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Oct  2003

RESIDUAL WOOD RESEARCH

Going after bark board

Research organization Forintek is continuing to work towards the commercial development of what could be a huge residual wood consuming product, bark board.

By Jim Stirling

Bark has been viewed historically as waste material, an expensive disposal problem. But work is ongoing to develop board products manufactured from bark.

Is the commercialization of bark board products nigh? Well, it’s undoubtedly closer than it has ever been in Canada, but a concerted effort is still required to direct the process over the top. It will take a significant infusion of capital and an accompanying commitment to exploiting market potential. But that word—potential—is most emphatically evident from the research and development surrounding one of the more beguiling wood residue products. Bark isn’t fashionable. It’s been historically viewed as a waste, an expensive disposal problem. In latter years, bark has been incorporated into hog fuel heating systems at sawmills and industrial plants, helping pay its way and marginally raising its profile. But undervaluing bark may prove a mistake. Consider what scientists have learned. There’s an enormous amount of the material.

At least 12 million bone dry tonnes of bark residues are produced annually as a byproduct of the Canadian forest products industry. Environmental regulations have outlawed beehive burners in several jurisdictions. In some parts of the country, however, the burners’ drawn-out phase-out program continues to raise the ire of groups concerned about air quality. Similarly, dumping unwanted bark residues in landfills is unacceptable. Simply out of necessity, it makes sense to find alternate uses for bark wastes in higher valued products. Developing board products manufactured from bark was identified as a promising opportunity in the early 1970s. Initial trials produced bark board that lacked durability and dimensional stability.

A key stage in the development process came a couple of years later when higher temperatures were used to manufacture a board product. The higher temperatures trigger a polymerization reaction between the phenols contained in the bark, creating a natural glue and a highly durable bark board panel. (Overall, about 30 per cent of bark reacts as a phenol adhesive.) Forintek Canada Corp has played a leading role in furthering bark board panel research. For about six years, Gary Troughton, senior composites research scientist with Forintek in Vancouver, has been involved with a team building on and modifying previous technology on a laboratory-, and later, a pilot press-scale. The results have been impressive, with Forintek filing patents in Canada and the US for various bark board and bark/hog fuel product manufacturing processes.

There’s no shortage of bark material, with Canadian mills generating an estimated 12 million bone dry tonnes of bark residues annually. Forintek’s Gary Troughton, with a bark board: “Theoretically, we’re looking at a panel product that could compete with OSB.”

Forintek’s research has indicated the mixing of bark species has little effect on bonding strength and dimensional stability properties in bark board. The bending strength can be greatly enhanced when bark board is overlaid with veneer. As an example, the modulus of rupture (MOR) and the modulus of elasticity (MOE) of spruce bark board is in the 1,000 psi and 250,000 psi range respectively. Add a 1/16th inch birch veneer overlay and the MOR and MOE values skyrocket to 7,000 psi and 1,200,000 psi respectively. Preliminary market/economic assessment analysis shows wood delivery costs and adhesives in products like particleboard and medium density fibreboard represent more than 50 per cent of manufacturing costs. Bark board, by comparison, requires no synthetic adhesives or waxes because of the polymerizing phenol factor.

And while bark does come with a cost attached, it is much lower than the 24 to 29 per cent delivered wood costs for the other two products. Bark board stacks up well when compared with the property attributes of other composite panels. Bark board was rated excellent in terms of dimensional stability, decay resistance, termite resistance and VOC and formaldehyde emissions. OSB and plywood could match bark board’s rating in formaldehyde emissions, but along with particleboard and MDF were rated only satisfactory to poor in the other categories quoted. One of Forintek’s more recent patents filed was on the manufacture of bark board incorporating a catalyst.

The addition of the catalyst allows a lowering of pressing temperatures, making the process more practical. Obviously, the catalyst does not compromise the characteristics of the board but it does, notes Troughton, help lower costs through faster pressing times. Troughton has officially retired from Forintek but continues doing consultant work for the research organization and helps mentor younger scientists. He says boards have been made and tested using bark from 10 different species of trees. The bark is typically reduced to about a three per cent moisture content and ground to a four millimetre size. Boards up to 30 by 30 inches have been manufactured in the pilot press process. Using different combinations of white wood with the bark can help produce better bonding strength.

Troughton says he hasn’t sought quantitative information but sees no impediment to using bark from lodgepole pine trees infested by the mountain pine beetle in the manufacture of boardproducts. Forintek’s research suggests the excellent dimensional stability and durability properties of bark/hog fuel boards could find homes in markets for siding, floor underlays (especially where wet), roof shingles and door and window core stock. Bark boards have good decay resistance and are too tough for termites which could open up Pacfic Rim markets. The first commercial bark board product is trickier to determine, says Troughton. “Theoretically, we’re looking at a panel product that could compete with OSB.” But an industrial scale partner is required first to take bark board to the next stage.

Troughton estimates it could cost $50 million to build a new composite bark board plant. That’s a tough call for a single forest company in an economic downturn and the continuing softwood lumber dispute situation. But a bark board consortium of interested companies might prove an economically feasible way of fulfilling the potential of bark board products.

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