. . . "Staple amenable to the process include those produced from regenerated cellulose, cellulose derivatives such as cellulose acetate, polycondensation products such as polyamides and polyesters and the polymers obtained by addition polymerization from ethylenically unsaturated low molecular compounds, for instance acrylonitrile, vinylidene chloride, vinyl chloride and copolymers thereof." . .