Leo A. Holt

Evaluation of the Effects of Temperature and UV-Absorber Treatments on the Photodegradation of Wool

A simple controlled-temperature irradiator is described, which permits fabric samples to be irradiated at air temperatures in the range 35°C to 85°C. Photodegradation of wool fabrics, as assessed by measurement of breaking loads, tear strengths, and yel lowness indexes, increases rapidly as the temperature of irradiation is raised, and occurs 3 to 4 times faster at 75°C than at 35°C. A procedure is described for assessing the level of photoprotection conferred on wool by treatment with a UV absorber of the 2-hydroxybenzophenone type. Consistent lifetime improvement factors are ob tained for most levels of photodegradation, and for exposure either to the artificial light source or to sunlight through window glass.

Studies in Wool Yellowing: Part XIII: Partial Bleaching With Visible Light

, Wool yellowed either by uv radiation or by heating in air at 150°C or in pH 8 buffer at 96°C can be partially bleached by visible fight, the optimum decolorization occurring in the blue region of the spectrum at 430-450 mμ. Amino acid residues in wool partly degraded during uv yellowing are not appreciably degraded further by exposure to longer wavelengths. Even under optimum conditions, bleaching with visible light barely reaches half the bleaching effect obtained with hydrogen peroxide, as measured in terms of the yellowness index. Irradiation at 290-310 mμ of a neutral solution of a mixture of the free amino acids present in wool decreases the concentrations of cystine and tryptophan and to a leaser extent of methionine, histidine, tyrosine, and possibly arginine. Irradiation of the yellowed amino acid mixture with blue light fails to produce bleaching and, both before and after yellowing, causes much less amino acid damage than uv irradiation. When cystine and tryptophan are mixed together in solution or as powdered solids and irradiated at 290-310 mμ the observed yellowing does not exceed that expected from the separate contributions of these two amino acids.

Fluorescent Whitening Agents Part V: The Use of Reducing Agents for Retarding the Yellowing of Fluorescently Whitened Wool by Sunlight

Immersion of fluorescently whitened wool in aqueous solutions of reducing agents during exposure to simulated sunlight has been shown to retard or prevent photoyellowing. The most effective reducing agents of the wide range examined were thioglycolic acid, sodium sulfite, and trishydroxymethylphosphine. Less photodecomposition of trytophan and histidine residues occurs during irradiation of either whitened or unwhitened wool in solutions of these reagents than in water, which may explain, in part, the role of reducing agents in inhibiting photoyellowing. In contrast, a study of bleached wool containing the bis(triazinylamino)stilbene whitener (I) showed that reducing agents do not affect signifi icantly the course or extent of photodecomposition of the whitener. Reducing agents were less effective inhihitors of yellowing when padded onto wool and dried than when used in aqueous solution. However, treatment of fluorescently whitened wool with tetrakishydroxymethylphosphonium chloride (THPC) by padding was found to provide good protection against yellowing in sunlight, especially for exposure in the wet state. Unfortunately the protective effect was not very durable to washing. The sulfonated triphenyl phosphine (II) was substantive to wool but provided good protection against yellowing only at high concentrations. Two water-soluble antioxidants of the hindered phenol type were also tested but were found to be ineffective.

A Fluorescence Microscopy Study of the Diffusion of Some Nonionic Compounds into Wool from Solvent Mixtures

Fluorescent nonionic pyrazolines were applied to wool from organic solvents under swelling conditions, and sections of the treated fibers were examined by fluorescence microscopy. The fluorescence was found to be associated with the intercellular regions of the fiber rather than the cortical cells.

Ultraviolet absorbers for retarding wool photo-degradation: Sulphonated long-chain substituted 2-hydroxybenzophenones

Abstract A series of sulphonated 2-hydroxybenzophenones containing 4-alkyloxy substituents of varying chain length has been synthesised and applied to wool fabrics. The higher members of the series, especially those with n -hexadecyloxy or n -octadecyloxy substituents, protect wool from photo-yellowing and photo-tendering more effectively than do the lower members. The higher members have the additional advantages that they are absorbed almost quantitatively during application and are not removed during laundering. The greater level of photo-protection provided by the higher members is unlikely to be due to their preferential location near the fibre surface, because redistribution of the absorber uniformly throughout the fibre does not reduce the level of protection. Other reasons for the observed differences in photo-protective behaviour are discussed.

Fluorescent Whitening Agents Part VI : The Whitening of Wool by Surface Application of Whitener/Polymer Solutions

Wool fabrics can be whitened by treatment with a solution containing both a fluorescent whitening agent and a polymer. After drying, this leads to the distribution of the whitener in a polymer film which surrounds the fibers, Many whitener/ polymer systems lead to good whitening, but few provide white wool of satisfactory stability to light. The nature of the polymer, as well as that of the whitener, influences the photostability of the surface-whitened fabric. The most light- stable systems give surface-whitened fabrics which yellow in simulated sunlight less rapidly than conventionally-whitened fabrics, the difference being very pronounced for exposure in the wet state. This result is attributed to the fact that whiteners cannot sensitize the photoyellowing of wool if insulated from the fiber in a polymer film. Most whitener/ polymer systems give a whitening effect which is durable to laundering but not to drycleaning. However, durability to drycleaning (as well as to laundering) can be achieved by using reactive whitener/polymer systems in which the whitener is covalently linked to a polymer which can be crosslinked at a later stage.

Sorption of perchloroethylene and toluene by wool and other textiles: influence of co-solvents

Perchloroethylene and toluene are sorbed by dry wool very slowly at room tem perature. Even at the boil several hours of treatment are required to introduce 2% by weight of these solvents into wool. The rate of uptake of perchloroethylene and toluene by conditioned wool is approximately ten times greater, and treatment with a perchloroethylene/water emulsion causes a further increase in rate of perchloro ethylene uptake. Addition of small amounts of methanol to perchloroethylene and toluene causes a vast increase in rate of uptake of the high molecular weight solvents. Wool treated with perchloroethylene/methanol (9: 1) for one hour at room temperature retains 14% perchloroethylene on drying. Similar effects are observed on treatment of cotton and polyester with solvent mixtures. Desorption of solvents from wool due to heating or extraction with methanol or water has also been studied.

Wool Setting: The Effect of Esterification

Esterification of wool fabrics with methanol, ethanol, n-propanol or n-butanol (containing 0.1 M HCl as catalyst) has been found to modify both amide and carboxyl side chains. Modification of amide groups is especially marked with the higher alcohols. The esterified fabrics set more readily than untreated fabric when steam-pressed in the presence of 0.05 M buffer (pH 7), but not when M potassium chloride is added to the buffer. The effect of esterification in enhancing the settability of wool can be explained in terms of the Donnan effect. In solutions of low ionic strength, the internal pH of a wool fiber differs from that of the external solution and this effect is accentuated on esterification. As a result, the internal pH of esterified wool is much higher than that of untreated wool. Since wool sets more readily in alkaline than in neutral solution, esterification enhances settability. At high ionic strengths, however, the Donnan effect is suppressed. The internal and external pH values are the same for both untreated and esterified fabrics, which therefore set at the same rate.

Fluorescent Whitening Agents Part VIII: The Photochemical Behavior of Coumarin and Stilbene Whiteners in Polymer Films and in Surface-Whitened Wool

Ultraviolet absorption and fluorescence spectroscopy have been used to determine the nature and extent of photo-decomposition of fluorescent whitening agents in polymer films and in surface-whitened wool. Irradiation of the coumarin (I) in polymer films at 365 nm gives rise to a mixture of photodimers which rapidly revert to I on irradiation at wavelengths less than 320 nm. Irradiation of the stilbene (II) at 365 nm also gives a photodimer which absorbs strongly around 350 nm, but this reverts only slowly to II on irradiation. Fluorescence studies indicate that there is an increase in the degree of aggregation of I in polymer films with increasing whitener concentration, and that the kinetics of whitener photodecomposition change from first-order at low whitener concentration (0.0025%) to second-order at the higher concentration (2.5%) used in surface-whitening. The coumarin (I) is more stable to light in poly(vinyl acetate) film cast from formic acid than in films cast from less polar solvents, probably because of differences in the degree of whitener aggregation. The photostability of I in poly(vinyl acetate) film is also improved if the film is heated for short periods or stored at room temperature for longer periods.

Substantivity of Various Anionic Surfactants Applied to Wool

Four compounds from each of the sodium alkyl sulphate, 3-alkyl-7-hydroxy cou marin sulphonate, and alkaryl-2-pyrazoline sulphonate series of anionic surfactants were applied to wool under conditions such that equilibrium distribution would occur throughout the fibers. The treated wools were then extracted under various conditions of time, pH, and temperature, and also with various surfactants or alcohols in the extraction solutions. Aqueous extractions, even at pH 10, were relatively ineffective in removing the more surface active members of each series. Solutions containing alcohols, especially isopropanol/pH 10 buffer (1:1), were particularly effective in ex tracting the surfactants from wool. The substantivities to wool of fluorescent anionic surfactants containing coumarin or pyrazoline fluorophores are similar to those of the sodium alkyl sulphate surfactants of similar critical micelle concentration.