Influence of lignin content on photodegradation in wood/HDPE composites under UV weathering

The aim of this work was to examine the influence the lignin component of wood on the photodegradation of high-density polyethylene (HDPE) in wood/HDPE (WPE) composites. The neat HDPE and wood/HDPE composites were prepared using a twin screw extruder followed by an injection moulder. The lignin content was varied from 0 to 29 %wt. of wood by the addition of delignified wood pulp into wood flour. The results suggested that the photodegradation of HDPE in WPE composites was accelerated by the presence of lignin; the chromophoric groups in the lignin enhanced UV adsorption onto the WPE composite surface. The carbonyl and vinyl indices, color, percentage crystallinity, and the melting temperature increased when the lignin contents were increased. The color fading in WPE composites resulted from photobleaching of lignin. In addition, the presence of lignin led to the development ofl cracks in WPE composites, especially at high lignin contents. For the effect of UV weathering time, the carbonyl and vinyl indices, discoloration, and percentage crystallinity increased as a function of UV weathering times, whereas the melting temperature of HDPE in both neat HDPE and WPE composites and water absorption of specimens decreased; the wood index in WPE composites increased during the initial UV weathering times and then decreased at 720 h weathering time.