Y. K. Kamath

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.

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.

The Wicking Kinetics of Liquid Droplets into Yarns

The wicking kinetics of liquid droplets into yarns is studied using a computerized imaging system. A new method is suggested for characterizing the yarn structure by monitoring droplet absorption. The method is based on the comparative analysis of the time needed for droplet disappearance as a function of droplet volume for various yarns. A mathematical model is developed to describe the wicking kinetics. We show that for wetting liquids, the time of droplet absorption T w is a linear function of the initial droplet volume squared V 0 2. For a given liquid-yarn pair, the slope of this relationship provides important information about the yarn properties. The linear relationship between T w and V0 2 is verified by experimental data for a typical spin finish. The model predicts that droplet wicking can occur even if the advancing contact angle θa is slightly greater than 90°. However, for nonwetting liquids, the relationship between T w and V 0 2 is nonlinear, and a criterion for droplet wicking into nonwetted yarns is obtained.

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.

Marangoni effect in the water wetting of surfactant coated human hair fibers

Abstract Wetting force curves have been obtained, using a technique based on the Wilhelmy principle, for individual human hair fibers treated with a cationic surfactant (stearyldimethylbenzylammonium chloride). The characteristic stick-slip nature of these curves has been attributed to desorption of the surfactant from the fiber surface into the wetting liquid at the contact line. Differences in surfactant concentration between the vicinity of the contact line and the bulk liquid give rise to surface tension gradient related flows in the film near the contact line, which result in apparent changes in contact angle and wetting force. Such surface flows originating from surface tension gradients are known as Marangoni effects. An apparent increase in contact angle and reduction in wetting force in the dynamic Wilhelmy measurement seem to result when the surface tension of the liquid at the contact line is lower than that of the bulk liquid, giving rise to a surface tension gradient. An instantaneous decrease in contact angle and increase in wetting force seems to be due to the jumping of the meniscus when the surface tension gradient is reduced by the diffusion of the surfactant into the bulk liquid. The amplitude and frequency of the stick-slip depends on the distribution of the surfactant and the nature of its binding to the fiber surface, respectively.

A computer model for wetting hysteresis 2. A virtual wettability scanning balance

Abstract We described previously a computer model for wetting hysteresis based on a theoretical analysis of the Wilhelmy wetting experiment. Applying this model to a number of virtual surfaces, we demonstrated that surface heterogeneity causes hysteresis in the wetting trace of an otherwise perfect solid. We now develop a model for the two-meniscus case to emulate liquid membrane wetting. This experiment scans a suspended solid specimen with a film of liquid contained in a loop attached to a vertical drive. After showing how variations in the size and proportion of surface energy domains affect the appearance of virtual wetting traces, we estimate the proportion of the surface covered randomly by two materials having different wettabilities, using real immersion and liquid membrane wetting data. The traces produced by the two models match the measured traces well. We are also able to mimic the effect of macroscale heterogeneity superimposed on surfaces featuring wetting hysteresis caused by microscale heterogeneity, specifically, fibers with non-uniform applications of finishing agents.

Irreversible Chemisorption of Formaldehyde on Cotton Cellulose

At low temperatures (lower than 65°C), sorption of formaldehyde on cellulose is reversible as indicated by complete extractability of the sorbed formaldehyde in water. At temperatures higher than 65°C, a fraction of the sorbed formaldehyde is irreversibly bound to cellulose and cannot be recovered by extraction with water. The extent of irreversible binding depends on the temperature and the time of exposure to formaldehyde. The moisture content of the fabric does not seem to have much effect on the binding reaction, especially at the high temperatures used in curing durable press fabrics. Over short periods of time at these temperatures, the amount of bound formaldehyde is a quadratic function of temperature. Thus, small amounts of free formaldehyde present in the fabric during durable press finishing would bind irreversibly to cellulose and are therefore unlikely to be a source of releasable formaldehyde during fabric storage and use.

Photodegradation of human hair: a microscopy study

Abstract This study uses various microscopy techniques to monitor the effects and extent of damage caused by UV radiation on the microstructure and physical nature of hair fibers. Field emission scanning electron microscopy (FESEM) is used to monitor the effects of UV irradiation on the physical nature of hair fibers. Long-term UV irradiation/humidification cycling causes thinning and fusion of the surface cuticle cell, as well as fusion of the cuticular sheath into a solid, rigid and brittle unit. Scale thinning and fusion observed during irradiation/humidification cycling are greatly reduced with UV exposure at low humidities without humidification cycling. However, upon post-treatment with water, fibers irradiated at constant low RH (without humidification cycling) show scale thinning and fusion of the surface cuticle cell similar to that of fibers exposed to irradiation/humidification cycling. This indicates that photodegradation occurs at low humidities as well. While chemical oxidation results in partial dissolution (1 h H 2 O 2 ) and then complete solubilization (4 h H 2 O 2 ) of the melanin granules, photochemical oxidation does not appear to significantly alter the physical nature of the melanin granules, even after long-term UV irradiation/humidification (95% RH) cycling. However, the severity of photodegradation of the protein (cuticula and melanin granules) during UV irradiation/humidification cycling becomes apparent upon contact of these fibers with alkaline hydrogen peroxide. Such contact results in instantaneous degradation of the already photochemically degraded components within the surface cuticle cells and highly accelerated solubilization of the melanin granules. Microfluorometry. Diffusion rates of fluorescent dyes can be used to characterize and quantify hair damage from different oxidative processes, such as chemical and photochemical oxidation. This method is well-suited to determine the diffusion coefficients as a function of radial distance from the center of a fiber cross-section and is useful in delineating the radial distribution of photo-oxidative damage. Ultraviolet (UV) microspectrophotometry. This technique is used to monitor formation of photodegradation products in unprotected hair fibers caused by UV radiation. The technique has been extended to study the effectiveness of UV stabilizers in protecting hair fibers against such photo-oxidative degradation of hair proteins. It has been shown by this method that restriction of a UV stabilizer to surface deposition or even peripheral penetration, does not appear to be successful in preventing photo-oxidative degradation. However, uniform distribution throughout the hair fiber during the humidification cycle and high uptake levels of the stabilizer appear to provide photo-stabilization. The success of a UV stabilizer in preventing photodegradation seems to be dependent on its ability to diffuse into the hair fiber as a result of its solubility and affinity towards the fiber.

Microfluorometric Studies of the Distribution of Finishes on Fibers and Yarns

A microfluorometric method is presented for studying the distribution of finishes on textile substrates. The method is based on the effect of microenvironment (such as microviscosity and micropolarity ) in preserving the excited states of fluorescent tracer molecules introduced into the finish. Different methods for introducing tracers into finishes are described, with a critical appraisal of their merits. Fluorescence intensity is shown to be related to the thickness of the finish film up to about 3 μm. Above this, the intensity levels off due to autoquenching effects. Various microfluorometric scanning modes suitable for studying filaments, yarns, and fabrics are described, and their relevance to the nature of the distribution of finish is discussed in detail. The importance of selecting an appropriate tracer is illustrated by applying the method to an autofluorescent substrate.

Thermomechanical and Swelling Behavior of Polymers Used in Wool Shrinkproofing

Thermomechanical and swelling properties of polymers used in wool shrinkproofing have been investigated. The studies involve a crosslinked polyamide, a polyacrylate, and a polyurethane. Swelling seems to be important only with the hydrogel type of polymer (crosslinked polyamide) used in this work. The mechanical modulus of the polymers is seen to be related to their shrinkproofing ability but does not seem to be the only factor. Torsional braid analysis shows that the loss tangent of the hydrogel-type polymer is drastically reduced when the polymer swells. This decrease is due to the low deformahility of chairk segments of the fully-swollen network, which might influence the bending be havior of single fibers. The high loss tangent of the polyurethane suggests that elastic hysteresis of the crosslinked network may be important in the shrinkproofing mechanism.