In plastic foam processes, supercritical fluids (SCFs) or gases are used as blowing agents in polymers. Solubility and diffusivity of the SCFs or gases in the polymers have direct effects on many properties such as rheological properties, plasticization behaviors, glass transitions, and crystallization of polymers. There are several methods to obtain diffusivity and solubility such as gravimetric, manometric, spectroscopic, and chromatographic methods. However, these methods are either expensive, complex, or sensitive to an electromagnetic field. In order to overcome these disadvantages, a new method was investigated to determine the solubility and diffusivity by measuring a dielectric property. In this study, we hypothesized that the solubility and diffusivity of a dissolved gas/SCF in a polymer can be measured from the dielectric constants of each component and the mixture. A new device was developed for the capacitance measurements at high temperatures and pressures. We first determined the capacitance values of a pure gas/SCF and a polymer matrix at a given temperature and pressure. Then, we determined the capacitance of a mixture after saturating the matrix with a gas. CO2 was chosen as a gas because it is widely used as a blowing agent with a relatively high solubility in various polymers. High density polyethylene was chosen as a matrix. The results showed that the capacitance of the gas/polymer mixture increased with the amount of dissolved CO2 indicating a strong relationship between the dissolved CO2 amount and the dielectric constant of the mixture. This relationship can be correlated to estimate the CO2 solubility in a polymer.

Relationship between gas solubility/diffusivity and dielectric property under high temperatures and pressures

2019 Fall National Meeting

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