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Interphases and Mesophases in Polymer Crystallization I
Polyethylene forms a two-dimensional hexagonal phase, stable at 3 GPa depending on molecular length, which in recent years has been claimed to intervene in crystallization prior to the formation of the usual orthorhombic phase even at atmospheric pressure. This claim is evaluated and shown to be without substance. There is very little evidence that the theoretical possibility of thin lamellae being more stable in the hexagonal phase than the orthorhombic at atmospheric pressure, if the former has sufficiently low fold surface free energy, does occur in practice. But the existence of single crystals of the orthorhombic phase unambiguously shows that they did not have a hexagonal precursor; that would have made them threefold twins. The overwhelming mass of evidence is that orthorhombic and hexagonal phases crystallize independently in accordance with the phase diagram and kinetic competition during growth, as has been understood since the hexagonal phase was discovered.
HDPE Geomembranes in Geotechnics
HDPE (High-density polyethylene) geomembranes are nowadays widely used for large-area liners and construction sealings in geotechnical engineering. Lining of water ponds, dams and dykes, landfill base liners and cover systems, remediation of contaminated sites, waterproof for tunnels, beneath highways and for various other civil engineering constructions are a few examples of application. The book covers all aspects of the HDPE geomembrane field: HDPE materials, geomembrane manufacture, textured geomembranes, properties, long-term performance and testing, installation and welding of geomembranes, quality assurance and control, leak detection, standards, recommendations and regulations. Various important topics are treated in detail. As part of it, the basic physical and chemical facts necessary to fully understand HDPE geomembrane properties and performance are carefully developed and explained.
Enhancing the Dissolution Rate of Atorvastatin by Solid Dispersion Technique
In the last few decades, solid dispersion (SD) technology had been studied as an approach to produce an amorphous carrier to enhance the solubility, dissolution rate, and bioavailability of poorly water-soluble drugs. The use of suitable carrier and methodology in the preparation of SDs play a significant role in the biological behavior of the SDs. Atorvastatin is a statin group HMG-CoA reductase inhibitor drug that is commonly used to adverse cardiovascular events and to lower blood total cholesterol and LDL-cholesterol. the solubility of atorvastatin in water is very low (0.1 mg mL− 1), which results in reduced bioavailability. In order to enhance its solubility, we have prepared solid dispersions (SDs) of atorvastatin at different drug: polymer ratios (1:2, 1:10, 1:20,1:25 and 1:40), using polyethylene glycol 6000 as polymer and different preparation methods (co-precipitate and melting methods) The characterization of the SDs was performed using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) The solubility of AT was improved by the incorporation PEG6000.
