Preparation of chitin nanofiber-graft-poly(l-lactide-co-ε-caprolactone) films by surface-initiated ring-opening graft copolymerization

This paper reports the preparation of chitin nanofiber-graft-poly(l-lactide-co-ε-caprolactone) films by surface-initiated ring-opening graft copolymerization of l-lactide (LA)/ε-caprolactone (CL) monomers from chitin nanofiber films. First, the chitin nanofiber film was prepared according to our previous method. Then, the film was immersed in water and lyophilized for pre-treatment. The non-treated or pre-treated film was immersed in a solution of LA/CL in toluene for 12 h. After tin(II)-2-ethylhexanoate as a polymerization catalyst was added to the mixture, which was heated at 80 °C for 48 h for the progress of copolymerization, the resulting film was washed and further subjected to Soxhlet extraction with chloroform. The IR spectrum of the obtained film exhibited carbonyl absorption at 1739 cm−1 due to the ester linkage of poly(LA-co-CL), suggesting the presence of poly(LA-co-CL). The powder X-ray diffraction and SEM measurements of the obtained film indicated that the graft copolymerization of LA/CL was initiated from hydroxy groups on surface of the chitin nanofibers. The mechanical properties of the films, which were evaluated by tensile testing, were affected by the amounts and the LA/CL composition ratios of the grafted polyesters.