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Cellulose–chitosan films were prepared using a physical method in which cellulose and chitosan were separately dissolved via freeze thawing in LiOH/urea and mixed in different proportions, the resulting films being cast and regenerated in water/ethanol. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) spectroscopy verified the composition changes in the nanocomposites due to different mixing ratios between the polymers. Tensile stress–strain measurements indicated that the mechanical performance of the cellulose–chitosan nanocomposites slightly worsened with increasing chitosan content compared with that of films comprising cellulose alone. Field emission scanning electron microscopy revealed the spontaneous formation of nanofibers in the films; these nanofibers were subsequently ordered into lamellar structures. Water uptake and microscopy analysis of film thickness changes indicated that the swelling dramatically increased at lower pH and with increasing chitosan content, this being ascribed to the Gibbs–Donnan effect. Slow material loss appeared at acidic pH, as indicated by a loss of weight, and quantitative FT-IR analysis confirmed that chitosan was the main component released. A sample containing 75% chitosan reached a maximum swelling ratio and weight loss of 1500% and 55 wt%, respectively, after 12 h at pH 3. The study presents a novel way of preparing pH-responsive cellulose–chitosan nanocomposites with slow-release characteristics using an environmentally friendly procedure and without any chemical reactions.
Yang et al. (2019) studied this question.