Impact of Environmental Factors on Polymeric Films Used in Protective Glazing Systems

Abstract

Accelerated and natural aging of safety films used in protective glazing systems was investigated by the use of Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy, and tensile tests. Accelerated conditions involved simultaneous exposure of specimens to ultraviolet (UV) radiation between 295 and 450 nm and each of four temperature/relative humidity (RH) environments, i.e., (a) 30 °C at <1 % RH, (b) 30 °C at 80 % RH, (c) 55 °C at <1 % RH, and (d) 55 °C at 80 % RH. Outdoor weathering was performed in Gaithersburg, MD, in two different time periods. FTIR spectra indicate that different exposure conditions have no consequence on the nature and the proportions of the oxidation products, suggesting that similar degradation mechanisms were operative under all outdoor and indoor conditions. In the accelerated exposure, the rate of degradation is found to be influenced dominantly by UV radiation. The combination of UV radiation and temperature results in a cumulative effect, producing more rapid degradation. Analogous to the chemical changes, post-yield mechanical behaviors (such as strain hardening modulus and elongation to break) are markedly reduced, while the Young’s modulus is minimally affected. Photodegradation leads finally to instability in the polymer’s necking behavior and embrittlement, which is explained in terms of chain scissions of the tie molecules in the amorphous region. Samples subjected to outdoor weathering exhibit significantly slower photodegradation, but the degradation mechanism is the same so higher doses of environmental factors can be used to provide reliable acceleration in short-term aging tests.