PREPARATION OF MODERATE-TEMPERATURE SETTING ADHESIVES FROM SOFTWOOD KRAFT LIGNIN .2. EFFECT OF SOME FACTORS ON STRENGTH PROPERTIES AND CHARACTERISTICS OF LIGNIN-BASED ADHESIVES

The preparation of moderate-setting lignin adhesives was investigated. Softwood kraft lignin (NKL) was isolated from a commercial concentrated kraft pulping waste liquor. A mixture of NKL and phenol reacted with formaldehyde under alkaline conditions at 80-degrees-C for 2 hours. To the resulting LP-resin solution were added small amounts of resorcinol and paraformaldehyde for the adhesives. Three-ply plywoods using the adhesives were prepared by pressing at 10 kg/cm2 and 100-degrees-C for 10-15 minutes, and their dry and wet tensile shear strenghts were tested. A satisfactory adhesives consisted of the following weight quantities: NKL 80, phenol 20, 37% formalin 75, methanol 20, NaOH 8, water 55, resorcinol 20 and paraformaldehyde 4. The analytical results of LP-resins showed that acetates of LP-resins were composed of ether insolubles (EI) and solubles (ES). The former was a reactive coplymer of NKL and phenol with M(n) of 4,000-6,000.