Abstract: Lignin concentrate solutions with at least about 40% total solids, having viscosities not higher than 10,000 cps. at 25.degree. C. and comprising normally water-insoluble and phenol-insoluble Kraft lignin dissolved in solvents comprising phenol and water or phenol-water-sodium hydroxide or ammonia are provided. The concentrates contain lignin to phenol weight ratios of less than 70:30 and more than 40:60 and preferably 50:50, and optionally, 2 to 20%, based on the weight of lignin, of sodium hydroxide or ammonia.The concentrates are storable and suitable for shipment and may be employed as phenol extenders in applications normally using phenols. They are particularly tailored for use in replacement of 25% to 100% of the phenol component in the production of phenol/formaldehyde resins and, when so employed, provide phenol-lignin-formaldehyde (PLF) resins that are useful in the formulation of plywood adhesives.

Abstract: Novel lignin-phenol-formaldehyde resins, suitable for use as wood bonding adhesives, are provided by a two-step method which comprises reacting formaldehyde and phenol in the presence of an alkaline catalyst for a period sufficient to produce a partially condensed phenol-formaldehyde resin, thereafter reacting said precondensed resin with sodium hydroxide, formaldehyde and a lignin concentrate having at least 40% solids and comprising lignin dissolved in (a) phenol and water; or (b) phenol, water and sodium hydroxide or ammonia, the lignin to phenol weight ratios in said solution being less than 70:30 and more than 40:60. The second stage of the method is conducted at reflux temperature initially after which reaction is conducted below reflux temperature to control the degree of condensation.