Tailormade dry fractionation of vine shoot to produce fillers for biocomposites

Biocomposites reinforced with lignocellulosic fillers is gaining more and more interest in different industries. The cheapest and most environmentally virtuous lignocellulosic fillers are those obtained from either agricultural, forestry or food industries wastes and by-products. It is now well-known that functional properties of composite materials are mainly related to the intrinsic properties each constituent, the filler content and the dispersion state and the properties at the filler/matrix interface. However, modify only one criterion often generates structural changes of either the matrix or the filler, resulting in a tricky understanding of reinforcing effects. To better understand structure/properties relationships in biocomposites the production of lignocellulosic fillers with controlled and contrasted characteristics is essential. Additionally, properties of fillers are generally system-dependant due to the variability of both structure and composition of lignocellulosic biomass (Montano et al., 2013; Berthet et al., 2015).Previous work has shown that the size and the surface hydrophobicity of wheat straw particles can be controlled by combining dry grinding and sorting processes (Montano et al., 2013). In this work, we focused on the production of fillers by dry fractionation processes, from vine shoot which is a regional valuable by-product of vine culture. Vine shoot was comminuted by a combination of grinders which generated different mechanical stresses as shear, impact and compression (A. Barakat et al., 2014). The micron-size lignocellulosic fractions obtained displayed differences in term of size and morphology (evaluated by laser granulometry and image analysis), biochemical composition and solid surface energy (deduced from contact angle measurements) according to the milling process. Contrasted fractions were selected for the production of biocomposites by melt extrusion.