Photochemical Reactions in Silk

Silk is more readily deteriorated by the action of light than any other natural textile fiber. While the nature of the deteriora tion has not been clear, it has been known that the rate of decompo sition may be considerably altered by pretreatment of the fiber with solutions of various chemical compounds. For example, silk treated with dilute solutions of basic compounds is more stable toward the action of light than untreated silk, whereas silk treated with dilute solutions of mineral acid exhibits greatly decreased stability under the same conditions. An investigation by Research Associates of the Textile Foun dation at the National Bureau of Standards of the influence of a number of reagents on the photochemical deterioration of silk now reveals that the rate of deterioration is in part influenced by the cationic content of the silk. The removal of cationic substances, . by two independent methods results in practically identical de creases in the stability of the fibers to light. On the other hand, the stability is readily restored by treatment with basic compounds. Inorganic bases produce a number of undesirable effects, such as a harsh "feel" and a tendency for the cloth to yellow. These effects can be eliminated by the use of any one of a number of different organic basic compounds. It was further shown that the inaetivation of the carboxylic acid groups of silk by methylation with diazomethane does not ap preciably change the photochemical behavior of the fiber but that the methylation of only a small percentage of the hydroxyl groups of tyrosine results in a marked increase in photochemical stability. The results suggest that alteration of the tyrosine hydroxyl groups by reaction with various reagents is responsible for at least part of these stabilizing effects.