Estimating service lifetimes in weathering: an optimistic view

Abstract

Directly correlating lifetime to coating composition by using standardized, artificial exposures, or even natural exposure, is often very difficult. However, significant progress can be made by breaking down the problem into smaller questions, which can be separately addressed. If one understands the physical parameters that affect end-use properties, then one can also group, and thus correlate, properties according to whether they depend on processes at the surface or in the bulk of a coating, or whether they depend on defects. A scheme is presented that shows how one can use knowledge from analytical physical or chemical materials science in a statistical model related to the ''chemical paradigm.'' Simple physical models that use this information, about the initial state of the coating and its rate of degradation, can be used to compare the performance of coatings and estimate, simply, service lifetime depending on the property of interest, in the environment of interest. One can see that different properties are sensitive in different ways to the degradation process and decay with a different rate. Thus, although properties may be determined by the same degradation process, and location within a coating, they do not correlate directly. These approaches show how to organize our knowledge of degradation processes, and environments, and be able to make some testable predictions on how coating properties deteriorate.

Soluble organic additive effects on stress development during drying of calcium carbonate suspensions

“…Croll [23,24] carried out one of the first systematic studies on the drying behavior of solvent-cast polymer films. He showed that the magnitude of the residual drying stress in a polymer coating is a function of the Young's modulus (E) of the polymer, the volume fraction of solvent at the point of solidification (φ s ), and the volume fraction of solvent in the dry film (φ r ), according to:…”

Corrosion Control of Steel by Organic Coatings

“…With many of these systems, simultaneous control over cure kinetics and solvent release allows for enhanced adhesion and impermeability as does polymer structure (the presence of polar groups) and the mechanism of cure, that is, polymerization after (but not before) application. Some systems (vinyl esters, unsaturated polyesters), as well as those binders crosslinking via condensation-type polymerization mechanisms (phenolics and other formaldehyde-based systems), exhibit high internal stress from shrinkage on polymerization (especially when applied at excessive film thicknesses) and this may be disadvantageous to sustained adhesion [23,24]. Epoxies, however, curing by addition polymerization, shrink less and exhibit much improved adhesion, making very valuable binders for barrier coatings.…”

“…Perhaps, more importantly, certainly with thermosetting (chemically curing systems) internal stress development on drying, arising from solvent release and/or from polymerization, will increase as film thickness increases [24,34]. The stress produced by the conversion of thick films (even strongly adherent epoxies) is capable of overcoming the adhesion of the coating, even over abrasive blasted surfaces.…”

“…that the film is able to withstand before undergoing brittle failure (either cracking or delaminating) at some later epoch in the life of the system. These untoward stress conditions may be ameliorated by reducing the amount of film applied in any single coat [24]. Flat, platelike pigments also tend to reduce the amount of internal stress buildup in coating films [23].…”

Model-based analysis of photoinitiated coating degradation under artificial exposure conditions

“…8 To analyze and improve the correlations between laboratory and field data and increase the understanding of coating behavior during accelerated exposure conditions it is of relevance to quantify the underlying physical and chemical mechanisms and develop overall modeling tools. [9][10][11] Mathematical models can also help to map the coupling of individual rate phenomena.…”