Thermal modification of acrylonitrile yarns

Claim 1

IN THE METHOD OF THERMALLY MODIFYING YARNS COM POSED OF A POLYMER CONTAINING ACRYLONITRILE WHICH COMPRISES SUBJECTING SAID YARNS TO AIR AT A TEMPERATURE WITHIN THE RANGE FROM APPROXIMATELY 300*F. TO THE DEPOLYMERIZATION TEMPERATURE OF THE POLYMER FOR AT LEAST APPROXIMATELY ONE-HALF HOUR WHEREBY SAID YARNS COMPOSED OF A POLYMER CONTAINING ACRYLONITRILE ARE EXPOSED TO SAID MODIFYING TEMPERATURES FOR A PERIOD OF TIME SUFFICIENT TO RESULT IN A NEW FILAMENTARY MATERIAL WHICH CONTAINS AT LEAST APPROXIMATELY 60% BY WEIGHT OF A THERMOSTABLE, NON-IGNITIBLE, THERMALLY MODIFIED MATERIAL, THE IMPROVEMENT WHICH COMPRISES IMPARTING TO SAID YARNS, PRIOR TO THERMAL MODIFICATION, A TWIST DETERMINED BY EMPLOYING A TWIST CONSTANT OF APPROXIMATELY 70-250.