Studies on Lignin-Based Adhesives

Paper and Board Industry contributes to both water and air pollution in the form of spent sulfite liquor (SSL) as a waste to water ways and use of Urea formaldehyde (UF) as a glue to air. Reuse of SSL from paper mills if used as such or in combination with UF and phenol formaldehyde (PF) as an adhesive will not only reduce the extent of water and air pollution but will also compete with the high prices of synthetic resin.\ud SSL containing 18% total solid at pH 7.5 collected from the digester of Adamjee Paper Mills Nowshera, NWFP, using sodium based neutral sulfite process of pulping for grassy pulp material, was subjected to various experiments.\ud 1. UV/IR studies of SSL revealed that it belongs to the hardwood lignin family\ud 2. SSL concentrated to 50% total solids and polymerised with Conc. H2SO 4 at PH 2 and 3 was used in different composition (6-12% W/W) as an adhesive for medium density (0.7 g/cm2) particleboard. 8-10% concentration of SSL at PH 3 resulted in particleboard of highest strength, while high water resistant boards were obtained with SSL at PH 2. Poplar and bagasse boards prepared from 10% SSI, at different press times, met the requirements of American Standard (AM. Std CS 236) even at a press time of 8 minutes. The strength property or the SSL bonded poplar board is comparable to the UF bonded poplar board, but its water resistance is comparable only at a press time of 20 minutes. Strength property of the SSL bonded bagasse board is not comparable to that of UP bonded bagasse boards but its water resistance is comparable even at a press time of 12 minutes. The properties of the boards were also compared with UF bonded commercial poplar and bagasse boards and were found to be equally good.\ud 3.Particleboard were prepared from different composition of SSL and UF by using 30 kg/cm2 pressure at 210°C for 16 minutes. Modulus of Rupture showed little change on increasing the concentration of UF in SSL-UF adhesive, while water resistance of boards remained almost the same at and above 30% UF in the adhesive.\ud 4.Particleboard was prepared from 70:30 of SSL to UF pressed at 30 kg/cm2, 210°C for different press time (8 - 16 minutes).Maximum MOR was obtained at a press time of 12 minutes, while Modulus of Elasticity and water resistance of board increased with the increase of press time. 5 Particleboards were prepared from SSL and UF at a fix glue composition 70:30 and pressed at 30 kg/cm2 for 12 minutes at various press temperatures (180-220°C). Board prepared at a press temperature of 2000C was found to be of the highest strength and water resistance.\ud 5.The results obtained from this study were compared with the American Standard CS 236, German Standard DIN 68761 and also with UF board prepared during this study. Commercial UF bonded poplar boards were also tested for comparison purposes. The results are very encouraging.\ud 6.Different resins were prepared by gradual replacement of phenol by lignosulfonate in PF resol type of adhesive. Various physical properties of the resin were measured. The strength of adhesives was evaluated by Glue Block Shear test in two wood species, in both dry and wet states. Maximum shear strength and wood failures was obtained by 20% addition of lignosulfonate to PF adhesive. No significant difference was found in shear strewth and\ud wood failure of the two wood species in two states, indicating that the adhesives obtained are water proof. The results obtained from this study were compared with different commercial glues and were found superior in both states even at an adhesive composition 50:50 of PF to lignosulfonate. The strength of PF lignosulfonate adhesive was also tested by measuring glue failing load and wood failure of plywood in both dry and wet states. No significant difference was observed in glue failing load of dry and wet specimens, which is indicating that the adhesive obtained from various composition of PF and lignosulfonate is water resistant. It has been found that 70% of phenol can be successfully replaced by lignosulfonate. The glue shear load of plywood in both the states met the requirements imposed for Pak. Std. 871, 1970. Wood failure of the plywood was compared with commercial standard CS 35-45 and the results were equally good