Enhancement of Adhesion Characteristics of Low-density Polyethylene Using Atmospheric Plasma Initiated-Grafting of Polyethylene Glycol
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The low-density polyethylene/aluminum (LDPE/Al) joint in Tetra Pak food container provides stability and strength to food packaging, ensures protection against outside moisture, and maintains the nutritional values and flavors of food without the need for additives in the food products. However, it was found that the adhesion strength of LDPE with Al is weak or almost non-existent, due to the non-polar hydrophobic LDPE surface. Therefore, it was necessary to apply surface treatment to LDPE. Plasma-assisted grafting of the LDPE surface with different molecular weight compounds of polyethylene glycol (PEG) was used to improve LDPE/Al adhesion. It was found that this surface modification contributed to significantly improve the wettability of the LDPE surface, as was confirmed by contact angle measurements. The chemical composition changes after plasma treatment and modification process was observed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). A surface morphology was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Adhesion characteristics of LDPE/Al adhesive joints were analyzed by the peel tests. The most significant adhesion improvement of the PEG modified LDPE surface was achieved using 10.0 wt.% aqueous (6000 M) PEG solution, while the peel resistance increased by approximately 54 times in comparison with untreated LDPE.