SIZE-EXCLUSION CHROMATOGRAPHY OF THE SOLUBLE LIGNIN PRODUCTS FROM HYDROGEN-PEROXIDE BRIGHTENING OF MECHANICAL PULPS

The molar mass distributions and yields of soluble lignin degradation products formed during the alkaline hydrogen peroxide brightening of s pruce mechanical pulp have been determined. These distributions depend on pH, the extent to which the pulp was subjected to solvent extracti ons, H2O2 concentration and reaction time. At and below pH 11, there i s an excellent correlation between the brightness and b() values on p ulp and the amounts of residual peroxide and lignin derived products i n solution. Brightening reactions lead primarily to products with inte rmediate molecular mass values between 1500 and 6000. During multistag e brightening, the products formed are initially those with high ioniz able phenolic hydroxyl and low carbohydrate contents, and carbonyl-con taining moieties. NMR and UV spectroscopic analysis show that products formed include lignin and carbohydrate-containing species. The lignin -originating products from the later stages contain a lower relative c oncentration of ionizable phenolic groups and more visible-absorbing a nd carbohydrate-containing species. Brightness and b() gains during m ultistage brightening were exponential with product yield.