Influence of interphase properties on the effective behaviour of a starch-hemp composite

Elasticity behaviour of a fully biopolymer composite is studied using both numerical and experimental approaches. Hemp fibre-starch composite is thermomoulded using a varied content of hemp fibres. On one end, mechanical testing reveals loss of stiffness due to limited load transfer with the increase of fibre content. On the other end, two-phase theories predict a reinforcement trend due to contrast of phase properties. In order to meet both ends, a numerical study is performed to study sensitivity of the predicted mechanical response to geometrical and mechanical considerations. Filler content, arrangement and interphase properties are some of the major studied effects. Interphases are accounted numerically to exhibit the mismatch of load transfer due to imperfect interface behaviour. Finite element results are discussed based on geometrical and mechanical considerations using a sensitivity analysis. Identification of interphase parameters for the tested experimental conditions is attempted successfully. The threephase model is able to detect where the two-phase system approximation is valid. In addition, strong interphase properties are identified despite the apparent loss of stiffness. Such loss turns to be related to fibre clustering, which makes thermomoulding processing not suitable to achieve fibre volume contents above 10% if not combined with an energetic mixing stage. (C) 2014 Elsevier Ltd. All rights reserved.