A Dual-Anchor Cardanol-Based Epoxy Dimer Enables Molecular-Level Interface Engineering and Toughening of Immiscible Polyester Blends

ECSD dimeric architecture offers multi-epoxide sites for in-situ interfacial covalent stitching. • Saturated succinate spacers enhance chain mobility while preventing thermal degradation pathways. • In-situ covalent stitching eliminates the coarse sea-island separation. Improving the interfacial adhesion of immiscible polyester blends through rational molecular design remains a critical challenge for developing high-performance sustainable polymer materials. Herein, a cardanol-derived epoxy dimer (ECSD) was designed and synthesized as a bio-based reactive interface regulator for poly(lactic acid) (PLA)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) blends. The unique dual-anchor molecular architecture of ECSD, consisting of two epoxidized cardanol-derived units connected by a flexible succinate spacer, provides multiple reactive sites and facilitates preferential localization at the PLA/P34HB interface. Surface-energy analysis based on interfacial tension calculations revealed the thermodynamic tendency of ECSD to reside at the phase boundary, while the epoxy groups enabled interfacial reactions with terminal functional groups of the polyester chains during melt processing. This molecular-level interface regulation effectively strengthened interfacial adhesion, refined phase morphology, and improved stress transfer efficiency within the blend system. At an optimized ECSD loading of 2 phr, the notched Izod impact strength increased from 8.1 to 33.8 kJ/m 2 , accompanied by an enhancement in work of fracture from 4.27 to 17.84 MJ/m 3 , while maintaining a Young’s modulus of 1178 MPa. In addition, ECSD-modified blends exhibited improved thermal stability and regulated enzymatic degradation behavior due to the formation of a more stable interfacial structure. This work demonstrates that a cardanol-derived epoxy dimer provides an effective molecular design strategy for constructing robust interfaces and achieving balanced mechanical performance in immiscible polyester blends. Download: Download high-res image (272KB) Download: Download full-size image