A simple model to describe the thixotropic behavior of paints

Abstract

We propose a simple rheological model to describe the thixotropic behavior of paints, since the classical hysteresis area, which is usually used, is not enough to evaluate thixotropy. The model is based on the assumption that viscosity is a direct measure of the structural level of the paint. The model depends on two equations: the Cross-Carreau equation to describe the equilibrium viscosity and a second order kinetic equation to express the time dependence of viscosity. Two characteristic thixotropic times are differentiated: one for the net structure breakdown, which is defined as a power law function of shear rate, and an other for the net structure buildup, which is not dependent on the shear rate. The knowledge of both kinetic processes can be used to improve the quality and applicability of paints. Five representative commercial protective marine paints are tested. They are based on chlorinated rubber, acrylic, alkyd, vinyl, and epoxy resins. The temperature dependence of the rheological behavior is also studied with the temperature ranging from 5 ºC to 35 ºC. It is found that the paints exhibit both shear thinning and thixotropic behavior. The model fits satisfactorily the thixotropy of the studied paints. It is also able to predict the thixotropy dependence on temperature. Both viscosity and the degree of thixotropy increase as the temperature decreases.

Thermo‐Rheology of a Proline‐Based Surface‐Active Ionic Liquid: Mixtures with Water and n‐Octane

“…These trends are in good agreement with those reported for protic IL ternary mixtures [16] and other thixotropic materials [15]. S3 shows the Carreau model parameters for the ternary systems (R 2 > 0.979).…”

“…Regarding the hysteresis loop, the area became smaller with increasing temperature (halving from 25 to 55°C). Thixotropic dependence with temperature was previously reported [15]. This fact could be related to the structural order-disorder of the IL interactions.…”

“…Thixotropic dependence with temperature was previously reported [15]. Thixotropic dependence with temperature was previously reported [15].…”

Rheological and mucoadhesive characterization of poly(vinylpyrrolidone) hydrogels designed for nasal mucosal drug delivery

“…This means that shear causes breakdown of inter-particle interactions (Jauùregui-Beloqui et al, 1999). The hysteresis loop area was evaluated to quantify the degree of thixotropy or rheopexy (Armelin et al, 2006). A thixotropic system is characterized by the presence of a positive hysteresis loop, whereas a negative hysteresis loop results from rheopexy.…”

Vegetable oil‐based highly branched polyester modified epoxy based low VOC high solid industrial paint

“…Figure 4 shows the shear viscosity as a function of shear rate for both the paints. Viscosity at high shear rates must be controlled in a narrow range to give sufficient film buildup and coverage without extreme brush or roller drag, or too high pressure in spray painting 33. The low shear rate viscosity must be high enough to prevent in‐can settling and sagging after painting.…”