Abstract
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.Graphical abstract
Highlights
Ecological awareness has driven the search for substituents and new materials derived from renewable resources using environmentally friendly processing routes
The nanocomposite samples were immersed in aqueous solutions at pH 3, 5, 7, 9, and 11 at 25 °C for 6, 12, 24, 48, and 72 h, respectively
Since the co-crystallization of cellulose and chitosan would affect the structural features of the nanocomposite films, we studied the crystallinity using X-ray diffraction (XRD)
Summary
Ecological awareness has driven the search for substituents and new materials derived from renewable resources using environmentally friendly processing routes. Cellulose and chitin are polysaccharides that support organisms in the plant and animal kingdoms, respectively Their chemistries are relatively similar, having b-1,4 bonds between repeating sugar units and complex networks of hydrogen bonding and hydrophobic interactions maintaining the polymer chain structures (Medronho and Lindman 2014; Yang et al 2016). Besides cellulose and chitosan composites, efforts have been made to form functionalized composite materials, such as chitosan–cellulose nanofibers (Fernandes et al 2011), chitosan–cellulose nanowhiskers (Li et al 2009), and chitosan–cellulose multi-component composites (Tang and Alavi 2011). These composite materials can be given anti-microbial or wound-healing properties, pH sensitivity, or other functionalities. Dissolving and preparing cellulose–chitosan composites in a compatible solvent without previous derivatization would be advantageous
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