Furfural-based phenolic resins for plywood panels: From basic concepts to upscale production

In this work, the use of furfural, a bio-based platform chemical, was investigated as a sustainable alternative to petrochemical formaldehyde in Phenol Formaldehyde (PF) resins, which are used in the manufacturing of wood-based products such as plywood. The catalytic condensation of phenol with furfural was studied at various temperatures (45–135^oC) to determine the reactivity of furfural towards formation of the respective dimers and oligomers. A pretreatment was applied to partially convert furfural to furfuryl alcohol which facilitated the condensation of phenol with furfural, at temperatures >90^oC. PF-Furfural (PFFu) resins were prepared at semi-pilot scale (2–3 Kg) following typical industrial protocols aiming at the gradual replacement (20–80 wt%) of formaldehyde. The properties of the PFFu resins were characterized by various methods (solids, pH, viscosity etc.) and ¹³C NMR analysis. The PFFu resins with up to 60 wt% replacement of formaldehyde by furfural exhibited typical properties for such PF-type resins; however, viscosity and gel time were gradually decreased and increased, respectively, indicating the relatively reduced reactivity of furfural at the applied synthesis conditions (i.e. 90-100^oC) compared to formaldehyde. Plywood panels prepared with PFFu resins, demonstrated enhanced mechanical performance compared to the reference PF resin — such as improved shear strength (>1.5 N/mm²) and wood failure (≥85 %) thereby meeting the requirements of the European standard EN314–2:1993. Furthermore, all panels prepared with furfural-containing resins exhibited significantly lower free formaldehyde emission (0.01–0.18 mg/m²h) compared to the reference panels (0.20 mg/m²h). The results highlight the possibility of formaldehyde replacement by furfural in the production of sustainable plywood products.