A STUDY OF THE VISCOSITY METHOD FOR THE DETERMINATION OF DAMAGE IN SILK

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Abstract
A method described by Trotman and Bell for the detection of damage in silk by measuring the viscosity of its solution in aqueous zinc chloride has been studied.The effect of the temperature and the time of digestion on the viscosity has been investigated, and it is shown that a higher temperature with a shorter period of digestion gives equally satisfactory results, and is more convenient for a routine test.The mechanism of the change in viscosity with time of digestion has been studied, and it is shown to be a dispersion process followed by hydrolysis of the silk.Damage to weighted silk may be determined by this method if the silk is deweighted before dispersion in the zinc chloride solution.The method has been used to determine the damage resulting from the treatment of silk with boiling dilute acid, boiling dilute alkali, light, and superheated steam. The viscosity of the damaged silk has been correlated with its tensile strength to give the viscosity method a quantitative basis. The amino nitrogen content of the silk was also determined and has been correlated with the tensile strength and viscosity. The results show that there is a difference between the hydrolysis of silk occurring in boiling dilute acid and that occurring during the corresponding alkali treatment. In the former, hydrolysis of the silk with formation of free amino groups occurs previous to dispersion, whereas in alkali it appears that the disintegration of the fibre into fibrils takes place very readily and that the fibrils are then rapidly dispersed in the alkaline solution before appreciable hydrolysis can occur. That the photochemical decomposition of silk is an oxidation process is confirmed. The action of steam appears to differ from that of acid, alkali, or light.

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