Compounding and mechanical properties of biodegradable hemp fibre composites

Up to now the reinforcing potential of hemp fibres has not been exhausted, as the fibres are bundled and, therefore, a homogenous distribution of fibres and matrix has not been possible. In the present study the fibre bundles used for the composites were degummed by means of biological processes and steam explosion. The degummed fibres, separated into single cells, were integrated into the brittle poly (3-hydroxybutyrate-co-hydroxyvalerate) matrix and into the ductile co-polyester amide matrix by means of a co-rotating twinscrew extruder. Composites with a fibre volume fraction of up to 42% could be achieved. The tensile strength of the ductile material was almost doubled by the reinforcement with 27% of fibres to 30 MPa, the E-modulus was quadrupled to 3.5 GPa. No improvement of the tensile strength of the brittle matrix could be achieved, whereas its E-modulus was increased up to 6 GPa. As the composite behaviour is determined by the matrix, the fibre reinforcement is accompanied by a reduction of the impact strength.