Effect of Temperature and Pressure on Surface Tension of Polystyrene in Supercritical Carbon Dioxide

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry B., 111, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/jp065851tThe surface tension of polymers in a supercritical fluid is one of the most important physicochemical parameters in many engineering processes, such as microcellular foaming where the surface tension between a polymer melt and a fluid is a principal factor in determining cell nucleation and growth. This paper presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendant drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and good qualitative agreement with experiment is obtained. The physical mechanisms for three main experimental trends are explained using SCFT, and none of the explanations quantitatively depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the slope of surface tension change with temperature is dependent on pressure.Natural Sciences and Engineering Research Council of Canada (NSERC) Canadian Foundation for Innovation (CFI) Canada Research Chairs (CRC) Progra

Operational maps between molecular properties and environmental stress cracking resistance (ESCR)

This is the peer reviewed version of the following article: Sardashti, P., Stewart, K. M. E., Polak, M., Tzoganakis, C., & Penlidis, A. (2019). Operational maps between molecular properties and environmental stress cracking resistance. Journal of Applied Polymer Science, 136(4), 47006. https://doi.org/10.1002/app.47006, which has been published in final form at https://doi.org/10.1002/app.47006. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Environmental stress cracking (ESC) is one of the main failure mechanisms involved in polymer fractures. This paper focusses on the environmental stress cracking resistance (ESCR) of polyethylene (PE) in which ESC occurs through a slow crack growth mechanism. In order to predict the ESCR of PE, it is necessary to fully understand the molecular structure of the resin. This paper demonstrates the relationships between molecular structure characteristics and material responses based on experimental characterization and published literature trends. Relationships between ESCR, molecular weight (MW), percentage crystallinity, and density were used to create ESCR and molecular structure maps, which can be used to improve the development of PE resins with a desirable (better/higher) ESCR. These maps along with a logical flow chart offer practical prescriptions and describe pathways towards the development of PE with a desirable ESCR. In addition, this paper presents case studies that demonstrate the effectiveness of this approach.The authors gratefully acknowledge financial support from the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Research Chair (CRC) program, and the Ontario Graduate Scholarship (OGS) program. Many thanks also go to Imperial Oil Limited, Sarnia, ON, Canada, for financial support and for providing resins for the study over many years

Rheological characterization of controlled-rheology polypropylenes using integral constitutive equations

Controlled-rheology polypropylene melts were prepared via molecular modification of a commercial polypropylene resin. A peroxide-initiated degradation was performed, resulting in materials with different molecular weight distributions. These resins were subjected to rheological characterization, and an integral constitutive equation of the K-BKZ type was used to study the effect of molecular weight characteristics on their rheological properties. Data for the linear viscoelastic spectrum and shear viscosities was used to obtain the model constants. The same constitutive equation has been used to predict the stress and Trouton ratios for simple shear and simple elongational flows, thus giving a quantitative assessment of the viscoelastic character of the melts. The results show the effect of the molecular modification on the rheological behavior of the melts. Polymers produced at higher peroxide concentrations exhibit reduced viscoelasticity manifested in less shear-and strain-thinning behavior. The present work clearly shows the potential of integral constitutive equations in fitting and interpreting experimental data and, thus, giving a much better understanding of the rheological behavior of commercial polymers