The effect of the beech wood steaming condensate on curing behaviour of urea-formaldehyde adhesive

Abstract

This study explores the potential of using condensate generated during beech wood steaming (BSC) as an eco-friendly additive in urea-formaldehyde (UF) adhesives for wood-based panel (WBP) production. The research aimed to assess the hardening behavior of pure commercial UF resin and UF with added condensate (UF-BSC), investigating the potential catalytic effect of BSC on the hardening characteristics of UF adhesives. Changes in chemical structure after the curing process were observed with Fourier transform infrared spectroscopy (FTIR). The curing kinetics was studied by differential scanning calorimetry (DSC) under a dynamic scanning regime with heating rates of 5, 10, and 20 °C/min. Obtained data were analyzed using Kissinger-Akahira-Sunose (KAS) and Friedman (FR) kinetic iso-conversional methods to estimate the activation energy (E_a) of the curing reaction in the investigated UF adhesive systems. The results of DSC analysis imply that BSC lowers the temperature of the curing reaction of UF adhesive along with the prolongation of the curing reaction. The obtained kinetic data supported by FTIR and chemical analysis suggest that phenolic compounds present in BSC interfere with the main curing reactions leading to lower peak temperatures but higher activation energy. Тhis suggests that BSC increased the number of active sites involved in the reaction and, consequently, the number of collisions. BSC, as wastewater of the wood processing industry, can be efficiently utilized as an environmentally friendly, inexpensive substitute for deionized water in UF adhesive formulations for WBP manufacturing.