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Modified Buckwheat Husk as a Filler for Urea–Formaldehyde Resin in Plywood Production
The aim of the presented research was to determine the suitability of both non-modified and modified buckwheat husk (BH) as a filler for urea–formaldehyde adhesive in plywood production. The effect of two modification methods, acetylation and silanization, was investigated. Infrared spectroscopy outcomes confirmed that both acetylation and silanization of the filler had occurred. Based on the results, it was found that the introduction of BH had a significant effect on both the adhesive properties and the characteristics of the manufactured plywood. The application of non-modified husks led to a reduction in viscosity and an extension of the gelation time, and the produced plywood boards were characterized by reduced bonding quality and increased delamination. Modification of the husk surface by acetylation and silanization with 3-aminopropyltriethoxysilane contributed to the noticeable improvement in the resin properties. On the other hand, the improvement in plywood properties, consisting of the increase in bonding quality and reduced delamination, was observed only in the case of the silanized husk. Furthermore, the use of non-modified and acetylated husk did not significantly influence the formaldehyde emission. The reduction in the investigated emission of formaldehyde was observed only in the case of variants containing 15 and 20% of silanized buckwheat husk.
Modification of Urea-Formaldehyde Resin with Triethylenetetramine: Effect on Adhesive Properties and Plywood Strength
Due to its multiple amino groups, triethylenetetramine (TETA) can be used as an effective formaldehyde scavenger contributing to the reduction in formaldehyde emission from plywood. This study aimed to evaluate the effect of small TETA loadings on the properties of urea-formaldehyde (UF) resin and the performance of the resulting plywood. Adhesive mixtures containing 0%, 0.5%, 1.0%, and 1.5% TETA were prepared and characterized in terms of pH, viscosity, solids content, and gel time. The incorporation of TETA significantly increased adhesive pH and gel time, while viscosity and solid content were not significantly affected. The analysis of formaldehyde content and spectroscopic and thermogravimetric analyses of the cured adhesives showed reduced formaldehyde content, changes in chemical structure, and enhanced thermal stability at lower temperatures but accelerated degradation at higher temperatures. Formaldehyde emission from plywood was reduced; however, bonding quality and mechanical performance decreased with higher TETA content. Nevertheless, the wet shear strength of all variants exceeded 1 N/mm2. Adhesive formulation containing 0.5% TETA was selected as the optimal variant, providing environmental benefits while maintaining satisfactory plywood performance.