Blends of maleic-anhydride-grafted polyethylene with polyethylene for improved cathodic disbondment performance

Buried metal structures such as pipes are usually protected by a coating, o ften in conjunction with cathodic protection (CP). Whilst this minimizes co rrosion, it can also lead to the loss of adhesion between the protective co ating and metal structure by a phenomenon called cathodic disbondment (CD). In this study, various medium-density polyethylene (MDPE) compositions wit h maleic-anhydride-grafted-polyethylene (MAH-g-PE) have been formulated to investigate the effect on CD performance, as well as both wet and dry bond strength. The results indicate an improvement in both CD performance and bo nd strength for all compositions. Differential scanning calorimetry (DSC) a nd pressure-volume-temperature (PVT) experiments are used to characterize t he polymer formulations developed and to aid in the understanding of the re asons for such improvement. Energy dispersive X-ray spectroscopy (EDXS) has been used to obtain surface analysis data on disbonded materials in order to evaluate the failure mode during the CD process. It is found that there may be an optimum loading of the polar functional groups in MDPE necessary for the best CD performance, and that wet adhesion strength (rather than dr y) is an important parameter to assess and understand the CD performance of coatings. (C) 2001 Society of Chemical Industry.