Interfacial studies of carbon fibre/polycarbonate composites using dynamic mechanical analysis

Abstract

Unidirectional composite material samples with ultrahigh modulus carbon fibres, treated and untreated by oxygen plasma, and a polycarbonate matrix were prepared and tested. Dynamic mechanical analysis (DMA) was used to study interfacial fibre/matrix interaction and the fragmentation test method was applied to determine interfacial shear strength. For the composite samples with treated carbon fibres, analyzed by DMA, a consistent shift of the loss modulus peak toward higher temperature was observed. The damping ratio was highly affected by residual stresses along the carbon fibre direction due to the large difference of thermal expansion coefficients of matrix and fibres. Critical fibre length and interfacial shear strength, obtained from the fragmentation test, showed substantial improvement for treated fibres as compared to the untreated ones. Plasma oxidation of the fibre surface improved considerably the fibre-matrix interaction. Care must be taken interpreting the DMA results, due to specific characteristics of the system studied.