Preparation and characterization of crosslinked glyoxalated polyacrylamide paper‐strengthening agent

To obtain additives that could simultaneously increase the dry strength and wet strength of paper sheets, we synthesized a series of crosslinked cationic glyoxalated polyacrylamide (GPAM) resins by using acrylamide (AM), 2‐methacryloxyethyl trimethyl ammonium chloride (DMC), N‐methylolacrylamide (NMA), 2‐mercaptoethanol, and glyoxal as the main materials. GPAM demonstrated excellent properties and had a good strengthening ability under the following polymerization conditions: dosage of AM = 55 wt %, dosage of the cationic monomer DMC = 5.5 wt %, dosage of the crosslinking monomer NMA = 8.0 wt %, dosage of chain‐transfer agent 2‐mercaptoethanol = 1.0 wt %, dosage of glyoxal = 30 wt %, and charge of the initiator (ammonium persulfate/sodium bisulfite = 1 : 2) = 0.5 wt %. The products were characterized by Fourier transform infrared spectroscopy, 1H‐NMR, size exclusion chromatography, and Ubbelohde viscometry. The copolymers with a viscosity‐average molecular weight of approximately 26,000 and a polydispersity index of 1.460 had a much better strengthening ability. When these GPAM resins were used as paper‐strengthening agents, the mechanical strength of the paper was remarkably enhanced, and the dry and wet tensile indices of the handsheets increased by 24.6 and 381%, respectively, compared with those of handsheets without GPAM.