Study of the correlation between flexible food packaging peeling resistance and surface composition for aluminum-metallized BOPP films aged at 60°C

Abstract

ABSTRACTThis study investigated the correlation between surface composition and peeling resistance in food packaging films by studying the heat aging of fabricated films over varying periods of time. The films consisted of a layer of aluminum (Al) metallized, biaxially oriented polypropylene (BOPP) bonded with a polyurethane (PU) adhesive onto another polymeric layer of low-density polyethylene (LDPE). The Al metallized films were prepared by physical vapor deposition (PVD) and aged at 60°C for either 5 or 15 days. The resulting aluminum surfaces were analyzed using X-ray photoelectron spectroscopy (XPS) and found to contain aluminum oxide (Al2O3) and trihydroxide (Al(OH)3). The XPS characterization also revealed a 29% increase in the Al(OH)3 layer thickness of the aged sample relative to a non-aged sample. Atomic force microscopy (AFM) was applied on investigations of possible morphology changes. The aluminum and PU adhesive surface energies were also determined using contact angles measurements and the aluminum surface energy was found to increase by as much as 11.7% compared to the non-aged sample, while the PU adhesive surface energy was at least 65% higher than that of the metallic substrate. The peeling resistance of the laminated aluminum was determined by average peel strength measurements and it was found that the variation in peel strength was related to changes in the Al2O3 layer thickness. The delaminated samples were analyzed using scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) and showed the cohesive failure of the aluminum film.