Effect of hydrothermic ageing on dielectric and mechanical properties of rigid poly(vinyl chloride)

An accelerated hydrothermic ageing (according to N.F.T. 54043 method) was p erformed on samples of rigid poly(vinyl chloride). The test consisted of sa mple immersion in boiling water at 100 degreesC for different exposure peri ods up to 480 h. The samples were removed from the boiling water every two hours for mechanical and dielectric characterization and color test. The di electric measurements carried out on aged samples, up to 40 h, showed that the permittivity remained almost constant and its value was found to be 2.3 in the range -100 to +62.8 degreesC. However, as the temperature approache s the glass transition (T-g = 88.3 degreesC), the permittivity was observed to increase rapidly. It was also found that the permittivity of aged sampl es was lower than that of the non-aged samples. The dielectric loss factor (tan delta) measurements with respect to temperature have confirmed the pre sence of two relaxations: beta at low temperature (around -35 degreesC) and a near the T-g. The combined action of water and temperature reduced the i ntensity of the corresponding relaxation peaks. The sample color index was evaluated up to 480 h using the SYNMERO scale in order to estimate the degr adation extent. Unexpectedly, elongation at break under uniaxial traction r emained unaffected by the hydrothermic ageing, meaning that two competing p rocesses were involved simultaneously (sample degradation via chain scissio n and sample plastification via water absorption).