Interfacial Properties and Barrier Performance of Recycled PP/EVOH Multilayer Plastics Using SEBS-g-MAH

This study examines the influence of SEBS-g-MAH (styrene ethylene butadiene styrene grafted maleic anhydride) content (0, 10, and 20 wt%) on the oxygen and moisture barrier properties, as well as the morphological and chemical structural changes in multilayer plastics composed of recycled polypropylene (PP) and ethylene vinyl alcohol (EVOH). Oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) analyses revealed a gradual decrease in permeability with increasing SEBS-g-MAH content, indicating improved barrier performance. Fourier-transform infrared (FTIR) spectroscopy confirmed the formation of ester bonds between the anhydride groups of SEBS-g-MAH and the hydroxyl groups of EVOH, as evidenced by a distinct absorption peak near 1735 cm⁻¹. This covalent interaction suggests enhanced interfacial compatibility. Transmission electron microscopy (TEM) revealed significant morphological evolution: without SEBS-g-MAH, EVOH domains were irregularly and coarsely dispersed within the PP matrix, whereas the addition of 10 wt% SEBS-g-MAH led to smaller domains and improved interfacial diffusion. At 20 wt%, the EVOH phase was finely and uniformly distributed, indicating stabilized phase morphology. These improvements in both chemical and morphological compatibility contributed to reduced interfacial tension, suppressed phase separation, and enhanced blend homogeneity. Overall, the results highlight the effectiveness of SEBS-g-MAH as a compatibilizer for recycled PP/EVOH plastics, providing a promising strategy for the development of sustainable, high-performance packaging materials.