Influence of weathering on visual and surface aspect of wood plastic composites: Correlation approach with mechanical properties and microstructure

Abstract

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.

Linear Low Density Polyethylene/Poly (Vinyl Alcohol)/Kenaf Composites: Effect of Natural Weathering on Functional Group, Weight Loss Characteristics, Tensile, Morphological and Thermal Properties

“…Moreover, all peaks (1245, 1144-1056, 990, 898-719 cm -1 ) belong to cellulose, hemicelluloses or lignin of KNF (Harini & Harsojo 2014;Pang et al 2017). As can be seen in Figure 2(b) and 2(c), the peak intensity of C=O (carbonyl group) and OH (hydroxyl group) increased with increasing weathering duration due to the oxidation of composites surface (Badji et al 2017) and KNF being exposed on the weathered composite surface (Sarifuddin et al 2014). In addition, it is obvious that the characteristic peaks of cellulose, hemicelluloses or lignin of KNF decreased with prolonged weathering duration is probably attributed to KNF being detached from the exposed composite surfaces, as shown in the later surface morphology micrographs.…”

“…Many researches explored the effect of natural weathering on properties of natural fibers/thermoplastic composites. For instance, Badji et al (2017) investigated the visual aspect, surface topography and mechanical properties of wood-polypropylene composites under natural weathering conditions. They noted that degradation by weathering has induced surface roughness, gloss loss and decrease in tensile properties of the composites, particularly at higher wood fraction.…”

Natural weathering of hemp fibers reinforced polypropylene biocomposites: Relationships between visual and surface aspects, mechanical properties and microstructure based on statistical approach

“…Principal Component Analysis (PCA) is a useful statistical technique for finding relationships between parameters in high-dimensional dataset by including several parameters at a same time. In a previous paper, the correlations between properties of PP and WPC were assessed after natural and artificial weathering thanks to this analysis [3].…”

“…Rugosimetry A MICROMESURE STIL system equipped with a STIL CHR150 optical sensor was used to evaluate the roughness by altitude measurement of each surface point on the sample without contact with the sample according to the ISO 25178 international standard. More details are given in a previous paper [3]. A bidimensional scanning allows obtaining the image of the sample surface located at a precise distance from the STIL optical sensor.…”

“…Biocomposites strongly lost strength and stiffness [3][4][5][6][7] and the presence of natural fibers were evidenced to give rise to materials surface defects, gloss being compromised by these surface aspect changes [3,8,9]. The natural reinforcing part also instigated the biocomposites discoloration by photo-induced oxidation [3,9,10]. Some solutions can be brought to avert these variations, for example by adding chemical stabilizers [11].…”