クラフトリグニン樹脂接着剤の製造

Abstract

The preparation of kraft lignin-based wood adhesives with high tensile shear strength and water resistance was investigated. Softwood and hardwood kraft lignins (NKPL and LKPL) were isolated from industrial concentrated waste liquors in yields of 15.8% and 15.0% based on solids, respectively. A mixture of lignin and phenol (85 : 1570 : 30) was hydroxymethylated by reacting with formaldehyde in an alkaline aqueous methanol for 2 hours at 80°C. The reaction products. hydroxymethylated was named a lignin-phenol resin (LP). Walnut powder was added to LP for a lignin-based adhesive (LPA). LPAs produced from NKPL or LKPL containing over 20% of phenol had high dry tensile shear strength bonds when hot-pressed for 615 minutes at 140°C, but their wet strengths after 48-hour boil deteriorated strikingly. Alternative lignin-based adhesives (LPRA) which consisted of 8070% LP, 2030% resorcinol and so forth developed satisfactory bonds in either dry or wet strength when hot-pressed for 615 minutes at only 75100°C. All of 3-ply shinanoki plywoods bonded with LPRAs provided higher wood failure in the wet test than in the dry test. Ether soluble fractions (LP-2) from acidified LP contained hydroxymethylated phenols such as 2, 4, 6-trihydroxymethylphenol, so the resorcinol together with paraformaldehyde was found to be used as crosslinking agents between ether insolubles (LP-1) such as hydroxymethylated lignin-phenol copolymers and LP-2 to form water-insoluble macromolecule for adhesion. LPRA required less energy for bonding and yielded high-quality bonds, indicating that it may be useful as wood adhesives for various kinds of wood products.