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Lignin, a byproduct from the chemical processing of lignocellulosic biomass, is a polyphenolic compound that has potential as a partial phenol substitute in phenolic adhesive formulations. In this study, HBr and HI were used as reagents to demethylate an alkali lignin (AL) to increase its hydroxyl content and thereby enhance its reactivity for the preparation of phenolic resins. Analyses by FT-IR, 1H-NMR and 2D-NMR(HSQC) demonstrated both a decrease in methoxyl groups and an increase in hydroxyl groups for each demethylated lignin (DL). In addition, the molar amounts of phenolic hydroxyls, determined by 1H-NMR, increased to 0.67 mmol/g for the HI-DL, and 0.64 mmol/g for the HBr-DL, from 0.52 mmol/g for the AL. These results showed that HI, a stronger nucleophilic reagent than HBr, provided a higher degree of AL demethylation. Lignin-containing resins, prepared by copolymerization, met the bonding strength standard for exterior plywood with DL used to replace as much as 50 wt.% of phenol. The increased hydroxyl contents resulting from the lignin demethylations also imparted faster cure times for the lignin-containing resins and lower formaldehyde emissions. Altogether, the stronger nucleophilicity of HI, compared to HBr, impacted the degree of lignin demethylation, and carried through to measurable differences the thermal properties and performance of the lignin-containing PF resins.

Resin acids in the diethyl ether extracts of Picea glauca, Pinus ponderosa and Pinus banksiana seed cones were identified by gas-liquid chromatography of their methyl-ester derivatives. For these seed cones, abietic, dehydroabietic and isopimaric acids comprised 63.7-80.5% of the total resin acids identified. In P. banksiana, the resin acid composition of the seed cones was shown to be significantly different from that in either the leaves, bark or wood. Investigation of the role of resin acids in the apparent decay resistance of woody conifer tissues to white-rot fungi involved the incorporation of abietic, dehydroabietic and isopimaric acids individually, or äs a l: l: l mixture, into decay susceptible sweetgum (Liquidambar styraciflua) wood lest blocks which were subsequently exposed to cultures of Irpex lacteus and Trametes versicolor. Inhibition of decay by /. lacteus was observed for test blocks treated with abietic and dehydroabietic acids, but not isopimaric acid. With T. versicolor, only those test blocks treated with abietic acid showed less decay when compared with controls. Comparisons of the decay levels with the moisture contents of resin acid treated test blocks, and the analyses of residual resin acid contents of decayed blocks, indicate that resin acids provide decay resistance by their water repellency and inherent decay resistance rather than general toxicity.Holzforschung / Vol. 48 / 1994 / No. 4

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