H.-D. Weigmann

Interactions between Solvents and Polymers in the Solid State

Abstract One of the goals of modern polymer research is to achieve an understanding in rigorous and quantitative terms of the molecular chain configuration and of the spatial arrangement of the polymer molecules in the solid state. This problem is of particular interest for oriented semicrystalline polymers such as textile fibers which have both crystalline and amorphous domains or phases. This duality in structure has found expression in many models including the micellar concept, the fringed micellar concept, and fringed fibrillar concept, and more recently the crystalline imperfection model. While there is no universal agreement about an exact description of the fine structure of semicrystalline polymers, it is generally accepted that some of the chains or chain segments are preferentially oriented and aggregated by close packing with neighboring molecules into cohesive structural units which are usually referred to as crystallites. Polymer chain folding is frequently involved in the development of cry...

Wicking of Spin Finishes and Related Liquids into Continuous Filament Yarns

Using a simple electronic method for measuring wicking times, we have shown that horizontal wicking of liquids into continuous filament yarns follows the Lucas-Wash burn equation. We have investigated the effects of the liquid properties, viscosity, and surface tension, and of the liquid-solid interaction parameter cos θa. We have found that transient effects due to surfactant adsorption play a significant role in wicking, and that cos θa values of ∼0.7 or higher are necessary for wicking to take place. Certain kinds of fluorosurfactants seem to have a considerable negative effect on the wicking of model finishes in yarns and on the distribution of these finishes on the surfaces of constituent fibers.

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 IV: Effects of Solvents on the Mechanical Properties of Various Textile Yarns

In order to provide a rational basis upon which future developments in nonaqueous finishing and other processing of textile materials may be based, a basic study is being undertaken of the interactions between textile fibers and a wide spectrum of organic solvents. In this paper are reported the effects on mechanical properties of a polyester yam of 26 organic solvents differing widely in chemical and physical characteristics. The yams were conditioned in each solvent for 16 hr at 21°C and their load-extension behavior determined in the solvent. While many solvents were found to have only minor effects on the mechanical properties, several solvents caused major changes in the shape of the load- extension curve of the polyester yam. The active solvents caused a decrease in the initial modulus, a decrease in the yield stress, and an increase in extensibility. In several cases a significant plastic flow region could be noted. Dioxane, acetone, trichloroethylene, tetrachloroethane, methylene chloride, nitrobenzene, nitromethane, acetonitrile, and di methylformamide (DMF) were among the most active solvents. These solvents also caused a major irreversible longi tudinal shrinkage of the yarn, and the mechanical properties of the yarn were only partially recovered after removal of the solvent and reconditioning to a standard condition. The interactions between the solvents and the polyester yarn, as estimated by the decrease in the yarn elastic modulus, were correlated with the solubility parameter δ of the solvents. It was observed that maximum interactions take place with solvents whose solubility parameter approaches that of polyethylene terephthalate δ=10.7. There is some indica tion that these strongly interacting solvents fall into two groups: one with δ values ranging from 9 to 10, the other with δ values ranging from 11.5 to 13. It is suggested that these ranges may reflect specific solvent interactions with the aro matic and aliphatic segments of the polyester molecules.

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 II : Isothermal Shrinkage Kinetics of a Polyester Yarn

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.

Surface Wettability Scanning of Long Filaments by a Liquid Membrane Method

A technique is presented for characterizing the surface wettability of relatively long filaments based on scanning the filament with a liquid membrane. This technique overcomes the limitations of specimen size and crimp, which are inherent in the bulk immersion method for evaluating wettability changes along a filament. The technique can be used to study the surface distribution of finishes on long filaments, provided the wettability characteristics of the finished surface are significantly different from those of the untreated filament under the conditions of measurement. If the method is to be used to study finish distribution, an appropriate liquid must be used for the membrane, and guidelines for selection of such a liquid are discussed.

Dyeability of Nomex® Aramid Yarn

Treatments in highly polar solvents, such as dimethyl formamide, dimethyl acet amide, and dimethyl sulfoxide, under suitable conditions have been found to improve the dyeability of Nomex® yam so that it can be dyed under atmospheric conditions in a reasonable length of time without the aid of a carrier. Essentially, these solvents provide chemical energy to the yam, permitting rearrangements of the polymer chains through breakage and reformation of interchain hydrogen bonding. The changes in dyeability may be attributed to orientation changes or to microvoid formation occurring in the fiber structure during treatment.

Microspectrophotometric Study of Ozone Fading of Disperse Dyes in Nylon

The fading of disperse-dyed nylon by atmospheric ozone can pose a problem at high environmental temperatures and humidities. In attempting to devise ways to inhibit such fading, researchers have suggested that the reaction between ozone and dye occurs chiefly at the fiber surface—that ozone does not penetrate inward, but that the dye diffuses outward from the fiber interior due to the concentration gradient set up as surface dye is destroyed. This mechanism has been supported, though not proved, by observations that dye diffusion is also sensitive to humidity in such systems, that rates of dye loss due to ozone exposure correlate with dye desorption rates into water, and that dye loss, like dye diffusion, depends on the square root of time and on the size of the dye molecule. These findings were based on determinations of total dye content in fiber specimens; however, adapting the techniques of microspectro photometry to fibers, as described in this paper, makes it possible to observe directly the locus of dye destruction in the fiber and to determine the relative dye loss at selected locations, such as at the edge and center of a fiber cross section. The coefficient of diffusion of the dye within the fiber can also be evaluated using the micropho tometer. These capabilities have been applied to the ozone fading of nylon 6 dyed with C.I. Disperse Blue 3, and the experimental results do not correlate with a math ematical model based on the hypothesis of dye destruction exclusively at the fiber surface. On this basis it is postulated that, in addition to dye diffusion toward the fiber surface, ozone penetration into the fiber contributes substantially to the fading process.