Measurements of longitudinal shrinkage and volume swelling of polyester (PET) fibers in a wide variety of solvents were made at room temperature for time periods sufficient to establish quasiequilibrium conditions. Evaluated in terms of the solubility parameters ( & d e l t a ; ) concept, these results, together with iodine displacement studies, indicate that: (1) PET may be treated as an ( AB ) x alternating copolymer, where A is a semirigid aromatic residue —CO-C 6 H 4 — with a δ-value of 9.8, and B is a flexible aliphatic ester residue —O-CH 2 -CH 2 -O-CO— with a δ-value of 12.1 ; and (2) the preferential interaction of a solvent with either of the two PET residues provides the necessary chemical energy to disrupt intermolecular cohesive forces between the polymer chains, permitting relaxation of internal orientation forces and shrinkage of the fiber. It is shown by successively treating PET in solvents of increasing plasticizing strength that solvent-induced crystallization, a secondary process involving chain folding of the newly relaxed chains, does not inhibit shrinkage at lower temperatures. Therefore, room temperature chemical annealing is viewed as being similar to low-temperature (<175°C) thermal annealing, where small crystallites are formed which confer negligible dimensional stability on the fiber undergoing shrinkage.. ' ABSTRACT Five samples of fabric treated with a silicone resin to prevent felting were examined for the presence of fiber bonds, using optical microscopy, micromanipulation, and measurement of the force required to withdraw a single fiber from the fabric. In all cases fiber bonds were found to be present and to be responsible for the resistance to felting. A sample of similarly treated tops, which acquired very little resistance to felting as a result of the treatment, was also examined. The fibers in this sample were coated with the resin but showed no fiber bonding, and their frictional properties were similar to those of normal, untreated fibers. Stress is laid on the difficulty which may sometimes be encountered in demonstrating the presence of interfiber bonds, and on the need for examination by micromanipulation before the conclusion is reached that they are not present.
SynopsisThe Hildebrand and the Hansen solubility parameters of the aromatic and the aliphatic ester residues of poly(ethy1ene terephthalate), PET, are evaluated and compared to those determined experimentally. The interactions of nonaqueous solvents with the aromatic and aliphatic ester residues of PET are also described in terms of their relative basicity and acidity in the Lewis sense, where the aromatic residue may be taken as a Lewis acid and the aliphatic ester residue may be taken as a Lewis base.
The effects of an aqueous-dodecylsulfate solution buffered to pH 5 at 100°C on the structure and physical properties of an oriented semicrystalline PET yarn were measured as a function of time. Chain relaxation resulting in longitudinal shrinkage is shown to be the primary molecular event, and crystallization to be a secondary process involving the newly-relaxed amorphous chains. Four major structural events are observed: 1) longitudinal shrinkage, 2) crystallization leading to structural stabilization, 3) surface stress concentration, and 4) rapid hydrolysis and decline in molecular weight following surface cracking of the fibers to relieve surface stress concentrations. Comparison of the effects of aqueous, thermal, and solvent (dimethylformamide) treatments of PET suggests that the molecular mechanisms and kinetics of aqueous and of thermally-induced changes are similar. Solvent-induced changes are to a large extent controlled by diffusion processes. Aqueous and solvent-treated PET are similar, in that there is an increase in structural "porosity" as a result of crystallization in the swollen state.
SynopsisThe extent of solvent-induced shrinkage, swelling, and crystallization of polyester is found to be dependent on the initial morphology of the material. However, the nature of the interaction of nonaqueous solvents with the aromatic and the aliphatic ester residues of poly(ethy1ene terephthalate) is found to be independent of morphology and only dependent on the differences in the stereochemical nature of the given solvent and polyester residue.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.