Finnish Plywood Particleboard, and Fiberboard with a Lignin-Base Adhesive

A lignin-base adhesive has been developed at the Finnish Pulp and Paper Research Institute for the plywood, particleboard, and fiberboard industry. In this adhesive, high-molecular-weight lignin derivatives are isolated from spent sulfite liquor or liquors from alkaline pulping processes by ultrafiltration, and are copolymerized during the hot-pressing stage with phenol-formaldehyde resin; this yields a strong and water-resistant glueline. The adhesive contains 40 to 70 percent lignin, dependent upon the type of application. This implies a substantial reduction in adhesive costs, as lignin is much cheaper than phenol-formaldehyde resin. Full-scale plywood mill tests, same of them running continuously for several weeks, have been performed with this adhesive. The properties of the plywood meet the requirements imposed for exterior-grade plywood. In the gluing of Douglas-fir plywood with this adhesive, wood failures have exceeded 85 percent after both vacuum and boiling tests. Weather-resistant particleboards have been manufactured, using high-frequency or combined high-frequency-contact heating, with pressing times of 10 to 12 seconds per millimeter. Fiberboards have been made in a mill scale test, utilizing alkali lignin and phenol-formaldehyde resin in a proportion of 50:50. On comparison of the properties of the boards with other boards made with ordinary commercial phenol-formaldehyde resin, they were found to be equally good.

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