Nanolignin, a Coupling Bio-Agent for Wood-Plastic Composites

Abstract

The influence of nanolignin coupling bio-agent on some characteristics of polypropylene-wood flour composites was studied. Thus, nanolignin was prepared by the acidic method, and then different ratios of it (0, 1, 3 and 5 wt%) were added to a polypropylene-wood flour mixture. After mechanically mixing wood flour, nanolignin, and polypropylene, the mixture was injection molded. ASTM methods were used to measure the structural properties of nanolignin, and prepared composites' water absorption, thickness swelling, bending modulus, and bending, tensile and impact strengths. Transforming the original lignin to nanolignin did not change the chemical bonds of the material. The addition of nanolignin yielded improved mechanical and physical properties of the composites prepared. Higher strength and dimensional stability are presented by nanolignin-containing composites when comparing them with those prepared with normal lignin. Nanolignin was shown by SEM (Scanning Electron Microscope) observation to be uniformly dispersed within the polymer matrix. Wood polymer composites (WPCs) with nanolignin exhibited comparable properties with the control samples prepared using maleic anhydride polypropylene (MAPP).

Maleated nanolignin as a new coupling agent for wood-plastic composites

“…Decreasing water absorption and thickness swelling of the WPCs by addition of nanolignin can be explained by the hydrophobic nature of nanolignin which acts as a water repellent. 8 Moreover, the cracks and voids which formed in the WPCs manufacturing process were filled with nanolignin and resulted in the prevention of the penetration of water into the inner parts of the composites. Figures 6 and 7 also show that modification of nanolignin by maleic anhydride reduced further water absorption of the composites than unmodified nanolignin.…”

“…A comparison between the IR spectra of nanolignin and maleated nanolignin indicated that the intensity of the 1700 cm À1 which is related to the -COOH group increased in the maleated nanolignin, a clear indication of the anhydride ring opening to form maleic acid. 8 The intensity of the 2800 cm À1 band related to the C-O groups and 1200 cm À1 band assigned to the C = C bonds also increase in maleated nanolignin, this again being due to the addition of maleic anhydride. Furthermore, the nanolignin modified with the maleic anhydride showed a smaller peak at 3420 cm À1 (the hydroxyl group) than the virgin nanolignin.…”

“…One of the foremost applications of lignin is to use it as a coupling agent in WPCs. 7,8 However, the previous research has shown that WPCs with lignin as coupling agent had lower mechanical strength than those prepared with MAH-g. The main challenge about the applications of lignin as coupling agent is related to its complicated and changeable macromolecular structure.…”

“…Grafting maleic anhydride to the lignin molecules is one of the best methods to use the advantages of both nanolignin and maleic anhydride. Younesi-Kordkheili 8 showed that maleated lignin improves the properties of the wood-based panels made from thermoset resins. Hence, the aim of the research work presented here is to investigate the performance of maleated nanolignin as a new coupling agent on the properties of WPCs compared to MAH-g as a common coupling agent.…”

“…9 One way to deal with this problem is to convert unordered raw lignin into uniform nanoparticles. Younesi-Kordkheili and Pizzi 8 indicated that WPCs with nanolignin as coupling agent presented comparable physical properties as the control samples prepared using maleic anhydride-polypropylene (MAPP). However, the strength of the composites made from nanolignin was still weaker than those prepared with MAPP as coupling agent.…”