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This paper investigated specific surface treatments, aimed to improve the adhesion between PLA and rice and Einkorn wheat husks. In the first part, husks were treated by alkaline solutions at three concentrations (2, 5 and 10%) at room temperature for different times between 6 and 48 h. Results revealed that the alkaline treatment dissolved a fraction of waxes, lignin and hemicellulose, so that the polarity of their surface was increased and therefore alkaline treated husks were more sensitive to moisture. Moreover the alkaline treatments have more influence on wheat than on rice husks, as shown by chemical composition determination, FTIR measurements and ESEM observations. In the second part, husks were treated by two kinds of organosilanes (␥-aminopropyltriethoxysilane (APS) and ␥-glycidoxypropyltrimethoxysilane GPS)). These silane treatments were applied either alone or on previously alkaline treated husks (NaOH 5% for 24 h). The results showed that silane treatments reduced the moisture sensitivity and raise the energy surface of the husks. In the last part, treated husks were incorporated into polylactic acid (PLA) to produce biocomposites. Biocomposites reinforced by husks treated by alkaline solution and silane have higher bending moduli and stresses than those reinforced by untreated husks and husks treated by silane alone. It can be supposed that the PLA/husks adhesion was enhanced. No difference was observed according to the silane nature.

The use of hemp fibres as reinforcements in polymer composites requires a thorough understanding of the hemp fibres transformation processes to obtain a constant quality. In this context, the upstream processing termed field retting is considered. Retting allows a subsequent fibre separation from the plant stems by degradation of cementing compounds by microorganisms. This operation depends on weather conditions and is currently empirically carried out in fields, so that a large variability in the hemp fibres quality (color, morphology, biochemical composition, thermal properties and mechanical properties) is resulting. Therefore, the present study aims to investigate the influence of different retting durations (up to 9 weeks) on hemp fibres properties when harvested at the beginning of flowering growth stage to survey their temporal dynamic. Various assessments were applied on fibres: color observations, morphological (optical microscope), surface (ESEM) and biochemical (gravimetry) analyses, spectrocolorimetric measurements (pectins content), thermogravimetric (TGA) analysis, and mechanical in tensile mode testings. The results reveal that increasing the field retting duration leads to a change of color characteristics from light green to grey due to the development of microbial communities (most probably fungal and bacteria) at the stem surface. A separation of the fibres bundle to elementary fibres occurs with the degradation of pectins during retting. An increase of thermal stability of the fibres is also observed. Both increase of cellulose fraction and crystallinity induce an enhancement in tensile properties.

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.