Investigation of the temperature dependence of the coefficients of diffusion for dye in untreated and solvent-treated polyester yarns has shown that solvent treatments that increase dyeability do not change the dye-diffusion mechanism. The free-volume mechanism, which depends on polymer segmental mobility for the transport of dye through temporary holes, is operative in solvent-treated as in untreated polyester. The significant increase in dye-diffusion coefficients resulting from solvent treatment is attributed to increased segmental mobility in noncrystalline domains of the treated fiber. This increased segmental mobility is reflected in lowered α-dispersion temperatures, as determined from dynamic mechanical properties. Treatments with dimethylformamide and heat treatments at temperatures approximately 80°C higher both yield polyester yarns that have the same segmental mobility, as indicated by dynamic mechanical measurements, but the saturation dye uptake in the solvent-treated yarns is much higher. This increased amount of dye is believed to be held in voids in the fiber structure formed during solvent treatment. Diffuse scattering in small-angle x-ray diffraction patterns of solvent-treated yarns has been taken as evidence for the existence of such voids.

Pretreatment of polyester yarns with a strongly interacting solvent (dimethylformamide) leads to modifications of the fiber structure which permit rapid diffusion of even “high-energy” disperse dyes under atmospheric conditions without the addition of carriers. A comparison of the effects of solvent pretreatments with the effects of thermal pretreatments on the dyeing behavior has been carried out. Pretreatment in a strongly interacting solvent leads to a high degree of swelling and at higher temperature to the formation of crystallites within the swollen structure. It appears that the swollen structure can be stabilized, depending on the size and stability of the crystallites formed, leading to cavitation and void formation upon subsequent removal of the interacting medium. It is suggested that a rigid pore mechanism of dye diffusion becomes operative in this structure, as opposed to the free volume mechanism of diffusion in thermally-treated polyester yarns.

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.

A cotton twill fabric was subjected to a durable-press treatment with dihydroxy dimethylol ethylene urea (Permafresh-183) of increasing severity. The mechanical properties of the fabrics and of single fibers withdrawn from the treated fabrics were evaluated and the relationships between fiber and fabric properties were analyzed. Statistically significant correlations between such important fabric properties as abrasion resistance, tear strength, tensile strength, and energy-absorbing capacity, on the one hand, and fiber mechanical properties, on the other, show conclusively that chemical treatments which alter fiber structure and properties are responsible for the modified fabric behavior. At the same time, the importance of fiber geometric arrangements in spun yarn and fabric structures, in terms of fabric properties, are pointed out. Thus, while this work has shown the functional relationships between fiber mechanical properties and fabric characteristics, careful attention must be given to fiber-fiber interactions, particularly in relation to chemical modification treatments.

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