Dynamic mechanical properties initial changes

Figure 1. The sample was allowed to equilibrate at 20°C In this chand>er under a dry nitrogen purge. At some initial time, 20°C liquid tap water was introduced and circulated through the environmental chamber. For each sample, the water temperature was subsequently cycled between 50 C and 20 C. These temperatures were selected since they correspond with the onset and peak values of the tertiary dynamic mechanical tan 6, w transition. Enough time was allowed between temperature changes to establish "equilibrium" dynamic mechanical property values associated with each hygrothermal state.

The degradation follows an apparent first order reaction with an initial rate (up to 2000 hours exposure in a QUV apparatus) that is faster than the subsequent rate. An assessment of the kinetic data in terms of proposed reaction mechanisms and concurrent changes in properties such as dynamic mechanical behavior can serve as a preliminary basis for evaluation of the material s ability to retain useful properties for time periods consistent with certain design requirements for solar energy system applications. 

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