Preparation and Study on the Properties of LDPE-Thermoplastic Starch Blends; Part I: Effect of PE-g-MA on the Mechanical Properties and Flow Behavior

In this work, effect of maleic anhydride grafted- LDPE (PE-g-MA) on the mechanical, morphology and flow behavior of biodegradable LDPE-thermoplastic corn starch (TPS) blends were investigated. TPS was prepared by mixing neat starch and glycerol (35wt. %) at room temperature. The mixture then was melt-compounded using an internal mixer at 140oC, rotor speed of 60 rpm for 8 minutes. LDPE-TPS blends containing different contents of TPS (0-40wt. %) with (3wt. %) and without the addition of PE-g-MA, were prepared using a single-screw extruder. Surface morphology of the prepared blends was investigated by Scanning Electron Microscopy (SEM). Also, mechanical properties and flow behavior of the prepared samples were carried out by means of related standard test methods. Scanning electron micrographs of the samples show improvement in dispersion of the starch particles in LDPE matrix in the presence of PE-g-MA as a compatibilizer. Also, the results of mechanical properties indicate that as TPS concentration increases, the ultimate tensile strength, elongation at break, Young’s modulus and relative impact strength of the blends decrease. However, the compatibilized blends represent higher mechanical properties than the blends without any compatibilizer. Furthermore, the addition of starch to LDPE decreases the melt flow index values of the samples and subsequently increases their apparent viscosity.The results of rheological tests also indicate that as shear rate increases, the apparent viscosity of the samples decreases (shear thinning).