Comparison of essential oils compositions of Nepeta persica obtained by supercritical carbon dioxide extraction and steam distillation methods

Essential oil of Nepeta persica cultivated in Iran was obtained by steam distillation and supercritical (carbon dioxide) extraction methods. The oils were analysed by capillary gas chromatography using flame ionization and mass spectrometric detections. The compounds were identified according to their retention indices and mass spectra (EI, 70 eV). The effects of different parameters such as pressure, temperature, modifier volume and extraction times (dynamic and static) on the supercritical fluid extraction (SFE) of N. persica oil were investigated. The results showed that under the pressure of 20.3 MPa, temperature of 45 °C, methanol of 1.5% v/v), dynamic extraction time of 50 min and static extraction time of 25 min extraction was more selective for the 4αβ,7α,7aα-nepetalactone. Twelve compounds were identified in the steam-distilled oil. The major components of N. persica were 4αβ,7α,7aα-nepetalactone (26.5%), cis-β-farnesene (4.4%) and 3,4α-dihydro-4aα,7α,7aα-nepetalactone (3.5%). However, by using supercritical carbon dioxide under optimum conditions, only two components have more than 90.0% of the oil. The extraction yield based on steam distillation was 0.08% (v/w). On the other hand, using SFE extraction yield in the range of 0.22–8.90% (w/w) were obtained at different conditions. The results show that, in Iranian N. persica oil, 4αβ,7α,7aα-nepetalactone is a major component.     

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl₂ catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry     

Graft polymerization of acrylic acid onto starch using potassium permanganate acid (redox system)

Graft polymerization of acrylic acid (AA) onto rice starch using postassium permanganate/acid redox system as initiator was investigated. When starch was reacted with KMnO₄ solution, MnO₂ was deposited onto starch. The dependence of MnO₂ amount deposited was directly related to KMnO₄ concentration. Subjecting the MnO₂-containing starch to a solution consisting of monomer (AA) and acid (citric, tartaric, oxalic and hydrochloric acid) formed poly(AA)–starch graft copolymers. The graft yield, expressed as meq COOH/100 g starch, was measured by the amount of MnO₂ deposited, AA concentration, material-to-liquor ratio, kind and concentration of acid, as well as temperature and duration. Finally, the newly prepared poly(AA)–starch graft copolymers were applied to cotton textiles to determine their suitability as sizing agents. The highest graft yield was obtained with citric acid and the least with hydrochloric acid, with tartaric and oxalic acid in between. The graft yield increased by increasing the concentration of acid to a certain concentration beyond which grafting leveled off. A similar trend was observed when the magnitude of grafting was related to the amount of MnO₂ deposited. The graft yield increased by increasing the polymerization temperature from 30° to 50°C. Increasing the temperature to 60°C is accompanied by decreased grafting. On the other hand, fabric samples sized with poly(AA)–starch graft copolymers acquire higher tensile strength, elongation at break, and abrasion resistance than that sized with native rice starch, i.e., poly(AA)–starch graft copolymers serve as good sizing agents for cotton textiles. A tentative mechanism for grafting rice starch with AA using the KMnO₄/acid redox system was elucidated. © 1995 John Wiley & Sons, Inc.     

PVD Coating of Mg–AZ31 by Thin Layer of Al and Al–Si

Although magnesium alloys have the advantage of high specific strength, they have poor atmospheric corrosion resistance. An important method of improving the corrosion resistance is by applying a coating layer. In this work, the physical vapor deposition (PVD) technique is used for coating a magnesium (Mg) AZ31 sheet substrate with a thin layer of high purity aluminum (Al) and Al–12.6% Si. Aluminum is expected to be suitable as a coating layer on Mg sheets, due to its corrosion resistance and its formability. Before coating, the substrate was subjected to several consecutive surface preparations, including sand-blasting, mechanical grinding, mirror-like polishing, ultrasonic etching, and finally ion etching by magnetron sputtering (MS). PVD coating was conducted using a PVD machine with max electron beam power and voltage of 100 kW and 40 kV, respectively. This was either with or without plasma activation, and with variable substrate speeds ranging between 10 and 70 mm/s. During MS ion etching and coating, the substrate temperature increased. The substrate temperature increased with the application of plasma activation and with lower substrate speeds. The coating-layer thickness varied inversely with substrate speed. A thinner coat with finer morphology was obtained in the case of plasma activation. Other results included coating layer characteristics, diffusion between the AZ 31 substrate and the Al coating layer, adhesion of the coating layer to the substrate, and corrosion resistance by a humidity test.     

Synthesis and characterization of (poly (N-vinyl formamide)—pregelled starch—graft copolymer

Bromate / cyclohexanone redox system was investigated as a novel initiator for graft copolymerization of N-vinyl formamide onto pregelled starch. A number of variables in the grafting reaction were investigated including N-vinyl formamide, cyclohexanone, bromate ion, sulphuric acid and pregelled starch concentrations, material to liquor ratio along with polymerization time and temperature. The graft copolymers were evaluated in terms of graft yield, graft reaction efficiency and homopolymer formation (%). The optimum conditions for grafting of N-vinyl formamide onto pregelled starch are: N-vinyl formamide 50% based on weight of substrate, cyclohexanone 15 mmol / l, bromate ion, 30 mmol / l, liquor ratio 10, pH 6, time 120 min., and temperature 40°C. On the other hand, characterizations of the resultant copolymers with respect to swelling capacity, solubility %, metal ion up-take and suitability as a sizing agent for cotton textiles were investigated. The results obtained reflect that, the resultant copolymer shows better results for the aforementioned properties in comparison with that obtained from native pregelled starch as a starting substrate.     

Bimetallic Pt-Metal catalysts for the decomposition of methanol: Effect of secondary metal on the oxidation state, activity, and selectivity of Pt

We present here a study of methanol (MeOH) decomposition over a series of bimetallic Pt-M catalysts, with M = Au, Pd, Ru, Fe. All samples have the same initial size distribution (3 nm nanoparticle height), support (ZrO₂), and preparation conditions. Therefore, differences in the electronic and catalytic properties of the samples tested are related directly to the addition of the secondary metals (M). We find that the oxidation state as well as the activity of Pt is heavily influenced by the addition of the secondary metal. PtO is found to be highly stable in these systems and increasing concentrations of metallic Pt are associated with the surface segregation of metal M due to its affinity for the oxygen present during air annealing.     

Hot water defrosting of a horizontal flat plate cooling surfaceDégivrage par eau chaude d'une surface de refroidissement de plaque plane horizontale

Removal of frost from an jupward facing horizontal cooling plate at a subfreezing temperature using a hot water spray is studied experimentally. The variation of the frost layer with time is approximately linear. A simple analytical model predicts the trend of the frost thickness-time change.