Synthesis of Mixed Chitin Esters via Acylation of Chitin in Deep Eutectic Solvents.

The development of efficient derivatization methods of chitin, such as acylation, has been identified to confer new properties and functions to chitin. In this study, we investigate the synthesis of mixed chitin esters via the acylation of chitin in deep eutectic solvents (DESs) comprising 1-allyl-3-methylimidazolum chloride and 1,1,3,3-tetramethylguanidine based on a previous study that reported the development of efficient acylation of chitin in the DES to obtain single chitin esters. A stearoyl group was selected as the first substituent, which was combined with several bulky acyl and long oleoyl groups as the second substituents. After dissolution of chitin in the DES (2 wt%), the acylation reactions were conducted using stearoyl and the desired acyl chlorides for 1 h + 24 h at 100 °C in the resulting solutions. The IR and 1H NMR spectra of the isolated products confirmed the structures of mixed chitin esters with two different substituents. The substituent ratios in the derivatives, which were estimated via the 1H NMR analysis, were changed according to the feed ratios of two acyl chlorides.

Fabrication of all-chitin composite films.

The aim of this study is to propose a first concept for the procedure to prepare an all-chitin composite. The fabrication of all-chitin composite films was investigated for the first time via the mixing of low-crystalline matrix dispersions with high-crystalline fiber dispersions. Self-assembled chitin nanofiber (ChNF) films, prepared from a chitin ion gel, were treated with aqueous NaOH for deacetylation, followed by treatment with different types of aqueous acids via ultrasonication to produce dispersions. When the treatment was carried out with 1.0 mol/L aqueous acetic acid, we obtained a scaled-down ChNF (high-crystalline chitin fiber) dispersion, as previously reported. The crystallinity was reduced by treatment with 1.0 mol/L aqueous trifluoroacetic acid for 10 min at room temperature via ultrasonication and subsequent treatment for 24 h at 50 °C with stirring to produce a low-crystalline chitin matrix dispersion. The resulting two dispersions were mixed, and treated by suction filtration and drying to produce all-chitin composite films. The mechanical properties of the obtained composite films with appropriate weight ratios of the two components were superior to those of the high-crystalline scaled-down ChNF film. All-chitin complexes are expected to be used in the future as sustainable materials for a variety of applications.