Glyoxalated polyacrylamide resins

These products are prepared by crosslinidng a low molecular weight polyacrylamide (PAM) with glyoxal. The PAM is normally a copolymer of acrylamide and a quaternary ammonium cationic monomer which is prepared in aqueous solution. This results in a cationic polymer which is attached to pulp fibers. The cationic backbone is then crosslinked with sufficient glyoxal to react with most, but not all, of the PAM backbone amide groups. On storage, the resin continues to crosslink and can ultimately gel. In order to achieve the desired stability, paper mills dilute the resin on receipt. At 25 °C, a 10% solution will gel in about 8 days, whereas a 6% solution will take about 65 days to gel at room temperature. 

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Farley, C.E. (1988), Glyoxalated polyacrylamide wet strength resin, Tappi Wet rmd Dry Strength Short Course Proceedings. 

Water molecules are so small and cellulose and so hydrophilic that this solution usually affords only temporary protection. Formaldehyde, glyoxal, polyethylen-imine, and, more recently, derivatized starch (50) and derivatized cationic polyacrylamide resins (51) have been used to provide temporary wet strength. The first two materials must be applied to the formed paper, but the other materials are substantive to the fiber and may be used as wet-end additives. Carboxymethylcellulose-calcium chloride and locust-bean gum-borax are examples of two-component systems applied separately to paper that were used to a limited extent before the advent of the amino resins. Today three major types of wet-strength resins are used in papermaking polyamide-polyamine resins cross-linked with epichlorohydrin (52) are used in neutral to alkaline papers cationic polyacrylamide resins cross-linked with glyoxal are used for acid to neutral papers and melamine-formaldehyde resins are used for acid papers. 

Some commercial low molecular weight polyacrylamides (LMPAM) are manufactured in solution and sold at 10-50% solids. For example, LMPAM containing DADMAC comonomer is made at 40% solids and can be reacted with glyoxal to produce a strengthening resin for paper. Furthermore, LMPAM hydrolyzed with sodium hydroxide to polyacrylate is manufactured at 30% solids and is used as an antisealant. High molecular weight poly(acrylamide) is also prepared in solution at 2-6 wt% solids and is often further modified using, for example, the Mannich reaction. 

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