Effects of Temperature Sequencing During Hygrothermal Aging of Polymers and Polymer Matrix Composites: The Reverse Thermal Effect

摘要

The effects of moisture absorption on vinylester (Derakane 441-400) resin and vinylester/glass fiber (EXTREN) composite have been investigated. Moisture uptake for the neat polymer under isothermal aging conditions in water, was found to obey Fick's second law. Information of moisture uptake at room temperature, 45°C, 66°C and 84°C was used to compute diffusion coefficients and the Arrhenius activation energy. In this study Tg of the polymer was monitored, as a function of moisture content using a DMA for 66°C aging conditions. Also, chemical structure changes were studied for both unaged and fully saturated specimen at 66°C using FTIR. Specific interactions in the form of hydrogen bonding with water were found to exist. Samples were aged in water under a 66°C-room temperature-66°C temperature profile, wherein changes in exposure temperature were made only upon saturation at the previous temperature. The reverse thermal effect was found to exist and information on the hydrogen bonding was used to explain anomalies in moisture uptake profiles. The physical response of the polymer subjected to the above mentioned temperature profile were made by measuring the in-situ full field strains both in the V and 'y' directions using Moire interferometry. This application for Moire facilitated the estimation of temperature induced strains (i.e. α = thermal coefficient) and moisture induced strains (i.e. β = moisture coefficient).