Effects of Aging in an Aqueous Solution of NaCl on Impact Strength and Structure of Bisphenol A Polycarbonate

The responses of the impact strength and structure of bisphenol A polycarbonate (PC) to aging in a 5 wt% aqueous solution of NaCl were studied in detail. The results of the Izod notched impact test showed that the impact strength decreased from 71.1 kJ/m(2) to 17.5 kJ/m(2) after an aging time of only 1 day in the aqueous solution of NaCl. The surface appearance of the aged PC observed by polarizing optical microscopy indicated that a large number of microvoids formed, and the size and number of these microvoids increased substantially with an increase in the aging time. The glass transition temperature, measured by differential scanning calorimetry, underwent a slight decrease after aging in the NaCl solution. In addition, no crystallization could be inferred from the heating curves. Thermal gravimetric analysis showed that the thermal decomposition temperature moved to a lower temperature, and the changes of the NaCl solution pH values indicated that hydrolysis was the dominant mechanism of degradation during aging in the aqueous solution of NaCl. Furthermore, the presence of NaCl accelerated the hydrolysis during the early stages of aging. A ductile-brittle transition caused by aging was inferred from observations of fracture surfaces using scanning electron microscopy.