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The blends of high-density polyethylene (HDPE) and poly(l-lactic acid) (PLLA) were prepared by melt blending method in an extrusion mixer with a postextrusion blown film attachment. The ratios of HDPE/PLLA blends were taken as 100/0, 95/5, 90/10, 85/15, and 80/20. The 80/20 blend was further compatibilized by adding maleic anhydride-grafted polyethylene in different ratios (up to 8 wt%). Based on the mechanical properties of the films, the compositions HDPE80 (80% HDPE and 20% PLLA) and HD80C4 (80% HDPE, 20% PLLA, and 4% compatibilizer) were found to be optimum and considered for further analysis. The thermal properties of these selected blends were investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA study revealed that the addition of the PLLA somewhat decreased the thermal stability of HDPE. DSC investigation showed that the blends were partially miscible only. X-ray diffraction (XRD) analysis enlightened that the crystallinity of blends was slightly increased with addition of PLLA. Immiscibility of the two polymers was diminished in the presence of compatibilizer, as indicated by the scanning electron microscopy (SEM) of the blends. These partially biodegradable blends may be used for flexible packaging applications. POLYM. ENG. SCI., 54:2155–2160, 2014. © 2013 Society of Plastics Engineers