Chitosan as a matrix of nanocomposites: A review on nanostructures, processes, properties, and applications.

Chitosan is a biopolymer that is natural, biodegradable, and relatively low price. Chitosan has been attracting interest as a matrix of nanocomposites due to new properties for various applications. This study presents a comprehensive overview of common and recent advances using chitosan as a nanocomposite matrix. The focus is to present alternative processes to produce embedded or coated nanoparticles, and the shaping techniques that have been employed (3D printing, electrospinning), as well as the nanocomposites emerging applications in medicine, tissue engineering, wastewater treatment, corrosion inhibition, among others. There are several reviews about single chitosan material and derivatives for diverse applications. However, there is not a study that focuses on chitosan as a nanocomposite matrix, explaining the possibility of nanomaterial additions, the interaction of the attached species, and the applications possibility following the techniques to combine chitosan with nanostructures. Finally, future directions are presented for expanding the applications of chitosan nanocomposites.

Thermal degradation and lifetime of ß-chitin from Dosidicus gigas squid pen: Effect of impact at 9.7 GPa and a comparative study with α-chitin.

The kinetics of thermal degradation of ß-chitin extracted from Dosidicus gigas squid pen, was studied at normal conditions as well as after being subjected to the action of high-pressure impact of 9.7 GPa. The integral iso-conversional procedure of Kissinger-Akahira-Sunose (KAS) recommended by the ICTAC kinetics committee was applied to the non-isothermal data obtained from thermogravimetry (TGA). Lifetimes were predicted without assumption of any reaction model. Heating rates of ß = 10, 15, 20 and 25 °C/min under nitrogen atmosphere were used from room temperature to 1300 °C. A comparative study with α-chitin was performed. All the samples were structurally and chemically characterized by several techniques. The extracted ß-chitin was found to be in the monohydrate form; while with the action of high-pressure impact, it was transformed into ß-chitin dehydrate showing slightly higher stability. Reliable prediction for lifetimes considering working temperatures over 425 K was found for α and ß-chitin.

Hydroxyapatite crystallization in shrimp cephalothorax wastes during subcritical water treatment for chitin extraction.

The extraction of calcareous chitin from shrimp cephalothorax was successfully achieved using a subcritical water treatment to attain a deproteinization up to 96%. The treatments also increased the crystalline domain size in the α-chitin fibers. An experimental design of Taguchi allowed the optimization of experiments. The macroelements identified in all samples were Ca, P, S, K, Cl and Al, whereas Cr, Mn, Fe, Ni, Cu, Zn, Br and Sr were also detected as microelements. The assigned crystalline phases by XRD were α-chitin, calcite, HAP and traces of quartz. The presence of these phases was corroborated by ATR-FTIR and SEM-EDS analyses. The highest content of α-chitin (82.2wt%) was obtained for the 0.17 chitin:dH2O (wt/wt) ratio for 30min treatment at 260°C. Noteworthy, this treatment promotes the crystallization of both minerals as microcrystals of calcite and nanocrystals of hydroxyapatite with needle and flake shapes as well as intermediate morphologies.