Among the most extensively used chemicals in the paper industry are wet strength resins. They enhance the performance of paper products ranging from tissue to board. Environmental concerns are questioning the use of several of these additives and a strong effort is being made to replace these chemicals with benign ones. This paper reports one such study. Highly water soluble polyfunctional carboxylic acids
succinic acid, citric acid, tricarballylic acid, and 1,2,3,4-butanetetracarboxylic acid (BTCA) when applied in a 1% solution to paper, dried, and heated (120 – 150 °C) with a catalyst develop wet strength as high as 55%. The effectiveness of these acids is in the ordertetrafunctionat>trifunctional >difunctional. This sequence is a reflection of their ability to form multiple anhydrides. Additional experiments indicate that the wet strength is the result of crosslinking of the hydroxyl groups in cellulose. The wet reinforced papers are easily dispersed under alkaline conditions. The crosslinking of the papers results in an increased dimensional stability.
Most wet strength chemicals are added at the wet-end where they are substantively adsorbed on the pulp and cured during the drying process. In contrast, the chemicals used in this study are water soluble and therefore are applied to the paper by a saturation technique. Additional research will focus on the optimization of their delivery.