This study aims to assess and understand simultaneously the changes in visual aspect, surface topography and mechanical properties of a wood flour reinforced polypropylene (PP) composite under natural and artificial weathering conditions. Compounds were produced through twin-screw extrusion followed by injection molding in order to obtain dog bone samples. A one-year natural outdoor exposure and a xenon-arc accelerated weathering were studied. As expected, mechanical performances are decreased under UV exposure. This performance degradation goes along with important changes in visual aspect. In addition to commonly used microscopy observations, other methods such as colorimetry, spectrogoniometry and confocal rugosimetry are used to characterize the surface aspect through color, gloss and roughness properties. These analyses revealed that ageing induces a surface bleaching, a wood particle protrusion and numerous micro-cracks. Moreover the chain scission attested by Size Exclusion Chromatography (SEC) and lixiviation on the surface induces roughness and gloss loss. Otherwise biocomposites were more degraded under natural weathering. This paper gives new insights in understanding how weathering affects physico-mechanical properties of wood plastic composites (WPC). For that, the Principal Component Analysis (PCA) gives global overview about effects of type of weathering and wood rate on physical, mechanical and chemical properties by calculating their contributions to the drawing of axes (Principal Components) during PCA.

This work aims to understand the degradation induced by multiple injection molding cycles on numerous properties of wood flour reinforced polypropylene (PP) composites. The influence of the initial wood particle size was studied as well as the influence of the addition of polypropylene grafted with maleic anhydride (PPgma) as a coupling agent at a given rate. Biocomposite compounds (20wt% of wood flour) are produced by twin-screw extrusion. Then, multiple injection and grinding cycles were performed (up to 7 cycles) to obtain normalized samples. The evolution of the wood flour particle characteristics is first assessed by SEM observation, size measurements and nanoindentation experiments. Then, the evolution of the PP matrix microstructure is determined by SEC tests (average molecular weight measurements), rheometer tests and DSC (polymer crystallinity). Finally, material mechanical properties are measured at a macro-scale thanks to tensile tests. Our experimental results show that the composite mechanical properties remain quite stable after 7 processing cycles despite wood flour degradation and PP degradation.

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Biocomposites has gained increasing attention in recent years. The environmental impacts of end-of-life (EoL) treatments of those emerging materials should be evaluated before they are produced and installed commercially, to ensure a minimal impact of these products all along their life cycle. Life cycle assessment (LCA) was carried out to evaluate environmental impacts of the EoL treatments of wood flour (WF) reinforced polypropylene (PP/WF) and flax fibers reinforced polylactic acid (PLA/Fl). The aim was to evaluate which EoL was the most environmental friendly to manage those emerging wastes in France and to help stakeholders of the waste sectors in their decisions. The attributional LCA was realized using the methodological framework of the international standard ISO 14040:2006. The study only focuses on the EoL of the biocomposites with four scenarios: incineration, landfill, composting and recycling. Mid-point indicators were evaluated thanks to the Recipe method. Results were also normalized to the annual mean environmental impact of a European inhabitant. For both biocomposites, recycling EoL scenario presents the lowest environmental impacts except for the freshwater eutrophication impact of the PP/WF EoL. Models should be completed in the future when new data will be available. Results obtained for both biocomposites are in agreement with the European waste hierarchy. If recycling of plastic is difficult to implement, incineration would be the preferable option for the PP/ WF composite, while composting would be the other choice for PLA/Fl material.

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