Microstructure–Properties Relationships in Compatibilized Recycled Polyethylene Blends: Insights From PiFM and Raman Spectroscopy

The microstructure of polymer blends significantly influences their mechanical properties, with performance primarily determined by blend composition, morphology, and processing conditions. This study examines the mechanical properties, morphology, and microstructure of recycled polymer blends composed of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyamide 6 (PA6), and ethylene vinyl alcohol (EVOH), with and without compatibilizers: polyethylene grafted with acrylic acid (PE-AA), 2,2′-(1,3-Phenylene)bis(2-oxazoline) (1,3-PBO) and 2,2′-(1,4-Phenylene)bis(2-oxazoline) (1,4-PBO). Tensile testing shows that a PE-AA and 1,4-PBO combination enhances strain at break by 50%, suggesting improved interfacial adhesion. The blend with partial replacement of LDPE by LLDPE exhibits the highest strain at break (increased by 125%) and the narrowest droplet size distribution. Scanning electron and photo-induced force microscopy confirm a droplet-matrix morphology, with PA6 forming the core and EVOH the droplet shell. Mechanical performance correlated more strongly with droplet count than with droplet size. Raman spectroscopy and photo-induced force microscopy detected spectral changes, indicating chemical interactions contributing to improved mechanical properties. Differential scanning calorimetry did not indicate any significant effects of compatibilizers on phase miscibility. These findings highlight the role of linear low-density polyethylene in optimizing mechanical properties.