Lignin based adhesives for particleboard production

The purpose of this study was to utilise lignin as a partial substitute for phenol in PF \nresins. To achieve this, initially brown rot lignin was produced by a bioconversion \ntechnique. During the course of the study, it became clear that the production of \nbrown rot lignin had a limited success. \nSince brown rot lignin could not be obtained in sufficient quantity and purity by a \nbioconversion method, other alternative lignin production methods, as well as \ncommercially available lignin, were chosen; namely production of lignin from black \nliquor and Alcell® (organosolv) lignin. Before performing production of resin \nformulations, the lignin sources were characterised in terms of reactivity and \nphysical properties of lignins. Both lignins had a similar reactivity, but organosolv \nlignin was found to be more pure, with a low ash content. Since isolation of lignin \nfrom black liquor in laboratory conditions is more complex and requires more time, \nit was decided to use organosolv lignin for subsequent production of lignin-based \nreSIns. \nThe lignin was introduced to the resin in two different ways. The first method was \nthe replacing of a certain percentage of phenol with lignin (as supplied) directly into \nresins. In the second method, lignin was modified prior to resin manufacture by \nphenolation. Different degrees of phenol substitution (from 5% to 60%) were tried \nfor the production of lignin-based resins. \nBond qualities of lignin-phenol-formaldehyde (LPF) , phenolated-ligninformaldehyde, \ncommercial phenol-formaldehyde (PF _com) and laboratory made \nphenol-formaldehyde (PF _made) resins were assessed by using an Automatic \nBonding Evaluation System (ABES), prior to production of particleboards, in order \nto eliminate some of the poor quality resins. The effect of press temperature and time \non bond strength appeared to be highly significant, as the lignin substitution levels \nincreased. Up to 30% phenol substitution was achieved without sacrificing bond \nstrength. The bond strength values of phenolated-lignin-formaldehyde resins were \nsimilar to commercial phenol-formaldehyde and laboratory made phenolformaldehyde \nresins, but better than the LPF resins. It was apparent that resins \ncontaining a high level of lignin substitution gave the poorest bond strength values. \nFrom these results, some of the resins were eliminated, prior to particleboard \nproduction. \nIn order to evaluate the quality of lignin-based resins, particleboards were produced \nand mechanical and physical tests performed. Effect of press platen temperature \n(140°C, 160°C, 180°C) and press cycle time (5 min, 8 min, IS min) on the \nmechanical properties of particleboard, produced by using lignin-based resins, were \ninvestigated. It was found that particleboards bonded with up to 30% lignin content \nresins gave similar mechanical and physical properties to commercial phenolformaldehyde \nresin, as long as a sufficient heating regime and time were applied.