The effect of accelerated aging on the surface mechanical properties of polyethylene

The surface mechanical properties of polyethylene subjected to accelerated aging in Weathering Tester (QUV) and weatherometer (WOM) chambers were determined by a nanoindentation technique. It was observed that the apparent surface hardness was three times greater than that of the bulk after 1600 h of exposure in the WOM chamber, and a similar increase was also observed after 800 h of exposure in the QUV chamber. The elastic modulus at tip penetration depths of 500 nm also shows a significant increase from 400 to 2000 MPa for samples aged in the QUV chamber during 800 It. For aging times of 200 h and lower the variations in surface mechanical properties are small and restricted to a thin layer, with thickness lower than I pm for samples aged in both WOM or QUV chambers. The modifications in nanomechanical properties were correlated with the corresponding chemical processes due to aging, measured through the carbonyl index profile obtained from ATR-FTIR. An interpretation for the surface cracking of aged LDPE based on differential increases in elastic modulus at different depths is presented. (C) 2003 Elsevier Science Ltd. All rights reserved.