USE OF EUCALYPTUS AND ACACIA-MOLLISSIMA BARK EXTRACT-FORMALDEHYDE ADHESIVES IN PARTICLEBOARD MANUFACTURE

In this work we have studied the possibility of utilization, in adhesives manufacture, of the tannin extracts of E. astringens and E. sideroxylon and those of Acacia decurrens, formerly mollissima, barks issuing from Moroccan afforestation. To overcome the high viscosity and to improve the reactivity of these extracts, treatment with sulfite ions are realized in the current study. Before that, the average molecular weight of acetylated extracts, before and after treatment, were estimated by size exclusion chromatography (SEC) analysis. The reactivity characteristics of these products were determined by differential scanning calorimetry (DSC). The results obtained from tannin-formaldehyde adhesives were compared with those obtained with phenol-formaldehyde (PF) synthetic resin and to values recommended for exterior particleboards by ACNOR standards. The obtained results from this study shows that the sulfonation of these extracts results in a significant reduction of their molecular weight and their viscosity. The enthalpic analysis shows that the glue mixtures based on tannins give almost the same kinetic parameters values, although slightly less performant, than those obtained with PF resin. The results obtained for laboratory boards prepared with mixtures of tannin-formaldehyde show that the obtained values from internal bond tests are above those of Canadian standard but the formulations obtained from Eucalyptus tannins yield an insufficient water resistance. These results are broadly in accord with those stipulated by the ACNOR standard for the particleboards formed with urea-formaldehyde resin, and consequently, these formulations can be used in interior applications, where the water resistance is not specified.