The origin of residual internal stress in solvent‐cast thermoplastic coatings

Abstract

/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Science, 23, pp. 847-858, 1979 The origin of residual internal stress in solvent-cast thermoplastic coatings Croll, S. G. Journal of Applied Polymer SynopsisExperiments on polystyrene and poly(isobuty1 methacrylate) coatings cast from toluene have shown that residual internal stress is independent of dried coating thickness and initial solution concentration. A theory is presented that predicts the magnitude of the stress and shows that it has no dependence on thickness or initial solution concentration. Internal strain is calculated from the volume of solvent lost after the coating has solidified. This solidification point is identified with the solvent concentration that is sufficient to depress the glass transition of the polymer to the prevailing experimental temperature. A one-to-one correlation is confirmed between the volume of solvent lost from solution during drying and the volume change of the polymer film.

Characterization of sol–gel coatings deposited on a mechanically treated stainless steel by using a simple non-destructive electrical method

“…In this regard, it has been observed that the coatings do not exhibit cracking below a certain critical thickness ranging from 0.5 to 1¯m. 53) The analysis of the cracking evolution of the deposited films (see Fig. 7) shows that not only the amount of deposited ceramic (see Fig.…”

Using the Internal Stress Concept to Assess the Importance of Moisture Sorption-induced Swelling on the Moisture Transport through the Glassy HPMC Films

“…The Poisson's ratio of the HPMC films was taken as 0.35, which is a common approximation value for many polymeric materials (4,14,15). Due to the difficulties of the determination of the fraction of moisture at solidification point, in this study a value of 0.12 was taken, while Croll (1979) suggested a value of 0.162 for polyisobutyl methacrylate.…”

“…Due to the difficulties of the determination of the fraction of moisture at solidification point, in this study a value of 0.12 was taken, while Croll (1979) suggested a value of 0.162 for polyisobutyl methacrylate. Despite this arbitrariness, the trend of the correlation between the excess of internal stress and the moisture content remains the same and the estimated internal stresses are in the same order of magnitude as the values reported by others (7).…”

Characterization of coating systems

“…Internal stresses arise due to shrinkage of the film upon solvent evaporation, thermal stress due to the difference in thermal expansion of the substrate and film, and volumetric stress as the substrate swells during storage. Equation 4 can be used to estimate total internal stress (P) within a film coating, [41][42][43][44] where E is the elastic modulus of the film, ν is Poisson's ratio, Φ s is the volume fraction of solvent at the solidification point of the film, Φ r is the volume fraction of solvent in an air dried film, Δα cubic is the difference in coefficient of thermal expansion between the film and substrate, ΔT is the difference between the Tg of the film and the temperature during manufacturing and storage, ΔV is the volumetric change of the substrate, and V is the original volume of the substrate core.…”