Cornelia Dansizer

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.

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.

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.

The Stabilization of Irreversibly Deformed Keratin Fibers Part I: Mechanism of Recovery

The mechanism of recovery of keratin fibers from deformation in aqueous solutions was investigated. Above a transition temperature of ~70°C the deformation of the fibers became at least partially irreversible and the reversibility of the α-β-transformation was completely destroyed. Various levels of an irreversible disorientation of the native structure could also be obtained by holding the fibers in the extended state above the transition temperature for various lengths of time. The level of disorientation obtained under these conditions is reflected in the stress level reached during stress relaxation. Upon release of the fibers, instantaneous recovery occurred which was proportional to the stress just prior to release. The total recovery can be kept at this level if an SH-blocking reagent is added prior to the release of the fibers, indicating that the second, slower phase of recovery is controlled by an SH-catalyzed disulfide interchange mechanism. A similar behavior could be observed for highly reduced fibers, in which case the formation of stable thioether linkages during setting presumably prevents the second phase of recovery. The removal of disulfide bonds from contraction-opposing positions is the rate-determining factor of the second phase of recovery

The Stabilization of Irreversibly Deformed Keratin Fibers Part II: Mechanism of Stabilization

The significance and relative contribution of the various factors that contribute to the stabilization of the extended state of the keratin fibers have been investigated. In this context, the stress relaxation of extended keratin fibers in 7.2 M LiBr solutions, as well as their recovery and recrystallization behavior, were studied. A kinetic analysis of stress relaxation in 7.2 M LiBr at a strain of 60% indicated that the controlling mechanism is an SH-catalyzed disulfide inter change with an activation energy of 22.9 kcal/mole. The recrystallization in a stable β-configuration of the chemically molten and extended keratin fibers is only possible after a structural rearrangement which removes disulfide bonds from stressed positions. If this rearrangement is prevented, the β-crystallites remain unstable even after an extended re crystallization time. Stabilization of the extended state by the formation of stable covalent cross links is not possible, unless crystallization of β-crystallites is permitted. The formation of β-crystallites alone, on the other hand, is also not sufficient to stabilize the extended state, unless the β-configuration is supported by stable covalent cross links. After a melting-extension-recrystallization cycle at 96°C, the total longitudinal deformation of the keratin fibers approaches 125%, which would correspond to the theoretical α-β-translation distance.

Longitudinal Swelling of Permanently Set Wool Fibers

The longitudinal swelling of permanently set wool fibers was measured by a desorption method as a function of the time the fibers were held in the extended state. It was found that, after a setting treatment involving extensions below 40%. the longitudinal swelling, following an initial rapid increase, was independent of setting time and the dimensional changes of the fiber resulting from the setting process. At a setting ex tension of 60%, a maximum in longitudinal swelling is reached, which is followed by a rapid decrease and then by a gradual decrease with increasing times of setting. The results are interpreted in terms of differences in the stabilization mechanism for the extended configuration, depending on the strain level. Elimination of free sulfhydryl groups, before the fibers are released from extension, decreases chain mobility and, therefore, decreases disordering during the subsequent recovery step.

Mechanical Properties of Feather and Down Fibers Part I: Measurements at 65% RH and 70° F

The elastic moduli of European goose feather barbs and down filaments have been measured at 70° F. and at 65% RH and various pressures of dry air. These latter meas urements at various dry-air pressures have been made to estimate the effects of air- damping on vibroscopic determinations of several fiber properties, have indicated the air-damping effects to be significant but relatively small, and are described in detail in Part II of these papers [6]. A detailed series of measurements has been made at 65% RH and 70° F. of the extensional properties, the bending modulus, and the torsional modulus. The breaking extension is about the same for all the different materials studied, but for the other extensional properties—such as elastic modulus—the properties of the feather barbs are greater than those of the down filaments, and generally the properties of the vane barbs (straight) are greater than those of the fluff barbs (curly). A similar finding holds for the corresponding cross-sectional areas. As in the case of the exten sional properties, the bending and torsional moduli of the feather barbs are greater than those of the down filaments, and vane feather barbs exhibit larger moduli than do fluff barbs. The significance and limitations of these measurements are discussed.

Effect of Polymer Deposition and Washing Medium on the Felting Shrinkage of Chlorinated Wool Fabrics

The felting shrinkage of chlorinated wool fabrics treated with a group of preformed polymers has been investigated. The results suggest that after polymer deposition on the fabric, interfiber bridges and transient adhesive junctions formed between the fibers prevent relative fiber movements when the fabric is subjected to bending deformations in a washing medium. In the case of Hercosett-treated fabrics the shrinkproofing mechanism seems to include the elimination of directional bias in the movement of fibers by fiber lubrication. This latter mechanism is probably prevalent in fabrics made from Hercosett-treated top. These results are supported by the frictional and mechanical behavior of the polymers. The effect of surfactants in the washing medium on felting shrinkage depends on their ionic nature. Anionic and nonionic surfactants seem to reduce shrinkage by interfiber repulsions and limited fiber lubrication. Although they are operating by the same mechanisms, wettability of the fibers seems to be a key factor in the case of cationic surfactants. Differences in the concentration dependence of the surface tension of the three surfactants support this hypothesis.

Mechanical Properties of Set Keratin Fibers

Various degrees of set, and sets of various degrees of permanence, were imparted to four keratin fiber types: human hair, kid mohair, a noncrimp coarse wool, and a fine high-crimp wool. The sets were imparted in a water system at 97° C and at room temperature. The mechanical properties at 70° F and 65% RH of the set fibers were measured and examined in relation to the type and degree of set imparted. In general, fibers with a permanent set are weaker and more extensible than fibers with a temporary set. Significant differences in behavior were observed among the four fiber types.