Evaluation of thermodynamic theories to predict interfacial tension between polystyrene and polypropylene melts

Abstract

The commonly used thermodynamic theories (mean field theory and the square gradient theory) to predict interfacial tension between polymers have been modified. The results of these theoretical developments have not yet been fully tested and compared to experimental data. In this paper, experimental data for the effects of temperature, molecular weight, and molecular weight dispersity on interfacial tension for polypropylene/polystyrene polymer pairs are compared with the predictions of the new versions of the above theories. To evaluate these theories, it is necessary to know the Flory‐Huggins interaction parameter for the polymer pairs studied. The relation correlating the Flory‐Huggins interaction parameter to the Hildebrand solubility parameter was not suitable for evaluating the theoretical predictions of interfacial tension. Instead, the Flory Huggins interaction parameter was expressed as the sum of an enthalpic contribution, χH, and entropic contribution, χs. In the absence of reliable experimental values, a method was developed to evaluate the two contributions, based on interfacial tension data. The procedure provided an interaction parameter that is allowed to depend on molecular weight. When this approach was used, the predictions of only the new version of the square gradient theory were in good agreement with the experimental data for the influence of temperature and molecular weight on interfacial tension. However, the theory predicted the effect of polydispersity on interfacial tension only at high temperatures.

Influence of temperature, molecular weight, and molecular weight dispersity on the surface tension of PS, PP, and PE. I. Experimental

“…However, this only happens for higher temperature, showing, once again, that the lower value of the surface tension for polydisperse samples is due to a migration difference of the short molecules to the interface (polymer–air). Similar results already have been shown by Kamal et al34…”

Effect of Temperature and Compatibilizer on Interfacial Tension of PE/PA-6 and PP/EVOH

“…The temperature coefficient of 0.036 is in the range of temperature coefficients reported for most of polymer pairs [1,27] [13]. The temperature coefficient of 0.036 is in the range of temperature coefficients reported for most of polymer pairs [1,27] [13].…”

Understanding droplet coalescence and its use to estimate interfacial tension

“…The spinning drop tensiometry (Vonnegut 1942), its application to polymers (Elmendorp and de Vos 1986;Joseph et al 1992), the pendant drop method (see for example Kamal et al 1997), the filament thread method (Cohen and Carriere 1989), the embedded disk retraction method (Rundqvist et al 1996), the ellipsoidal drop retraction (Luciani et al 1997) or combinations of such methods (filament thread method -ellipsoidal retraction, Tjahjadi et al 1994), all require a very well designed drop or filament to be inserted into another polymer, which is sometimes very difficult. In our instrument, all that is needed is to mix two polymers without having to worry about shaping droplets.…”