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Effects of Ultraviolet Radiation Exposure on Vinyl Ester Matri Resins: Chemical and Mechanical Characterization.


pdf icon Effects of Ultraviolet Radiation Exposure on Vinyl Ester Matri Resins: Chemical and Mechanical Characterization. (706 K)
Signor, A.; Chin, J. W.

American Society for Composites, 16th Technical Conference. Proceedings. September 9-12, 2001, Blacksburg, VA, 1-12 pp, 2001.

Keywords:

ultraviolet radiation; atomic force microscopy; vinyl ester; composite materials; photodegradation; FT-IR

Abstract:

The increased use of fiber-reinforced vinyl ester composites in outdoor applications has led to questions concerning the environmental durability of these materials, particularly as related to UV exposure. In this work, artificial ultra-violet (UV) degradation was carried out on neat vinyl ester matrix specimens using an integrating sphere-based UV exposure chamber. Significant changes were observed in the bulk mechanical properties, surface chemistry, and surface topography after 1000 h and 4000 h of exposure. ASTM D 638 Type-V specimens with a nominal thickness of 1.6 mm were tested in tension. A transition from slightly ductile to brittle behavior was observed along with a decrease of up to 40% in average strain-to-failure and a decrease of up to 60% in the average specific toughness (toughness normalized to cross-sectional area) after exposure. Changes in the hardness and modulus of the surface after exposure were studied by using an atomic force microscope (AFM) nanoindentation technique. A significant increase in the apparent hardness of the exposed surface was accompanied by an increase in the apparent Young's modulus of the near-surface region. Topographical changes, including an increase in both the number and size of surface defects on the exposed surface were observed using optical microscopy and tapping-mode AFM. Chemical changes in the exposed surfaces were also observed using Fourier-Transform Infrared - Attenuated Total Reflectance (FTIR-ATR) spectroscopy.