Evolution of mechanical and barrier properties of thermally aged polycarbonate films

Polycarbonate (PC) films of two different grades (Macrolon (R) LED 2245 and Macrolon (R) AL 2447) were elaborated and thermally aged at 100, 120 and 140 degrees C during intermediate and long times of aging. The physical aging effect on the film properties was analyzed by infrared spectroscopy, water contact angle, thermal and tensile tests, and water and gas permeation and sorption measurements. The effect of thermal treatment on PC properties was revealed, especially for the film aged at 120 degrees C. Aging caused a continual increase of PC glass transition temperature and relaxation enthalpy, an increase in Young's modulus and yield strength values and a decrease in the elongation at break. These results were attributed to the reduction of the free volume because of the PC conformational changes. The film barrier properties using liquid water and gas (N-2, O-2 and CO2) molecules as probes were studied in order to highlight the free volume evolution. It was shown that physical aging caused a reduction of water and gas permeability. This fact was mainly explained by the decrease of the solubility coefficient with the aging time increase.