# Effect of Plasma Surface Modification on Print Quality of Biodegradable PLA Films
## 2 Materials and Methods
### Testing of Selected Film Properties before and after Plasma Treatment  
The contact angles of distilled water, diiodomethane 99% CH\({}_{2}\)I\({}_{2}\) (Sigma-Aldrich, Taufkirchen, Germany) and ink were measured. Measurements were made using a DSA 100 drop shape analysis system ([PERSON], Hamburg, Germany) using the tangent method and sessile drops of the liquids deposited using 0.5 mm diameter needles before and immediately after treatment. The results presented are the average of five measurements.The surface free energy of the film as well as its polar and dispersion components were calculated based on contact angle measurements with water and diiodomethane. The Owens-Wenth method was used for these calculations [27; 29].  
Surface roughness were analyzed using a Sensofar Pl\(\upmu\) Neox microscope (Sensofar Metrology, Terrasa, Spain). The following parameters for topographic images were used: objective 50 \(\times\) 0.95 N in white light, measured area 768 \(\times\) 576 pixels (254.64 \(\times\) 190.90 \(\upmu\)m\({}^{2}\)), layer thickness 15.2 \(\upmu\)m, threshold 15%. The analysis was performed on the surface in three areas.  
\begin{table}
\begin{tabular}{c c c} \hline  & **Nativia BOFLA NTSS** & **EarthFirst PLA BCP** \\ \hline Abbreviation used & NTSS & BCP \\ \hline Surface free energy (mJ/m\({}^{2}\)) & 37 & 38 \\ Gloss (GU) & 80 (45\({}^{\circ}\)) & 125 (60\({}^{\circ}\)) \\ Haze (\%) & 1.5 & 7.0 \\ Moisture vapor transmission rate & 440 & 155 \\ MVTR (g/m\({}^{2}\)/d) & & \\ Oxygen transmission rate O\({}_{2}\)TR & 1100 & 450 \\ (cm\({}^{3}\)/m\({}^{2}\)/d) & & \\ Tensile strength MD/TD & & \\ (N/mm\({}^{2}\)) & & \\ \hline \end{tabular}
\end{table}
Table 1: The characteristics of the films used in the study.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **Ink 1** & **Ink 2** & **Ink 3** \\ \hline Trade name & FlexiWet (Chespa) & Urania (Chespa) & Wilfex (Chespa) \\ Kind of resin & Acrylic & PA & NC/PU \\ Kind of ink & water-based & solvent-based & solvent-based \\ \hline \end{tabular}
\end{table}
Table 2: The characteristics of the inks used in the study.  
Weight change analysis of the samples was performed using a Sartorius LE 225D-OCE semimicrob balance (Sartorius, Gottingen, Germany). Samples of 50 \(\times\) 50 mm were weighed immediately before and after activation, and the average of four determinations was reported as the mass change value.  
More details of the measurement runs are reported in earlier works [29; 30].  
Determination of tensile properties of films was carried out according to ISO 527-3 using a static testing machine Roell (ZwickRoell GmbH & Co. KG, Ulm, Germany) and testXpert software. The reported results are the average for the five tested samples.  
The change in color and gloss of the film due to activation was evaluated using a spectrophotometer SpectroEye (GratagMacbeth/X-Rite GmbH, Neu-Isenburg, Germany) and triple angle gloss meter PicoGloss 503 (Erichsen GmbH & Co. KG, Hemer, Germany), respectively. Spectrophotometric measurements were performed under the following instrument operating parameters: light source D65, observation angle 2\({}^{\circ}\) and no filter. Gloss was determined according to the EN ISO 2813 standard. 20\({}^{\circ}\) measurement angles were used, because the measurements made at a 60\({}^{\circ}\) angle were greater than those made at 70 GU.