No abstract

A multistage algorithm coupled with the SAFT equation of state is demonstrated on supercritical antisolvent (SAS) fractionation of a model polyethylene with ethylene and 1-hexene. Staging is found to improve the overall solvent selectivities, especially for lights removal. The degree of improvement increases with decreasing size of lights: the smaller the lights the greater the sensitivity to staging. As for the single-stage fractionation, conditions that favor high solvent densities, e.g., high pressure and low ethylene concentration, usually favor high capacities but low selectivities.The temperature effect, however, is not monotonic.

Investigated in this study are the changes in structure and properties of a tetracalcium phosphate/dicalcium phosphate anhydrous/calcium sulfate hemihydrate (TTCP/DCPA/CSH) cement immersed in Hanks' solution. Experimental results show that the phase transition involving the hydration of CSH and formation of calcium sulfate dihydrate (CSD) continues up to 7 d of immersion. The phase transition from TTCP/ DCPA to hydroxyapatite (HA) is substantially completed after 14 d; after that, both CSH and CSD phase largely diminished, whereas HA becomes and remains to be the only dominant phase throughout 42 d of immersion. A maximum compressive strength is reached; after that, the cement gradually decreases in strength. After 42 d, its CS value is down to 8 MPa. The long-term pH value of the Hanks' solution wherein the cement is immersed remains in the range between 5.4 and 7.0. The cytotoxicity test reveals that the viability value of the cells incubated with conditioned medium of cement extraction is 85% that of Al 2 O 3 control and 84% that of blank medium for an extraction ratio of 0.2; and 90% that of Al 2 O 3 control and 93% that of blank medium for an extraction ratio of 0.1.

The present study investigates £-radiation effect on structure and selected properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH) cement immersed in Hanks' solution. The results indicate that, at a dosage of 25 kGy, the working and setting times of the cement paste derived from £-ray-sterilized TTCP/DCPA/CSH powder did not change significantly. At 50 kGy or higher, however, both significantly decreased. A dose of 25 kGy caused the 1-d compressive strength of the cement to decrease by 15%. Further increases in £-ray dose did not further change the strength. After immersion for 1 day, the pH values of all non-sterilized and sterilized samples were in the range of 7.68.0. The XRD patterns of non-sterilized and sterilized powders were substantially similar. After immersion for 1 day, TTCP phase was still distinguishable, while CSH peaks were largely diminished and apatite phase became dominant. The non-sterilized sample had a significantly higher apatite conversion ratio than those of £-ray-sterilized samples. The average 1-d porosity values of all sterilized and non-sterilized samples were similar (3133%). The £-ray-sterilized cement samples had coralline type morphology with numerous tiny apatite crystals and micropores. Compared to the sterilized samples, the non-sterilized cement showed a smoother and denser morphology.