Nonexchangeable versus Epoxy-Assisted Exchange-Capable Reactive Compatibilization in EVOH/HDPE Blends: Morphology, Mechanical, Thermal, and Gas–Barrier Properties

Nonexchangeable and exchange-capable reactive compatibilization offer distinct routes to engineer interfacial connectivity in immiscible semicrystalline polymer blends, yet their consequences for crystallization, relaxation, and transport remain incompletely understood. Here we establish a controlled comparison of nonexchangeable reactive compatibilization and exchange-capable reactive compatibilization in ethylene-vinyl alcohol copolymer (EVOH)/high-density polyethylene (HDPE) blends formed by reactive compatibilization. The nonexchangeable network is generated by anhydride–hydroxyl coupling at the interface, whereas the exchange-capable network is constructed by incorporating an epoxy component to create exchangeable β-hydroxy-ester linkages that enable transesterification-assisted topology rearrangement. Despite similarly refined morphologies and strengthened interfacial adhesion, the two reactive compatibilization produce sharply different thermomechanical signatures: the epoxy-assisted exchange-capable system exhibits higher gel fractions and more pronounced rubbery modulus retention, together with faster stress relaxation. These exchange-enabled interfaces fundamentally rebalance strength and ductility, raising elongation at break from 9.6% to 81.4% while maintaining original high modulus. In contrast, nonexchangeable reactive compatibilization more effectively suppresses gas transport, significantly reducing the O 2 permeability of the EVOH/HDPE blend relative to the uncompatibilized blend. This work clarifies how nonexchangeable versus exchange-capable interfacial chemistry governs crystallization kinetics, viscoelastic relaxation, and barrier–toughness trade-offs in semicrystalline blend networks, offering guidance for designing advanced packaging materials that combine high barrier, high toughness, and reprocessing tolerance.