Controlled Dispersion and Setting of Cellulose Nanofibril-Carboxymethyl Cellulose Pastes

This work investigated the redispersion and setting behavior of highly loaded (similar to 18 wt.% solids in water) pastes of cellulose nanofibrils (CNFs) with carboxymethyl cellulose (CMC). A single-screw extruder was used to continuously process CNF + CMC pastes into cord. The adsorption of CMC onto the CNFs was assessed through zeta potential and titration which revealed a surface charge change of similar to 61% from - 36.8 mV and 0.094 mmol/g COOH for pure CNF to -58.1 mV and 0.166 mmol/g COOH for CNF + CMC with a CMC degree of substitution of 0.9. Dried CNFs with adsorbed CMC was found to be fully redispersible in water and re-extruded back into a cord without any difficulties. On the other hand, chemical treatment with hydrochloric acid, a carbodiimide crosslinker, or two wet strength enhancers (polyamide epichlorohydrin and polyamine epichlorohydrin) completely suppressed the dispersibility previously observed for dried-untreated CNF + CMC. Turbidity was used to quantify the level of redispersion or setting achieved by the untreated and chemically treated CNF + CMC in both water and a strong alkaline solution (0.1 M NaOH). Depending on the chemical treatment used, FTIR analysis revealed the presence of ester, N-acyl urea, and anhydride absorption bands which were attributed to newly formed linkages between CNFs, possibly explaining the suppressed redispersion behavior. Water uptake of the differently treated and dried CNF + CMC materials agreed with both turbidity and FTIR results. [GRAPHICS] .

Automated summary

This study investigated the redispersion and setting behavior of highly loaded pastes of cellulose nanofibrils with carboxymethyl cellulose under different chemical treatments. Analysis using turbidity and FTIR showed significant effects of different treatments on the properties of nanofibril pastes.