Wetting properties of food packaging

A top-view vibration system for measuring the apparent contact angle corresponding to the global energy minimum was applied in quantifying the effect of plastic film, roughness, and surface treatment on wettability. Liquids representing typical pure liquids (diiodomethane, ethylene glycol) and food products (10% ethanol, 3% fat milk, 10% sucrose, triolein) were tested on low linear density polyethylene (LLDPE) and polyethylene terephthalate (PET), exposed, or not, to commercial corona discharge treatment (CDT). Apparent contact angle values increased with surface tension of the liquid. The counterpart data derived by the common advancing method were higher, and could lead to erroneous values and misleading interpretations. The major effect of CDT was to enhance surface polarity by significantly increasing the polar component of surface free energy. Interactions between the packaging material and food could have a major effect on product quality, and should therefore be taken into consideration.