Morphology-driven gas barrier enhancement in polyethylene/polyamide blends: Toward upcycling of recycled blown-films

This study investigates how processing-induced morphological modifications can enhance the permeability and performance of Low-Density Polyethylene (LDPE) and Polyamide 6 (PA6) blends derived from multilayer flexible packaging. Microstructure characterization using DSC, Raman, and FTIR spectroscopy revealed that the crystallinity of the PE phase and the hydrogen bonding interactions within the PA phase were not affected by variations in the film-blowing processing parameters. Gas permeation modeling based on the Maxwell-Wagner-Sillar (MWS) model confirmed that droplet elongation is a key strategy for improving gas barrier properties. Asymmetric in-plane stretching is expected to produce elongated, cigar-like dispersed domains, whereas more symmetric stretching conditions tend to form oblate spheroids oriented within the film plane. The latter morphology leads to lower oxygen permeability, as oxygen molecules are more constrained to diffuse through the dispersed barrier phase. To analyze the effects of shear-induced morphology, the Lattice Boltzmann Method (LBM) was employed to simulate droplet deformation in a slit die geometry designed to replicate the film blowing process. The results demonstrated a deformation gradient along the channel height, with droplet breakups occurring near the walls and in systems containing larger droplets. Following initial breakups, Rayleigh instability dominated, driving to further droplet fragmentation, particularly in regions with high shear rates and long residence times. To enhance mechanical performance, polyethylene-grafted maleic anhydride (PE-g-MA) was used as a compatibilizer, resulting in improved ductility due to a finer, more stable morphology and better interfacial interactions. This research highlights an experimentally validated predictive modeling approach for optimizing recycled LDPE/PA6 barrier films by linking processing conditions, morphology, and permeability. The findings offer valuable insights for the industry, enabling the design of high-barrier recycled films by adjusting the processing parameters, suitable for packaging applications, reducing reliance on virgin materials, and promoting a more sustainable circular economy.