Polymeric materials with crosslinked matrix have been widely used in many sensitive applications, due to their resilience against extreme environmental conditions. However, the perorfmance of these materials slowly degrade with time depending on the exposed enviormental and mechanical loads. In this study, we investigate the effects of the degradation of polymeric materials due to the extended exposure to sunlight, which can be simulated through controlled accelerated photo-oxidative aging, using ultraviolet (UV) radiation as the main catalyst of this phenomenon. The effects on the mechanical behavior and chemical properties of four polymeric adhesives were accordingly monitored throughout the study. The materials range in hardness with the Polyurethane adhesive being the hardest and acting elasto-plastic, followed by an Acrylic which exhibits greater hardening with time, a Polyurethane sealant, which behaves in an elastomeric manner, and a silicone sealant, which is the softest of the set. Samples were prepared and subjected to UV radiation at three different temperatures namely 45, 60 and 80°C, for different aging periods ranging from 1 day for higher temperatures and 150 days for lower ones. The samples were then subjected to the Fourier transform Infrared spectroscopy (FTIR) test to monitor the change in the chemical composition of the materials along with the aging durations and conditions. The materials were then subjected to mechanical testing along with two modes of mechanical loading which are, simple tension until failure and a double-cyclic test with progressively increasing strain limits after every two successful cycles until the sample reaches failure. The samples are loaded at constant strain rates throughout both tests. These tests revealed the change of behavior of our materials along with the aging periods and conditions. The changes in mechanical behavior vary between each material depending on the aging temperature and period, with the changes ranging from hardening to softening, embrittlement, or an increase in the maximum strain the material can endure before failure. The overall observations  confirmed  matrix hardening occur due to photo-oxidation, however, due to the range of temperatures used throughout the aging process, it will be neutralized by softening induced by thermo-oxidation. Depending on the temperature, the competition between two phenomena dictates the material performance in the long-run.  A visible correlation can be noted between the changes in the mechanical behavior and the changes in absorbance of Infrared (IR) radiation in the FTIR spectrum, as the greater the crosslinking throughout the polymer matrix, the lower the absorbance of IR radiation due to the increased stiffness of the overall macro-molecular structure.


Experimental Investigation on the Performance Loss of Cross-Linked Polymers During Photo-Oxidative Aging

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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