Crab (<i>Brachyura</i>) shell acid and alkali treatments: Influence on thermal and structural properties of isolated acetamide-rich natural polymer

Abstract

Exoskeleton of crab comprises a dominating mineral (calcium carbonate, CaCO3), protein and a natural polymer (chitin). Chemical treatments have been employed at different instances to isolate pure chitin from different sources. It is thus necessary to investigate how this treatment will influence the features of chitin isolated from the same source (crab). In this study, 0.4, 0.8 and 1.2 M hydrochloric acid (HCl) were separately used to demineralize crab shell particles and this was followed by deproteinization with 0.4 and 1.2 M sodium hydroxide (NaOH) at 100 °C. Results showed that chitin properties were influenced by concentrations of reagents. Fibrils of different forms and surface appearance were observed via Scanning Electron Microscopy (SEM). The highest crystallinity index of 71% was possessed by chitin extracted using 0.4 M HCl and NaOH while 65.5% remained the least displayed by chitin extracted with 1.2 M HCl and NaOH. This trend was similar for chitin’s thermal stability where Thermogravimetric analysis (TGA) results informed that using the highest concentrations of 1.2 M HCl and NaOH provided chitin with 80.12 kJ/mol activation energy. On the other hand, 112.54 kJ/mol was calculated for chitin isolated with the minimum demineralization and deproteinization reagents used in this study.