No abstract

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.

rhe broad spectrum of interactions hetween a polyester yarn and different organic solvents has been investigated with a new experimerltal methocl called dynamic shrinkage. This technique is based on the measurement of the length changes of polyester yarns immersed in a solvent at programmed rates of heating.The dynamic shrinkage curves of a polyester yarn in various solvents are usually composed of a noncquilibrium and an equilibrium shrinkage region. From the former, it is possible to estimate the activation energies for the shrinkage process. From the equilibrium shrinkages, two analytical approaches have been used to estimate the glass-transition temperatures of about 22 polyester-solvent systems. The lowering of the glass-transition temperature of polyester by organic solvents is expressed as a function of their total solubility parameter. A bimodal distribution with interaction maxima at solubitity parameter values of 10 and 12 is observed. 'I'he effects of solvent-induced crystallization on the transition temperatures of polyester-solvent systems are discussed.

The kinetics of the shrinkage of a drawn polyester yam in a number of organic solvents, including toluene, acetonitrile, dimethylformamide (DMF), trichloroethylene, perchloroethylene, and tetrachloroethane, were investigated at several temperatures. The shrinkage process proceeds at a maximum rate after an induction period which is believed to be associated with diffusion of the solvent into the fiber structure. The temperature dependence of the maximum shrinkage rate follows the Arrhenius relationship. Activation energies ranging from 23 to 36 kcal/mol were found for the various solvents, compared to 13 kcal/mol for the shrinkage in the dry state. The equilibrium or final shrinkage values were found to increase linearly with temperature, thereby allowing extrapolation to a zero-shrinkage temperature. This latter value is believe to be an approximation of the glass-transition temperature of the polyester-solvent system. Horizontal shifting along the temperature axis of the curves relating final shrinkage to temperature resulted in a master shrinkage curve for the solvents investigated. The extent of shifting is also believed to be associated with the glass-transition temperature of the system.