Effects of Ultraviolet Radiation Exposure on Vinyl Ester Matri Resins: Chemical and Mechanical Characterization.
Effects of Ultraviolet Radiation Exposure on Vinyl Ester
Matri Resins: Chemical and Mechanical Characterization.
Signor, A.; Chin, J. W.
American Society for Composites, 16th Technical
Conference. Proceedings. September 9-12, 2001,
Blacksburg, VA, 1-12 pp, 2001.
ultraviolet radiation; atomic force microscopy; vinyl
ester; composite materials; photodegradation; FT-IR
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)