Towards sustainable wood fillers from agroforestry for Wood-Plastic Composites (WPC): Key roles of wood species and filler characteristics
Résumé
Current environmental concerns push towards more sustainable and local practices for
biomass production. In this regard, agroforestry has been highlighted by researchers and poli-
cies as a highly efficient approach for carbon sequestration (between 1.5 and 4 t C/ha/year),
and a sustainable alternative to deforestation with many agricultural benefits: deeper root-
ing of trees in soil, enhanced biomass productivity, crop fertilization... Agroforestry implies
regular branch cuts that are processed into wood chips and mostly used as energy wood or
soil mulching. New higher added-value chains could be considered such as reinforcements or
specific molecules for bio-based materials and chemistry.
Besides, since 90’s, Wood-Plastic Composites (WPCs) have experienced significant growth,
particularly in building (decking & siding), and constitute the largest share of bio-based com-
posites developed at an industrial scale. Nevertheless, the quality of WPCs and variability
in their performance are major technological issues for their implementation in industrial
applications. This is due to difficulties in tracing the origin of wood fillers and the different
processing steps, from drying and defibration process to composite manufacturing, that are
not well controlled. Indeed, numerous interdependent parameters govern the final proper-
ties of WPCs, such as biochemical composition, presence of contaminants (binders, wood
treatment residues, varnishes...), (micro)structure, thermal stability, mechanical properties
of wood fillers, and the control of their milling/sieving and further processing into composite
materials.
In this context, the development of quality-controlled agroforestry wood fillers in terms of
granulometry, chemical composition and physical (microstructure, mechanical) properties is
therefore strategic for their implementation in wood-based products. This work investigates
the influence of wood species (poplar, oak, walnut, chestnut)) and filler size and shape on the
microstructure and mechanical properties of polypropylene (PP) / wood composites manu-
factured by extrusion/injection moulded. Moreover, woods from three recovery platforms in
Brittany (mix of several species) were also investigated to evaluate the potential of existing
agroforestry feedstocks