Effect of UV ageing on debonding of double glass laminates based on different crosslinking and thermoplastic PV encapsulants

Abstract

To evaluate the potential of novel thermoplastic polyolefin (TPO) encapsulants as alternative for peroxide crosslinking ethylene vinyl acetate (EVA) copolymer and polyolefin elastomers (POE), compressive shear glass laminates were prepared and characterized using EVA and POE benchmark grades and TPO film adhesives (TPO-3.5, TPO-F and TPO-UV). The specimens were exposed to Xenon arc light with an UV irradiation of 40 W/m2, a black panel temperature of 65 °C and relative humidity of 10 % for up to 3,000 h. Visual, optical, mechanical and chemical changes were assessed by light microscopy, UV–visible–near infrared (UVVISNIR) spectroscopy, compressive shear testing, as well as differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) on fractured surfaces. In contrast to EVA and POE laminates, enhanced birefringence was detected due to a higher degree of crystallinity of the TPO encapsulants. Nevertheless, the investigated TPO double-glass laminates revealed a significantly better ultimate mechanical shear performance at 60 °C, also after UV exposure for 3.000 h. TPO-3.5 was the best-performing grade after 3,000 h followed by TPO-UV, TPO-F, EVA and POE. While the aged and fractured EVA, POE, TPO-F and TPO-UV laminates exhibited carboxylic acid signatures differing in intensity, no carboxylic acid residues were detected on the fractured TPO-3.5 surface. TPO-3.5 is characterized by a lower melt flow index and hence, a higher average molar mass compared to TPO-F and TPO-UV. For the crosslinked EVA and POE, the test temperature was already within the melting range of the non-crosslinked, polyethylene rich phase of these peroxide crosslinked encapsulants.