Characteristics of beech bark and its effect on properties of UF adhesive and on bonding strength and formaldehyde emission of plywood panels

This research examined beech bark from a plywood manufacturer to determine its effectiveness in reducing wastes, protecting the ecological environment, and producing more eco-friendly wood-based materials. Beech bark was characterized and evaluated as an adhesive filler in plywood manufacturing, and the effects on the bonding quality and the formaldehyde emission of the plywood panels were examined. Plywood panels were made of formulations with urea-formaldehyde (UF) resin filled with three different concentrations of bark flour (BF): 1 wt%, 3 wt%, and 5 wt%. Compared with solid beech wood, beech bark has a higher lignin and extractives content and lower holocellulose content. It was confirmed that the bark absorbs formaldehyde and the solution with 5 wt% of bark absorbed the most formaldehyde. Panels with UF/BF formulations at a bark content of 1 wt%, 3 wt%, and 5 wt% had higher wet bonding strengths than those made with the control sample. The most significant reduction in formaldehyde emission (up to 42.3%) of plywood panels and the achievement of high bonding strength was observed for UF/BF samples with a bark concentration of 5 wt%. The bonding strength of plywood panels with all investigated BF concentrations met the requirements of the EN 314-2 standard.