High-energy ball milling (HEBM) was performed before melt mixing to fabricate a novel blend containing 85 wt % of a high density polyethylene (HDPE) and 15 wt % of a maize starch, using neither compatibilizer nor plasticizer materials in the blend formulation. Scanning electron microscopy and rheometry results revealed a strong interface between the two phases of the blend. Formation of the interface with high strength was ascribed to the grafting reactions, taking place between the phases during the HEBM process, and corroborated by Fourier transform infrared characterizations. A possible formation mechanism for the starch-grafted polyethylene was proposed based on the measurements and comprehensive analysis. Interestingly enough, when compared to HDPE mixtures which contained the same amount of the starch, but were made only by conventional melt blending, the ball mill-mediated sample showed superior mechanical and biodegradation properties. These properties enhancements were related to both the HDPE/starch strong interface and the damaged starch originated by the mechanical action of the milling process. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 145-152, 2013