Correlation between precision of spinneret hole machining and the uniformity of polyacrylonitrile filaments

Abstract

UDC 677.051.125.262:677.494.745.32 and Yu. V. ValetkinWe present comparative results of tests on commercial and experimental platinum/palladium spinnerets in forming polyacrylonitrile fi lament yarn of 50 tex. The experimental spinnerets were made with holes of high precision diameter (0.08±0.001 mm). The spinnerets were characterized by their integrated throughput (the fl ow-through time for distilled water) while the fi lament yarns were characterized by their linear density. We demonstrate a correlation between the fi lament linear density and the fl ow-through time. In this case, the criteria for uniformity of the fi lament with respect to linear density (variance, range, mean-square deviation, coeffi cient of variation) are statistically signifi cantly smaller for the experimental spinnerets than for the commercial spinnerets.We know that chemical fi lament yarns and tows have transverse nonuniformity (with respect to cross section) and longitudinal nonuniformity (with respect to length) [Ref. 1, p. 213]. Transverse nonuniformity is determined by the irregularity of individual fi laments in a strand [2], while longitudinal nonuniformity is determined by the nonuniformity in the properties of fi lament yarns in an arbitrary length segment [3]. The reason for both types of nonuniformity is assumed to be the nonuniformity of the individual fi laments in the cross section of the fi ber strand. It is due to nonuniformity in the properties of the polymer system to be processed (solution, melt) [1], the precision within which the spinneret holes are made [2, 4-6], the conditions for forming and subsequent treatments in the production steps for obtaining the chemical fi bers [1][2][3][4][5][6].In the literature, generally parameters are given describing the nonuniformity in the physical and mechanical properties of fi laments, where the determining parameter is considered to be the nonuniformity in the transverse cross section [3,4]. Furthermore, insuffi cient information is available about the reasons for the nonuniformity and the parameters describing it for fi lament yarns as a whole. And high irregularity, for example with respect to linear density, reduces the unit breaking load (strength) of the fi laments. Therefore study of the irregularity in fi lament yarns continues to be an important problem, especially study of the correlation between the linear density of fi lament yarns and the precision of the geometric characteristics of the spinneret.There have been many attempts to theoretically and experimentally study the correlation between tolerances for the diameter and length of the spinneret hole and the nonuniformity of the individual fi bers with respect to thickness. A comprehensive review of this work is given in [7]. It is reported in particular that:-the coeffi cient of variation for the diameters of individual fi laments of a polyvinyl alcohol fi ber is approximately equal to twice the coeffi cient of variation for the diameters of the spinneret holes [2]; -the distribution curves for the calculated ...