Reaction of Wood with Cyclic Anhydrides

The production of moisture resistant particleboard by treatment with a maleic anhydride -glycerol mixture and using phenol formaldehyde as the matrix material has been investigated (Fujimoto etal., 1987). Boards prepared from modified wood showed considerable improvements in modulus of elasticity and internal bond strength when compared to control boards. Composites made from aspen fibres modified with SA, MA or acetic anhydride using phenol-formaldehyde (PF) or polypropylene as binder have also been studied (Clemons etal., 1992 Rowell etal., 1993b). The reaction of wood with MA was found to proceed at a slower rate than with SA. The volume increase due to modification 

The stress relaxation properties of SA-modified wood in media of different pH have also been studied (Nakano etal., 1990a,b, 1991 Nakano, 1993a,b). It was found that an increase in pH led to an increase in stress relaxation properties due to side chain ionization, with maximum swelling of the wood occurring between pH 5-8. In addition, cross-linking within the wood was achieved by treatment with bivalent or trivalent metal ions. The rheological properties of maleic acid esterified wood also show that thermoplasticity is imparted to the wood by such modification (Norimoto etal, 1992). 

The use of maleic anhydride as a compatiblizer between wood particles and bisphenol A-based polyesters resins has been investigated (Han etal., 1991). In this study, the MA was added directly to the composition of woody matrix filler and resin rather than by pre-modification of the wood. It was found that composite properties were improved by addition of MA, probably due to esterification of the wood occurring during the kneading process. The modification of sawdust using maleic anhydride has been performed in order to provide a compatible filler for polyester resins (Marcovich etal., 1996). Modification was performed at room temperature using a solution of maleic anhydride in acetone, in some cases catalysed with sulphuric acid. It was claimed that bonding occurred under these mild conditions from IR spectroscopic evidence only. 

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Reactions of wood with cyclic anhydrides do not yield a by-product, leaving the modified wood polymers with a covalently bonded carboxylic group an example is reaction with succinic anhydride (SA) (Figure4.1a). With reactions above 100°C there is some formation of diester observed (Figure 4.1b), resulting in cross-linking within the cell wall matrix (Matsuda, 1987). 

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