Oxygen and Water Vapor Permeability

Prior to the measurements, all samples were stored at 23 ◦C and 50% r.h. All tests were conducted at the Fraunhofer IVV, where these methods are accredited.

The reciprocal gas permeability of coated substrates *Q*laminate is the sum of the reciprocals of the gas permeability of the substrate *Q*substrate and the coating *Q*coating (Equation (6)). The oxygen permeability (*OP*) of the coating *OP*coating is calculated from the oxygen transmission rate (*OTR*) of the coating *OTR*coating and the respective coating thickness *d*coating. The *OTR* was measured according to DIN 53380-3 [45] with an automatic high barrier oxygen transmission rate system (OX-TRAN 2/21, MOCON, Minneapolis, MN, USA). A humidity of 50% r.h. and a temperature of 23 ◦C was applied. With reference to the standard conditions (STP, 273 K; 1013 hPa), *OP*coating is given in cm3 (STP) μm m−<sup>2</sup> d−<sup>1</sup> bar−<sup>1</sup> according to Equation (7) [46]. The normalization to a thickness of 100 μm as *OP Q*<sup>100</sup> in cm3 (STP) 100 μm m−<sup>2</sup> d−<sup>1</sup> bar−<sup>1</sup> is reasonable.

$$\frac{1}{Q\_{\text{laminate}}} = \frac{1}{Q\_{\text{substrate}}} + \frac{1}{Q\_{\text{coating}}} \tag{6}$$

$$OP\_{\text{coating}} = OTR\_{\text{coating}} \times d\_{\text{coating}}\tag{7}$$

The water vapor transmission rate *WVTR* of coated polymer substrates and cast films was measured gravimetrically using the cup method described in the DIN 53122-1 [47]. Films with an exposed area *A* of 50.3 cm<sup>2</sup> for coated polymer films and 44.2 cm<sup>2</sup> for cast films with a thickness *d* were used. The bottom of the cup was filled with anhydrous silica gel. The initial weight of the sealed measuring cells was determined, and they were transferred to a desiccator containing a saturated KOH solution to maintain a humidity of 85% r.h. at 23 ◦C. The samples were weighed 5 times within a timeframe *t* of 144 h until the weight gain Δ*m* over a time increment Δ*t* was constant. Transmission rates of the coated films are calculated according to Equation (8). The transmission rate of the pure coating is determined by Equation (6). Films of different thicknesses can be compared via the water vapor permeability *WVP* in g (STP) μm m−<sup>2</sup> d−<sup>1</sup> as calculated by Equation (9) and after further normalization to a thickness of 100 μm (g (STP) 100 μm m−<sup>2</sup> d<sup>−</sup>1).

$$WVTR = \frac{\Delta m}{\Delta tA} \tag{8}$$

$$WVP = WVTR \times d \tag{9}$$

#### Mechanical Testing

Uniaxial tensile tests were carried out on a zwickiLine Z2.5 (Zwick, Ulm, Germany) testing machine as described in the DIN EN ISO 527-3 [48]. The samples were cut in dimensions of 100 mm × 20 mm. After a preload of 0.1 N, a constant extension rate of 25 mm min−<sup>1</sup> was applied. The ultimate tensile strength σUTS and the elongation at break ε<sup>f</sup> were read from the stress-strain curve σ vs. ε. Young's modulus *E* was evaluated according to Hooke's law from the linear-elastic relationship in the initial region of the stress-strain curve (Equation (10)):

$$E = \frac{\sigma}{\varepsilon} \tag{10}$$
