Alternate ultraviolet radiation conditioning

Abstract In this chapter, we report the findings of experimental investigations conducted on durability of glass fiber-reinforced polymer (GFRP) composites with and without the addition of montmorillonite nanoclay. First, neat and nanoclay-added epoxy systems were characterized to evaluate the extent of clay platelet exfoliation and dispersion of nanoclay. GFRP composite panels were then fabricated with neat/modified epoxy resin and exposed to six different conditions, i.e. hot-dry/wet, cold-dry/wet, ultraviolet radiation and alternate ultraviolet radiation-condensation. Room temperature condition samples were also used for baseline consideration. 

GFRP samples of size 60 mm x 12.5 mm x 3.5 mm cut from the panels were subjected to six basic environmental conditions. These were cold (subzero dry, CD), cold (subzero wet, CW), hot (elevated temperature dry, HD), hot (elevated temperature wet, HW), ultraviolet radiation (UV) and alternate ultraviolet radiation and condensation (UC). In addition, room temperature (RT) condition samples (neat, 1 and 2 wt%) were used to generate baseline data. 

For ultraviolet radiation (UV) and alternate ultraviolet radiation and condensation (UC) conditioning, the samples were kept in a QUV/Se weathering chamber (Q-Panel Lab Products, Cleveland Ohio). The samples were conditioned to UV radiation only and to alternate exposure to UV radiation for 4 hours followed by condensation for 4 hours. Phelps and Long [52] reported that thermal energy was sufficient to break bonds in cured epoxy, thus the temperature in the QUV chamber was elevated to provide accelerated degradation maintained at 60°C. The conditioning for this set was carried out for 5, 10 and 15 days. 

Ultraviolet radiation (UV) and alternate ultraviolet radiation and condensation (UC) conditioning... 

The previously discussed principles of grafting-to and grafting-from can also be applied for the modification of polymer surfaces with polymer brushes. However, the binding of linkers and polymerization initiators to polymer surfaces is not as straightforward as it is for oxidic inorganic materials. Thus, dedicated pretreatments are usually necessary. These may include rather harsh reaction conditions due to the chemical inertness of many polymers (see Chapter 3). Alternatively, radiation treatment of polymers (to form radicals) followed by exposure to air may be used to form peroxides and hydroperoxides, which can be directly used as initiators for thermally or ultraviolet-induced graft polymerizations [16,17] (see Chapter 2). 

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