The uncertainty in contact angles from the Wilhelmy tensiometer was analyzed using standard error propagation techniques involving partial derivatives across the full range of wettability, from completely wetting to non-wetting surfaces. Uncertainties in force, sample perimeter, and liquid surface tension of 1% were shown to yield uncertainty in contact angles of a few degrees over the middle range of wettability, but exceeded 10° at the extremes.

The uncoated side of dispersion-barrier-coated paperboards was exposed to positive and negative direct current corona treatments in order to confirm the occurrence of backside treatment and clarify its effects on the usability of the paperboard. The main component of the coating dispersions was hydroxypropylated potato starch and the effects of talc and styrene-butadiene latex additions on backside treatment were evaluated. Coatings with a high talc proportion showed excellent initial grease resistance, but corona-induced strikethroughs caused a drastic decrease in grease penetration time. The root-mean-square roughness measurements revealed moderate surface roughening at the backside, indicating thus backside treatment. The alterations in surface free energies and rapeseed oil contact angles confirmed the occurrence of backside treatment. The high polarization potential of latex played a key role in these observations. At the same time, the inertity of talc had a stabilizing effect but it did not prevent backside treatment completely. X-ray photoelectron spectroscopy results verified that backside treatment occurs also when the barrier-coated side of the substrate is treated with corona, indicating that a dispersion coating layer does not prevent this undesired phenomenon. Bearing in mind that expressing customized information or including personalized elements in food packages or disposable cups and plates is under great interest, it can be assumed the exposure of packaging materials to corona will become more common in the near future, and the need for optimizing bio-based packaging materials for such purposes is obvious.

Polymeric hard/soft combinations consisting of a rigid, thermoplastic substrate and an elastomeric component offer many advantages for plastic parts in industry. Manufactured in one step by multi-component injection moulding, the strength of the thermoplastics can be combined with sealing, damping or haptic properties of an elastomer. Bonds of self-adhesive liquid silicone rubber (LSR) on high performance thermoplastics such as polyetheretherketone (PEEK) or polyphenylene sulphide (PPS) are especially interesting e.g. for medical applications due to their outstanding resistance properties. To ensure good adhesion between the two components, surface treatments from an atmospheric pressure plasma jet (APPJ) and a Pyrosil^® flame are applied. Chemical changes on the thermoplastic surfaces are verified by water contact angle measurement (CA) and X-ray photoelectron spectroscopy (XPS). Plasma treatment causes a decline in water contact angle, indicating the formation of functional groups, especially –OH, on the surface. XPS measurements confirm the increase of oxygen on the surface. Thus, the number of functional groups on the thermoplastic surface is enlarged by plasma treatment, leading to stronger bonding to the organofunctional silanes of the self-adhesive silicone rubber. A thin layer of silanol groups is created by the Pyrosil^® flame on the thermoplastic substrates, which could be verified by XPS. A hydrophilic behaviour of the coated surface is noticed. Both surface modification methods lead to enhanced adhesion properties of self-adhesive LSR on thermoplastic surfaces. This is confirmed by 90°- peel tests of the injection-moulded composites leading to an increase in peel force by the applied surface modification techniques.

Different types of PLA films treated by corona are currently available in the market for coating or printing applications. However, data relative to its impact on PLA film properties are scarce and do not generally consider industrial scale production. The objective of this study was to assess the impact of corona treatment on the surface, structure and barrier properties of bi-oriented PLA films produced at industrial scale. Thus, a comparative study between corona treated (CT) and non-corona treated (NCT) PLA films was conducted. The surface of films was studied using Attenuated Total Reflectance Fourier Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and goniometry measurements. The structure of films was analyzed with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and uniaxial tensile analysis. The barrier properties of films to three gases (He, O2, CO2) were also determined. This study unambiguously revealed that corona treatment led to modifications in both surface and bulk of PLA films. In particular, surface analysis displayed the well-known capability of corona treatment to chemically and physically modify the surface of PLA films at the nanometer scale by increasing polarity and roughness. The structural analysis displayed a slight increase in the crystallinity degree and slight modifications in mechanical properties of films. This probably originated from temperature increase associated to corona treatment, which favored physical changes (e.g. relaxation, crystallization) of a part of the bi-orientated PLA chains, and therefore highlights the importance of such an industrial step on the film properties for packaging applications. As a result of these modifications, the barrier properties of films to three gases (He, O2, CO2) are also slightly improved.