Technological characterisation of second selective thinning wood of Toona ciliata (Meliaceae) – Part II

Abstract

Australian red cedar (Toona ciliata M.Roem.) is a reforestation forest species with significant potential for use in engineered materials within industry. This study aimed to evaluate the wood technological properties after the second selective thinning of an 8-year-old plantation. From 78 harvested trees, a random subset of 10 trees was selected for the fabrication of standardised test specimens. The technological properties evaluated were (1) physical – apparent specific mass at 12% moisture content and shrinkage; (2) mechanical – modulus of elasticity, modulus of rupture, and brittleness; (3) weathering; (4) surface macrostructure – colour; (5) chemical – soluble and insoluble lignins, extractives, holocellulose and ash contents; and (6) thermal – thermogravimetric analysis and calorific value. The apparent specific mass was 370 g m^-3, the calculated shrinkage anisotropy was 2.33% and the swelling anisotropy was 2.42%, which fit the classification ‘excellent quality’. The elasticity modulus was 6 019 MPa and flexural strength was 57 MPa. The mechanical properties other than brittleness were not compromised by weathering exposure. However, accelerated ageing testing as a simulation of natural ageing showed a change in the colour of the wood and an increase in mechanical properties. The calorific value of the wood (4 634.03 kcal kg^-1) was similar to that reported for other fast-growing woods at even more advanced plantation ages. The thermal stability of the wood was comparable to other fast-growing species used for energy purposes, due especially to the high holocellulose content.