Alfred Tcherbi-Nartech, Ph.D. (2013)
Dissertation Topic: Durability Assessment of Epoxy Matrix Used in Fiber Reinforced Nanoclay-Epoxy Composites Exposed to UV Radiation
Major Professor: Dr. Mahesh Hosur, Research Associate Professor of Materials Science and Engineering
B.S.: Mechanical Engineering, Byeloussian Agrarian State University, Minsk, Belarus
M.S.: Mechanical Engineering, Tuskegee University, Tuskegee, AL
Detrimental effect of UV radiation on polymer degradation has raised major concerns about long-term durability issues related to outdoor applications of fiber reinforced polymer composites, notwithstanding the advantages they offer over traditional materials. In the current study, attempts were made to thoroughly understand polymeric material behavior under UV radiation and subsequent exploration of ways to mitigate the effect while enhancing materials performance. Hence, objective of this research study was to evaluate the influence of different amounts of montmorillonite nanoclay on degradation of SC 15 epoxy resin exposed to varying amount of UV radiation, commonly used as matrix in fabricating fiber reinforced polymeric composite materials.
Addition of nanoclay particles into polymers has shown to influence the degradation mechanism of polymers in a variety of ways. Numerous studies have been conducted in this area using different polymer nanoclay systems; however, there have not been a systematic study using polymer composite cured to different degrees. Diglycidyl ether of bisphenol A based epoxy resin SC 15, was modified with 1 – 3 wt. % montmorillonite nanoclay - Nanomer® I.28E to form epoxy nanocomposites and exposed to UV radiation. Initial exposure of most polymer composites to UV radiation leads to property enhancement due to residual post curing. Therefore, efforts were made in this study to investigate the effects of different amounts of montmorillonite nanoclay on rheological, cure behavior and subsequent development of SC15 composite material properties.
Samples for the study were fabricated using results from cure kinetic studies with various weight percent of nanoclays cured to 70, 80 and 90% without post curing and identical set of samples fabricated according to manufacturers’ recommended cycle and exposed to up to 2500 hours of UV radiation. Systematic evolution and subsequent deterioration of thermo-mechanical and viscoelastic properties, along with thermal stability and service life predictions were monitored and characterized every 500 hours for partially and fully cured samples for comparisons.
Addition of nanoclay decreased the viscosity and consequently affected the cure behavior and evolution of physical properties. Nanoclay also exhibited catalytic behavior, which decreased with increasing clay content during curing while properties increased with increasing clay content irrespective of the extent of cure. Thermo-mechanical and viscoelastic properties of partially cured samples were lower in unconditioned samples compared to fully cured samples. However, overall properties of partially cured samples enhanced over time while those of fully cured degraded for the same period. As a result, there was delay in onset of deleterious effects of UV radiation of partially cured samples.