Thermal treatment of theraplastic filaments for the preparation of surgical sutures

In a method for producing a monofilament suture composed of a thermoplastic polymeric composition, said thermoplastic polymeric composition selected from the group consisting of poly(p-dioxanone), polyethylene, polypropylene, polyvinylidene fluoride, poly(glycolide, cotrimethyl carbonate), homopolymers and copolymers of lactide and glycolide and copolymers of p-dioxanone with lactide, glycolide and .epsilon.-caprolactone, comprising the steps of melt extruding and quenching the polymer to form a continuous suture filament, drawing the suture filament to achieve molecular orientation, relaxing or annealing the drawn suture filament to relieve internal stresses, and thereafter sterilizing the filament to render the filament suitable for use as a surgical suture, the improvement comprising exposing the suture filament to a temperature in excess of the melting temperature of the polymeric composition during or subsequent to drawing the said suture filament and prior to the relaxation or annealing of said drawn suture filament, said exposure being for a time and at a temperature effective to obtain a suture filament having a lower order of crystallinity in the outer core area and a higher order of crystallinity in the inner core area.