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

Abstract

Buried metal structures such as pipes are usually protected by a coating, often in conjunction with cathodic protection (CP). Whilst this minimizes corrosion, it can also lead to the loss of adhesion between the protective coating and metal structure by a phenomenon called cathodic disbondment (CD). In this study, various medium-density polyethylene (MDPE) compositions with 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 bond strength for all compositions. Differential scanning calorimetry (DSC) and pressure-volume-temperature (PVT) experiments are used to characterize the polymer formulations developed and to aid in the understanding of the reasons 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 dry) is an important parameter to assess and understand the CD performance of coatings. © 2001 Society of Chemical Industry