Grafting polyanhydride polymers to cellulose nanofibers

Abstract Poly(ethylene-alt-maleic anhydride), PEMA, and modified PEMA with pendant poly(ethylene glycol) oligomers (PEG3, PEG10, PEG20) in anhydrous acetone were grafted onto mechanically produced cellulose microfibrils, CNF. The grafted CNF had up to 4.7 mmol/g of carboxylic acid groups from the hydrolyzed PEMA. Before and after grafting, the concentrations of individualized microfibrils were low (< 10% wt/wt). Atomic force microscopy revealed that the main CNF components were intermeshed microfibrils, microfibril bundles, and ribbons a few µm wide. Mastersizer particle size distributions were usually bimodal, with 10–20 µm and 100–200 µm peaks. We proposed the smaller peaks were individualized ribbons and the larger were flocculated ribbons and microfibrils. Based on the images of dried ribbons adsorbed on cationic glass and the shapes of aqueous ribbons sitting near the non-adhesive anionic glass, the PEMA-treated ribbons were stiffer than the PEMA-PEG grafted ribbons. Perhaps the high anhydride concentration on PEMA facilitated more crosslinking of the CNF surfaces compared to PEMA-PEG polymers with about 10 times less reactive anhydride groups. There was evidence that PEG-rich grafted polymers partially inhibited the formation of CNF aggregates in water.