Use of starch granules melting to control the properties of bio-flour filled polypropylene and poly(butylene succinate) composites: Mechanical properties

The feasibility and industrial potential of using bio-flours from tropical crop residues, in particular starch containing bio-flours, for the manufacture of bio-composites was investigated. Polypropylene (PP) and poly(butylene succinate) (PBS) were compounded with bio-flours from pineapple skin (P) and from non-destarched (CS) and destarched (C) cassava root by twin-screw extrusion. In CS composites, two levels of starch granules melting were achieved by adjusting the extrusion temperature, enabling control of morphological and mechanical properties. The use of bio-flours reduced tensile strength by 26-48% and impact strength by 14-40% when the proportion of bio-flour was increased to 40% w/w, while flexural strength initially increased upon addition of bio-flours, before decreasing at higher loads. The use of compatibilizers, in particular maleic anhydride-polypropylene (MAPP) in PP composites with 30% bio-flour resulted in tensile strength similar to non-compatibilized composites with 10% bio-flour (34-35 MPa). MAPP also increased flexural strength to higher levels than pure PP, resulting in a stronger, but less flexible material.