Dispersion polymerization of L-lactide in supercritical carbon dioxide

Triblock (A-B-A) oligomers of ε-caprolactone (ε-CL) (A) and poly(ethylene glycol) with an average molecular weight of 400 (PEG400) (B) were synthesized with three different molecular weight in the range of 2–6 kDa by changing the ratio of PEG400/ε-CL. These oligomers were then used in dispersion polymerization of L-lactide in supercritical carbon dioxide (scCO₂) as stabilizers. 5% stabilizer in the polymerization recipe allowed synthesis of poly(L-lactide) (PLLA) in scCO₂ in the powder form with a weight average molecular weight of around 60 kDa with polymerization yields around 80%. Interestingly, there was almost no effect of stabilizer molecular weight on polymerization. L-lactide polymerization in scCO₂ without any stabilizer was also possible but both the PLLA molecular weight and polymerization yield were lower, and the product was as aggregates instead of powders. A stabilizer concentration of 5% in the polymerization recipe was found adequate. Further increases in the stabilizer load resulted lower molecular weights and lower yields.     

Geometric design of solar-aided latent heat store depending on various parameters and phase change materials

The cylindrical latent heat storage tanks considered here are part of a domestic heating system. In this study, the performances of such energy storage tanks are optimized theoretically. Two different models describing the diurnal transient behaviour of the phase change unit were used. The first is suited to tanks where the phase change material (PCM) is packed in cylinders and the heat transfer fluid (HTF) flows parallel to it (mode 1). The second is suited to tanks where pipes containing the fluid are embedded in the PCM (mode 2). The problem (treated as two-dimensional) is tackled with an enthalpy-based method coupled to the convective heat transfer from the HTF. A series of numerical tests are then undertaken to assess the effects of various PCMs, cylinder radii, pipe radii, total PCM volume in the tank, mass flow rates of fluid, and inlet temperatures of the HTF on the storing time. In addition, optimal geometric design of the store depending on these parameters and PCMs is presented.     

Composition of the essential oil of Stachys sericantha,S. gaziantepensis,and S. mardinensis (Lamiaceae) from Turkey

The genus Stachys L. one of the largest genera of Lamiaceae and Stachys species are used by many people for the therapeutic value of their essential oils. In this study, water-distilled essential oil of three species of Stachys was analysed. The analysis was performed by using gas chromatography-flame ionisation detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS) systems simultaneously. The major components found were hexadecanoic acid (23.7%), dodecanoic acid (11.3%), and caryophyllene oxide (10.7%) for S. sericantha P.H. Davis (endemic); α-pinene (53%), β-pinene (8.2%) for S. gaziantepensis M. Dinc and S. Do?u (endemic); Menthyl acetate (15.3%), isomenthone (15.0%), pulegone (10%), spathulenol (7.0%), and caryophyllene oxide (6.7%) for S. mardinensis (Post) R. Mill.