Biodegradable polymers have the same properties and functions as general synthetic polymers, but are distinct in that they can be broken down by microorganisms without polluting the environment. In this study, the modification of starch was executed to change property of starch from hydrophilic into hydrophobic with three different approaches. These experiments are intended to enhance compatibility between starch and LDPE. The first approach is the esterification reaction between the hydroxyl groups of native starch (NS) and acetic anhydride (called MS). The second is graft copolymerization of acrylonitrile and styrene onto starch (GS). The third is the esterification reaction between the hydroxyl groups of starch and the side groups of ionomer (IS). The first and second classes of polymers were investigated by IR spectrum. The progress of third experiment was measured using the pH meter. The mechanical properties of pure LDPE and its blends with three classes of biodegradable polymers compared by means of tensile strength, percent elongation, and Young's modulus, and rheological behaviors were also observed by capillary rheometer. The morphology of blends was investigated by SEM photographs. In cases of IS and NS, tensile strengths decrease at the 10% starch, but after that increase gradually. But MS and GS show a continuous decrease in tensile strength as the composition of starch is increased. The percent elongation decreases remarkably as small amount of modified starch is added. After 10%, the percent elongation decreases gradually. The Young's modulus increases generally in the overall range of starch composition. The shear viscosity increases uniformly at the overall shear rate as the composition of starch is increased. In the morphology, IS is shown the best compatibility.
