Mechanical Insights Into Polymeric Multilayers Films Using Nanoindentation and the Structural Compliance Method

Abstract

This study introduces a novel approach to characterising the mechanical properties of polymeric multilayer films used in photovoltaic (PV) backsheets through nanoindentation (NI). While traditional methods, like tensile testing, measure overall mechanical performance, NI enables layer‐specific analysis, which is essential for understanding multilayer structures. Here, we employ the structural compliance correction method to address challenges of specimen‐scale flexing and edge effects in NI, enabling accurate measurements of hardness and elastic modulus across distinct film layers. Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and Raman spectroscopy were used to identify the different film layers, which included polyamide (PA), polyvinyl fluoride (PVF), polyethylene terephthalate (PET) and an aromatic polyester‐based urethane adhesive. The NI results reveal substantial variation in mechanical properties across layers, with PET showing the highest hardness (200–250 MPa) and modulus values (4–5 GPa). PA offered a hardness of 100–150 MPa and a modulus of 2–3 GPa, followed by PVF with 50–100 MPa hardness and 1–2 GPa modulus. The adhesive layer had the lowest hardness (1.2–1.4 MPa) and modulus (200–400 MPa). Importantly, the structural compliance correction reduced measurement errors caused by specimen‐scale flexing and edge effects. Additionally, we observed a small indentation size effect in PET and the adhesive. This study highlights the importance of the structural compliance correction in NI of multilayer films and paves the way for more precise degradation mapping and longevity predictions in polymeric film applications.

Citation

Christoefl, P.; Jakes, J. E.; Geier, J.; Pinter, G.; Oreski, G.; Stone, D.; Teichert, C. 2026. Mechanical Insights Into Polymeric Multilayers Films Using Nanoindentation and the Structural Compliance Method. Strain. 62(2): e70032. 16 p. https://doi.org/10.1111/str.70032.