EXPLORATORY PRODUCTION AND CHARACTERIZATION OF COMPOSITE FROM NATIVE AND MODIFIED STARCHES REINFORCED WITH ACRYLONITRILE

Abstract

Starches were isolated from tubers of cassava (Manihot esculenta), bitter yam (Dioscorea dumentorum), white yam (Dioscorea rotundata) and cocoyam (Xanthosoma sagittifollium) by wet extraction method. The percentage yield of the starches ranged between 21.00% and 47.73% with cassava starch having highest percentage yield and bitter yam starch having least value. The isolated starches were subjected to chemical modification by phthalation and acetylation method. The native and modified starches were characterized using Fourier Transformed Infra-red Spectroscopy (FTIR). Functional properties such as water absorption capacity, oil absorption capacity, swelling power, solubility, gelation temperature, least gelation capacity, amylose content and pH were determined using standard procedures. Acetylation increased the water absorption capacity, oil absorption capacity, swelling power, amylose content solubility, bulk density and reduced the gelation temperature of the starches while phthalation decreased water absorption capacity, oil absorption capacity, swelling power, solubility and gelation temperature of the starches. Native cocoyam, white yam, and bitter yam starches had the lowest least gelation concentration (6%).The pasting property showed that the peak viscosity ranged between 72.00 and 5039.00 BU, the trough values ranged between 69.00BU and 3500BU, the peak time value ranged between 3.40 and 7.00 min, the setback values ranged between 474.00 and 2060.00 BU and the breakdown values ranged between 3.00 and 2341 BU. The Scanning Electron Microscopy (SEM) revealed the surface disruption of starch granules after modification. X-Ray Diffractometry (XRD) showed that modification reduced the crystalline contents of the native starches remarkably while amorphous contents increased. The Thermogravimetric analysis (TGA) showed that phthalation increased the thermal stability of the starches. Catalyst (CaO) was prepared from snail shell by calcining the snail shell in a muffle furnace at temperature of 800 ºC for 4 h and it was characterized. The SEM analysis of the calcined shell revealed porousity and spherical shape of the catalyst, the EDX analysis indicated that elements Ca (70%), C(5.27%) and O(24.73%) were present in the CaO. Grafted copolymers were prepared from the native and the phthalated starches using acrylonitrile as monomer by heating at 120 oC for 6 h in the presence of calcined shell (CaO) catalyst and characterized. The FTIR spectra of native and phthalated starches showed various functional groups; Phthalated cassava starch showed new absorption bands at 1924.96cm-1, Phthalated cocoyam starch showed new absorption bands at 1849.73 cm-1, Phthalated bitter yam starch showed new absorption bands at 1703.14 cm-1 Phthalated pupuru showed new absorption bands at 1932.67 cm-1,due to the carbonyl group of the ester (evidence that phthalation reaction has occurred). The SEM of native and modified starches of grafted copolymers revealed differences in phthalated grafted copolymer in comparism to their corresponding native copolymers. The results of grafted copolymer revealed from XRD analysis that Phthalated starch /grafted copolymer exhibited a highly crystalline nature, compared to unmodified grafted copolymer. The TGA analysis proved that Phthalated starch /grafted copolymer showed better thermal stability compared to unmodified grafted copolymer. Laminated plastic was prepared from the native and phthalated grafted copolymers, the water absorption capacity, the swelling property and water solubility of the phthalated derived Laminated plastic was reduced in comparism to their corresponding native laminated plastic. phthalated derived Laminated plastic revealed better mechanical properties and can be useful in food packaging.