# Mechanical Properties and Formaldehyde Release of Particleboard Made with Lignin-Based Adhesives
## 1 Introduction
An approach using mild reaction conditions is the base-catalyzed depolymerization of lignin and the addition of the hydrogen peroxide, considered to be an environmentally friendly oxidant [37]. The contribution of lignocellulosic to the performance of the engineered wood panels is presented in several papers. Calcium lignocellulosiconate [38] magnesium and sodium lignocellulosicates [39], ammonium lignocellulosicate [40; 41; 42] or modified ammonium lignosulfonate [43] were used as adhesives for lowering formaldehyde emission and improve the mechanical properties of the panels. A mixture of phenol formaldehyde adhesives and lignosulfonate (up to 20% of lignosulfonate in the adhesives) was shown to improve the shear strength of wood glued joints gradually [44]. The incorporation of lignosulfonates may replace between 40% and 70% of PF adhesive [33]. Research on phenol replacement by different quantities and types of lignin up to a maximum of 40 wt.% resulted in the best performance for pine kraft lignin with a phenol substitution degree of 20% [45]. The wider industrial application of lignosulfonates in the composition of wood adhesives is limited by the increased hydrophilicity of finished wood-based panels, longer press times and the availability of crosslinkers [46; 47]. Other results indicated that organosolv lignin was a feasible replacement for up to 30% of the phenol in particleboard-type PF adhesives [48]. Recent research works [47; 49] have shown that magnesium lignocellulosicate (15%wt. reported to wood) is a suitable adhesive for obtaining eco-friendly fiberboards with satisfactory mechanical and physical properties. Their remarkably low formaldehyde content (1.1 mg/100 g, super E0 grade) made these panels suitable for interior design. Pressure from environmental and health regulators led to formaldehyde emission requirements becoming more stringent. Thus, super-E0 (\(\leq\)1.5 mg/100 g acc. to Perforator method ENISO 12460-5. or \(\leq\)0.3 mg/L acc. to Desiccator method JIS A 1460) and E0 (\(\leq\)2.5 mg/100 g, or \(\leq\)0.5 mg/L) classes of panels are promoted [50]. Other investigations were conducted with the aim to study lignocellulosic with the addition of cross-linkers. Studies showed improvement of particleboards performance by using ammonium lignosulfonate with polymeric diphenylmethane diisocyanate (PMDI) and furfuryl alcohol as cross-linkers. PMDI is a promising cross-linker that works for most bio-based adhesives [39; 51; 52], due to the reactive isocyanate's groups. Sugars, as cross-linkers, bear both primary and secondary alcohol groups, which theoretically could be used for crosslinking reactions. Other crosslinkers are mentioned in the literature: alternative aldehydes (glyoxal, glutaraldehyde), polyacids (citric acid, maleic anhydride) [52]. The present paper aims to evaluate the mechanical properties and formaldehyde emission of particleboards made with magnesium lignosulfonate-based adhesives. The influence of cross-linkers such as PMDI and glucose on the formaldehyde release and mechanical performance of the panels has been also investigated.