High-consistency modification of cellulose fibers: Resource-efficient introduction of cationic charges, and their effect on fiber and nanofibril properties.

Quaternized cellulose fibers and cellulose nanofibrils (CNFs) are attractive candidates for the development of new renewable and biodegradable materials. However, the etherification reaction, through which functionalization is commonly achieved, provides low efficiencies, limiting industrial interest in the modification. This work primarily aims to increase the efficiency for the quaternization of cellulosic fibers while keeping the fiber-structure intact. This was achieved using high-consistency kneading to mix and modify the fibers at far higher solids contents than previously reported, efficiently limiting the alkaline hydrolysis of the reagent. Increasing the solids content from 5 to 45 wt% improved the reaction efficiency from 2 % to unprecedented 38 %. Characterization of the fibers showed that high-consistency quaternization affected the wet dimensions of the fibers, with enhanced swelling and fibrillation being obtained. Based on the tensile testing of handsheets made, it was concluded that quaternizing the fibers enhanced the strainability of the material, from 1.8 to 6.7 %, and that kneading achieved a concomitant increase in stress-at-break, from 15 to 103 MPa. CNFs produced from fluidized high-consistency-quaternized fibers had dimensions comparable to those produced from hand-mixed fibers, having aspect ratios above 200, the CNF films produced were transparent, tough, and with a high propensity to sorb water.