sterilizing dosage level of gamma radiation, is of great practical value. Particularly in such articles as clothing and household goods made from woven or non-woven fabrics of dyed or pigmented PP fibers, in which goods slight discoloration is acceptable, this invention is of commercial importance.