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

Chuensangjun, Chaniga, Kanomata, Kyohei, Kitaoka, Takuya, Chisti, Yusuf, Sirisansaneeyakul, Sarote
Journal of polymers and the environment 2019 v.27 no.4 pp. 847-861
acetates, buffers, cellulose, cellulose fibrils, cellulose nanofibers, crystal structure, crystallites, nanocomposites, oxidation, pH, polymerization, pulp, sodium bromide, sodium hypochlorite, softwood, solvents, temperature, thermal properties
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.