Effects of ultraviolet radiation exposure on vinyl ester resins: characterization of chemical, physical and mechanical damage

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 ultraviolet (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 morphology after 1000 and 4000 h of exposure. 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 after exposure. Changes in the hardness and modulus of the surface after exposure were studied by using an atomic force microscopy (AFM) nanoindentation technique. A significant increase in the apparent hardness of the exposed surface was accompanied by an increase in the apparent modulus of the near-surface region. Morphological 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 and x-ray photoelectron spectroscopy (XPS).