In situ Grafting of Chitosan onto Cellulosic Fibers Using Maleic Anhydride for Paper Wet Strength Improvement

The wet strength of paper is an important property in its various applications. In this paper, chitosan was employed as an additive to improve the wet strength of paper using a dipping process, and maleic anhydride (MA) was used to improve the retention of chitosan. The underlying mechanism was the bridging effect of MA, via the formation of esters between MA and cellulose and amides between MA and chitosan, both of which were supported by the FT-IR results. The temporary and permanent wet strengths of the paper increased significantly, and the key parameters were 1) the concentration of MA and chitosan, 2) dipping duration, and 3) curing temperature. The temporary and permanent wet strengths reached 31.6% and 29.7%, respectively, at a concentration of treating solution of 1%, dipping time of 12 h, and curing temperature of 90 °C. At a curing temperature of 170 °C under otherwise the same conditions, both the temporary and permanent wet strengths were higher than 50%.