https://pure.rug.nl/ws/files/6693298/2006ProgPolymSciNalawade.pdf

Supercritical carbon dioxide as a green solvent for processing polymer melts: Processing aspects and applications

Applications of supercritical CO2 in the fabrication of polymer systems for drug delivery and tissue engineering

Creating a high-efficiency bubble nucleation agent for a polymer foaming process is essential for increasing bubble density as well as decreasing bubble size. Spherulites (crystalline phase) grown in a semicrystalline poly(L-lactide) (PLLA) matrix enhanced carbon dioxide (CO2) bubble nucleation in a batch foaming process. Several sites for PLLA spherulite formation were observed at a hold-temperature of 110 °C after CO2 saturation in molten PLLA, which was heated to 180 °C at 11 MPa. By depressurizing the system from 11 MPa to atmospheric pressure, the dissolved CO2 in the PLLA matrix became supersaturated, and CO2 bubbles nucleated around growing PLLA spherulites. The number of nucleating bubbles increased as a function of increasing spherulite quantity and area. A faster linear spherulite growth rate and a lower hold-temperature created more bubbles around the spherulites. From these observations, it was concluded that the growing spherulites expelled CO2 from the advancing spherulite−amorphous phase in...

Effect of Growing Crystalline Phase on Bubble Nucleation in Poly(L-Lactide)/CO2 Batch Foaming

This paper discusses the research conducted to achieve an accurate bubble-growth model and simulation scheme to describe precisely the bubble-growth phenomena that occur in polymeric foaming. Using the accurately measured thermophysical and rheological properties of polymer/gas mixtures (i.e., the solubility, the diffusivity, the surface tension, the viscosity, and the relaxation time) as the inputs for computer simulation, the growth profiles for bubbles nucleated at different times were predicted and carefully compared to experimentally observed data obtained from batch foaming simulation with online visualization. A polystyrene/carbon dioxide (PS/CO2) system is used herein as a case example. It was verified that the cell-growth model is capable of thoroughly depicting the growth behaviors of bubble nuclei nucleated under varying processing conditions without using any fitting parameter. These results indicate that the established model accounts for most of the physics behind the bubble-growth phenomena...

Computer Simulation of Bubble-Growth Phenomena in Foaming

Measurement of gas solubility and diffusivity in polylactide

The solubility and diffusivity of supercritical carbon dioxide (sc-CO2) in low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ethylene-ethylacrylate copolymer (EEA) and polystyrene (PS) were measured at temperatures from 150°C to 200°C and pressures up to 12 MPa by using the Magnetic Suspension Balance (MSB), a gravimetric technique for gas sorption measurements. The solubility of CO2 in each polymer was expressed by Henry's constant. The interaction parameter between CO2 and polymer could be obtained from the solubility data, and it was used to estimate the Pressure-Volume-Temperature relationship and the specific free volume of polymer/CO2 mixtures. The diffusion coefficients were also measured by the MSB for each polymer. The resulting diffusion coefficients were correlated with the estimated free volume of polymer/CO2 mixture. Combining Fujita's and Maeda and Paul's diffusion models, a model was newly developed in order to predict diffusion coefficients for the polymers studied. Polym. Eng. Sci. 44:1915–1924, 2004. © 2004 Society of Plastics Engineers.

Dai Nakagawa

Papers

Measurement and prediction of diffusion coefficients of supercritical CO2 in molten polymers