Book Description

The use of supercritical carbon dioxide, scCO is a gas under atmospheric conditions, it can be used as a processing aid and then easily removed from a polymer through evaporation to obtain the original physical properties of the unplasticized polymer matrix. In addition, CO has been shown to be more environmentally friendly in comparison to many of the traditional organic plasticizers. However, the biggest challenge hindering the widespread use of CO as a plasticizer involves a lack of understanding of and data quantifying its effect on polymer swelling and the concomitant reduction in material viscosity. In this work, a three-step approach is used to investigate and quantify the physical phenomena associated with CO-induced plasticization of polymer melts. First, a novel experimental apparatus was designed and constructed to measure equilibrium swelling, swelling kinetics and diffusion of CO into a polymer melt. It was found that diffusion of CO pressure had a negligible effect on the diffusion coefficient; however, the system temperature directly affected the diffusion coefficient. Increased pressure was found to enhance the extent of swelling whereas a maximum was observed with increasing temperature, at pressures above 15 MPa. The Sanchez-Lacombe equation of state was found to be in good agreement with the experimentally calculated variables, and thus, can be used as a predictive tool to obtain physical properties of the CO-PDMS system. Secondly, a high pressure extrusion slit die rheometer was constructed to measure the viscosity of polymer melts plasticized with low concentrations of CO. Polystyrene, poly(methyl methacrylate), polypropylene, low density polyethylene, and poly(vinylidene fluoride) were all investigated. CO was found to be an efficient plasticizer for all of these polymer materials, generally lowering the viscosity of the melt 30-80%, depending on processing conditions. Predictive viscoelastic scaling models based on free-volume principles and a p.