Elastic polypropylene yarn and process

摘要

Elastic filaments are made by melt-spinning under conditions to produce "gamma orientation" a stereoregular polypropylene to which has been added 0.1 to 0.8 mole of an azido cross-linking agent per mole of polypropylene and heat-treating the filaments thereby formed at 105 DEG to 160 DEG C. in the relaxed state. The polymer containing the azido cross-linking agent is subjected before or during extrusion from a spinneret to a temperature above 100 DEG C. "Gamma orientation" is defined as meaning an orientation of the molecules of the filament in a direction or in a plane not parallel to the axis of the filament. The spinning of the polymer is conducted under conditions which produce the characteristic property referred to in Specification 935,809 as gamma orientation. Such orientation is produced during the melt draw down of the polymer, its magnitude depending upon the viscosity of the polymer and the amount of such melt draw down. By melt draw down is meant a permanent elongation of the filament in the molten state prior to any solidification of the filaments as they leave the spinneret. The polymer containing the azide compound is extruded at a temperature sufficiently high to cause the azide to react with the polypropylene. The polymer containing the azide may be extruded at 260 DEG to 310 DEG C. to form filaments which are melt drawn at a melt draw ratio between 10 and 100: 1, and heat treated at 140 DEG to 155 DEG C. in the relaxed state for a minimum period of about 2 minutes. The azido cross-linking agent may be a sulphonazide having the formula R(SO2N3)x or an azido-formate having the formula In both formulae R is an organic hydrocarbon radical inert to polypropylene and x is an integer from 2 to 8.