Degradation of a polyester‐urethane coating: Physical properties

Abstract

In this article we studied the evolution of thermomechanical properties of a polyester-urethane coating during degradation under different degradation conditions, i.e., aerobic and anaerobic conditions with and without dry/wet cycling during degradation. Dynamic mechanical and thermal analyses show that under aerobic conditions the coatings become stiffer and more brittle in the glassy state. This stiffening is probably due to the increase in the amount of hydrogen bonding and the formation of oxidized groups which increase the polarity of the material and enhance the interactions of the polymer segments. However, oxidation reactions result in a considerable decrease in cross-link density and stiffness in the rubbery state. Both changes, in the glassy and rubbery states, give rise to development of internal stresses. These stresses increase as the degradation process proceeds. Nevertheless, for samples exposed to anaerobic conditions, the stiffness remains constant in the glassy state and the cross-link density slightly increases as a result of degradation. This reconfirms the dominance of the effect of oxidation reactions on the mechanical failure of the coatings. Oxygen permeation measurements show a more-or-less time-independent diffusion coefficient and a gradual decrease in solubility of oxygen as a function of exposure time. This results in a slight decrease in oxygen permeation (mainly in the early stage of the degradation) as degradation proceeds.

Effects of ZnO quantum dots on the photostability of acrylate photopolymers used as recording materials

“…The chemical modifications could induce changes in the mechanical properties of polymer films. These latter are generally monitored by dynamic mechanical analysis (DMA) [55,58]. However, it was mentioned in the literature that AFM-nanoindentation was an alternative technique to DMA [59,60].…”

Weathering of a polyester-urethane clearcoat: Lateral inhomogeneities

“…While having all the weathering stress factors applied to the coating at the same time might give a fair overview about the trend of the overall changes of the coating, more insight is created if these stress factors are applied in controlled, decoupled and systematic ways. Therefore, in this paper, we study the surface topology of the coating by means of atomic force microscopy (AFM) under aerobic and anaerobic weathering conditions, as well as in the presence and in the absence of water during weathering, similar to the previous papers [19,20].…”

“…Moreover, how the physical changes are linked to the chemical evolution of the coating as a result of weathering is of particular interest to the scientists in the field [15e18]. Therefore, in previous papers [19,20] we studied chemical and physical changes of a clearcoat of interest under different weathering conditions. In addition, by correlating the changes in the physical properties to the chemical evolution of the coating as a result of weathering, we have increased the insight into the mechanisms of degradation of such a coating.…”

MARTINI-based simulation method for step-growth polymerization and its analysis by size exclusion characterization: a case study of cross-linked polyurethane

“…This expected increase in T g can be explained by two mechanisms, i.e., (a) as cross-linking proceeds, the cooperative movements of polymer segments (beads) become more limited due to the new bond formations and (b) the newly formed urethane groups strengthen the molecular interactions by forming hydrogen bonds. 9 We also calculated the mean squared displacement of the beads as a function of conversion and a more-or-less linear decay is observed, see the ESI, † Section S4. Thus, a linear increase in T g with conversion is a reasonable trend one would expect.…”

“…Moreover, the morphology of a cross-linked PU system combining hard and soft domains can significantly influence the properties of the network. A great deal of experimental work has been devoted to investigating the morphology of PU systems through different analysis methods, e.g., scattering, 8 thermomechanical, 9 and scanning probe microscopy techniques. 10 In parallel, a considerable number of molecular dynamics (MD) simulation studies has been performed to give complementary insights into the matter.…”