Mechanical Properties and Structure of Methacrylamide (MAA) Grafted Silk Fibres

Graft copolymerizalion was performed on silk fibres by using methacrylamide (MAA), and changes in the mechanical properties and structure were investigated. Young's modulus of the MAA grafted silk fibre was analysed by applying the law of mixture by regarding the MAA grafted silk fibres as a composite comprising silk fibres and a MAA polymer resin. Young's modulus of the MAA polymer in the MAA grafted fibres was calculated to be approximately 4.6 GPa, which was larger than the value of a MAA polymer film. The MAA polymer in the MAA grafted silk fibres was oriented with respect to the fibre axis. When the volume fraction of the fibre in the MAA grafted silk fibres was more than 0.8, the tensile strength of the MAA grafted silk fibres agreed with the strength calculated by assuming that the failure of the MAA grafted silk fibres was caused by the failure of silk fibres and the MAA polymer was strained to the same extent as the silk fibres. The wide-angle X-ray diffraction measurements showed that crystallites in silk fibres treated with MAA to a large polymer add-on were destroyed by this treatment. The fracture of the MAA polymer matrixas well as the destruction of crystallites in silk fibres influenced the strength of the MAA grafted silk fibres when the volume fraction of the fibre was less than 0.8.