Hibdridni Nd-Fe-B/barijum-ferit magnetni materijali sa epoksi matricom

Lately, there has been great attention paid to the research of bonded hybrid composites with improved dynamic mechanical capacities capable of replacing bonded Nd-Fe-B magnetic materials, by using cheaper (ferrite) materials instead of the Nd-Fe-B powder while retaining the satisfying values of the maximum magnetic energy. The objective of this study is to assess how different contents of Nd-Fe-B and/or barium ferrite particles can affect morphological, dynamic mechanical and magnetic properties of bonded composite materials. The interactions between employed magnetic powders and the interactions between magnetic powders and polymer binder are considered. For the examination of the magnetic behaviour, a vibrating sample magnetometer (VSM) is used. Different shapes and sizes of the obtained hysteresis loops are used for comparison and prediction of the polymer bonded materials properties. The homogeneous distribution of the magnetic particles in the polymer matrix is validated using scanning electron microscopy (SEM). The elastic and damping behavior examined by dynamic mechanical analysis (DMA) show improved properties for hybrid composite materials.Istraživački trend u oblasti polimerom vezanih (bonded) Nd-Fe-B magnetnih materijala se reflektuje kroz razvoj bonded hibridnih kompozita sa poboljšanim dinamičko-mehaničkim svojstvima i primetno nižoj ceni zbog zamene skupe Nd- Fe-B legure jeftinijim magnetnim materijalima (ferit) uz postizanje zadovoljavajućih vrednosti maksimalne magnetne energije. Cilj ovog rada je da ukaže i predvidi uticaj različitog sadržaja Nd-Fe-B i/ili barijum feritnih čestica na morfološka, dinamičko mehanička i magnetna svojstava bonded magneta. Posmatrane su i analizirane interakcije između magnetnih prahova, kao i interakcije između magnetnih prahova i polimernog veziva i njihov uticaj na finalna svojstva bonded magneta. Za ispitivanje magnetnog ponašanja korišćen je vibraconi magnetometar (VSM). Različite veličine i oblici dobijenih histerezisnih krivih su poređeni i korišćeni za predviđanje svojstava ispitivanih kompozitnih materijala. Homogena raspodela magnetnih čestica u polimernoj matrici je potvrđena korišćenjem skenirajućeg elektronskog mikroskopa (SEM). Elastična svojstva i svojstvo prigušenja oscilacija ispitivano je korišćenjem dinamičko mehaničke analize (DMA) koja ukazuje na poboljšana svojstva kod hibridnih kompozita

Direct ultrasound-assisted extraction and characterization of phenolic compounds from fresh houseleek (Sempervivum marmoreum L.) leaves

The effects of ultrasound power and frequency on the yield of total extractive substances (TES), total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity (AOA) of fresh houseleek leaves extracts obtained by direct ultrasound-assisted extraction (DUAE) were studied. Preliminary extraction of plant material was performed using methanol, acetone and 2-propanol by Soxhlet extraction. It was found that maximum TES yield could be obtained by methanol extraction (2.91±0.02), followed by acetone and 2-propanol with a TES yield of 2.32±0.01 and 2.01±0.03 g per 100 g of fresh plant material, respectively. In the fresh houseleek leaves extracts obtained by DUAE and methanol as the chosen solvent, TPC, TFC and AOA were in the ranges of: 40.5–85.9 mg gallic acid/g dry extract, 12.7–19.3 mg rutin/g dry extract and 24.6–108.2μg/ml, respectively. The results showed that the increase in the ultrasound power and extraction time have positive and significant (p < 0.05) effects on the TPC, TFC and AOA, while the increase in the ultrasound frequency leads to a decrease in the TPC, TFC and AOA of the extracts. A chromatographic analysis of crude extract identified the following: kaempferol 3-O-(6’’-O-malonylglucoside)- 7-O-glucosyde, kaempferol 3-O-glucoside-7-O-rhamnoside, luteolin 5-O-(6’’-O-malonylglucoside), kaempferol 3-O-(6’’-O-acetylglucoside)-7-O-rhamnoside, genkwanin 5-O-glucoside, luteolin 5-O-(6’’-O-malonylglucoside), kaempferol 3-O-(6’’-O-malonylglucoside), kaempferol 3-O-rhamnoside, quercetin, genkwanin 4’-O-glucoside and hyperoside. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172047

Hemijski sastav i antioksidativna aktivnost etarskog ulja Thymus serpyllum L.

Wild thyme (Thymus serpyllum L.) is a popular remedy regarding both tradetional and conventional medicine. It is used as the antiseptic, aromatic, expectorant, stomachic, antispasmodic, carminative and preservative substance. For the purpose of this paper, wild thyme essential oil was isolated from the dried herb T. serpyllum by hydrodistillation. Original semi-industrial distillation device SP-130 performing distillation by water and steam was used for the hydrodistillation of T. serpyllum essential oils. The temperature during the hydrodistillation in the device SP-130 ranged from 100-102 °C at atmospheric pressure, and the whole process lasted 5 hours. The isolated essential oil is a liquid of light yellow colour and the odour characteristic of the genus Thymus. Obtained yield of essential oil was 0.08 %, with 65 components identified in the tested essential oil. The most represented chemical groups are sesquiturpene hydrocarbons with 35.1%, and oxygenated sesquiturpenes with 34.8%. The main components of essential oil of T. serpyllum were: trans-nerolidol (24.2%), germacrene D (16.0%), thymol (7.3%), δ-cadinene (3.7%) and β-bisabolene (3.3%). The essential oil showed significantly better ability to neutralize DPPH free radicals (IC50 = 0.503 μL/mL) compared with synthetic antioxidants BHA and BHT. Synthetic chemical compounds such as BHA and BHT are used in food industry as antioxidants due to their ability to prolong the shelf-life of foodstuffs by protecting them against deterioration caused by oxidation, such as fat rancidity, colour changes, degradation of the flavor and loss of nutrient value. In recent years, there is a considerable interest in finding natural compounds that could replace sinthetic antioxidants because of adverse toxicological reports on many synthetic compounds. Lamiaceae herbs and their essential oils or extracts application has proven to be the effective preservation agents for the extension shelf-life of foodstuffs, indicating their potential use in food industry as functional ingredients and food additives. The antioxidant activity of extracts from some Lamiaceae herbs is comparable to that of the most common synthetic antioxidants BHT and BHA. Free radicals are a major cause of many degenerative diseases, such as atherosclerosis, cancer, cardiovascular diseases, inflammatory bowel diseases, skin aging, old age dementia and arthritis. Epidemiological data and randomized clinical trials provide sample indications that antioxidants play a fundamental role in the prevention of cancer and cardiovascular diseases. They act as scavengers of reactive oxygen species and metal chelators that protect human cells and reduce oxidative damages. Natural antioxidants are important in the food industry because they can have a double functionality, that is, they can be useful as a food preservation agents while providing important health benefits for humans by maintaining our health and preventing disease. This investigation showed that the essential oil of T. serpyllum can be an important source for the production and application in the food industry as nutritional supplements, functional food components or natural food antioxidants.Cilj ovog rada bio je ispitivanje hemijskog sastava i antioksidativnog potencijala etarskog ulja majčine dušice (Thymus serpyllum L.). Etarsko ulje majčine dušice izolovano je iz osušene herbe T. serpyllum postupkom hidrodestilacije. Za hidrodestilaciju etarskog ulja T. serpyllum koriščen je originalni poluindustrijski destilacioni uređaj SP-130 koji radi na principu destilacije vodom i vodenom parom. Gasnohromatografskom analizom određene su najzastupljenije komponente kod etarskog ulja T. serpyllum: trans-nerolidol (24,2%), germakren D (16,0%), timol (7,3%), δ-kadinen (3,7%) i β-bisabolen (3,3%). Etarsko ulje je pokazalo značajno bolju sposobnost neutralizacije slobodnih DPPH radikala (IC50 = 0,503 μL/ml) u poređenju sa sintetskim antioksidansima BHA i BHT

Total polyphenols from Solanum retroflexum Dun. fruit: extraction and optimization by response surface methodology

Total phenolic (TPC), flavonoid (TFC) content and antioxidant activity (AOA) of Solanum retroflexum fruit extracts obtained by conventional extraction with different aqueous ethanol solution (25, 50, 75% v/v), temperatures (20, 40, 60 A degrees C) and extraction time (15, 30 and 45 min) were investigated. The extract obtained by 75% aqueous ethanol at 60 A degrees C after 45 min shows the highest AOA determined by DPPH (EC50 = 60.67 mg/ml) and FRAP (1.55 A mu mol Fe2+/mg) methods. TPC and TFC were in ranges from 63.50 +/- 0.43 to 92.07 +/- 1.07 mg of gallic acid/g of dry extract and from 29.17 +/- 0.35 to 48.22 +/- 0.43 mg of rutin/g of dry extract, respectively. In order to commercialize the extraction of polyphenolic compounds, as the most important group of the plant bioactive compounds, the extraction conditions were optimized by response surface methodology. Under proposed optimum extraction conditions (60 A degrees C, 40.3 min and ethanol concentration of 74.7%) extract with the maximal TPC (92.29 mg gallic acid/g of dry extract) could be obtained. The set of the extraction conditions which gave the maximum TPC while simultaneously minimizing the time, energy and ethanol consumption were also proposed (economic extraction conditions). The results confirm that this insufficiently tested fruit represent a good source of polyphenolic compounds and are worthy of further investigation

Fazna topologija elastomernih blendi NR/BR sa aktivnim punilom

The relations between the structure and mechanical properties of a polymer blend of natural (NR) and polybutadiene (BR) rubber (i.e. a NR/BR blend with the weight ratio of the components 70/30) filled with active carbon black were analysed. The properties of the individual phases in the blend were resolved by modeling the stress-strain relationship according to the Bauer procedure for high extensions. The obtained results indicated that BR is the dispersed phase, having a higher modulus, which was also confirmed by the much better fit of the experimental data to the series type of phase coupling according to the Takanayagy theory.U radu se analizira zavisnost strukture i mehaničkih svojstava elastomernih materijala na bazi prirodnog (NR) i polibutadienskog (BR) kaučuka punjenih aktivnim čađima i blende ovih smesa NR/BR u masenom odnosu 70/30. Svojstva individualnih faza u 70/30 NR/BR blendi mogu se na zadovoljavajući način definisati modelom koji uzima u obzir zavisnost napon-deformacija pri velikim istezanjima. U sistemu NR/BR dispergovana faza BR ima viši modul u odnosu na kontinualnu NR fazu, te se interakcija izmedu faza blendi može modelovati na redni način

Hybrid Nd-Fe-B/barium ferrite magnetic materials with epoxy matrix

Lately a great attention has been paid to the research of bonded hybrid composites with improved dynamic mechanical capacities capable of replacing bonded Nd-Fe-B magnetic materials, by using the cheaper (ferrite) materials instead of the Nd-Fe-B powder while retaining the satisfying values of the maximal magnetic energy. The objective of this study is to assess how different contents of Nd-Fe-B and/or barium ferrite particles can affect morphological, dynamic mechanical and magnetic properties of bonded composite materials. The interactions between employed magnetic powders and the interactions between magnetic powders and polymer binder are considered. For the examination of the magnetic behaviour, a vibrating sample magnetometer (VSM) is used. Different shapes and sizes of the obtained hysteresis loops are used for comparison and prediction of the polymer bonded materials properties. The homogeneous distribution of the magnetic particles in the polymer matrix is validated using the scanning electron microscope (SEM). The elastic and damping behaviour examined by the dynamic mechanical analysis (DMA) show improved properties for hybrid composite materials

Practical Examples on Traceability, Measurement Uncertainty and Validation in Chemistry, Volume 2

Case studies on traceability, measurement uncertainty and validation for measurements of retinol and alfα-tocopherol in human serum, cyclamate in soft drinks, arsenic in ground water, sodium chloride in milk products, total organic carbon in waste water are presented in this book. Additionally, the idea and structure of the TrainMic® examples, which complement the TrainMic® theoretical presentations, are described in detail to give complete overview of the TrainMic® teaching material.JRC.D.4-Isotope measurement