Dyeing of the wood flour-poly(lactic acid) composite and its property evaluation.

In order to enrich the colors of wood flour ( WF)-polymer composites and then expand their applications, and also to investigate the influence and mechanism of colorants on overall properties of the composites, nine groups of wood flour-poly (lactic acid) (PLA) composites were prepared in this study by using wood flour of poplar (Populus tomentosa Carr. ) and biodegradable polymer PLA composites as raw materials and three types of food-grade colorants (carminum, tartrazine and fruit green) as additives. The loading levels of colorants were 1%, 2%, and 4%, respectively. Then, some physical and mechanical properties of the composites were tested, including washing resistance, flexural property, water uptake and dimension stability. FT-IR analysis was also used for characterization. The results showed that: 1) the colorants changed color of the composites to different extents. With the increasing loading of colorants, the washing resistance decreased and the reduction was more significant at higher temperature; 2) colorants reduced flexural strength of the composites to different extents, but it had little impact on flexural modulus. In this study, 2% fruit green affected less on flexural properties of the composites; 3) with fruit green addition of 2%, the water absorption and thickness swelling rate of the composites were the lowest and closed to the values of control without colorants; 4) FT-IR analysis showed that the colorants changed in processing or reacted with some substances in wood. In conclusion, both the type and loading level of colorants had effects on the color, physical and mechanical properties of WF-PLA composites. In this study, the overall properties of the composites reached the optimum when adding 2% fruit green.