METHOD FOR ON-SITE GLYOXYLATION OF POLYACRYLAMIDE

The present invention relates to a method for on-site glyoxylation of polyacrylamide in a paper mill, board mill or the like, where a discontinuous batch glyoxylation reaction of an aqueous reaction mixture is performed in a reactor vessel provided with a driven agitator to form an aqueous polymer composition comprising glyoxylated polyacrylamide. The method comprises forming or obtaining the aqueous reaction mixture having a start viscosity and comprising polyacrylamide base polymer having a weight average molecular weight of 30 000 - 300 000 g/mol and glyoxal. The concentration of the polyacrylamide base polymer in the reaction mixture is 1.5 - 8% above a Critical Concentration of the polyacrylamide base polymer. A feed of an alkali is added to the reaction mixture while measuring viscosity of the reaction mixture and/or a process variable that is related to the viscosity of the reaction mixture and the on-site glyoxylation reaction of polyacrylamide base polymer in the reaction mixture is allowed to proceed. When a predetermined end viscosity value is attained the feed of alkali is ended and acid is added to the reaction mixture. The aqueous polymer composition comprising glyoxylated polyacrylamide is removed from the reaction vessel.