Poly(lactic acid)/low density polyethylene polymer blends: preparation and characterization

Poly(lactic acid) (PLA) was melt blended with low density polyethylene (LDPE) with the aim of replacing commodity polymers in future applications. Because cost of PLA is quite high, it is not economically feasible to use it alone for day to day use as a packaging material without blending. In this work, PLA was blended with LDPE in different ratios by using a laboratory scale single screw extruder. The prepared blends were characterized in terms of rheological and mechanical properties. Rheological properties were studied using a capillary rheometer, and the Bagley's correction was performed. True shear rate (gamma(r)), true shear stress (tau(r)), true viscosity (eta(r)) and non-Newtonian index (n) were determined. The relationship between true viscosity and temperature was also studied, and the flow activation energy at a constant shear stress (E-tau) was determined. The mechanical properties of the blends were investigated on dog bone-shaped samples obtained by injection molding, tensile tests were performed using Testometric M350-10KN, stress at break, strain at break and Young's modulus were determined. Rheological results show incompatibility between the two polymers where the true viscosity of the blend decreased with increasing PLA content below the line of mixing rule, also it was found that the blend exhibits shear-thinning behavior over the range of the studied shear rates. The mechanical results also showed incompatibility between PLA and LDPE in the blend, where stress at break and Young's modulus of the blend increased with increasing PLA content, whereas strain at break of the blends was similar to that of neat PLA. (c) 2012 Curtin University of Technology and John Wiley & Sons, Ltd.