Organic Acid Lignin From Rice Straw in Phenol-Formaldehyde Resin Preparation for Plywood

Acetic acid/formic acid/water (AA/FA/H 2 O, 50/40/10 ratio) was used to fractionate rice straw into lignin, hemicellulosic sugars, silica and dissolving pulp. In this paper, lignin separated from rice straw was utilized in the preparation of lignin-phenol-formaldehyde resins. AA/FA/H 2 O lignin was characterized as having lower molecular weight (M w ), lower methoxyl group and higher phenolic hydroxyl group, which increased its reactivity. The methoxyl group per C 9 unit was 0.87 and 0.75 for the rice straw lignin and the AA/FA/H 2 O spent liquor lignin, respectively. AA/FA/H 2 O lignin-phenol-formaldehyde (LPF) resins were produced in one-step preparation, with different content of lignin. The formaldehyde/phenol mole ratio (F/P) was 2.0 and the NaOH/phenol mole ratios (S/P) were between 0.3 and 0.5. The percentage of substitution of phenol by lignin was between 40 and 60%. The shear strength of plywood was tested, and the plywood bonded with LPF resin showed comparable results to those of the phenol-formaldehyde bonded plywood. The results indicated that the substitution of 50% phenol by AA/FA/H 2 O lignin is feasible in the preparation of phenol-formaldehyde resin.