Thermo-oxidation and hygrothermal effects on cyanate ester polymer materials

Cyanater ester (CE) and siloxane-modified cyanate ester (SMCE) and their graphite composites were investigated.; Thermo-oxidation experiments showed that SMCE gains weight when aged in the air at 100°C but shows virtually no weight gain when aged in argon at 100°C. CE resins show no weight gain when aged in the air or argon at 100°C.; Differential scanning calorimetry (DSC) tests show that glass transition temperature of SMCE decreases about 35°C after aged in the air at 100°C for 3.4 x 106 sec (∼40 days). Three-point bend tests indicated that the flexure strength of SMCE decreased by 20% after aging in the air for 7.63 x 106 sec (∼3 months). FITR results suggest SMCE degrades at 100°C in tile air due to the thermo-oxidation process. The degree of thermo-oxidation of the polymer resin depends strongly on the supply of oxygen from the environment and the diffusion of oxygen in SMCE resin.; Hygrothermal tests show water diffusion in cyanate ester based polymer and its composites is non-Fickian type. FTIR spectroscopy shows that water molecules diffusing into the polymer structure interact chemically with the cyanate ester polymer network. The interaction causes some water molecules to be trapped in the polymer network, thus the water absorption curves deviate from Fickian behavior. Calculation of activation energy supports the contention that water diffusion occurs mainly through the polymer matrix in the composite materials.; Three-point bend tests show that the flexure strength of CE and SMCE decreases with increasing aging temperature. The flexure strength of CE based composites decreases significantly only at high temperature. Results also show the surface degradation of SMCE and CE based composite materials and delamination of SMCE based composite materials after aging in 95°C distilled water for more than 2000 hours. (Abstract shortened by UMI.)...