Investigating the Structure–Property Relationships of Paramylon Ester/PBAT Blends for Sustainable Packaging

In this study, an ester from paramylon, paramylon propionate hexanoate (PaPrHe), was synthesized and blended with poly(butylene adipate-co-terephthalate) (PBAT). The effects of structure and morphology on the thermal and mechanical properties of the blends were investigated. Dynamic mechanical analysis showed that the blends were immiscible throughout their compositional range. After selectively etching PBAT using enzymes and conducting SEM analysis, it was found that blends with a high proportion of PaPrHe (up to 70%) had a phase-separated morphology with significant particle agglomeration, leading to inferior mechanical properties. However, when the PBAT loading was increased to 50%, a cocontinuous, weblike morphology was observed that improved the mechanical properties. Further increasing the PBAT concentration resulted in a unique submicrometer-level bead dispersion with a mean particle diameter of 0.7–1.3 μm, which enhanced the mechanical properties significantly, particularly the impact strength. The highest impact strength was exhibited by the 70% PBAT blend (54.1 kJ/m2), surpassing that of pure PBAT (37.1 kJ/m2) and PaPrHe (9.7 kJ/m2). Additionally, by uniaxial stretching at room temperature and annealing at 80 °C, blend films with tensile strengths up to 120 MPa could be obtained. Overall, PaPrHe/PBAT blends have the potential for use in mulch films and sustainable packaging applications.