S. B. Ruetsch

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.

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.

UV Stabilization of PET Fibers: Microscopy Study

Ultraviolet microspectrophotometry is used to monitor the radial diffusion of three uv stabilizers in high molecular weight PET fibers. Under identical application con ditions, the benzotriazole and benzotriazine derivative stabilizers show peripheral penetration only, whereas the benzophenone derivative stabilizer diffuses throughout the fiber cross section. Peripheral penetration of the benzotriazole and benzotriazine derivatives does not prevent polymer photodegradation in the unprotected interior, whereas all regions of the fiber are protected by the more uniformly distributed ben zophenone stabilizer. Heavy peripheral deposition of the benzotriazole stabilizer pre vents these highly protected regions from polymer photodegradation.