equipped with a heater and stirrer was charged with a mixture of 1 520 parts of e caprolactam and 80 parts of aminocaproic acid the mixture was then flushed with nitrogen and was stirred and heated to 255 u00b0 c over a 1 hour period at atmospheric pressure to produce a polymerization reaction the heating and stirring was continued at atmospheric pressure under a nitrogen sweep for an additional 4 hours in order to complete the polymerization nitrogen was then admitted to the reactor and a small pressure was maintained while the polymer was extruded from the reactor in the form of a polymer ribbon the polymer ribbon was subsequently cooled pelletized washed and then dried the polymer was a white solid having a relative viscosity of about 50 to 60 as determined at a concentration of 11 grams of polymer in 100 ml of 90 percent formic acid at 25 u00b0 c astm d 789 62t the polymer pellets were blended with about 2 4 percent of finely divided antimony oxide sb 2 o 3 in a conventional blender and melt extruded under pressure of 1 5000 psig to a 70 orifice spinnerette to produce a fiber having about 3 600 denier the fiber was collected drawn at about 3 2 times the extruded length and textured with a steam jet to produce yarn suitable for use in carpet this yarn will hereinafter be called yarn a a control yarn containing no antimony oxide was prepared in the same manner as described above this yarn will hereinafter be called yarn b the yarns were then two plied by twisting two ends together with a 1 5 s twist the yarns were.