Development of a Compatibilizer-Free Polyethylene/Starch Blend via Solid-State Processing

This paper reports an innovative procedure for producing PE/starch blends in the absence of any compatibilizer,while maintaining the mechanical and biodegradation properties equal or even superior to those of corresponding compatibilized blends. The procedure consisted in the first step of mixing a high density polyethylene (HDPE) and pristine starch in solid states by high energy ball milling (HEBM) process, in order to obtain a ball milled HDPE/starch master batch, (HD-S)b. Subsequently, a certain amount of the master batch was melt blended with pure HDPE in an internal mixer, until a blend containing 85 wt% of the HDPE and 15wt% of the starch was achieved, HD/(HD-S)b. Investigations of rheological and morphological properties revealed that a strong interface was formed between the HDPE and starch phases of the blend. Formation of the interface with high strength was ascribed to the grafting reactions taking place between the HDPE and starch phases during the HEBM process,corroborated by FTIR spectroscopy characterizations. Interestingly enough, when compared to the mixtures containing 75 wt% of the HDPE, 15wt% of the starch and 10 wt% of a maleic anhydride grafted PE, as compatiblizer, made solely by conventional melt blending method, the HD/(HD-S)b showed superior mechanical properties. These properties enhancements were related to both the HDPE/starch strong interface and damaged starch originated by the mechanical action of the milling process.

Keywords:

Polyethylene , Starch , Solid-state processing , mechanical properties