Parametric study on the effectiveness of treatment of polyethylene (PE) foils for pharmaceutical packaging with a large area atmospheric pressure plasma source

Atmospheric pressure plasmas have been developed in the last decades for many material treatment applications such as cleaning and activation of surfaces, interaction with in-vivo and in vitro tissues and, as such, they play an increasing role in disinfection and sterilization of surfaces. Heat sensitive polymers can be plasma treated with the final aim of microbial inactivation: given for granted such a capability for many different atmospheric pressure plasma sources, in this work, we focus on the investigation of the effectiveness of the treatment of a polyethylene (PE) polymer foil commonly used for pharmaceutical packaging by means of a Dielectric Barrier Discharge (DBD) operated on a “large area” at atmospheric pressure in ambient air. For effectiveness of the treatment we considered the uniformity of the variation of water contact angle (WC) induced by the plasma on different positions of the treated area (for example, 160×300 mm) and the capability not to affect negatively the properties of the plasma treated packaging material in terms of weldability (for example, hot plate weldability). The surface of the polymer foil has been characterized by measuring the variation of water contact angle (WCA) in different position on the treated sample; Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) has been used to investigate the surface oxidation of the treated samples; moreover, polymer weldability after plasma treatment has been tested on a packaging machine that includes a contact hot plate. This procedure allowed correlating surface oxidation with polymer weldability and with plasma treatment parameters. Results show that it is possibile to select geometrical (DBD gap width; for example, 2mm) and generator operating conditions (for example, 12kV, 100Hz) suitable to obtain uniform change in WCA (for example from 98.2° to 55°) while maintaining good weldability for the treated material. Aging of the treated polymer for what concerns WCA has also been considered, together with treatment time compatible with the final industrial on-line treatment, forming and welding process.