Preparation and Evaluation of Rice Bran-Modified Urea Formaldehyde as Environmental Friendly Wood Adhesive

In this study, defatted rice bran (RB) is used to prepare an environmentally friendly adhesive through chemical modifications. The RB is mixed with distilled water with ratios of 1:5 and 1:4 to prepare Type A and Type B adhesives, respectively having pH of 6, 8 and 10. Type A adhesive is prepared by treating RB with 1% potassium permanganate and 4% poly(vinyl alcohol), whereas Type B is formulated by adding 17.3% formaldehyde and 5.7% urea to RB. Viscosity, gel time, solid content, shear strength, Fourier transform infrared (FTIR) spectroscopy is carried out, and glass transition temperature (T-g), and activation energy (E-a) are determined to evaluate the performance of the adhesives. E-a data reveal that adhesives prepared at mild alkaline (pH 8) form long-chain polymers. Gel time is higher in the fabricated adhesives than that of the commercial urea formaldehyde (UF). FTIR data suggest that functional groups of the raw RB are chemically modified, which enhances the bondability of the adhesives. Shear strength data indicates that bonding strength increases with increasing pH. Similar results are also observed for physical and mechanical properties of fabricated particleboards with the adhesives. The results demonstrate that RB-based adhesives can be used as a potential alternative to currently used UF-based resin

Efeito da variação do ph e da temperatura de síntese no desempenho de adesivos à base de creosoto vegetal desmetilado-formaldeído Effect ph variation and synthesis temperature on the performance of thermosetting adhesive formulations based on demethylated wood creosote-formaldehyde

O objetivo deste trabalho foi a produção de adesivos para madeira a partir de creosoto desmetilado. Para isto, foram sintetizadas diferentes formulações de adesivos para madeira a partir de creosoto desmetilado e paraformaldeído, variando-se o pH inicial da formulação (12,00, 12,25, 12,50, 12,75, 13,00, 13,25 e 13,50) e a temperatura de síntese (60 e 70 °C), para possibilitar a verificação dos melhores pHs e da melhor temperatura para elaboração do adesivo. Foi verificado, por meio da avaliação do gel time, que a melhor temperatura de síntese foi 70 °C. Foram realizadas, então, análises por DSC (calorimetria diferencial exploratória), para obtenção dos parâmetros cinéticos e caracterização das formulações adesivas de creosoto desmetilado sintetizadas a 70 °C. Os adesivos foram utilizados para colagem, a quente (160 °C) e sob pressão (12 kgf/cm²), de lâminas de Araucaria angustifolia. Após a colagem, foram realizados os ensaios de resistência mecânica ao cisalhamento por tração, para condição seca e úmida. Verificou-se que a resistência da linha de cola e a porcentagem de falha na madeira para os adesivos de creosoto desmetilado sintetizados a 70 °C foram inferiores às do adesivo de fenol-formaldeído sintetizado em laboratório, que foi utilizado como padrão.<br>The objective of this work was the production of adhesives based on demethylated creosote for bonding of wood. Different formulations of demethylated wood bcreosote/formaldehyde were evaluated aiming at improving their bonding properties. The initial pH value and the synthesis temperature were varied in order to obtain the best values for producing the adhesives. Thus, seven pH values (12.00, 12.25, 12.50, 12.75, 13.00, 13.25, and 13.50) and two different temperatures (60 °C and 70 °C) were applied. It was observed by gel time evaluation that the best synthesis temperature was 70 °C. The kinetic parameters were obtained through DSC analysis (differential scanning calorimetry) to characterize the demethylated creosote adhesive formulations synthesized at 70 °C. The adhesives were used for hot bonding (160 °C) and under pressure (12 kgf/cm²) on Araucaria angustifolia sheets. After bonding, mechanical resistance tests were carried out under both dry and wet conditions. It was verified that shear strength and wood failure under dry and wet conditions for demethilated wood creosote-based adhesives synthesized at 70 °C were lower than for laboratory-synthesized phenol-formaldehyde adhesive, used as standard