Method for on-site glyoxylation of polyacrylamide

A method for on-site glyoxylation of polyacrylamide in a paper mill or board mill, 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 for use in a manufacturing process of paper or board, the method comprising:

• forming or obtaining the aqueous reaction mixture comprising polyacrylamide base polymer and glyoxal, wherein the polyacrylamide base polymer has a weight average molecular weight in a range of 50 000-300 000 g/mol;
• determining alkali consumption of the reaction mixture;
• adding to the reaction mixture, on the basis of the determined alkali consumption, a pre-determined amount of alkali which is needed for adjusting the reaction mixture's pH value within a range of 8-10;
• optionally adjusting the aqueous reaction mixture's temperature to a temperature range of 15-40° C.;
• allowing the on-site glyoxylation reaction of polyacrylamide base polymer in the reaction mixture to proceed;
• measuring viscosity of the reaction mixture and/or a process variable that is related to the viscosity of the reaction mixture;
• adding acid to the reaction mixture for lowering the pH value of the reaction mixture <8, when a predetermined end viscosity value is attained;
• and
• removing the aqueous polymer composition comprising glyoxylated polyacrylamide from the reaction vessel.