**2.3 Aging stresses, levels, and timings**

A first round of tests was performed placing the sample in the oven at a temperature of 270°C for 864 h. Indeed, as it will be exposed in the next section, 270°C is too a low temperature to produce a remarkable aging in PI samples (**Table 1**). Therefore, a second aging cycle lasting 294 h was performed. Knowing the potential negative impact of hydrolysis on PI films, this cycle was carried out placing the samples in a climatic chamber at 80°C with a relative humidity of 80%. Eventually, a last cycle lasting 432 h was carried out placing the samples in the oven at 320°C.

**Figure 3.**

*Test plan for thermal aging at 270°C.*

**Figure 4.** *Test cell for PDIV tests.*


**Table 1.**

*Thermal aging processes.*
