Studies of the development of fibrillar structure in nylon 6

Abstract

The writers have been examining the production of trilobal nylon 6 filaments mimicking certain commercial production techniques in a laboratory setup. In the course of this work, we have observed some rather special fiber properties that appear to depend upon the quenching conditions to which the fiber is subjected after it emerges from the spinneret prior to its take-up preceding any drawing treatments. The quenching conditions that were introduced involve maintaining the temperature of the molten filament while it moves through the first 5 cm of filament line after emerging from the spinneret followed by quenching in enhanced turbulence, which, it is hoped, provided a rapid chill at the surfaces of the fiber. Subsequently, the as-produced filaments, which approximated a commercial carpet yarn, with an appropriate trilobal geometry were subjected to tensile testing and a tensile factor, or a figure of merit, determined for the tensile quality of the fiber in the form of an index, which was originally due to Rosenthal' and describes the tenacity-elongation exchange relationship. The factor we use is the product of the breaking tenacity and the square root of the numerical value of the elongation expressed as a percentage. Nominally, the commercial products and the process that we were studying produced values of the order of 35-38 in this index. The delayed quenching processes tended to produce filaments that gave tensile figures of merit in excess of 40 (42 in one particular quenching configuration). The yarn product with this higher property was subjected to a closer examination, and the work reported in this letter followed.Small lengths of the filaments were sectioned and examined longitudinally in a thermal microscope at heating rates of 10°C/min until very close to the terminal melting. After the disappearance of the primary birefringence of these filaments, lines of residual birefringence were observed in the tips of the lobes of the trilobal filament, which persisted for several degrees above the normal melting point; namely, 216220°C. Further, in nonpolarized light, optical examination of the melting sections revealed that the tips of the lobes tended to extend beyond the shrunken surfaces of the cut ends, suggesting a thermally more stable element in the tips than in the body of the trilobal yam. A similar kind of stability was observed earlier by one of the writers' in polyethylene filaments that had been extruded just above the conditions for melt fracture. When short sections of these filaments were examined near the melting point in a thermal microscope, the central portions of the filaments retained their original cut lengths but the body pulled back into a more GF less equilateral "glob" around the central spike, which persisted to relatively