Hydroxymethylated lignin-bonded Douglas-fir flakeboard

A hydroxymethylated lignin (HML) adhesive system is one of several alternative adhesive systems being investigated by the Forest Products Laboratory. Douglas-fir flakeboards bonded with HML were evaluated by measuring modulus of rupture, modulus of elasticity, thickness swell, water absorption, and internal bond strength before and after accelerated aging. The values obtained were compared with those from Douglas-fir flakeboards of similar density bonded with 6 percent (ovendry basis) commercial phenolic resin. The HML-bonded flakeboards compared favorably with flakeboards bonded with the commercial phenolic resin when a mat moisture content (MC) of greater than or equal to 16 percent and a total adhesive content of 12 percent (ovendry basis) were used. The high mat MC of the HML-bonded flakeboards necessitated the use of long press times at a fairly high press temperature to prevent blown boards. Nonetheless, the combination of high mat MC and long press time improved the dimensional stability of the flakeboards. In addition, Fourdrinier screens used as release mechanisms were found to aid in venting steam from the panel surfaces. This resulted in higher core temperatures in the panels during the press cycle. Cost data are unavailable for the HML adhesive system, and therefore an economic comparison between this adhesive and other adhesives cannot be made at this time.

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