Propolis extract as a bio-based modifier of urea-formaldehyde adhesive in particleboard production

The presented research concerned the use of propolis extract as a modifier of urea-formaldehyde (UF) adhesive for the production of particleboard. The adhesive formulations differed in both the modifier content (1, 3 and 5%) and the extract concentration (50 and 70%). The results of differential scanning calorimetry, rheometric analysis of the cross-linking process and thermogravimetric analysis showed an acceleration of the curing process, a slight increase in viscosity and a decrease in the thermal stability of the cured adhesive mixtures. Moreover, the Fourier transform infrared spectroscopy analysis of the cured adhesives showed a reduction in the intensity of the peaks characteristic of the UF adhesive due to the applied modification. Furthermore, particleboards bonded with the mixtures containing 3 and 5% of 70% extract and 5% of 50% extract were characterized by significantly improved strength properties (bending strength, modulus of elasticity, internal bond), better water resistance (thickness swelling, water absorption) and reduced formaldehyde content. The adhesive mixture modified with 5% of 70% propolis extract was considered the optimal variant providing the most significant improvement in the properties of produced particleboards.