Chapter 5 - Thermal degradation characteristics of chitin, chitosan, Al2O3/chitosan, and benonite/chitosan nanocomposites

Abstract

The various applications of the biopolymer chitosan (CS) in different fields make it very interesting for both researchers and industrialists. Depending on the intended use, CS can be used alone or combined with other materials to form CS derivatives or CS-based nanobiocomposites in order to improve its specific properties to find specific applications in many industrials fields. This attractive effect of CS is related to its various functional groups, which play an important role in the formation of the different materials envisaged. In addition, the biopolymer CS is biodegradale, environment friendly, naturally occurring, and readily available in large quantities. It is easily obtained by deacetylation of chitin (CT) biopolymer, which can be found as a supporting material in many aquatic organisms, terrestrial organisms, and some microorganisms. The deacetylation process seems to be the most important step on which depends the chemical and physical properties of CS and consequently determines the fields in which it can be used. This chapter presents the preparation of CS by deacetylation of CT from shrimp shells collected in Morocco. The optimization of the parameters involved in the deacetylation process was examined in detail leading to a significant degree of deacetylation (DD=83%). The thermal stability of the starting CT and CS are investigated by thermogravimetric analysis (TGA/DTA) at various heating rates, and compared with those of the elaborated bionanocomposites bentonite/CS (Bt/CS) and Al2O3/CS (Al2O3/CS). The kinetic parameters, such as the apparent activation energy (Ea) and preexponential factor (A) were determined using Ozawa–Flynn–Wall (OFW) and Kissinger (KIS) isoconversional methods. The modified catalytic Sestak–Berggren (SB) method used the conversion function, f(α)=cαm(1−α)n with the adjusted values of m, n, and c. It was found that the simulated curves issued from the model best fit those issued from the experimental data, indicating the same scission mechanism for the degradation of CT, CS, Bt/CS, and Al2O3/CS. Spectroscopic techniques such as FTIR, XRD, SEM, and DSC were used to characterize the studied samples.