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.

When CO2 is dissolved into a polymer, the viscosity of the polymer is drastically reduced. In this paper, the melt viscosities of low‐density polyethylene (LDPE)/supercritical CO2 solutions were measured with a capillary rheometer equipped at a foaming extruder, where CO2 was injected into a middle of its barrel and dissolved into the molten LDPE. The viscosity measurements were performed by varying the content of CO2 in the range of 0 to 5.0 wt% and temperature in the range of 150°C to 175°C, while monitoring the dissolved CO2 concentration on‐line by Near Infrared spectroscopy. Pressures in the capillary tube were maintained higher than an equilibrium saturation pressure so as to prevent foaming in the tube and to realize single‐phase polymer/CO2 solutions. By measuring the pressure drop and flow rate of polymer running through the tube, the melt viscosities were calculated. The experimental results indicated that the viscosity of LDPE/CO2 solution was reduced to 30% of the neat polymer by dissolving CO2 up to 5.0 wt% at temperature 150°C. A mathematical model was proposed to predict viscosity reduction owing to CO2 dissolution. The model was developed by combining the Cross‐Carreau model with Doolittle's equation in terms of the free volume concept. With the Sanchez‐Lacombe equation of state and the solubility data measured by a magnetic suspension balance, the free volume fractions of LDPE/CO2 solutions were calculated to accommodate the effects of temperature, pressure and CO2 content. The developed model can successfully predict the viscosity of LDPE/CO2 solutions from PVT data of the neat polymer and CO2 solubility data.

Solubility of carbon dioxide (CO 2 ) in a lowdensity polyethylene (LDPE)/titanium dioxide (TiO 2 ) composite was measured using a magnetic suspension balance (MSB) at a temperature from 423 to 473 K and pressures up to 15 MPa. The effect of the TiO 2 concentration on the solubility is investigated by varying TiO 2 content in the range of 0 -20 wt %. Extending the Sanchez-Lacombe equation of state and its mixing rule for binary mixture, a scheme of calculating CO 2 solubility in composite from MSB data is developed. The solubility of CO 2 in the composites increases in proportion to pressure and exponentially decreases with temperature. The apparent solubility, which is defined by the weight of dissolved CO 2 per unit weight of the composite, decreases as the TiO 2 content increases. However, the true solubility, which can be defined by the weight of dissolved CO 2 per unit weight of polymer, is constant, although the TiO 2 content is changed.

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Molecular weight reduction of natural rubber (NR) with hydrogen peroxide (H2O2) oxidizing agent is limited in biphasic water-toluene systems that is attributed to mass transfer. In this work, CO2 was applied to the (aqueous H2O2)-(toluene-NR) systems with the objective of improving reaction efficiency. Experiments were performed on the reaction system with CO2 at 12 MPa and at reaction temperatures and times of 60°C–80°C and 1 h–10 h to evaluate the reaction kinetics. CO2 could enhance the NR molecular weight reduction by lowering the activation energy (from 121 kJ·mol−1 to 38 kJ·mol−1). The role of CO2 in the reaction system seems to be the formation of oxidative peroxycarbonic acid intermediate and promotion of mass transport due to the reduction in the toluene-NR viscosity and interfacial tension. The epoxidized liquid NRs (M̅n=4.9×103 g·mol−1) obtained from NR molecular weight reduction was further processed to prepare hydroxyl telechelic NR (M̅n=1.0×103 g·mol−1) and biobased polyurethane.

Compounds of poly(ethylene-co-vinyl acetate) (EVA with vinyl acetate content 33%) with three different organic peroxides, namely, dialkyl peroxide, peroxyester peroxide, and peroxyketal peroxide, were prepared with a twin screws extruder and a two-roll mixing mill. The cure behavior of the EVA compounds was analyzed from rheographs, which were obtained by a moving die rheometer (MDR) at various curing temperatures between 150˚C to 170˚C. The effects of organic peroxides on cure behavior were examined. The dynamic curing obtained by the torque rheometer provided sufficient experimental data to show that dialkyl peroxide is not suitable because it has a high half-life temperature and its by-products can discolor the final product. Peroxyester peroxide is good for curing at temperatures in the range of 150˚C to 160˚C, which accomplished an ultimate cure within 5 to 8 minutes. Also, the peroxyketal peroxide has higher performance, which decreased the optimum cure time to 3 minutes. The thermal decomposition mechanism of organic peroxide was applied to explain how the cure behavior is affected by generated free radicals.

Water-assisted injection molding (WAIM) has been widely used for tubular plastic parts due to its advantages of relatively low cost and fast cycling time. However, the non-uniform distribution of the wall thickness, especially at the sharp corner, is still a basic problem in the WAIM process. This work presents the effects of sharp corner angles on wall thickness distribution in sections near corners for various processing conditions of the WAIM process, including melt temperature, mold temperature, water delay time, water holding time, and holding pressure. Three grades of polypropylene (PP) resins with different melt flow indices were studied using seven mold geometries that varied the angle of the sharp corner section. The wall thickness distribution at the corner sections were characterized in terms of inner and outer residual wall thicknesses, hollow core ratio, and the percentage of difference between the inner and outer wall thicknesses. In addition, computational fluid dynamic simulations with Moldflow Plastics Insight version 4.1 were performed for each sharp corner angle. It was found that the wall thickness distribution of the straight tube was more uniform than those of the curve tubes. Water injection delay time and water pressure were the major parameters that had a significant impact on the hollowed core ratios, while the percent difference between inner and outer wall thicknesses was mainly influenced by melt temperature.