Enhancement of the Interfacial Adhesive Strength between Low Density Polyethylene and Aluminum Foil for Packaging Applications

Abstract

The low-density polyethylene/aluminum (LDPE/Al) joint in Tetra Pak liquid containers provides stability and strength to the food package, ensures protection against outside moisture, and maintains the nutritional values and flavors of food without needed for additives in the food products. However, the poor adhesion of LDPE to Al, due to the inert non-polar LDPE surface, is a limiting factor and extra polymeric interlayers or surface treatment is required. Two surface modification techniques were employed in order to identify the most appropriate method that achieves stronger adhesion properties, which are : air-flow corona discharge, and corona plasma assisted grafting of the LDPE surface with different molecular weight compounds of polyethylene glycol (PEG) .In brief, it was found that these surface modification techniques contributed to significantly improvement in wettability and polarity of the LDPE surfaces as was confirmed by contact angle measurements. The chemical composition changes after plasma treatment and PEG grafting-to processes were observed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Furthermore, surface roughness and morphology were analyzed before and after LDPE surface treatment by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Adhesion characteristics of LDPE/Al adhesive joints were analyzed by the mechanical peeling test as well as thermodynamic work of adhesion. The most significant adhesion improvement of the LDPE /Al laminate was achieved for corona-treated 10.0 wt.% PEG (6000M) based-aqueous solution grafted into LDPE surface, where the peel resistance value was 163 N/m.