Mechanical and Thermal Degradation Properties of Silk from African Wild Silkmoths
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Variations among silk of four African wild silkmoths, Argema mimosae, Anaphe panda, Gonometa postica, and Epiphora bauhiniae, was studied regarding their mechanical properties and thermal degradation behaviors. Cocoon shells and individual degummed fibers were examined using tensile testing, thermogravimetric analysis, and scanning electron microscope (SEM). A. mim- osae and G. postica cocoon shells had marginally higher initial moduli and strains at maximum stress. The stress–strain curves of Bob- myx mori and A. panda degummed fibers lacked clear yielding points. G. postica fibers had the highest breaking energy (76.4 J/cm3) and breaking strain (41.3%). The ultimate tensile strength was the highest for B. mori (427 MPa). Fiber pull-out and detachment was predominant in fracture surfaces of both the cocoon shells and the fibers. Wild cocoon shells and degummed fibers had higher tem- perature for dehydration loss than B. mori. A. mimosae fibers (11.9%) and G. postica cocoon shells (13.3 %) had the highest weight loss due to dehydration. E. bauhinae cocoon shells and B. mori fibers had the highest total weight losses of 97.2 and 93.4%, respec- tively. The African silks exhibited variations in their mechanical and thermal degradation properties related to their physical and chemical structure and composition.