A continuous process for manufacturing a blended polymer includes mixing a native starch, a polyolefin, and a compatibilizer; and forming the blended polymer from the resulting mixture using an extruder. The process can also include mixing the native starch, the polyolefin, and the compatibilizer in the extruder. The polyolefin can be a petroleum- or bio-based polyethylene, and the compatibilizer can be a maleic anhydride grafted polyolefin. The process can further include mixing a processing aid such as glycerin, and forming the blended polymer into a film.