Biogradable Starch Film from Cassava, Corn, Potato and Yam

Abstract

Starch is the major carbohydrate reserve in plant tubers and seed endosperm where it is found as granules each typically containing several million amylopectin molecules accompanied by a much larger number of smaller amylose molecules. Starch films were prepared from starch extracted from cassava, corn, potato and yam with and without plasticizers to evaluate the effects of the type and quantity of plasticizer on the mechanical properties of the starch films obtained. Ubbelohde viscometer was used to determine the intrinsic viscosity and molecular weight of the prepared films in dimethylsulfoxide (DMSO)/water solution (90%/10% v/v). The molecular weights of the films were found to range from 2.70 × 10¹³ – 2.14 × 10¹⁷ for films prepared from corn starch, 2.86 × 10¹⁰ – 1.01× 10¹⁷ for films prepared from yam starch, 2.69 × 10¹³ - 3.97 × 10¹⁷ for films prepared from potato starch and 4.15 x 10⁶ - 4.05 × 10⁸ for films prepared from cassava starch. The molecular weights of the films were found to decrease with increase in the plasticizer content because the bonds between starch-starch molecules were replaced with the bond between starch-water molecules. This led to the reduction in the chain length of both the amylopectin and amylose, and hence reduction in the molecular weight average. Amylose and  amylopectin molecules contribute to mechanical properties and hygroscopic properties of starch. The effects of plasticizer on mechanical properties of film prepared from corn starch and yam starch were investigated at six levels of plasticizer content. The tensile strength of the films prepared from corn starch ranged from 0.10MPa - 5.20MPa, 0.05MPa - 5.10MPa for films prepared from yam starch, 0.09MPa - 5.74MPa for films prepared from potato starch and 0.51MPa – 5.33MPa for films prepared from cassava starch. The value of Young’s modulus was found to range from 0.39MPa -104.06MPa for films prepared from corn starch, 0.33MPa - 49.32MPa for films prepared from yam starch, 0.36MPa – 191.33MPa and 3.14MPa – 97.5MPa for films prepared from cassava starch. The tensile strength of films was influenced by the type and the content of plasticizer used.Generally, the Young’s modulus and the tensile strength of the films decreased with increase in plasticizers content, with concurrent increase in elongation at break and tensile strain of the films due to increase in ductility of the films. Glycerol exhibited more plasticizing effect on both starches than sucrose due to the hygroscopic or hydrophilic nature of glycerol.

Keywords: biodegradable, starch films.