Neil A. Evans

Effect of Photostability of 2-Pyrazoline Fluorescent Whitening Agents on the Rate of Yellowing of Whitened Wool

Sulfonated 2-pyrazolines containing two, three, and four phenyl groups have been synthesized and examined as fluorescent whitening agents for wool. Although the photostability of these whiteners increases as the number of phenyl substituents is increased, the rate of photoyellowing of wool containing these whiteners has been found to be independent of the whitener used. The rate of photoyellowing of wool treated with the diaryl-2-pyrazoline (Ha) increases with increasing whitener concentration up to 0.4% owf and then remains constant up to a concentration of 1.6% owf—the highest level studied.

The Effect of Phenylbenzotriazole Derivatives on the Photoyellowing of Wool

The effects of a range of water-soluble 2 arylbenzotriazoles on the photoyellowing rate of bleached wool have been investigated. Variation in substitution pattern in the 2 aryl ring yielded vastly different effects. Some retardation of photoyellowing is observed with derivatives containing a hydroxyl group ortho to the benzotriazole ring, whereas the rate is accelerated by derivatives devoid of such a suhstituent or with an amino group in this position.

Photoprotection of wool with sulfonated 2-(2′-hydroxyaryl)-2H-benzotriazoles

Abstract A range of phenolic benzotriazolesulfonic acids containing a wide variety of substituents has been synthesized. These compounds protect wool to a significant extent against photo-tendering and, in some cases, against photo-yellowing. The protective effect is dependent on the nature and position of the substituents and is enhanced by (1) locating the sulfonic acid group distant from the hydrogen-bonded phenolic group and (2) placing bulky alkyl groups ortho to this phenolic group. The protective effect of one of the best photostabilizers (II) has been studied in detail and has been found to depend on both the concentration of the photostabilizer and the pH at which it is applied. The photostabilizer (II) also protects dyed wool to some extent against photo-fading as well as against phototendering.

Photofading of Rhodamine Dyes III. The Effect of Wavelength on the Fading of Rhodamine B

The action spectra for fading of Rhodamine B (C.I. 45170) are similar for irradiations in aqueous solution and on wool, bleached wool and nylon fabrics, suggesting that the mechanisms of fading are similar in all cases and that the fiber plays no significant photosensitizing role. In solution, the quantum yield for photodegradation varies markedly with the wavelength of the incident radiation, ranging from 1.1 × 10-6 mols/einstein at 540-560 nm to 8.4 × 10-6 mols/einstein at 325-345 nm. On the basis of the results presented, it is calculated that visible radiation (400-600 nm) is responsible for approximately 80% of the fading when Rhodamine B dyed wool is exposed to sunlight.

Photofading of Rhodamine Dyes Part IV: Effect of Sulfoxides on the Photostability of Rhodamine Dyes

A range of basic dyes and an acidic dye have been dyed onto wool at room temperature using dimethyl sulfoxide as the solvent. When fluorescent Rhodamine dyes are dyed to low depths of shade by this method, the lightfastness of the dyeings is enhanced compared with wool dyed conventionally. There are two possible explanations for this enhanced lightfastness: (1) the dye is aggregated in the fiber when dyed from dimethyl sulfoxide, or (2) dimethyl sulfoxide directs the dye to different sites in which the dye is more stable to light.