Studies in Wool Yellowing. Part XVIII: Processes for Retardation of Sunlight Yellowing of Fluorescent-Brightened Wool

Abstract

Dear Sir:Despite the findings of Graham and Statham [4] and Fallow and Tucker [3] that fluorescent-brightened wool is much more susceptible to sunlight yellowing than unbrightened wool, fluorescent brighteners [6] are still widely used during the processing of wool intended for sale in white or pastel shades. The high level of whiteness that current fashion demands seems to be obtainable only by the use of brighteners. It is, therefore, highly desirable to discover new brighteners having superior lightfastness, when applied to wool, than the brighteners presently available. In the meantime, alternative means to improve the lightfastness of brightened wool must be devised. ' The yellowing of brightened wool is a more complex phenomenon than the yellowing of unbrightened wool, owing to the extra discoloration arising from photodecomposition of brightener or photosensitization of wool by brightener. An investigation into the problem has commenced in these laboratories, and initial findings are now reported. These mainly confirm and extend the work of previous investigators [3,4,5].. -An attempt was first made to compare 20 of the various brighteners currently available with respect to lightfastness, when applied to wool, and to find which particular chemical class of brightener is more suitable for application to wool. Information as to the exact structure of a brightener was not always available from the manufacturer, but we were usually informed of the class [9, 10] to which the brightener belonged, such as stilbene, coumarin, or pyrazoline. Stilbenes could also be recognized by the rapid changes, due to cis-trans isomerization, in the uv absorption spectrum, which occurred when an aqueous solution was exposed to diffuse daylight [12]. Brighteners are usually exhausted onto wool (J-1 hr) at pH values of 4-5 and temperatures between 40 and 95°C, at a level of 0.1-1.0% on the weight of wool. Added sodium hydrosulfite or sodium formaldehyde sulfoxylate (2-3 g/liter) acts as a reductive bleach with respect to the color normally present in natural wool [2,11]. As a general rule, stilbenes a appeared to require a higher level (ca. 1%) and higher temperature of application (80-95° ) than coumarins or pyrazolines (ca. 0.2%, 40-60° ). Both the initial whiteness and subsequent lightfastness of a brightener can vary considerably, according to the conditions of application and/or irradiation [1,14]. A thorough investigation of the relative merits of brighteners would have entailed an enormous number of tests, and this was not carried out. Instead, each brightener was merely applied in accordance with the recommendations of the supplier. Under these conditions, three brighteners, which seemed to be all stilbenes, performed reasonably well. These were Leucophor PAF (Sandoz), Photine HV (Hickson and Welch), and Lumicol WFG (origin unknown, supplied by Edgar

A Process for Simultaneously Bleaching Wool and Stabilizing Set

“…o 1t can be seen from Table I that thiourea-formalde-hyde bleaches the wool, in agreement with earlier observations [7]. Yellowness-index data suggest that this bleaching effect is most efficient when the two chemicals are added as an after-treatment, although some bleaching occurs when thiourea is added prior to, and formaldehyde after, the steam-setting.…”

“…However, there was less uptake of fluorescent brightener in the steaming treatments, while the yellowing and loss of fluorescence of the fabrics on irradiation was greater. In accord with previous work [5,7], application of brightener alone accelerated the rate of yellowing of wool fabric, whereas additional treatments with thiourea-formaldehyde had some bleaching action and protected the wool, albeit less than by the conventional method [5], against yellowing on irradiation. Although the mechanism of setting is still a matter of some conjecture, it is well established that set may be stabilized by the destruction of free thiol groups and/or the introduction of crosslinking reagents [2,8].…”

“…yellowness indexes after irradiation for 6 hr in a wet state) ; nevertheless, the convenience offered by the faster method may offset the lower degree of protection in certain instances. The brightener Photine HV (Hickson and Welch), which has previously been satisfactorily applied to wool [4,7], was applied as an after-treatment in the setting process (after steaming and pressing). Results of experiments are recorded in Table II.…”

Mechanism of photoprotection of wool with formaldehyde and thiol derivatives

“…The application of a mixture or pre-condensate of thiourea and formaldehyde (TUF) followed by thermal curing to improve the photostability of wool has been previously investigated in a number of studies [1][2][3][4][5]. The treatment was first developed for use on silk [6] and had some limited commercial use on wool treated with fluorescent whitening agents (FWAs) in the 1970s, but, unfortunately, the benefit of the treatment is significantly reduced following the first laundering cycle.…”

The Effect of Wool on the Photolysis of a Model Stilbene Fluorescent Brightener

“…Photosensitized degradation of wool keratin by fluorescent brightcners has been studied by a number of workers [2][3][4][5][6]8]. Changes observed in the wool and brightener have been expressed in terms of fluoresccnce decay of the brightener, discoloration of the wool, rendering of tensile properties, and changes in the amino acid composition of the treated wool.…”