Hydrodistillation versus microwave-assisted hydrodistillation of sage herbal dust: kinetics, chemical profile and bioactivity

Essential oils are gaining attention from the academic and industrial communities due to numerous biological activities and a broad spectrum of applications. With the arrival of the “green era”, there was a need to reduce the production of waste materials and to make better use of natural resources. Due to the ever-increasing market of functional foods, the search for new natural, bioactive components is a hot topic on which a lot of research effort is being focused currently and biorefinery has recently emerged as a promising approach which could lead towards a sustainable concept of production. Therefore, the aim of this work was the valorization of sage herbal dust which is being generated as a by-product from filter tea factories. Conventional hydrodistillation (HD) and microwave-assisted hydrodistillation (MWHD) were applied for the essential oil recovery. The influence of heating (205 and 410 W) and microwave irradiation (90, 180, 360, 600 and 800 W) power on distillation kinetics and the chemical profile of the essential oils was evaluated. Empirical mathematical models were used for the modeling of process kinetics. The chemical profile was evaluated by HPTLC and GC-MS and monoterpenes (camphor, α-thujone, and eucalyptol), sesquiterpenes (viridiflorol) and diterpene polyphenols (epirosmanol) were the most abundant compounds identified. The high antioxidant capacity of the obtained essential oils, determined by the DPPH assay, suggested that sage herbal dust could be successfully utilized as a raw material for essential oil recovery

Removal of copper ions from aqueous solutions by sugar beet shreds and poplar sawdust in a fixed-bed column

The potential use of sugar beet shreds and poplar sawdust for copper ions removal from aqueous solution in a fixed-bed column was investigated. Experiments were performed in a glass column (inner diameter 2.204 cm and length 50 cm), in the down-flow mode with a flow rate set to approximately 12 mL/min. Concentration (C0) and the pH of the inlet solution were 100 mg/L and 4.5, respectively, and 10 g of the adsorbent were used to form a bed of nearly 19 cm in length. Sugar beet shreds and poplar sawdust were milled and sieved through the set of sieves, and the fraction of 400 to 600 μm was used for the adsorption experiments. The consecutive aliquots of 50 to 150 mL were collected at the bottom of the column, and they were analyzed for the content of the Cu(II) ions (C), according to the standard method of complexometric titration [1]. The column adsorption process is described regarding the effluent concentration-volume profile, or the breakthrough curve, obtained from the plot of Ct/C0 versus volume of the effluent. The shape of the curve gives an insight into the dynamic behavior of the process [2, 3]. Various mathematical models can be used to describe fixed-bed adsorption [4, 5]. In this research, the novel two-stage approach for the breakthrough curve modelling was applied. The fit quality, expressed as coefficient of determination (R2 ) and the sum of squared errors (SSer), showed that this model fits the experimental data more accurately than any other commonly used one-stage model. Namely, R2 and SSer for sugar beet shreds were 0.9984 and 9.69·10-3 , respectively, while for the poplar sawdust they were 0.9999 and 2.87·10-4 , respectively. The characteristic value that describes this two-stage phenomenon is moiety of each stage, p. In the case of sugar beet shreds it was 0.43, while for the poplar sawdust it was 0.85. These results suggest that the adsorption of the copper ions onto examined biosorbents occurs under multiple mechanisms, occurring simultaneously but shifting in the dominance. When using sugar beet shreds as an adsorbent, these mechanisms are nearly equal in their dominance (0.43 to 0.57). In the case of the poplar sawdust one mechanism is significantly more dominant then other (0.85 to 0.15), and the misuse of onestage models is usual and more likely. However, the extensive mathematical and statistical analysis confirmed the validity of the two-stage modelling approach for the copper biosorption onto sugar beet shreds and poplar sawdust

Hitozan/bentonit granule za tretman otpadnih voda

Aim of this research was synthesis of chitosan/bentonite nanocomposite beads for colored wastewater treatment by adsorption. Influence of preparation procedure on the morphology, adsorption and thermal properties has been studied. It was proved that procedure method affects morphology, as well as enthalpy of absorbed water evaporation, which depends on the molarity of NaOH, and does not affect glass transition temperature. Chitosan adsorption capacity was improved by addition of modified bentonite, which is desirable in colored wastewater treatment.Cilj ovog istraživanja je bila sinteza hitozan/bentonit nanokompozitnih granula za prečišćavanje obojenih otpadnih voda metodom adsorpcije. Proučavan je uticaj postupka pripreme na morfologiju, kao i na adsorpciona i toplotna svojstva nanokompozitnih biopolimera. Dokazano je da način pripreme hibridnih granula utiče na morfologiju, kao i na entalpiju isparavanja adsorbovane vode čija vrednost zavisi od molarnosti NaOH, a ne utiče na temperaturu prelaska u staklasto stanje. Sposobnost adsorpcije hitozana je poboljšana dodavanjem modifikovanog bentonita, koji je poželjan u tretmanu obojenih otpadnih voda

Preparation and properties of nanoparticles suspensions and their composites

U ovom radu pripremljeni su različiti polimerni i keramički nanostrukturni materijali, u cilju ispitivanja uticaja vrste i udela nanopunila (čađ, fuleren, silicijum(IV)oksid, aluminijum(III)oksid i titanijum(IV)oksid) na strukturu, reološko i toplotno ponašanje kompozita, dobijenih na osnovu stirena, metilmetakrilata i akrilamida, primenom različitih metoda sinteze. Ispitivan je uticaj prisustva različitog udela nanočestica (1, 3 i 5 % m/m) na kinetiku polimerizacije stirena, i na oblast prelaska u staklasto stanje polistirenskih hibridnih materijala. Sintetisana je i serija nanokompozita polimerizacijom metilmetakrilata u prisustvu čestica (silicijum(IV)oksid, aluminijum (III)oksid i titanijum(IV)oksid) različitih dimenzija i hidrofilnosti, ali istog zapreminskog udela (1 % v/v). Na osnovu primene izotermne diferencijalno skanirajude metode (DSC), razvijen je kinetički model za opisivanje dve razičite reakcije tokom polimerizacije vinilnih monomera (reakciju prvog reda i samoubrzanje), i izračunata je debljina međufaznog sloja polimera na čestici u cilju određivanja njegovog uticaja na temperaturu prelaska u staklasto stanje hibridnih materijala. Za ispitivanje strukture i morfologije polistiren/silicijum(IV)oksid nanokompozita dobijenih metodom isparavanja rastvarača, korišdene su infracrvena spektroskopija sa Furijeovom transformacijom (FT-IR) i skanirajuda elektronska mikroskopija (SEM). Radi utvrđivanja uticaja udela hidrofobnog silicijum(IV)oksida (2, 5, 10, 15 i 30 % m/m) na toplotnu postojanost polistirenskih materijala, primenjene su istovremena termogravimetrijska i diferencijalno skanirajuda analiza (TG-DSC). Takođe, određen je uticaj veličine čestice fulerena C60 i submikronske čestice čađi na reološka svojstva polistirenskih kompozita sintetisanih taloženjem polimera iz rastvora. Ispitivanjem reološkog ponašanja hibridnih materijala, proučavan je uticaj veličine čestica, molekulske mase polimera i indeksa polidisperznosti na viskoznost polistirenskih kompozita. Na osnovu in-situ reoloških analiza polimerizacije u toku želiranja suspenzije nanočestica aluminijum(III)oksida u vodenom rastvoru monomera metakrilamida i N,N’-metilenbisakrilamida, utvrđena je jaka katalitička aktivnost površine aluminijum(III)oksida na nastajanje slobodnih radikala. Radi nalaženja veze između željenih svojstava keramičkih proizvoda i načina njihovog dobijanja, proučavan je uticaj uslova vođenja polimerizacije na slaganje čestica u dobijenom odlivku i na gustinu krajnjeg sinterovanog proizvoda.In this work, polymeric and ceramic nanostructured materials were prepared using different methods, in order to investigate the influence of nanofiller content and its type (carbon black, fullerene, silica, alumina and titania) on the structure, rheological and thermal behavior of composites, based on styrene, methylmethacrylate and acrylamide. The effect of particles content (1, 3 and 5 wt. %) on the kinetics of styrene radical polymerization and on the glass transition temperature of polystyrene/silica composites was investigated. A series of polymethylmethacrylate nanocomposites containing 1 vol. % of silica, alumina or titania particles (differing in dimensions and surface properties) was obtained. On the basis of isothermal differential scanning calorimetry (DSC), the kinetic model for describing two reactions during vinyl monomer polymerization (first order and autoacceleration) was developed, and the thickness of interfacial layer formed on nanoparticle surface was determined, in order to investigate its influence on the glass transition temperature of polymethylmethacrylate hybrid materials. The structure and the morphology of polystyrene/silica nanocomposites prepared by solvent evaporation were investigated using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The influence of  hydrophobic silica content (2, 5, 10, 15 and 30 wt. %) on polystyrene thermal stability was studied by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). The effect of fullerene C60 and submicron carbon black particle size on rheological properties of polystyrene composites prepared by the rapid coprecipitation was determined. Following the rheology of hybrid melts, the influence of filler size, molecular weight and polydispersity of polymer matrix on the viscosity of polystyrene composites was studied. On the basis of in-situ rheology analysis of polymerization process during the gelation of alumina nanoparticles suspension in aqueous solution of methacrylamide and N,N’- methylene bisacrylamide monomers, the strong catalytic activity of alumina surface on the free radicals formation was determined. In order to find the correlation between desired properties of ceramic products and their preparation procedure route, the influence of polymerization conditions on the green body structure and sintered body density was studied in details

Isoconversional kinetic analysis of the alkyd/melamine resins curing

The curing reaction for the mixtures of alkyd resins based on ricinoleic acid, phthalic anhydride and three polyols (glycerin, trimethylolpropane or ethoxylated pentaerythritol) with two different commercial melamine resins was investigated by differential scanning calorimetry (DSC). The curing kinetics analysis was performed using the isoconversional methods (Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman). Isoconversional methods were carried out with three heating rates (5, 10 and 20°C/min) in a scanning temperature range from 40 to 250°C. It was found that the curing activation energy of resin mixtures is influenced by alkyd and melamine resin type due to the catalytic effect of hydroxyl group on the reactions. The dependence of apparent curing degree on time, which was obtained by mathematical transformations of dynamic DSC data using Ozawa-Flynn-Wall method, describes well the isothermal DSC experiments

Modification of epoxy resins with thermoplastic segmented polycarbonate-based polyurethanes

In this work, epoxy hybrid materials were synthesized by addition of thermoplastic segmented aliphatic polyurethanes with good elastic properties. The modified epoxy samples were obtained by curing of previously homogenized mixture of prepared polyurethane melts, epoxy resin and crosslinking agent Jeffamine D-2000. The influence of different weight content of polyurethanes (5, 10 and 15 wt. % compared to pure epoxy resin) as well the influence of different hard segments of elastomers (20, 25 and 30 wt. %) on the curing of modified epoxy systems was studied. The curing was followed by differential scanning calorimetry (DSC), in dynamic regime from 30 to 300°C, at three heating rates (5, 10 and 20°C/min). With the increase of hard segments content of polyurethanes added in higher concentration (10 and 15 wt. %) into epoxy matrix, the temperature of maximum ratio of curing was shifted to lower values (from 205 to 179°C). Obtained DSC data were analyzed using two integral methods (Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose) and one differential kinetic model (Friedman). The significant differences were observed in the second part of the epoxy curing (for the reaction degrees higher than 60 %), where the values of activation energies remarkably increase. The addition of polyurethane elastomers retarded the curing process due to decreased mobility of reactant molecules caused by higher viscosity of reaction mixture. By detailed analysis of determined kinetic parameters, it is concluded that the influence of slow diffusion is more pronounced in the presence of thermoplastic polycarbonate-based polyurethanes, which confirmed their effect on the mechanism of epoxy curing. The highest tensile strength and hardness showed the DGEBA modified with the polyurethane with highest hard segment content. Increasing the hard segment content of polyurethane and its concentration in matrix, the tensile strength of modified epoxy was increased. The elongation at break of modified epoxy samples was significantly improved by addition of polycarbonate-based polyurethanes with low hard segment content, due to higher content of flexible soft segment chains. [Projekat Ministarstva nauke Republike Srbije, br. III 45022), i Pokrajinski Sekretarijat za nauku i tehnološki razvoj (projekat 114-451-2396/2011-01). Autor iz Praga duguje zahvalnost „the Grant Agency of the Czech Republic“ (Czech Science Foundation, project No. P108/10/0195).

A Novel Approach for Simulation and Optimization of Rubber Vulcanization

The kinetic model, encompassing the curing and reversion phenomena of the NR/SBR rubber vulcanization process, was developed by means of the finite element method simultaneously with heat transfer equations, including heat generation due to curing reactions. The vulcanization simulation was conducted for three spheres of different diameters (1, 5 and 10 cm) and two rubber wheels, one of which was a commercial product of the rubber industry. The proposed advanced simulation model, based on products’ two-dimensional axisymmetry, includes cooling after vulcanization, during which the crosslinking reactions continue to take place as a result of the products’ heated interiors. As a criterion for removing the product from the mold, an average vulcanization degree of 0.9 was set, whereby, during cooling, the vulcanization degree increases, due to crosslinking reactions. Based on the minimal difference between the maximal and minimal vulcanization degrees, which did not exceed a value of 0.0142, the optimal process parameters for each product were determined, achieving homogeneity and obtaining high-quality rubber products, while simultaneously ensuring a more efficient vulcanization process and enhanced cost effectiveness for the rubber industry