Domain-specific functionalization of cellulose fibers via itaconic anhydride-mediated esterification

Abstract Softwood kraft pulp is known to produce one of the strongest papers, with main application areas in tissues, packaging, and high-quality or specialty papers. These tailored applications often crave chemical modification of the fibers to optimize and tailor their inherent properties. This paper presents two scalable methodologies, gas phase reactions and kneading reactions, for the esterification of bleached kraft pulp (BKP) with itaconic anhydride (ITA). Itaconic anhydride is bioderived with a structure similar to succinic or maleic anhydride, two commonly used chemicals for modifying pulps to introduce charge groups on the cellulose fibers. Although similar in structure, itaconic derivatives also contain an exocyclic, out-of-chain unsaturation, which is useful for additional chemical modifications, such as Michael additions and polymerization reactions. The modification of BKP was performed on never-dried and water-free pulp, aiming to produce highly charged fibers while preserving the overall fiber structure and thereby their intrinsic properties. The reaction yields were investigated by varying molar ratio, temperature, and reaction time, and the modified fibers were characterized using ATR-FTIR, solid state CP/MAS 13 C-NMR, XRD, titration techniques, and water retention values. The different modification methods showed differences in the spatial distribution of the substituents, preferably modifying the fiber surface or the fiber wall interior. In general terms, modifications facilitated through kneading showed a higher degree of modification of the fiber wall interior, whilst gas-phase mediated reactions preferentially modified the fiber surface. This allows for tailoring the location of the modification, decorating the fibers within or on the surface, and opening routes for a customizable pulp.