Surface chemistry changes of weathered HDPE/wood-flour composites studied by XPS and FTIR spectroscopy

The use of wood-derived fillers by the thermoplastic industry has been growing, fueled in part by the use of wood-fiber-thermoplastic composites by the construction industry. As a result, the durability of wood-fiber-thermoplastic composites after ultraviolet exposure has become a concern. Samples of 100% high-density polyethylene (HDPE) and HDPE filled with 50% wood-flour (WF) were weathered in a xenon arc-type accelerated weathering apparatus for 2000 h. Changes in surface chemistry were studied using spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) was used to verify the occurrence of surface oxidation. Fourier transform infrared (FTIR) spectroscopy was used to monitor the development of degradation products, such as carbonyl groups and vinyl groups, and to determine changes in HDPE crystallinity. The results indicate that surface oxidation occurred immediately after exposure for both the neat HDPE and WF/HDPE composites; the surface of the WF/HDPE composites was oxidized to a greater extent than that of the neat HDPE. This suggests that the addition of WF to the HDPE matrix results in more weather-related damage. The results also show that while neat HDPE may undergo crosslinking in the initial stages of accelerated weathering, WF may physically hinder the ability of HDPE to crosslink, resulting in the potential for HDPE chain scission to dominate in the initial weathering stage. (C) 2004 Elsevier Ltd. All rights reserved.