Experimental Analysis of Polymer Nanocomposite Foaming Using Carbon Dioxide
In this research, environmentally benign carbon dioxide (CO2) was used as a physical blowing agent in the foaming of PS and PS nanocomposites due to the phase-out of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). CNFs (carbon nanofibers) and AC (activated carbon) were used as additive/nucleation agents in PS extrusion foaming. Both fillers showed promising application in insulation foams. The typical foaming process includes cell nucleation, cell growth, and cell stabilization. In this study, primary attention was given to the effects of the material related properties, solubility, diffusivity, and shear viscosity, on cell nucleation and cell growth. Two equations of state (EOS), Sanchez-Lacombe (S-L) EOS and perturbed chain statistical associating fluid theory (PC-SAFT), were used to model the solubility and also phase boundaries (binodal and spinodal curves). Nucleation is a very complex phenomenon in physical foam processing. Proposed scaling functions provide a possible way to calculate the energy barrier in the nucleus formation. Cell nucleation rate data were extracted from the literature and also by our experiments. The initial slope of the possible scaling function was calculated by the diffuse interface theory. A scaling function was correlated based on the calculation from experimental data. Shear viscosity of polymers and nanocomposites under high pressure CO2 were studied via unique modified high pressure Couette rheometry. The effects of nanoparticles on shear viscosity of polymer w/ and w/o CO2 were compared. The permeability coefficient, defined as the product of the solubility coefficient and diffusivity, of CO2 and water vapor in polymer nanocomposites and foams were measured near ambient temperature and pressure. The effects of nanoparticle and foam morphology on permeation were studied. To gain more insight on the early stages of the foaming process, in-situ observation of batch foaming and a quenching method were used to study foams with different cell growth times. In addition, the quantitative cell nucleation and growth rates were measured by our novel experimental setup. These cell nucleation rate data provided valuable information for modeling and theoretical correlation. Based on these experimental studies and modeling, a deeper and more comprehensive understanding of polymer and nanocomposite foaming was achieved.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:polymer nanocomposite foam carbon dioxide solubility nucleation cell growth permeation rheology
Date of Publication:01/01/2008