Comparison between the performance of nanolignin and modified lignin with ionic liquid as a compatibilizer in wood-plastic composites

The aim of this study was to compare nanolignin and ionic liquid (IL)-treated lignin as new compatibilizers in Wood-Plastic Composites (WPC). For this purpose, lignin was extracted from black liquor and modified with [Emim][OAc]. Then, the modified lignin was used as a compatibilizer in the WPC.  Nanolignin was prepared by an acidic method, and its performance was compared to that of ionic-liquid-treated lignin as a compatibilizer in the composites. Nanolignin and ionic liquid-modified lignin at the same levels (1, 3, and 5 wt%) were added to the wood flour and polypropylene mixture, and WPCs were manufactured using the hot press method. In the next step, all physical and mechanical properties of the prepared panels were analyzed using standard methods. FTIR analysis indicated that modification of lignin by an ionic liquid can change some chemical bonds and even produce new bonds.  However, the chemical structures of the virgin lignin and nanolignin were similar. The physical and mechanical properties of the prepared composites indicated that the addition of both forms of lignin significantly increased the dimensional stability, bending properties (flexural modulus and flexural strength), and impact strength of the composites. Based on the findings of this research, IL-treated lignin exhibited better physical and mechanical results as a coupling agent in wood plastic composites compared to nanolignin; thus, the composites with 5 wt% have the highest mechanical strength and dimensional stability among all lignin-containing samples.