Wet cross-linking of cellulose fibers via a bioconjugation reaction

A well-known bioconjugation reaction, the EDC-assisted reaction of carboxyl and amine groups, is shown to be extremely well-adapted for cross-linking fibers under papermaking conditions. By using such chemistry we obtained increases as high as 500% and 100% in the wet-web strength (WWS) of papers made from, respectively, unbeaten and beaten hardwood kraft pulps, after pretreating the fibers with carboxymethyl cellulose and using adipic dihydrazide as the cross-linker. These increments exceed previous attempts in most cases by about 1 order of magnitude. Experiments show that the cross-linking reaction does not counteract the beating effect, as has usually occurred in the past for other cross-linking routes, but instead complements it. The ability of EDC for promoting covalent bonding under very wet conditions appears to make it an excellent agent for the enhancement of the WWS of paper, the property that ultimately determines the runnability of a papermaking machine.