Simultaneous\nImprovement of Oxygen Barrier and Stiffness\nin High-Density Polyethylene via Effective Integration of Interface\nEngineering with in Situ Ethylene–Vinyl Alcohol Copolymer Nanofibrillation

In this study, we proposed a novel\ntechnique to simultaneously\nenhance the oxygen barrier properties and stiffness of high-density\npolyethylene (HDPE) while preserving its ductility. By utilizing in\nsitu nanofibrillation, fiber-in-fiber composites of an HDPE matrix\nand ethylene–vinyl alcohol (EVOH) nanofibers were fabricated.\nDue to the high interfacial tension between HDPE and EVOH, stemming\nfrom their differences in chemical structure and polarity, styrene/ethylene-butylene/styrene\ncopolymer grafted with maleic anhydride (SEBS-<i>g</i>-MA)\nwas used as a compatibilizer to improve the affinity between the two\npolymers. SEM images revealed that the presence of the compatibilizer\nresulted in smaller fiber sizes (reduced to 65 ± 27 nm from 147\n± 54 nm for 6 wt % compatibilized EVOH compared to noncompatibilized\nsamples), higher aspect ratios, and better distribution. Increasing\nthe aspect ratio and improving nanofiber distribution reduced HDPE’s\noxygen permeability by 61% after incorporating 10 wt % compatibilized\nEVOH nanofibers. Additionally, the nonisothermal and isothermal crystallization\nindicated that EVOH nanofibers reduced the amount of crystallinity\nand slowed crystallization kinetics. The alteration in HDPE crystalline\nstructure and its effect on permeability properties were also addressed.\nFinally, tensile test results indicated that the incorporation of\n10 wt % EVOH nanofibers, regardless of the presence of the compatibilizer,\nincreased HDPE Young’s modulus by around 50%. However, without\nthe compatibilizer, there was a significant reduction in HDPE elongation\nat the break. The incorporation of the compatibilizer allowed for\nincreased stiffness while preserving HDPE ductility. These promising\nfindings underscore potential applications across rigid and soft packaging.