| Abstract: | When starch was treated with KMnO4 solution, MnO2 was deposited overall the starch. The amount of MnO2 deposited relied on the KMnO4 concentration. Subjecting the MnO2-containing starch to a solution consisting of monomer (methacrylic acid, MAA) and acid (citric, tartaric, oxalic or sulphuric acid) resulted in formation of poly(MAA)-starch graft copolymer. The magnitude of grafting, expressed as meq. -COOH/100 g starch, was determined by amount of MnO2 deposited, MAA concentration, temperature and duration of polymerization as well as kind and concentration of the acid. Incorporation of cations such as Fe+3, Cu+2 and Li+1 had a significant effect on grafting. The highest extent and rate of grafting were obtained with citric acid and the least with sulphuric acid; tartaric acid stood in-mid-way position. The magnitude of grafting increased as the acid concentration increased till a certain concentration beyond which grafting levelled off. Similar trend was observed when the magnitude of grafting was related to the amount of MnO2 deposited. The extent and rate of grafting increased by raising the polymerization temperature from 30° to 50°C then decreased by raising the temperature further from 60° to 70°C. On the other hand, grafting enhanced significantly by addition of Fe+3, Cu+2 or Li+1 and followed the order Fe+3 > Cu+2 > Li+1. A tentative mechanism for grafting of starch with MAA using MnO2-acid system was elucidated. |
