Densification of New Zealand-grown Eucalyptus species: Effect of grain orientation and densification process on wood properties

Eucalyptus fastigata and Eucalyptus nitens were densified using a thermo-hydro-mechanical (THM) densification process. The THM treatment was applied either as surface densification of one wood surface or as bulk densification of the entire wood thickness. To understand the effect of grain orientation on final wood properties, both quarter-sawn and flat-sawn boards were densified. The Eucalyptus nitens boards were able to be compressed to a greater degree without being damaged compared to Eucalyptus fastigata boards. This led to substantial increases in surface hardness and surface density in Eucalyptus nitens. Additionally, levels of set-recovery (irreversible swelling from contact with water) for bulk densified Eucalyptus nitens were substantially lower than Eucalyptus fastigata and lower than literature values for other species with a similar density. The reason for this unusually low set-recovery is not known, but it is of potential interest for the commercial application of densified wood, where set-recovery is unacceptable and would need to be eliminated. Density profiles showed that the peak density was generally at, or very close to, the wood surface, giving the maximum increase in surface hardness for a given degree of densification. The properties following densification were not substantially different between the quarter-sawn and flat-sawn boards suggesting that densification was effective irrespective of grain orientation

Wood properties characterisation of thermo-hydro mechanical treated plantation and native tasmanian timber species

Thermo-hydro mechanical (THM) treatments and thermo-treatments are used to improve the properties of wood species and enhance their uses without the application of chemicals. This work investigates and compares the effects of THM treatments on three timber species from Tasmania, Australia; plantation fibre-grown shining gum (Eucalyptus nitens H. Deane and Maiden), plantation saw-log radiata pine (Pinus radiata D. Don) and native-grown saw-log timber of the common name Tasmanian oak (which can be any of E. regnans F. Muell, E. obliqua L’Hér and E. delegatensis L’Hér). Thin lamellae were compressed by means of THM treatment from 8 mm to a target final thickness of 5 mm to investigate the suitability for using THM-treated lamellas in engineered wood products. The springback, mass loss, set-recovery after soaking, dimensional changes, mechanical properties, and Brinell hardness were used to evaluate the effects of the treatment on the properties of the species. The results show a marked increase in density for all three species, with the largest increase presented by E. nitens (+53%) and the smallest by Tasmanian oak (+41%). E. nitens displayed improvements both in stiffness and strength, while stiffness decreased in P. radiata samples and strength in Tasmanian oak samples. E. nitens also displayed the largest improvement in hardness (+94%) with respect to untreated samples. P. radiata presented the largest springback whilst having the least mass loss. E. nitens and Tasmanian oak showed similar dimensional changes, whilst P. radiata timber had the largest thickness swelling and set-recovery due to the high water absorption (99%). This study reported the effects of THM treatments in less-known and commercially important timber species, demonstrating that the wood properties of a fibre-grown timber can be improved through the treatments, potentially increasing the utilisation of E. nitens for structural and higher quality timber applications