*2.3. Film Characterization*

#### 2.3.1. Thickness

The thicknesses of the deposited coatings were measured using an Elektrophysik Minitest 735 from Lumaquin, S.A. (Barcelona, Spain). Four values were measured at various points of the samples after each deposition, that is, PET film, PET/PLA fibers, and PET/PLA fibers/SiO2 microparticles. The average and the standard deviation values were determined.

#### 2.3.2. Morphology

The morphology of the resulting coatings and multilayer structures were examined by field emission scanning electron microscopy (FESEM) using a Hitachi S-4800 FESEM from Hitachi High Technologies Corp (Tokyo, Japan). An electron beam acceleration of 10 kV and a working distance of 8–10 mm were applied. The materials were sputtered for 3 min with a thin layer of gold/palladium layer prior to FESEM observation. Image analysis was carried out using the Image J Launcher v 1.05 software.

#### 2.3.3. Transparency

The absorbance of the films, related to transparency, was determined by UV-Vis spectrophotometry using a UV4000 spectrophotometer from Dinko Instruments (Barcelona, Spain) in a spectral range between 390 and 800 nm. The transparency (*T*) was estimated from the absorption at 600 nm (A600) and the thickness of the film in mm (*L*) following the equation *T* = *A*600/*L* (mm) [23]. For evaluating contact transparency, samples were placed on A4 paper sheets containing letters and imaged.

#### 2.3.4. Surface Wettability

The water contact angle (θ) was measured to estimate the wettability of the films with an optical tensiometer in a Video-Based Contact Angle Meter, Theta Lite TL 101 model (Biolin Scientific, Espoo, Finland) using the OneAttension v 3.1 software. A 5-μL droplet of distilled water was deposited on the material surface at room temperature and the image of the drop was recorded. Three different measurements were taken and averaged at different parts of the samples. The sliding angle was determined on a water droplet deposited over the surface whilst being tilted and analyzed with the online software Ergonomics Ruler of the Universitat Politècnica de València (UPV), Valencia, Spain (https://www.ergonautas.upv.es/herramientas/ruler/ruler.php).

#### **3. Results and Discussion**
