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Mechanical properties of Bombyx mori, twisted B. mori, and Tussah silk fibers were investigated. Their ultimate tensile strength, elongation at break, and Young’s modulus were examined by performing a uniaxial tensile test on a single fiber. Scanning electron microscopy was used to observe the morphology of two different types of silk fiber, and to measure their apparent diameters from which the cross-sectional area of the silk fiber for stress-strain analysis can be determined. Based on experimental results obtained, it was found that Tussah silk fiber has a relatively high extensibility as compared to B. mori silk fiber and other natural fibers. Weibull analysis was also used to quantify tensile strength reproducibility of the silk fiber. Both single and twisted B. mori silk fibers have a better reproducibility of tensile properties than Tussah silk fiber.

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In recent years, natural fiber-reinforced biodegradable thermoplastics are being recognized as an emerging new environmentally friendly material for industrial, commercial, and biomedical applications. Among different types of natural fibers, silk fiber is a common type of animal-based fiber, has been used for biomedical engineering and surgical operation applications for many years because of its biocompatible and bioresorbable properties. On the basis of our previous study, a novel biodegradable biocomposite for biomedical applications was developed by mixing chopped silk fiber and polylactic acid (PLA) through the injection molding process. This article is aimed at studying the dynamic mechanical and thermal properties of the composite in relation to its biodegradation effect. At the beginning, it was found that the initial storage modulus of a silk fiber/PLA composite increased while its glass transition temperature decreased as compared with a pristine PLA sample. Besides, the coefficient of linear thermal expansions (CLTE) of the composite was reduced by 28%. This phenomenon was attributed to the fiber-matrix interaction that restricted the mobility of polymer chains adhered to the fiber surface, and consequently reduced the T g and CLTE. It was found that the degraded composite exhibited lower initial storage modulus, loss modulus and tan delta (tan d) but the T g was higher than the silk fiber/PLA composite. This result was mainly due to the increase of crystallinity of the composite during its degradation process.