Structure–property relationships of reactively compatibilized PHB/EVA/starch blends

• In situ compatibilization is applied to PHB/EVA/starch blends by using maleic anhydride and benzoyl peroxide.
• The starch particle size was reduced by a factor of >100 (sub-μm scale) after the in situ compatibilization.
• The properties, notably the toughness, of the PHB/EVA/starch blends were improved by the in situ compatibilization.
• Starch-in-EVA-type (or core–shell-like) morphology was designed in the PHB/EVA/starch blends.
• The toughening mechanism of the PHB/EVA/starch blends was revealed based on local deformation mode.

A method is addressed to prepare poly(hydroxybutyrate)/poly(ethylene-co-vinyl acetate)/starch (PHB/EVA/starch) blends with fine dispersion of starch, i.e. by an in situ compatibilization in the presence of maleic anhydride (MA) and peroxide. The starch particle size is reduced from hundreds-μm to sub-μm after the compatibilization accompanied by an improvement in interfacial adhesion. Meanwhile, starch-in-EVA-type morphology is observed in the blends. The EVA and starch gradually changed into a (partially) co-continuous phase with increasing MA content. Consequently, toughness of the blends was improved as evidenced by an increase in elongation at break and tensile-fracture energy (work). Cavitation, fibrillation and matrix yielding are regarded as the toughening mechanism for the compatibilized blends. In addition, the Tg of the EVA phase is dependent on its phase morphology in the blends while the thermal behavior of the PHB was only slightly affected by the compatibilization.