Properties of formaldehyde-free environmentally friendly lignocellulosic composites made from poplar fibres and oxygen-plasma-treated enzymatic hydrolysis lignin

The objective of this paper was to evaluate the properties of formaldehyde-free, environmentally friendly lignocellulosic composites made from poplar fibres and plasma-treated enzymatic hydrolysis lignin (EHL) as a function of plasma processing time and power. The modulus of rupture (MOR), modulus of elasticity (MOE), internal bond strength (IB), and thickness swelling (TS) of the boards were determined. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy were employed to characterise the chemical changes and free radial formation on the surface of oxygen-plasma-treated EHL. The MOR, MOE, and IB of the samples increased with increasing plasma processing time and power, whereas the TS of the boards decreased. A plasma treatment of 200 W for 5 min was sufficient for the use of EHL as a natural binder in the production of high-performance lignocellulosic composites. The bonding improvement was most likely due to the generation of oxygen-related functional groups and the formation of phenoxy radicals on the surface of EHL after the oxygen plasma treatment.