Tunable Interfacial Compatibilization of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate)/Thermoplastic Starch Blends via the Calcium-Induced Egg-Box Formation of Methylated Pectin

This study investigates the role of pectin with a controlled degree of methylation (DM) as a naturally derived compatibilizer to enhance the interfacial compatibility of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH)/thermoplastic starch (TPS) blends. Pectin samples with varying DMs (27%, 53%, and 73%) were prepared via de-esterification and incorporated into TPS in the presence or absence of Ca²⁺ to enable the formation of an egg-box structure. While pectin alone had minimal effect on the blend morphology and mechanical performance, Ca²⁺ significantly altered the interfacial behavior. Scanning electron microscopy revealed a pronounced reduction in the TPS domain size upon egg-box formation; this morphological refinement was correlated with the enhanced tensile strength and oxygen barrier properties. Peel tests and rheological analysis further demonstrated a DM-dependent enhancement in the interfacial adhesion under Ca²⁺-mediated conditions. These results indicate that the interfacial alignment of the methylated carboxyl groups, governed by the DM and ionic crosslinking, plays a critical role in compatibilizing immiscible biodegradable blends. Thus, this study provides a sustainable and tunable strategy for the interfacial design of polymer blends by leveraging the polysaccharide structure and supramolecular assembly.
Key words: Pectin, Methylation degrees, Egg-box structure