M.G. Scott

Interactions of Nonaqueous Solvents with Textile Fibers Part VII: Dyeability of Polyester Yarns after Heat and Solvent-Induced Structural Modifications

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.

Interactions of Nonaqueous Solvents with Textile Fibers Part V : Application of the Solubility Parameter Concept to Polyester Fiber-Solvent Interactions

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.

Interactions of Nonaqueous Solvents with Textile Fibers Part VIII: Mechanism of Dye Diffusion in Solvent-Treated Polyester Yarns

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.

Interactions of Nonaqueous Solvents with Textile Fibers Part IX: Thermal Stability of Solvent-Induced Modifications in Polyester Fiber Structure

The thermal stability of heat- and dimethylformamide (DMF)-induced structural modifications in polyester yarns has been investigated by differential scanning calorimetry (DSC) and other techniques. While heat treatments produce a characteristic, sharp, premelting endotherm peak (PEP) at temperatures slightly above the treatment temperature, DMF treatments show a broad, diffuse PEP in their DSC curves at approximately 70°C above the treatment temperature. The appearance of a characteristic diffuse PEP in the DSC curve suggests the formation of crystallites with a wide distribution of thermal stabilities which only partially stabilize the swollen fiber structure. Small-angle x-ray scattering (SAXS) studies show that subsequent heat treatments even at low temperatures (120°C) cause a partial collapse of the void structure observed after a high-temperature solvent treatment. The partial collapse of the void structure is also reflected in decreased dyeability and increased density of the polyester fibers but has no effect on polymer segmental mobility, as indicated by the unchanged α-dispersion temperature. It is therefore suggested that the observed decrease in dyeability after subsequent heat treatments of DMF-treated polyester yarns is associated with the disappearance of the voids. The high levels of saturation dye uptake observed in fibers with a void structure appear to be due to an increase in the internal surface within the fiber structure and/or to the ability of dye molecules to form clusters in these voids. Thermal aftertreatments of dyed, void-containing fibers should also result in a collapse of the void structure, which might effectively entrap dye molecules in the fiber structure and consequently lead to high wash- and drycleaning-fastness.

Relation of Fiber and Fabric Properties in Durable-Press Cottons1

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.

PET Filaments with Radially-Differentiated Structure

An undrawn polyester monofilament was subjected to sequential solvent and thermal/stress crystallization during drawing to produce a radially-differentiated structure. Solvent-induced crystallization of outer regions of the filament was achieved using methylene chloride or dimethylformamide at room temperature. The thermal/stress crystallization of the filament core was conducted at a draw ratio of 4.0 at temperatures ranging from 90 to 120°C. The resulting filaments were characterized by measurements of density and mechanical properties, by wide-angle x-ray diffractometry, and by scanning electron microscopy. The structure of the outer regions of these novel filaments consists of highly- deformed spherulites, while the inner core is fibrillar in character with well-developed orientation and crystallinity. The extreme outer surface appears to be cavitated, leading to extremely high surface areas. It is proposed that such radially- differentiated filaments will have the combined desirable properties of spherulitic and fibrillar morphologies, such as high liquid-retention values, improved adhesion, and high strength.

Interactions of Nonaqueous Solvents with Textile Fibers: Part X: Effects of Thermal History on Polyester-Solvent Interactions

An investigation of the effects of prior heat treatments on the stabilization of the polyester structure towards subsequent treatments with dimethylformamide (DMF) has been carried out. The results indicate that a DMF treatment at 140°C can overcome changes in the polyester structure produced by prior heat treatment up to a temperature of about 180°C. Void formation and accompanying high dye uptake under atmospheric dyeing conditions are observed. Heat treatments around 200°C, however, stabilize the fiber structure, and subsequent solvent treatments do not produce irreversible swelling and void formation. A further increase in the heat-treatment temperature again permits void formation and high dye-uptake values to occur. A close correlation between dyeability and void volume calculated from density data is observed. A DMF treatment of a false-twist-set textured yarn leads to void formation and high dyeability, even though the heater temperatures used in the texturing process are near the critical temperature range at which stabilization to sub sequent solvent treatments has been observed. Evidence is presented suggesting that the yarns do not actually experience the temperature of the heaters but rather a significantly lower temperature.

Interactions of Nonaqueous Solvents with Textile Fibers Part VI: Effects of Solvent Treatments on Textured Polyester Yams

The interactions of three chlorinated hydrocarbon solvents with textured polyester yams have been investigated. The solvents perchloroethylene, trichloroethylene, and methylene chloride differ widely in their ability to interact with polyester fibers. Textralized and Superloft standard and cationic dyeable Dacron yarns have been included in this investigation. The dynamic and isothermal shrinkage behavior of the textured yarns reflects the diffusion of the solvents into the complex structures produced by the texturing process and the rate and extent of their interactions with the polymer. Characteristic shrinkage maxima are observed which are associated with the opening and closing of kinks, especially in the Textralized yam. More or less extensive overall shrinkage as a result of the solvent treatments produces an increase in the bulkiness of the textured yarns. The stability of the additional solvent-induced crimp and of the original thermally-induced crimp were studied. It could be shown that while the original crimp is essentially unaffected by the solvent treatment, the solvent-induced crimp is easily removed upon loading of the yam, and its recovery upon unloading is limited, depending on the nature of the solvent treatment.

Surface Properties of a Variety of Fibers

Geometric-rol1g&dquo;hne~s and fricti()t1al-foree measurements have been made on the surfaces of additional fiber, samples, in extension of experiments previously described [3, 4 J, using the sanie techniques. Tests were conducted at a fihcr-tnlverslng&dquo; speed of 36 ~,/~ec and, in the case of the frictional measurements, with a normal toad of 15.3 ny. The ambient a-ir of the chambers in in which the tests were made was at normal humidity and held at iO° F (21 °C) as nearly as possible. Sections of a razor blade were used as the stylus in the roughness measurements and as the stider in the friction tests.