Mechanical Properties of the Silk Degummed with Citric Acid and Ultrasound

Abstract

Silk, called the “Queen of Fibers,” is a continuous protein fiber produced by silkworm to form its cocoon. Raw silk fiber obtained by unwinding the cocoons of the silkworm Bombyx mori requires a great deal of handling and processing, which makes it one of the most expensive fibers. Because of the presence of sericin, raw silk is rough, hard, brittle, rugged, and without luster. The traditional method for silk degumming is with Marseilles soap, which is very expensive. Today, with new ecological and economic requirements, there are new methods for silk degumming, such as degumming with enzyme or with polycarboxylic acid, degumming with alkalis or with water. Recently, acid agents with the purpose to enhance the physical properties of silk replace soap. In general, the action of alkali is more aggressive than the action of organic acid. Citric acid, compared to the other organic acids, is cheaper, proven lack of toxicity, and ready availability. The aim of this paper is to investigate the influence of citric acid and ultrasound on silk degumming. For this purpose, silk fibers were degummed by the classic procedure, and with different concentrations of citric acid (15 and 30%), with and without ultrasound. The efficiency of the degumming was determined by measuring degumming ration and mechanical properties (fineness, tenacity, and elongation at break) of untreated and treated silk yarn.