Thermomechanical analysis of the tannins of Acacia Nilotica spp. Nilotica as a rapid tool for the evaluation of wood-based adhesives

In this article, autocondensation reactions of Acacia nilotica spp. nilotica (Ann) tannin extracts solutions have been studied at several pH values by thermomechanical analyzer (TMA). TMA has been chosen for this study as it has been shown to give results more rapidly and more precisely than panels. It also tends to exaggerate the differences in results which render it an excellent tool for comparison. Therefore, autocondensation reactions were studied and compared with its polycondensation reactions upon addition of different hardeners such as paraformaldehyde, urea, and PMDI at same pH values. The aim was to evaluate the tannin's reactivity and therefore its suitability for the production of commercially and technically viable tannin adhesives for wood products. The results of autocondensation showed that the maximum Young's modulus values (3300 and 3600 MPa) were obtained at pH 4. However, these values have been achieved at high temperature (160 and 208 A degrees C). Results of copolymerization reaction of the tannins with different hardeners revealed that some of these co-reactants were found to depress tannins autocondensations, while others appear to enhance the formation of the final networking. Polycondensation of the Ann tannins with 8% paraformaldehyde and 10% PMDI gave the maximum Young's modulus values at lower temperature (91-101 A degrees C) and acidic pH5. However, the addition of 20 and 30% PMDI achieved the best Young's modulus values 2300 and 3300 MPa, respectively, at pH 4. Furthermore, the obtained values were comparable to those obtained by the addition of urea and the self condensation reactions. This is very important for particleboard production from economical and technical point of view. It has been noticed that the addition of hardeners lowered the temperature of hardening, and the obtained values were more consistent with the pH acidity. The study concluded that the tannins of Ann were very reactive, and therefore, it could be a potential precursor for particleboard adhesives. The results also indicated that the tannins can be used alone, and it would possibly produce zero emission environmentally friendly particleboard.