Veneer product from fibre-managed plantation hardwood: Final report

Today Tasmania has approximately 235,000 ha of hardwood plantations. The majority of these are Eucalyptus nitens established for their pulpwood properties and not solid timber products. Over one million cubic metres of E. nitens logs were harvested in Tasmania in 2013-14 and this is expected to increase significantly in coming years. Given the size of the estate, there is considerable interest in finding higher-value processing options, which include engineered wood products such as, plywood, laminated veneer lumber and cross laminated timber.

Tasmania’s veneer products processor Ta Ann Tasmania Pty Ltd, and major plantation growing organisation Forico Pty Ltd, wish to examine if economically viable engineered wood products can be made from locally grown plantation hardwoods. Forico manages a significant portion of Tasmania’s plantation hardwood estate and exports both woodchip- and peeler logs harvested from it. However, previous studies and Ta Ann’s initial experience, has shown that there are difficulties in obtaining viable recoveries of veneer when rotary peeling E. nitens logs grown for pulpwood production. With support from a Commonwealth Grant Agreement, Ta Ann sought the assistance of the University of Tasmania’s Centre for Sustainable Architecture with Wood to investigate if plantation grown E. nitens can be utilised to produce a stress-graded formply product.

In the five plantation coupes investigated in this study, average log volume was higher in a midelevation a coupe which received the most intensive thinning and most effective rainfall. Average log volume was lower in the lowest elevation coupe where trees were not thinned or pruned and the logs had poor form and size, but the wood fibre was of a higher density and higher predicted stiffness. Total usable veneer recovered for the target product averaged across the five coupes was 30%, although a further 20-25% of veneer was cut to 6 x 3 ft sheet, which could be utilised in alternative Ta Ann products. In visual grading most of the long-grain veneer was assigned D-grade, which is generally regarded by the industry as being suitable for inner ply material for panels. There were no clear trends of either veneer percentage recovered, or veneer stiffness by position in the 6 m butt-log, however future studies could examine these relationship in logs extracted from different heights in the tree.

Results also showed that a F17 target stress-grade panel product of 83% E. nitens could be produced if long-grain veneer of higher stiffness were segregated by Metriguard machine and then arranged in the panel between native eucalypt faces. These panels were significantly different to panels of 83% E. nitens complied with long-grain veneers of lower predicted stiffness, where many failed to meet the target grade. Stress-grade F17 panels of 43% E. nitens with veneer of lower stiffness were manufactured, but had to use native Tasmanian oak species in the face and sub-face positions to improve panel strength, and achieve the desired grade. The majority of panels in all veneer arrangements tested were limited in stress-grade ratings by the values attained in perpendicular bending strength, which is determined by the properties of the short-grain veneer (veneer arranged perpendicular to a panels longer edge). Unfortunately short-grain veneer could not be assessed and segregated at Ta Ann’s Metriguard, though the veneer could be improved by peeling logs of higher predicted stiffness.

Based on the results from this study and the findings from previous ones it can be concluded that most veneer peeled from fibre managed E. nitens plantations can be utilised in formply panels, and that using selection techniques for log stiffness, it should be possible to peel a larger recovery of veneer for use in higher stress-grade rated panel products.