Résumé
Due to their excellent native mechanical properties, several biosourced materials are promising candidates as raw materials for manufacturing biocomposites with enhanced mechanical properties. However, classical composite forming techniques generally induce irreversible degradation of both structural and mechanical native properties of such materials. In this study, thermo-compression and ultrasonic compression moulding were used to form composite materials made up of starch powder and softwood pulp reinforcement fibres. The objective was to find a window of forming parameters enabling the preservation of the native structure and excellent mechanical properties of starch granules. The best set of investigated forming parameters (pressure, temperature, and starch powder moisture content) allowed us to obtain composite samples with good mechanical properties. For instance, their Young modulus ranged from 4 to 6 GPa and their mechanical strength from 30 to 70 MPa, depending on fibre content. The two processing techniques produced composite samples with similar mechanical properties but distinct microstructures. While a better control of the microstructure is achieved using thermo-compression moulding in terms of both coalescence of starch granules and crystallinity, ultrasonic compression moulding allows a significant gain in processing time.