CHEMICAL-CHANGES IN ENGINEERING THERMOPLASTICS

Parts molded from reground BPA polycarbonate (PC) resin recovered from used objects do not always give the desired physical properties as parts molded from virgin resin. This loss of properties appears due to a surface hydrolysis of the PC which results in a reduction in molecular weight and formation of bisphenol-A (BPA). The hydrolysis appears to be aided by exposure to uv-light and humidity. If the surface of the PC is washed with caustic solution, BPA and low MW oligomers are removed and many of the physical properties of the PC are restored.