Carboxymethyl cocoyam starch: Synthesis, characterisation and influence of reaction parameters

摘要

Twenty carboxymethyl starch derivatives of cocoyam starch were synthesized under different reaction conditions. The influences of sodium hydroxide concentration, sodium monochloroacetate concentration, water, type of organic solvent, reaction time and temperature were evaluated for degree of substitution (DS) and reaction eff iciency (RE). The optimal ratio of moles of NaOH per mole anhydroglucose unit (AGU), n(NaOH)(AGU) was 1.62. Increases in ratio of moles of monochloroacetate (n(SMCA)) to mole of AGU (n(AGU)) increased the DS progressively. The ratio of water to solvent (isopropanol, IPA) in the reaction media was optimal at H2O/IPA 0.16. Both RE and the DS increased with increase in reaction time within the studied time range (1-4 h). Increases in temperature enhanced both reaction efficiency and DS. Among the solvents studied, an isopropanol - water medium produced the optimal result. The starch paste clarity improved remarkably after carboxymethylation. Wide angle X-ray diffractometry revealed that starch crystallinity was reduced after carboxymethylation. C-13-NMR showed peaks at delta = 180.42 ppm, 80.35 ppm, 77.77 ppm, and 71.96 ppm, which were assigned to C-O, substituted C-2, C-3 and C-6, respectively. In addition, three signals appeared at delta = 74.16 ppm, 73.42 ppm and 72.59 ppm and they were assigned to the