bluuebunny/crossref_metadata_2025 huggingface dataset:
Concept of contemporary methods for monitoring and determination of cyanide in water
Authors: Cickaric Dragana , Rajakovic Ljubinka
Published: July 2008

The quality of life depends on water quality. Good water quality and the rational use of water are an absolute need of the new millennium. Although it is an ecological and health priority to prohibit the contamination of water and water protection, it is a responsibility for environmental engineers and chemists to develop and apply effective methods for monitoring and controlling of water quality, and at that way prevent ecological and technological catastrophe on time. In this paper modern methods and process for monitoring, control and detection of cyanide in water and wastewater are presented. Recent developments in instrumental techniques and treatment for determination of this toxic substance in water are described, particularly the methods according to green analytical aspects.
Demulsification based on the thermal treatment (cooling and heating) of W/O emulsions
Authors: Rajakovic Vladana , Skala Dejan
Published: July 2008

An important step in waste water treatment is the removal of oil from an O/W emulsion and the separation of oil and water into two phases, a process usually called demulsification. Modern methods of oil removal from waste water were described in the present study. Typical demulsification techniques include thermal, electrical, chemical, acoustic, or mechanical methods of emulsion treatment. The freeze/thaw process was found to be very effective for demulsification. In the freeze/thaw process, water removal from the W/O emulsion depends on the initial oil content, freezing temperature, freezing time, thawing rate and temperature. The described method is a non-destructive and physical method of emulsion treatment and because there is no addition of chemical agents there is no problem of further waste water treatment, which usually exists when chemicals are applied for demulsification. Different methods for oil content determination in the O/W emulsion were also applied and compared in this study (gravimetric, volumetric, measurement of oxygen consumption and emulsion pH, IR analysis of the emulsion, electro analytical measurement).
Thermo radial drying of paper coatings
Authors: Valent Vladimir
Published: July 2008

The thermo radial drying of material (paper) was discussed. The basic and most important parameters of the process of industrial drying (paper coatings) were defined.
Empirical models for viscosity variation in bulk free radical polymerization
Authors: Curteanu Silvia , Bulacovschi Victor
Published: July 2008

The validity of the Lyons-Tobolsky equation for bulk polymerization systems was verified by comparing simulation results to experimental data for different reaction conditions (temperature and initiator concentration). In this model, formerly applied for solution polymerization, the viscosity of the reaction mass was used instead of solvent viscosity. For example, the chemically initiated free radical polymerization of methyl methacrylate was considered to be achieved in a batch bulk process. In the Lyons-Tobolsky equation, the viscosity was calculated using the values of the conversion and molecular weight resulting from the kinetic model simulation. Consequently, a general discussion about the concordance between the simulation and experiment was useful, especially to emphasize the causes that generate modeling errors. It is more convenient to estimate the viscosity independently of conversion and molecular weight and, in this way, without solving the kinetic model. Empirical relations which correlate viscosity with time were elaborated using experimental viscosity data. Two kinds of models were proposed: a) two fifth order polynomials corresponding to the conversion domains before and after the gel effect; b) a model that fits the experimental data well in the whole conversion domain. Generally, these empirical models provide good simulation results and they can be easily handled.
The effect of hydrodistillation technique on the yield and composition of essential oil from the seed of petroselinum crispum (mill.) Nym. Ex. A.W. Hill
Authors: Stankovic Mihajlo , Nikolic Nada , Stanojevic Ljiljana , Cakic Milorad
Published: July 2008

The essential oil was isolated from the seed of Petroselinum crispum (Mill.) Nym. ex. A.W. Hill by using different techniques of Clevenger-type hydrodistillation. The highest yield of oil, after five consecutive hydrodistillation runs (3.9 mL/100 g of plant material), was obtained by the technique in which water from the still flask was separated by filtration and used together with fresh water for immersing the plant material in a subsequent distillation. Regardless of the technique used, the oil contained different amounts of ?-pinene, ?-p/nene, limonene, 2,3,4,5-tetramethoxy-1-allylbenzene, apiole and 1,2-benzenedicarbonic acid.
Synthesis of thermoplastic poly(ester-olefin) elastomers
Authors: Tanasijevic Branka , Elkhaseh Salem , Nikolic Marija , Djonlagic Jasna
Published: July 2008

A series of thermoplastic poly(ester-olefin) elastomers, based on poly(ethylene-stat-butylene), HO-PEB-OH, as the soft segment and poly (butylene terephthalate), PBT, as the hard segment, were synthesized by a catalyzed transesterification reaction in solution. The incorporation of soft hydrogenated poly(butadiene) segments into the copolyester backbone was accomplished by the polycondensation of ?, ?-dihydroxyl telechelic HO-PEB-OH, (PEB Mn = 3092 g/mol) with 1,4-butanediol (BD) and dimethyl terephthalate (DMT) in the presence of a 50 wt-% high boiling solvent i.e., 1,2,4-trichlorobenzene. The molar ratio of the starting comonomers was selected to result in a constant hard to soft weight ratio of 60:40. The synthesis was optimized in terms of both the concentration of catalyst, tetra-n-butyl-titanate (Ti(OBu)4), and stabilizer, N,N'-diphenyl-p-phenylenediamine (DPPD), as well as the reaction time. It was found that the optimal catalyst concentration (Ti(OBu)4) for the synthesis of these thermoplastic elastomers was 1.0 mmol/mol ester and the optimal DPPD concentration was 1.0 wt-%. The extent of the reaction was followed by measuring the inherent viscosity of the reaction mixture. The effectiveness of the incorporation of the soft segments into the copolymer chains was proved by Soxhlet extraction with chloroform. The molecular structures, composition and the size of the synthesized poly(ester-butylene)s were verified by 1H NMR spectroscopy, viscometry of dilute solutions and the complex dynamic melt viscosity. The thermal properties of poly(ester-olefin)s were investigated by differential scanning calorimetry (DSC). The degree of crystallinity was also determined by DSC. The thermal and thermo-oxidative stability were investigated by thermogravimetric analysis (TGA). The rheological properties of poly(ester-olefin)s were investigated by dynamic mechanical spectroscopy in the melt and solid state.
Protective properties of epoxy coatings electrodeposited on steel electrochemically modified by Zn-Fe alloys
Authors: Bajat Jelena , Miskovic-Stankovic Vesna , Kacarevic-Popovic Zorica
Published: July 2008

Epoxy coatings were electrodeposited on steel and steel modified by Zn-Fe alloys using the constant voltage method. Zn-Fe alloys were electrodeposited on steel at different current densities. The effect of the Zn-Fe alloy on the corrosion behavior of the epoxy coating was interpreted in terms of the electrochemical and transport properties. It was shown that the best properties, i.e. the largest values of the pore resistance and the smallest values of the coating capacitance, a longer period of almost constant Rp and Cp values, and the smallest diffusion coefficient of water through the epoxy coating, as well as the smallest amount of water absorbed inside the epoxy coating, were found for epoxy coatings on steel modified by a Zn-Fe alloy deposited at 4 A dm-2. During prolonged exposure to 3% NaCl, this Zn-Fe alloy significantly improves the corrosion stability of the epoxy coating: almost unchanged values of Rp and Rct were observed, due to the formation of a pseudo-passive layer of corrosion products, which is a good barrier to the transport of water, oxygen and electrolyte ions.
Biopolymer chitosan: Properties, interactions and its use in the treatment of textiles
Authors: Jocic Dragan , Topalovic Tatjana
Published: July 2008

The biopolymer chitosan is obtained by the deacetylation of chitin, the second most abundant polysaccharide in nature, after cellulose. It is becoming an increasingly important biopolymer because it offers unique physico-chemical and biological properties. Due to its solubility, chitosan allows processing from aqueous solutions. This review provides information on important chitosan properties, as well as on some interactions that are of special interest for chitosan application. It summarizes some of the most important developments in the use of chitosan in the treatment of textile materials. Special emphasis is given to improved dyeing properties of the textile material treated with chitosan.
Synthesis of ester-siloxane multiblock copolymers
Authors: Antic Vesna , Vuckovic Marija , Govedarica Milutin
Published: July 2008

It was shown that the two-stage transesterification/polycondensation reaction in the melt, can successfully be applied for the preparation of poly(butylene terephtalate-dimethylsiloxane) multiblock copolymers. Three series of co-polymers were synthesized, using poly(dimethylsiloxanes) bearing ester (two series) and hydroxy -end groups as reactants. The structure and composition of the obtained copolymers were determined by 1H NMR spectroscopy A mechanism, i.e. an order of reaction steps, involved in the preparation of the copolymers, was suggested.
Lyophilization: The process and industrial use
Authors: Przic Dejan , Ruzic Nenad , Petrovic Slobodan
Published: July 2008

This article presents a general overview of lyophilization and discusses the underlying principles of the process through the basics of: formulation, freezing, primary drying and secondary drying. In this article lyophilization is defined as a stabilizing process in which the substance is first frozen and then the quantity of the solvent is reduced first by sublimation (primary drying) and then by desorption (secondary drying) to values that will no longer support biological growth or chemical reactions. Special mention was made of the industrial use of the process and emphasis was placed on the lyophilization of pharmaceutical products and food industry products. Lyophilization equipment, as well as the formulation of materials that can be lyophilized, are described in sufficient detail to give information on the restrictions and advantages of lyophlization. Processing economics and comparison with conventional drying methods are presented. A historical overview of the process and future developments presented from the industrial viewpoint give an insight on the previous application of lyophilization and the prospects of its broad industrial use.
Kinetic models of reaction systems for the in situ epoxidation of unsaturated fatty acid esters and triglycerides
Authors: Jankovic Milovan , Sinadinovic-Fiser Snezana
Published: July 2008

Mathematical models that describe the kinetics of reaction systems for the in situ epoxidation of unsaturated fatty acid esters or triglyc?rides with organic peracids are reviewed in this paper. The advantages and inadequacies of each model are discussed. A mono-phase pseudo-first order kinetic model was compared with a two phase model based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) postulates proposed by the authors of this paper. The comparison was performed on the experimentally determined values for the in situ epoxidation of soybean oil by peracetic acid in the presence of different quantities of ion exchange resin used as the catalyst. It was concluded that a complete model for in situ epoxidation in the presence of ion exchange resin as the catalyst was still not given for perorganic acid formation. In particular, we report here the possibilities of the creation of an "ideal" model for in situ epoxidation.
Refractive indices of ternary liquid mixtures containing aliphatic alcohols at several temperatures
Authors: Sovilj Milan , Barjaktarovic Branislava
Published: July 2008

The refractive indices of ternary liquid mixtures (2-propanol+2-butanol+ethanol) and (chloroform+2-propanol+2-butanol) were measured at 20, 25, 30, and 35?C, and atmospheric pressure. The results were used to calculate the refractive index deviations over the entire mole fraction range for the mixtures. The refractive index deviations for the ternary mixtures were further fitted to empirical correlations (Cibulka Nagata-Tamura, and Lopez et al) to estimate the ternary fitting parameters. Standard deviations and average percentage deviations from the regression lines are shown. The best fit was obtained by the Nagata-Tamura empirical correlation. Some of the existing predictive equations for the refractive index deviations (Tsao-Smith, K?hler, and Colinet) were tested.
Correlation between UV-VIS spectra and the structure of Cu(II) complexes with hydrogenated dextran in alkaline solutions
Authors: Nikolic Goran , Cakic Milorad , Mitic Zarko , Nikolic Ruzica , Ilic Ljubomir
Published: July 2008

UV-VIS spectrophotometric investigations of Cu(II) complexes with hydroge-nated dextran showed that the complexation of Cu(II)-ions began at pH > 7. The formation of Cu(II) complexes with dextran monomer units was observed at pH 7-12. With further increase in solution pH > 12, the Cu(II)-dextran complex decomposed to Cu(OH)42~-ions and dextran. With increasing solution pH the absorption maximum of complex solutions increased and shifted to shorter wavelength (hypsochromic shift) compared with uncomplexed Cu(II). The UV spectra displayed bathochromic shifts. The changes of UV-VIS spectra with increasing in solution pH confirmed the formation of different kinds of complex species. The correlation between the results of UV-VIS spectrophotometry and the central metal ionligand coordination predicted that the copper binding within the complex depended on the pH and participation H2O molecules. Dextran complexes with Cu(II) were formed by the displacement of water molecules from the coordination sphere of copper by OH groups. The analysis indicated that the Cu(II) center was coordinated to two glucopyranose units of dextran. The spectrophotometric parameters of the investigated complexes were characteristic of a Cu(II)-ion in a square-planar or tetragon ally distorted octahedral coordination.
Critical review of relations for predicting the normal freezing point of organic compounds
Authors: Jovanovic Jovan , Grozdanic Dusan
Published: July 2008

This paper presents empirical relations for predicting the normal freezing point of organic compounds. Nine relations were tested with 90 organic compounds. The Meyer-van der Wyk and Kreglewski-Marano-Holder models are recommended for normal alkanes, and the Constantinou-Gani and Wen-Qiang II models for all tested organic compounds.
The fuel cell yesterday, today and tomorrow
Authors: Stanojevic Dusan , Tomic Milorad
Published: July 2008

The fuel cell has some characteristics of a battery carrying out direct chemical conversion into electric energy. In relation to classical systems used for chemical energy conversion into electric power, through heat energy and mechanical operation, the fuel cell has considerably higher efficiency. The thermo-mechanical conversion of chemical into electric energy, in thermal power plants is carried out with 30% efficiency, while the efficiency of chemical conversion into electric energy, using a fuel cell is up to 60%. With the exception of the space programme, the commercial usage of the fuel cell did not exist up to 1990, when the most developed countries started extensive financial support of this source of energy. By 1995, more than a hundred fuel cells were installed in the process of electricity generation in Europe, USA and Japan, while nowadays there are thousands of installations, of efficient energetic capacity. Because of its superior characteristics, the fuel cell compared to other commercial electric energy producers, fulfills the most important condition - it does not pollute or if it does, the level is minimal. With such characteristics the fuel cell can help solve the growing conflict between the further economic development of mankind and the preservation of a clean and healthy natural environment.
Willow wood (Salix alba) as a raw material for pulp production
Authors: Klasnja Bojana , Orlovic Sasa , Radosavljevic Nenad , Markovic Miroslav
Published: July 2008

The properties of willow wood (structural-physical and mechanical properties and chemical composition) were investigated to determine the parameters of the technological process of semichemical and sulphate pulp manufacture. The experimental material was willow wood Salix alba cl. 107/65/7. Semichemical and sulphate pulp were obtained in the laboratory. The yield, chemical properties and physical-mechanical properties of the obtained intermediate products intended for paper manufacture, were determined. The properties of poplar wood Populus deltoides Bartr. cl.725, were studied and its pulp production performed with the aim of comparison.
Economic state of the cellulose and paper industry under transition conditions
Authors: Cvetkovic Natasa , Grgurevic Slavenko
Published: July 2008

After many decades of relatively stable development, input development trends were stopped in the late eighties, when the cellulose and paper industry, as well as the whole society, entered the phase of "transition", marked by processes of (neo)liberalisation, disintegration and privatization and consequently processes of decreasing productivity and production as a whole. The transition has left difficult consequences in every part of the national economy, hence causing the economic process of anti-development.
Industrial applications and current trends in supercritical fluid technologies
Authors: Gamse Thomas
Published: July 2008

Supercritical fluids have a great potential for wide fields of processes Although CO2 is still one of the most used supercritical gases, for special purposes propane or even fluorinated-chlorinated fluids have also been tested. The specific characteristics of supercritical fluids behaviour were analyzed such as for example the solubilities of different components and the phase equilibria between the solute and solvent. The application at industrial scale (decaffeinating of tea and coffee, hop extraction or removal of pesticides from rice), activity in supercritical extraction producing total extract from the raw material or different fractions by using the fractionated separation of beverages (rum, cognac, whisky, wine, beer cider), of citrus oils and of lipids (fish oils, tall oil) were also discussed. The main interest is still for the extraction of natural raw materials producing food ingredients, nutraceuticals and phytopharmaceuticals but also cleaning purposes were tested such as the decontamination of soils the removal of residual solvents from pharmaceutical products, the extraction of flame retardants from electronic waste or precision degreasing and cleaning of mechanical and electronic parts. An increasing interest obviously exists for impregnation purposes based on supercritical fluids behaviour, as well as for the dying of fibres and textiles. The production of fine particles in the micron and submicron range, mainly for pharmaceutical products is another important application of supercritical fluids. Completely new products can be produced which is not possible under normal conditions. Supercritical fluid technology has always had to compete with the widespread opinion that these processes are very expensive due to very high investment costs in comparison with classical low-pressure equipment. Thus the opinion is that these processes should be restricted to high-added value products. A cost estimation for different plant sizes and different applications was also analyzed.
Gas-holdup in a 16.6 cm I.D. reciprocating plate column
Authors: Vasic Ljubisa , Bankovic-Ilic Ivana , Lazic Miodrag , Veljkovic Vlada , Skala Dejan
Published: July 2008

The effects of operation conditions (the vibration intensity and gas flow rate) on the gas holdup in a 16.6 cm i.d. two-phase reciprocating plate column (RPC) were studied. Distilled water and aqueous solutions of carboxymethyl-cellulose of different concentration were used as the liquid phase and air as the gas phase in this investigation. The gas holdup was measured after the gas flow and the reciprocating action had been stopped. An empirical correlation which correlates the gas holdup with the specific power consumption and the superficial gas velocity showed that the aeration intensity had a greater influence on the gas holdup than the intensity of agitation. Because the gas holdup was approximately the same in RPC's of different diameters, an equation relating the gas holdup with the specific power consumption and the superficial gas velocity was derived. The correlation could be used in the scaling up of reciprocating plate columns.
Catalytic conversion of ethanol on H-Y zeolite
Authors: Cegar Nedeljko , Penavin-Skundric Jelena , Skundric Branko , Petrovic Rada
Published: July 2008

The catalytic activity of the H-form of synthetic zeolite NaY was examined in this study. The catalytic activity was determined according to the rate of ethanol conversion in a gas phase in the static system. In the conversion of ethanol on synthetic NaY zeolite at 585, 595, and 610 K, on which the reaction develops at an optimal rate, ethene and diethyl ether are evolved in approximately the same quantity. After transforming the NaY zeolite into the H-form, its catalytic activity was extremely increases so, the reaction develops at a significantly lower temperature with a very large increase in the reaction rate. The distribution of the products also changes, so that at lower temperatures diethyl ether is elvolved in most cases, and the development of ethene is favored at higher ones, and after a certain period of time there is almost complete conversion of ethanol into ethene. The increase in catalytic activity, as well as the change of selectivity of conversion of ethanol on the H-form of zeolite, is the result of removing Na+ cations in the NaY zeolite, so that more acidic catalyst is obtained which contains a number of acidic catalytically active centers, as well as a more powerful one compared to the original NaY zeolite.
Coagulation and flocculation in the preparation of drinking water in a pilot plant
Authors: Ilicic Gordana , Maksimovic Milorad , Vojinovic Djordje
Published: July 2008

The objective of the practical part in this article was to explore the influence of different parameters on coagulation and flocculation processes as well as the influence of this stage on other stages in water purification. Analysis of the water samples was conducted in the chemical laboratory of Banja Luka Municipal Waterworks using standard methods for analyzing drinking water. The results are presented as diagrams that show the dependence of different parameters as a function of the residual turbidity and the content of natural organic matters in water. The following conclusions were drawn It is necessary to conduct the chemical treatment of raw water with the aim to satisfy chemical and bacteriological standards for drinking water. The best results were achieved with Al2(SO4)s as coagulant,. Counterrecoil sludge in an amount of 2-3% in relation with the total quantity of water has a positive impacts on coagulation-flocculation processes. 4. For effective purification, all the conditions for coagulation-flocculation must be adjusted for the filter to have a longer useful life. One of example is correction of the pH to pH=7, coagulant dose 20 mg/L Al2(SO4)s, flocculant dose 0.1 mg/L PE, counterrecoil sludge dose 90 L/h PM.
The synthesis and characterization of 2-mercaptoethyl methacrylate
Authors: Knezevic Marija , Katsikas Lynne , Popovic Ivanka
Published: July 2008

The synthesis of 2-mercaptoethyl methacrylate from methacrylic acid and 2-mercaptoethanol by etherification using acetyl chloride as catalyst was optimized. The purity of the obtained product was controlled by gas chromatography and its identity confirmed by H-NMR and FTIR spectroscopy. 2-Mercapto-ethyl methacrylate could find application as a chain transfer agent in radical polymerizations.
Bioethanol: State and perspectives
Authors: Tasic Marija , Bankovic-Ilic Ivana , Lazic Miodrag , Veljkovic Vlada , Mojovic Ljiljana
Published: July 2008

Processes of bioethanol production currently applied all over the world are reviewed in this paper. Attention is focused on potentially cheap biomass sources, as well as the most important operating factors controlling the progress and result of saccharification and fermentation reactions and affecting the yield of fermentable sugars and ethanol, respectively, such as: the type and concentration of acid, the type of enzyme, the type of working microorganism, operating temperature, duration time and pH. The hydrolysis conditions, namely duration time, temperature and sulfuric acid concentration, were combined in a single parameter, known as the "combined severity" (CS), in order to estimate the efficiency of bioethanol production from biomass. When the CS increases, the yield of fermentable sugars also increases. The decrease in the yield of monosaccharides coincides with the maximum concentrations of by-products, such as furfural and 5-hydroxymethylfurfural, which are well-known as yeast inhibitors. The highest ethanol yields has been obtained using the yeast Saccharomyces cerevisiae. With low oil prices and political reluctance to implement carbon taxes, fuel-ethanol production will remain uncompetitive unless some other form of cost reduction can be made, such as feedstock preparation costs.
Synthesis of N-and N,N-dialkyl-S-alkylthiolcarbamates by the rearrangement of N-and N,N-dialkyl-O-thioncarbamates
Authors: Milosavljevic Milutin , Marinkovic Aleksandar , Djordjevic Sinisa
Published: July 2008

A series of N- and N,N-dialkyl-S-alkylthiolcarbamates were synthesized by the rearrangement of N- and N,N-dialkyl-O-alkylthioncarbamates in the presence of diethyl sulfate. The synthesis of some compounds without catalyst was also performed. The compounds were identified by IR, 1H NMR and MS spectroscopic methods. The starting thioncabamates were obtained from the corresponding xanthogenacetates and amines and their structures were also confirmed by IR, 1H NMR and MS data. Some of the thiolcarbamates were characterized for the first time in the literature.
St. John's Wort Hypericum perforatum L.: Supercritical extraction, antimicrobial and antidepressant activity of extract and some component
Authors: Glisic Sandra , Popadic Sretko , Skala Dejan
Published: July 2008

St. John's Wort, the Hypericum perforatum L. is one of the most analyzed plant species today. Plant was characterized with a wide ecological spectrum and is a plant with beautiful yellow flowers. St. John's Wort was used and still is in used in traditional medicine all over the World. Many bioactive components from St. John's Wort like hypericine, hyperforine, qercetrine and essential oil, were isolated and have been used in medicine. The most popular use of Hipericum extract is as an antidepressant for the medicinal treatment of mild and high depression. The medical use of hyperforine in photodynamic therapy for cancer treatment has now been intensively analyzed. The extract of St. John's Wort showed high antimicrobial, even on pathogenic microorganisms as well as antiviral activity. The use of bioactive components from St. John's Wort depends on the possibility to isolate them in the pure state. It seems that supercritical extraction with carbon dioxide might to be the best solution for obtaining pure extract as well as some of the components present in the essential oil and extract of St. John's Wort. Such a conclusion is supported by the many results of recently performed and published in scientific journals.
Natural products for plant protection
Authors: Cekovic Zivorad
Published: July 2008

The advantage applying natural products, such as a secondary metabolites, in plant protection is shortly presented. Acceptable solutions for the enhanced ecological criteria, which are requested by the users of pesticides and consumers of agricultural goods, could be the replacement of classical pesticides by natural products in plant protection. Some natural products are already in use as insecticides, herbicides and fungicides because new biotechnological processes, fermentation and biotransformations provide procedures for their industrial production. In addition to biotechnical processes natural compounds possessing pesticide activities are also prepared by chemical synthesis. An active secondary metabolite must first be isolated from natural sauces and then, based on biological toxicological and ecological studies, acceptable compounds are selected for laboratory and industrial chemical synthesis. Several compounds possessing insecticidal, herbicidal and fungicidal activities, which have been successfully applied for plan protection are presented.
Textile dyeing by dyestuffs of natural origin
Authors: Smelcerovic Miodrag , Djordjevic Dragan , Novakovic Mile
Published: July 2008

The textile industry is one of the biggest industrial consumers of water especially dye houses which utilize synthetic dyes and other chemicals. Natural dyes are generally environmental friendly and have many advantages over synthetic dyes with respect to production and application. In recent years, there has been an interest in the application of these dyes due to their bio-degradability and higher compatibility with the environment. A review of previous work in the field of applying dyestuffs of natural source as possible textile dyes is given. From an ecological viewpoint, the substitution of chemical dyes by 'natural products' in textile dyeing may be feasible and may represent not only a strategy to reduce risks and pollutants, but also an opportunity for new markets and new businesses which can develop from the inclusion of ecology in trade policy.
Compressional behavior of knitted fabrics exposed to repeated wash and wear cycles
Authors: Stankovic Snezana
Published: July 2008

The quality requirements of knitted fabrics nowadays have become highly demanding in terms of appearance and comfort properties. It is well known that yarns are subjected to tension, bending, torsion and compression during the wear and care of apparels. The appropriate selection of raw materials could be the way to reduce the deformation of knits caused by mechanical forces. Keeping in mind the fact that natural fibers and man-made fibers can significantly differ in respect to elastic properties, natural fiber and synthetic fiber knits were produced for the experiment. The experimental material included three different variants of knitted fabrics: 100% hemp knit, 100% PAC knit and hemp 50%/PAC 50% knit. The behavior of knitted fabrics during the relaxation of compression was investigated. In order to indicate the change of the compressional properties of knitted fabrics, the same investigation after undergoing repeated wash and wear cycles (during eight weeks) was repeated. Although the structure of the tested samples was the same, there were differences in the compressional behavior of the knitted fabrics. It is obvious that the differences in the elastic properties of hemp and PAC fibers were projected into the knits. Compression curves were drawn in order to obtain an insight into the change of the compressional behavior of knitted fabrics during wear. These curves also enabled a comparative estimation of the compressional behavior of knits made of different yarn components. The surfaces proportional to the work of the compression for each of the cycles, as well as the work of compression between the first and the fifth cycles, of loading-unloading cycles were calculated. In order to compare the tested knitted fabrics, the hysteresis of compression was analyzed from the aspect of ability of elastic recovery. The change in compressional behavior of knits exposed to wear and care cycles was confirmed. However, analysis of the comparative compression behavior of knits before and after wear, indicated differences between the tested samples. The mechanical model for the lateral compression of fabrics derived from van Wyk's compression law, which explains the relationship between the pressure and volume of a fiber mass during compression is well known in the literature. In order to obtain a comprehensive insight into the compressional behavior of knitted fabrics, the results obtained were approximated with van Wyk'a equation.
Damage detection in laminar thermoplastic composite materials by means of embedded optical fibers
Authors: Kojovic Aleksandar , Zivkovic Irena , Brajovic Ljiljana , Mitrakovic Dragan , Aleksic Radoslav
Published: July 2008

This paper investigates the possibility of applying optical fibers as sensors for investigating low energy impact damage in laminar thermoplastic composite materials, in real time. Impact toughness testing by a Charpy impact pendulum with different loads was conducted in order to determine the method for comparative measurement of the resulting damage in the material. For that purpose intensity-based optical fibers were built in to specimens of composite materials with Kevlar 129 (the DuPont registered trade-mark for poly(p-phenylene terephthalamide)) woven fabric as reinforcement and thermoplastic PVB (poly(vinyl butyral)) as the matrix. In some specimens part of the layers of Kevlar was replaced with metal mesh (50% or 33% of the layers). Experimental testing was conducted in order to observe and analyze the response of the material under multiple low-energy impacts. Light from the light-emitting diode (LED) was launched to the embedded optical fiber and was propagated to the phototransistor-based photo detector. During each impact, the signal level, which is proportional to the light intensity in the optical fiber, drops and then slowly recovers. The obtained signals were analyzed to determine the appropriate method for real time damage monitoring. The major part of the damage occurs during impact. The damage reflects as a local, temporary release of strain in the optical fiber and an increase of the signal level. The obtained results show that intensity-based optical fibers could be used for measuring the damage in laminar thermoplastic composite materials. The acquired optical fiber signals depend on the type of material, but the same set of rules (relatively different, depending on the type of material) could be specified. Using real time measurement of the signal during impact and appropriate analysis enables quantitative evaluation of the impact damage in the material. Existing methods in most cases use just the intensity of the signal before and after the impact, as the measure of damage. This method could be used to monitor the damage in real time, giving warnings before fatal damage occurs.
Application of the activation model in the education/teaching of future food engineers
Authors: Mijic Ljubica , Segedinac Mirjana , Tomic Milana
Published: July 2008

Some problems during the course of chemical education in junior colleges may arise due to the usage of prescribed text books and fixed education plans and programs. Considering that the goal of modern chemical education is the training of qualified, research-capable students, it appears necessary to carry out investigation in chemical education as a whole, starting with elementary and all the way to the university level. The purpose of such investigations is the increased efficiency and quality of student knowledge. Knowing that modern chemical teaching is independent student work, students should be active subjects in the teaching process. It is expected that students are capable to make decisions by themselves and to take full responsibility for them. So, in order for students to be active subjects in the teaching process, it is necessary to modernize teaching, which assumes active work techniques.
Accidents with sulfuric acid
Authors: Rajkovic Milos
Published: July 2008

Sulfuric acid is an important industrial and strategic raw material, the production of which is developing on all continents, in many factories in the world and with an annual production of over 160 million tons. On the other hand, the production, transport and usage are very dangerous and demand measures of precaution because the consequences could be catastrophic, and not only at the local level where the accident would happen. Accidents that have been publicly recorded during the last eighteen years (from 1988 till the beginning of 2006) are analyzed in this paper. It is very alarming data that, according to all the recorded accidents, over 1.6 million tons of sulfuric acid were exuded. Although water transport is the safest (only 16.38% of the total amount of accidents) in that way 98.88% of the total amount of sulfuric acid was exuded into the environment. Human factor was the common factor in all the accidents, whether there was enough control of the production process, of reservoirs or transportation tanks or the transport was done by inadequate (old) tanks, or the accidents arose from human factor (inadequate speed, lock of caution etc). The fact is that huge energy, sacrifice and courage were involved in the recovery from accidents where rescue teams and fire brigades showed great courage to prevent real environmental catastrophes and very often they lost their lives during the events. So, the phrase that sulfuric acid is a real "environmental bomb" has become clearer.
The application of cyclodextrins in textile area
Authors: Djordjevic Dragan , Novakovic Mile , Konstantinovic Sandra
Published: July 2008

The application of Cyclodextrins for textiles was reviewed in this paper. Cyclodextrins are crystalline, water soluble, cyclic, non-reducing oligosaccharides consisting of six, seven, or eight glucopyranose units. Cyclodextrins are known as products which are able to form inclusion complexes. The ability of Cyclodextrins to form inclusion complexes can be used, e.g., to remove malodor from textile materials, etc. Furthermore, some modifications of the parent Cyclodextrins are possible. The derivatives can be reactive (e.g. cyclodextrin with a monochlorotriazinyl group), more hydrophilic (by means of hydrophilic side groups, such as hydroxypropyl and hydroxyethyl), less hydrophilic (by means of lipophilic side groups, such as ethylhexyl glycidyl) or ionic (by means of ionic side groups, such as hydroxypropyl trimethyl ammonium chloride).The methods for treating textiles are thus quite simple. The method using anchor-bearing Cyclodextrins is especially useful, since no fixation agent is needed, enabling they use of conventional textile treatment techniques and equipment. Furthermore, this method has virtually no limitations with respect to the textile materials that can be used.
Modification of ethylene-norbornene copolymer by Gamma irradiation
Authors: Kacarevic-Popovic Zorica , Secerov Bojana , Marinovic-Cincovic Milena , Nedic Zoran , Jovanovic Slobodan
Published: July 2008

The possibility of modifying polyethylene and many other polymers with high energy radiation has led to many useful applications. Due to their new combination of properties and the shortage of experimental data, the radiolysis of a new class of materials, cyclo-olefin copolymers (COC), polymerised from norbornene and ethylene using metallocene catalysts, is of great interest to the study of radiation chemistry and the physics of polymeric systems. Ethylenenorbornene copolymer, pristine and containing an antioxidant were subjected to gamma irradiation in the presence of air and in water. The irradiated copolymer was studied using IR and UV-vis spectrophotometric analysis. The radiation-induced changes in the molecular structure were correlated to changes in the glass transition temperature measured by the DSC method.
Kinetic investigation of the immobilization of chromotropic acid derivatives onto anion exchange resin
Authors: Savic Jasmina , Vasic Vesna , Adnadjevic Borivoj
Published: July 2008

The adsorption kinetics of pyrazol- (????) and imidazol-azo-chromo-tropic acid (IACA) onto Dowex 1-X8 resin, as a function of the dye concentration and temperature were investigated at pH 4.5. The pseudo-first- and second-order kinetic models and intraparticle diffusion model were used to describe the obtained kinetic data. The adsorption rate constants were found to be in the order of magnitude 10-2 min-1 for all of the used kinetics models. The adsorption capacity increases with increasing initial dye concentration. The study of adsorption kinetics at different temperatures (in the range from 5 to 25 ?C) reveals an increase in the rate of adsorption and adsorption capacity with increasing temperature. The activation energy (in the case of ???? 16.6 kJ/mol, and for IACA 11.3 kJ/mol) was determined using the Arrhenius dependence. Electrostatic interactions between the dye and resin beads were shown to be the adsorption mechanism.
Gravimetric and volumetric determination of the purity of electrolytically refined silver and the produced silver nitrate
Authors: Acanski Marijana , Savatovic Sladjana , Radic Mira
Published: July 2008

Silver is, along with gold and the platinum-group metals, one of the so called precious metals. Because of its comparative scarcity, brilliant white color, malleability and resistance to atmospheric oxidation, silver has been used in the manufacture of coins and jewelry for a long time. Silver has the highest known electrical and thermal conductivity of all metals and is used in fabricating printed electrical circuits, and also as a coating for electronic conductors. It is also alloyed with other elements such as nickel or palladium for use in electrical contacts. The most useful silver salt is silver nitrate, a caustic chemical reagent, significant as an antiseptic and as a reagent in analytical chemistry. Pure silver nitrate is an intermediate in the industrial preparation of other silver salts, including the colloidal silver compounds used in medicine and the silver halides incorporated into photographic emulsions. Silver halides become increasingly insoluble in the series: AgCl, AgBr, AgI. All silver salts are sensitive to light and are used in photographic coatings on film and paper. The ZORKA-PHARMA company (Sabac, Serbia) specializes in the production of pharmaceutical remedies and lab chemicals. One of its products is chemical silver nitrate (argentum-nitricum) (l). Silver nitrate is generally produced by dissolving pure electrolytically refined silver in hot 48% nitric acid. Since the purity of silver nitrate, produced in 2002, was not in compliance with the p.a. level of purity, there was doubt that the electrolytically refined silver was pure. The aim of this research was the gravimetric and volumetric determination of the purity of electrolytically refined silver and silver nitrate, produced industrially and in a laboratory. The purity determination was carried out gravimetrically, by the sedimentation of silver(I) ions in the form of insoluble silver salts: AgCl, AgBr and Agi, and volumetrically, according to Mohr and Volhardt. The purity of electrolytically refined silver obtained volumetrically, according to Volhard, was 99.49%. The results suggest that the purity of electrolytically refined silver was higher than 99%. After all of these determinations, the purity of electrolytically refined silver was examined by atomic absorption spectrometry and the results confirmed that the purity of electrolytically refined silver was 99.99%. Electrolytically refined silver contained other metals: Mn, Cu, Fe, Zn, Pb, Cd, and the contents of these metals were: 1.15 ppm; 0.75 ppm; 0.65 ppm; 1.82 ppm; < 0.07 ppm and < 0.01 ppm, respectively.
Phonon spectra in quantum wires
Authors: Ilic Dusan , Rakovic Dejan , Setrajcic Jovan
Published: July 2008

Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most important feature is that, beside the allowed energy zones (which are continuous as in the bulk structure), zones of forbidden states appear. Different values of the boundary parameters lead to the appearance of lower and upper energy gaps, or dispersion branches spreading out of the bulk energy zone. The spectra of phonons in corresponding unbound structures were correlated to those in bound structures.
The distinctiveness of measuring interlaminar fracture toughness by the mode I method
Authors: Djordjevic Isidor , Gordic Milan , Pesikan Danijela , Stevanovic Momcilo
Published: July 2008

Practical problems in measuring the interlaminar fracture toughness by the mode I method were pointed out in this paper. Unidirectional carbon fibre/epoxy resin composite was used in the experiments (as the test material). The composite was obtained by curing commercial Hexcel ply 6376 in a mould. The techniques of initial crack formation, solving problems of applying the correct stress on the specimen and the precise registering of crack growth were proposed. The reliability of suggested method was assessed by evaluating the dispersion of the results obtained, as well as by comparison with the literature data.
Biocompatible and bioadhesive hydrogels based on 2-hydroxyethyl methacrylate, monofunctional poly(alkylene glycol)s and itaconic acid
Authors: Micic Maja , Tomic Simonida , Filipovic Jovanka , Suljovrujic Edin
Published: July 2008

New types of hydrogels were prepared by the radical copolymerization of 2-hydroxyethyl methacrylate, itaconic acid and four different poly(alkylene glycol) (meth)acrylate components (Bisomers) in a water/ethanol mixture as solvent. The polymers swell in water at 25?C to yield homogeneous transparent hydrogels. All the hydrogels displayed pH sensitive behavior in buffers of the pH range from 2.20 to 7.40, under conditions similar to those of biological fluids. The presence of these two comonomers, which were added to HEMA, increased the swelling degree of the hydrogels and gave gels with better elasticity. The hydrogels were thermally stable in the vicinity of the physiological temperature (37?C). The copolymer containing pure poly(ethylene glycol) acrylate units generally had the best properties. The tests performed on the hydrogels confirmed that they were neither hemolytic nor cytotoxic. The copolymer samples showed better cell viability and less hemolytic activity than the PHEMA sample, confirming the assumption that poly(alkylene glycols) improve the biocompatibility of hydrogels. Due to their swelling and mechanical characteristics, as well as the very good biocompatibility and bioadhesive properties, poly(Bisomer/HEMA/IA) hydrogels are promising for utilization in the field of biomedicals, especially for the controlled release of drugs.