effect of application method of wet strength additives on paper properties

in order to simultaneously improve wet and dry strengths of paper and decrease environmental issues related to the wet strength resins, in this study effect of application method of wet strength additives on paper properties was investigated. wet strength resins were applied in four methods including spraying an aqueous glyoxal solution on to the surface of wet paper, addition of aminated polyacrylamide (paa), glyoxylated polyacrylamide (gpam) and polyamide-epichlorohydrin (pae) to the pulp suspension, and spraying of aqueous glyoxal solution on to the surface of wet paper containing paa. the results showed that wet strength of paper increased significantly after glyoxal spraying, which had high correlation with the amount of applied glyoxal. the glyoxal spraying had insignificant effect on the dry strength of paper, however tensile energy absorption (tea) of paper decreased and stiffness of paper with increasing glyoxal spraying. addition of paa to the pulp suspension slightly increased wet strength, while dry strength and tea of paper increased significantly. glyoxal spraying on the wet paper containing paa distinguished as the best method improving paper properties while simultaneously increased wet and dry strengths without increasing effect on the stiffness of paper. by this method, the best results obtained in the paper contained 0.4% paa and 1% glyoxal spraying which was optimum compared to the paper treated commercial gpam and pae resins.