Shear rate and cooling modeling for the study of candelilla wax organogels' Theological properties

摘要

The rheological properties evolution, during the organogelation by cooling of candelilla wax (CW) solution in safflower oil, was studied using computational fluid dynamics (CFD). A simulated storage modulus (G') model agreed satisfactorily with experimental observations. The gelation of 3% CW solutions was done using static conditions during the whole process (90-5 ℃), or by applying a shear rate (180, 300 and 600 s(-1)) during cooling from 90 ℃ to 52 ℃ and then continuing the cooling under static conditions up to the final temperature (i.e. 5 ℃). The proposed model predicts G' evolution as a function of temperature, and considers the final torque Γ_f of the sheared stage as an inductor of molecular flow alignment. Predictions revealed that the final solid-like component (i.e. G') increases as the shear rate increases up to a maximum for a shear rate of about 400 s(-1). Then, final G' value diminishes gradually, probably due to the destruction of microstructures that generate the gelation. The model was validated by graphical methods and variance measures. The results demonstrate the potential of CFD to allow the development of a model linking process variables (i.e. cooling and shearing) and rheological properties. This model can be successfully applied for process control purposes and for the design of organogels with predefined properties.