The suitability of five Western Australian mallee eucalypt species for wood-cement composites

Abstract

There are currently around 10 000 ha of mallee eucalypt plantations in Western Australia that have been established primarily for the production of eucalypt leaf oils. Planting rates are projected to increase dramatically in future. The financial viability of these plantations is dependent upon finding a commercial outlet for the small diameter wood and bark residues, which may constitute up to half of the harvested material. The potential for such residues to be utilised in cement-bonded wood composite panels was investigated here. The woody residues of five species of mallee eucalypts, as expected, inhibited the hydration reaction of Portland cement, but not to such an extent as to make the wood unsuitable for cement composites. The bark of one of the species, E. loxophleba ssp. lissophloia, inhibited the setting of Portland cement to such an extent that the residue of this species (with bark present) was unsuitable for use in wood-cement composites. Three out of the five mallee eucalypt species retained relatively good compatibility with cement even when bark was present in the residues. The flexural properties (MOR and MOE) of cement-bonded panels manufactured from chipped mallee eucalypt residues were low in comparison to similar boards made from radiata pine, probably because of the smaller particle size and lower aspect ratio of the eucalypt wood residues. Boards made from E. polybractea, E. horistes and E. kochii ssp. plenissima were stronger and more resistant to water than those made from E. angustissima and E. loxophleba ssp. lissophloia. On the basis of our findings, opportunities and challenges for the commercial utilisation of mallee eucalypt wood for wood-cement composites are discussed.