Interactions of Nonaqueous Solvents with Textile Fibers

Abstract

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 (δ) 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 ₆H₄— with a δ-value of 9.8, and B is a flexible aliphatic ester residue —O-CH₂-CH₂-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 intermo lecular 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 crys tallization, 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 under going shrinkage.