Kinetics of contraction of drawn nylon 66 in aqueous phenol

Abstract

SynopsisThe rate of contraction of drawn nylon 66 in aqueous phenol wfts investigated, and a method is described for correlating this cont,raction with a series of elementary rate processes. The rate constants so obtained were analyzed by absolute rate theory, and the variations of A H $ and ASS with phenol concentration gave evidence of the nature of the reaction steps. INTRODUCTIONNylon 66 fibers are dimensionally unstable in the presence of either heat or certain chemical agents (those capable of disrupting the nylon's intermolecular bonding). I n undrawn and slightly drawn fibers the tendency is to a length increase (along the fiber axis), while highly drawn filaments contract.I n our experiments the rate of longitudinal contraction of a drawn yarn has been used as a probe for following the kinetics of the interaction of nylon 66 with aqueous phenol. This interaction has previously been studied by several authors, l V 3 and the contraction (both thermal and chemical) has been ascribed to breakage of interchain hydrogen bonds, 1 , 2 , 4 followed by conversion of the polymer chains from the extended to the folded conformation4 and formation of new, stronger bond^.^,^,^The intention of this work is to calculate the rate constants and activation energies of these elementary processes and to relate them to fiber structure. EXPERIMENTAL SamplesThe samples used in these experiments were from an experimental nylon 66 yarn prepared by Chemstrand Research Center, Inc. The draw ratio was 4, and the yarn had 17 filaments with a total denier of 50 and a 0.5 twist per inch. The samples contained 0.025 f 0.015y0 Ti02 and no other additives. 427 428 JACOBS, REBENFELD, TAYLOR ApparatusThe apparatus consisted of a 500 ml, graduated cylinder surrounded by a glass jacket, through which water, held a t constant temperature (*O.O5"C), was circulated. The yarn ( =40 cm long) was looped through a wire ring (=50 mg in weight), which made immersion possible; otherwise the fiber would float until completely soaked by the solution. The yarn ends were held by a small clamp, which was suspended above the apparatus.The shrinkage of the fiber was measured in solution by means of the graduations on the cylinder. The length a t any given time could be determined to within 1 part in 350 while the fiber contracted. Phenol concentration and temperature were varied, and a t least five determinations were made for each set of conditions. Reproducibility was approximately 3% (coefficient of variation) of the average length change a t a given time. ReagentsCrystalline phenol (Baker reagent-grade, containing 0.15% HSP02 as preservative) was dissolved in distilled water to form solutions of 1, 2, 3, and 4% phenol by weight. Since no correction was made for the water content of the phenol (perhaps as high as lo%), these concentrations are