Oxygen plasma-treated enzymatic hydrolysis lignin as a natural binder for manufacturing biocomposites

This paper describes the investigation of the oxygen plasma treatment of enzymatic hydrolysis lignin (EHL) that was obtained from the lignocellulosic ethanol production processes. The application of EHL as a natural binder for biocomposite product manufacturing was in focus. To understand the effects of oxygen plasma treatment, the chemical changes on the surface of EHL were evaluated by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR) spectroscopy. Adding EHL into the cotton-stalk fiberboards has a beneficial effect on physical and mechanical properties. Moreover, adding oxygen plasma-treated EHL produced a 69.2% increase of internal bond strength (IB), a 78.2% increase of modulus of rupture (MOR), and a 49.8% reduction of thickness swelling (TS). The bonding improvement was probably due to the generation of more oxygen-related functional groups and free radicals on the surface of EHL after the oxygen plasma treatment.