Composite Polymer Protective Coatings for Use in Aggressive Media

摘要

Polymers serve as a basis for developing composite materials with outstanding properties for a variety of technological applications. It appears advisable to adopt this approach in order to develop state-of-the-art polymer protective coatings for use in a wide range of aggressive media.This report looks at the principal physical and chemical processes on which the operational capability of composite polymer protective coatings depends, insofar as these apply to coatings designed for use in highly aggressive media and under stringent operating conditions.Special attention is paid to mass transfer processes occurring in aggressive media, notably to sorption, diffusion and possibility of a selective binding of the medium by a polymer or by special additives. Methods for studying diffusion and sorption in aggressive media are considered. Integrated data are provided on profiles of aggressive media concentration in anticorrosive polymers and on anticipated rates of aggressive component penetration through the coating to the protected substrate. Attempts to develop polymer coatings acting as a total diffusion barrier similar to metal or glass enamel coatings are shown to lack feasibility. Potential for using a protective polymer coating as a selectively permeable layer is considered.The principal types of coating faults are considered, as well as their contribution to mass transfer processes and initiation of coating disintegration. A mechanical stability model for spot adhesion faults in thick linings has been developed, integrating the fault size with the in-service tolerance for adhesion and internal stress.In order to enhance the operational capability of coatings in aggressive environments a concept of sandwich construction has been proposed that would ensure an optimal arrangement of linings with diverse physical and chemical properties and features.The impact of a multilayered coating construction on coating properties is considered. It is shown that optimizing a multilayered structure dramatically reduces permeability to highly aggressive media, eases the overall internal stress, and reduces stress localization in dangerous spots of both coating and substrate. The concept of a multilayered coating construction makes it possible to build up a special layer that adheres to metal and is supposed not only to possess a certain mix of mechanical properties but also to ensure the required, preferably constant, adhesion strength under the impact of penetrating medium. In particular, this adhesion layer is an ideal place for putting corrosion inhibitors and protective additives to work, provided that overlying linings prevent inhibitor washout and reduce the inflow of aggressive medium, thus enhancing the impact of protective additives.Controlled diffusion properties make the concept of a multilayered coating construction especially useful for the development of environmentally friendly coatings.Based on the proposed concept, examples are given of development of certain state-of-the-art polymer coatings for a variety of critical applications.