Surface-Modified Cellulose Nanofibers-graft-poly(lactic acid)s Made by Ring-Opening Polymerization of l-Lactide

Highly crystalline cellulose nanofibers with a high density of carboxylate groups only on the surfaces were prepared from both softwood and non-wood cellulose pulp. The preparation method used 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of native cellulose fibrils in an aqueous TEMPO/NaBr/NaClO system and subsequent postoxidation with NaClO2 in acetate buffer (pH 4.8). The TEMPO-oxidized cellulose nanofibers (TOCNs) possessed a carboxylate content of 1.7 mmol g−1 and a crystallinity of 67–69% with a crystallite size of ∼3 nm. The TOCNs were used to produce highly crystalline TOCN-graft-poly(lactic acid) (PLA) nanocomposites via ring-opening polymerization of l-lactide in a polar aprotic solvent. Effects of the reaction temperature and the molar ratio of l-lactide to carboxylate surface groups, on the efficiency of surface grafting were investigated to potentially improve the crystallinity and thermal properties of the nanocomposites. The crystallinity of TOCN-g-PLA products was 59–66% greater than the crystallinity of neat PLA.