Tensile behavior and morphology of differently degummed silkworm (Bombyx mori) cocoon silk fibres

Tensile tests have been performed on silkworm cocoon silk fibres degummed using five different methods: distilled water, boracic acid-sodium borate buffer, sodium carbonate, urea and succinic acid. Using an electronic single-fibre tensile instron, the force-displacement curves were obtained for each condition. Effects of degumming on silk include a decrease in the initial elastic modulus and a decrease in the proportional limit (i.e., yield point). These results suggest that degumming weakens at least one type of non-covalent interaction of core fibrion, such as hydrogen bonds and Van der waal's bonds. The stress-strain curve determined from a force-displacement curve as resealed by the corresponding sample cross-sectional area failed to reproduce the actual mechanical properties of two fibroin core fibres because of variable degradation of the sericin coating. The two important factors associated with degumming could affect the tensile properties of silkworm silk: 1) the change in the microstructure of two core fibroin, and 2) the degumming ratio. SEM was used to observe visually the morphology and fractography of differently degummed cocoon silk fibres. Effects of different degumming treatments on the tensile behavior, mechanical properties, morphology and fractography of cocoon silk are clearly visible. (c) 2005 Elsevier B.V. All rights reserved.