To meet the challenge of procuring new sources of natural polymers without affecting the demands for food crops, a thermoplastic unripe banana flour (TPF) was produced, characterized, and blended with metallocene-catalyzed polyethylene (mPE). Both the pulp and peels of unripe banana were used to produce flour, whose stability and thermoplastic properties allowed blending with mPE in high proportions, that is, 50, 60, 70, and 80%. The blends were injection molded, and the thermal, mechanical, microstructural, and infrared spectral properties of the resulting samples were characterized. The blend containing 50% TPF yielded a robust, elastic, and nonbrittle material. Maleic anhydride grafting on mPE (mPE-g-MA) promoted interphase adhesion of the polymers and homogeneity in the blends. Grafting also influenced the mechanical, thermal, and microstructural properties of the blends. The characteristics of the blends make them ideal for designing biodegradable plastics while exploiting banana peels, which are usually considered agricultural waste. POLYM. ENG. SCI., 55:866–876, 2015. © 2014 Society of Plastics Engineers