November 2002 - Logging and Sawmilling Journal -

A new wood preservation method now under development could open the door for additional sales for treated wood.

A new wood treatment process—using carbon dioxide to introduce preservative into the structure of wood—could make better treatment feasible for difficult softwoods and hardwoods.

Canada’s pressure treated lumber manufacturing industry generates annual sales of around $500 million. But that figure could grow significantly if tough-to-treat wood species and products could be successfully treated, adding further to sales. The prospect is closer in light of promising research that could make better preservative treatment feasible for difficult softwoods, hardwoods and composite products like medium density fibreboard and laminated veneer lumber.

Research into the new preservation treatment method is being spearheaded by CSIRO Forestry and Forest Products. CSIRO—the Commonwealth Scientific and Industrial Research Organization—is Australia’s major provider of research and development for the forest, wood and paper industries. The organization’s focus and emphasis are on boosting the market success of wood products. It achieves that through collaboration with the global forest industry to meet demands of existing markets and in developing new markets.

Partners and interest in the new treatment process are located in the United States and Europe, and Canadian participation is encouraged. “We are in the process of forming a consortium with industries for further research towards commercialization of the project,” explains CSIRO’s Dr Abdul Qader. The new treatment technique uses a different medium or vehicle to introduce preservative into the structure of wood products.

It employs super-critical carbon dioxide instead of conventional dipping and pressurized treatment procedures using preservatives dissolved in water or oil. Gases become super-critical when subjected to pressures and temperatures beyond a critical point. In carbon dioxide’s case, that’s above 72.9 atmospheres and 31.1 degrees Celsius.

In a super-critical state, carbon dioxide assumes a liquid’s ability to dissolve compounds, while retaining the penetration properties of gas. After the treatment and falling from the super-critical state, the carbon dioxide conveniently reverts to a gas and dissipates, leaving the preservative deep within the wood. The result is a superior preservative penetration and retention in more wood types than conventional treatment methods, according to Qader’s research. His team began small scale testing using super-critical carbon dioxide on samples of Douglas fir, pine, LVL, MDF and species of eucalyptus hardwoods.

The research has subsequently expanded to larger samples of wood and wood products. A preliminary downside of this research looks to be its cost. Qader estimates the capital costs of treatment centres using the super-critical method’s high pressures and temperatures to be “considerably higher” than for conventional processes. But on the positive side, operating and maintenance costs would be lower. Also, there’s no need for stickering, drying or stock holding after treatment and no polluting VOC emissions.

And importantly, says Qader, the problems associated with residual solvent in wood treated using solvent-based techniques are eliminated. Products likely to prove themselves prime candidates for super-critical carbon dioxide treatment include window and home frames, decking, flooring and particleboard. Qader says the confidential nature of the research precludes releasing more details at this time. However, he adds, they are in the process of accepting more partners from interested research and industrial organizations. Qader can be contacted at [email protected]

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