Grafting polyanhydride polymers to cellulose nanofibers

Poly(ethylene-alt-maleic anhydride), PEMA, and modified PEMA with pendent poly(ethylene glycol) oligomers (PEG3, PEG10, PEG20) in anhydrous acetone were grafted onto mechanically produced cellulose microfibrils, CNFs. The grafted CNFs 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 CNFs 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 that the smaller peaks were individualized ribbons plus small aggregates, and the larger ones 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 CNFs surfaces compared to PEMA-PEG polymers with about 10 times less reactive anhydride groups. The presence of grafted PEMAc or PEMAc with pendent PEG chains had little influence on CNFs dispersibility.Graphical Abstract