Process for preparation of lignin resin

#During sulfite cooking about half of the solid wood substance (on the average) is chemically transformed by sulfonation, hydrolysis and oxidation to water soluble products, which are contained in the waste liquor. More than half of this dissolved organic wood substance is made up of lignin in the form of lignosulfonates. The lignin present in the waste liquors is therefore not the original lignin of the wood but a lignin derivative having properties which require a further chemical transformation in order to be useful.

#Lignin, like phenol, easily form condensation products with carbonyl compounds such as formaldehyde. Unlike the phenols, the lignin, on account of its high degree of polymerization, contains fewer phenolic hydroxyl-groups and thereby fewer active sites on the aromatic ring for linking with e.g. formaldehyde. If unmodified lignosulfonate is condensed with formaldehyde a three-dimensional network (a resin) will certainly be obtained but it will have a limited number of linking points and therefore will be more brittle and weaker than a phenol formaldehyde resin. Furthermore, sulfonic acid groups will enhance the water swellability of the network, which means an impairment of the water resistance of the bonded product.

#There have been a number of efforts by prior art workers to improve the properties of condensation products of formaldehyde and lignosulfonates. The object of our invention is to provide an improved process over what has gone before.

#Seven resins were prepared with varying compositions and under varying condensation conditions. The variables involved in the seven examples are indicated with X.sub.1, X.sub.2 . . . , X.sub.n, which are listed in table 1 and explained below.

#To a reactor were first charged X.sub.5 parts of water, X.sub.3 parts of formaldehyde in the form of a 37 percent aqueous solution (formalin) and X.sub.1 parts of phenol. The mixture was vigorously agitated and X.sub.2 parts of spray-dried fermented sulfite waste liquor were charged in portions. The powder of sulfite liquor with the trade name "Pellbond F" contained 70 percent of calcium lignosulfonate and 10 percent of sugar, the rest being low molecular calcium salts.

#The mixture was agitated until all of the "Pellbond F" was dissolved. X.sub.4 parts of concentrated sulfuric acid were then added.