Acetylation, crystalline and morphological properties of structural polysaccharide from shrimp exoskeleton
The extraction of a structural polysaccharide, a-chitin, from shrimp exoskeleton via chemical means using hydrochloric acid (HCl) and sodium hydroxide (NaOH) has been done. Concentrations of 0.4, 0.8 and 1.2 M for both HCl and NaOH were chosen to evaluate the acetylation degree (DA), crystalline structure and morphology of the chitin. The N-acetyl groups’ content in the structural polysaccharide ranged between 65.6 and 99.4% in decreasing order of both acid and alkali concentrations combination used. The magnitude of chitin average hydrogen bond energy EH was majorly influenced by OH(6). . .OC intra and CO. . .HN intermolecular hydrogen bonds as they showed more predominance than OH(3). . .O(5) and OH. . .OC intra and intermolecular hydrogen bonds. Chitin diffraction planes, crystalline index (Crl) and crystallite size (Dhkl) were investigated by X-ray diffraction (XRD) with reflections observed on (021), (110), (130) and (013) planes. The Crl occurred between 79.4 and 87.4%, while crystallite sizes were between 0.544 and 3.64 Å for the samples. Morphological study using scanning electron microscopy with energy dispersive spectroscopy SEM/EDS showed strong calcium and oxygen peaks. This established the shrimp shell surface to be composed of calcite and trace elements such as nitrogen and silicon. The observed a-chitin rough surfaces were attributed to the low degree deacetylation recorded during alkali treatment.