The influence of filler nanoparticles on the properties of elastomeric materials for special applications

Strukturiranje elastomernih kompozita dodavanjem različitih vrsta nanopunila je dovelo do značajnog poboljšanja njihovih primenskih svojstava, a samim tim i do povećanja njihove potencijalne primene kao pogodnih materijala za specijalne namene. U ovom radu, dobijene su dve grupe elastomernih hibridnih materijala za specijalne namene (na osnovu stirenbutadienskog elastomera i na osnovu termoplastičnih poliuretana). U prvom delu istraživanja, veliki doprinos u razvoju industrije gume je postignut strukturiranju stirenbutadienskih nanokompozita primenom nanočestica punila silicijum(IV)oksida različitih morfoloških svojstava, dobijenih hidrotermičkom i termičkom obradom, primenom tri eksperimentalno modelovana punila silicijum(IV)oksida (dobijena taloženjem iz Na-vodenog stakla sa sumpornom kiselinom), kao i hibridnog punila (kombinacije čestica aktivne čađi i SiO2 optimalnih svojstava). Izvršena je analiza uticaja strukture, površine i površinske aktivnosti nanopunila na ojačanje elastomera, kao i provera koncepata, modela i teorija ojačanja na neumreženim i umreženim sistemima stirenbutadienskih elastomera ojačanih modifikovanim punilima SiO2. Primenom mnogobrojnih metoda karakterizacije, sveobuhvatno je ispitan uticaj nanopunila na karakteristike mešanja, reološka svojstva pripremljenih hibridnih nanokompozita, sposobnost umrežavanja u neumreženom materijalu, kao i na toplotna, dinamičko-mehanička i mehanička svojstva umreženih nanokompozita, radi projektovanja i optimizovanja sastava SBR hibridnih materijala za razvoj modelnog protektora sa optimalnim svojstvima za ekološke ili "zelene pneumatike". Drugi deo istraživanja je bio posvećen dobijanju segmentiranih poliuretanskih elastomernih nanokompozita primenom alifatičnih polikarbonatnih diola i nanočestica bentonita, koji nalaze primenu u medicini, građevinarstvu, u industriji nameštaja i sportske opreme. Primenom mnogobrojnih metoda za karakterizaciju, ispitan je složen mehanizam uticaja tvrdih segmenata, termodinamičke nekompatibilnosti i prisustva nanočestica punila bentonita na strukturu i morfologiju, kao i na toplotna i dinamičko-mehanička svojstva pripremljenih poliuretanskih termoplastičnih elastomera. Dobijeni podaci o obrazovanju vodoničnih veza, termičkoj stabilnosti i termičkoj dekompoziciji, kao i o temperaturama prelaska u staklasto stanje i oblasti raskidanja čvorova fizičkih veza, predstavljaju značajan doprinos napretku strukturiranja poliuretanskih elastomera i nanokompozita na osnovu alifatičnih polikarbonatnih diola, i omogućavaju primenu ovih materijala za specijalne namene.The structuring of elastomeric composites by addition of different nanofillers has led to a significant improvement of their end-use properties, and therefore, to their potential application as suitable materials for special applications. In this work, two types of elastomeric hybrid materials for special purposes were obtained (based on styrene-bustadiene elastomer or on segmented thermoplastic polyurethanes). In the first part of the study, a major contribution to the development of the rubber industry was achieved by structuring styrene-butadiene nanocomposites, applying silica nanoparticles of various morphological properties: prepared by hydrothermal or thermal treatment, three experimentally prepared SiO2 fillers (obtained by precipitation from sodium silicate with sulfuric acid), as well as a hybrid filler (combination of carbon black and SiO2 fillers with optimal properties). The analysis of the influence of the nanoparticles structure, surface and surface activity on the reinforcment of SBR elastomers, as well as the verification of concepts, models and reinforcement theories on non-cross-linked and cross-linked systems of styrene-butadiene nanocomposites was performed. Using the numerous characterization methods, the influence of nanofillers on the mixing characteristics, the rheological properties of the prepared hybrid nanocomposites, as well as the thermal, dynamic-mechanical and mechanical properties of cross-linked SBR nanocomposites was studied, in order to design and optimize the composition of SBR hybrid materials for development of environmental friendly or "green" tyre protector model. The second part of the research was devoted to the preparation of segmented polyurethane elastomeric nanocomposites using aliphatic polycarbonate diols and bentonite nanoparticles, that have found the significant application in the medicine, construction, the furniture and sports equipment industry. Applying numerous characterization methods, a complex mechanism of the influence of the hard segments, thermodynamic incompatibility and the presence of bentonite filler on the structure and morphology, as well as on the thermal and dynamic-mechanical properties of the synthesized thermoplastic elastomers was studied. The obtained data on the hydrogen bonds formation, thermal stability and thermal decomposition, as well as the glass transition temperature and physical crosslink disruption temparature range, makes a significant contribution to the progress in structuring of polycarbonate-based polyurethane elastomers and their hybrid materials, and improves their potential applications for the special purposes

RHEOLOGICAL PROPERTIES AND THE ENERGETIC VALUE OF WHEAT FLOUR SUBSTITUTED BY DIFFERENT SHARES OF WHITE AND BROWN RICE FLOUR

In order to produce dough with a lower gluten content, more enriched with rice components and satisfactory rheological properties, the rheological properties, energetic value and cake baking properties of wheat and white or brown rice flour in shares from 3 to 30% (w/w) were investigated in this paper. The water absorption in wheat-rice flour mixtures was lower and decreased to 53.5% and 54.0% along with the increase of the white and the brown rice flour share, respectively, than in wheat flour, where it was 58.8%. In the dough made from rice flour, a gluten network had thinner filaments, about 2 and 1 μm in width for white and brown rice flour, respectively, compared to those in the dough from wheat flour only, where it was about 7 μm. The dough from rice flour had almost twice higher gelatinization maximum than the gelatinization maximum of the wheat flour only. The energetic values of the dough from rice flour were smaller than the energetic value of the wheat flour, for only 1.32%. Based on Cluster analysis, the white or brown rice flour share of 20% was pointed out

Sulfonylurea herbicides residues analysis in soil

Prosulfuron, rimsulfuron, thifensulfuron-methyl and tritosulfuron are widely used sulfonylurea herbicides (SUs), applied in low-dose rates. However, these herbicides under specific conditions as low temperature, poor rainfall, microbial activity. high pH of soil, can remain at low concentrations in soil and can affect the growth of sensitive plants. This paper presents the method that we developed for determination of prosulfuron, rimsulfuron, thifensulfuron-methyl and tritosulfuron residues in soil. Determination and quantification were performed by HPLC/DAD using Agilent Zorbax SB-C18 column (3.0 mm*250 mm. 5 um particle size). Mobile phase was acetonitrile/0.1% CH3COOH solution. Analyzed SUs showed linear calibrations from 0.05 to 0.2 mg/ml with correlation coefficient (1°) above 0.990%. The recovery data were obtained by spiking blank soil samples at two concentration levels (2.5-5.0 mg/kg), yielding average recovery between 95.56 and 99.79%. Precision values expressed as relative standard deviation (RSD) were between 0.91-1.11% for all SUs herbicides for the intraday precision. Considering the obtained values of analytical parameters, the proposed method proved to be an efficient and sensitive method for the determination of prosulfuron, rimsulfuron, thifensulfuron-methyl and tritosulfuron in soil samples

Acoustic voice analysis before and after voice therapy

Postoji više načina da se ispitaju efekti vokalne terapije kod poremećaja glasa. Najprecizniji način je primena kompjuterske analize glasa. Cilj ovog istraživanja je bio da se izvrši detaljna analiza akustičke strukture vokala A pre i posle terapije glasa kod pacijenata sa čvorićima na glasnicama, da bi dobili kvantitativnu verifikaciju uspeha vokalne rehabilitacije. Ispitano je 37 pacijenata ženskog pola, starosti 34,6±6,69 godina sa čvorićima na glasnicama. Kod svih je sniman i analiziran vokal A pre i posle jednomesečne vokalne terapije. Uspeh vokalne terapije je bio praćen kompjuterskom analizom akustičke strukture vokala. Obrađeni su parametri signala, šuma i tremora. Od analiziranih parametara vokala A, jedanaest je imalo poboljšanje (p<0,05, i p<0,01). Tri parametra su imala promene u smislu poboljšanja ali uočene razlike nisu bile statistički značajne (p>0,05). Na osnovu dobijenih rezultata konstatovano je da je vokalna terapija dala zadovoljavajuće rezultate ali da se sa vokalnom terapijom treba nastaviti do potpune stabilizacije glasa.We showed multidimensional acoustic analysis of A vowel sound in disorder speech state in patients with vocal fold nodules before and after voice therapy. The aim of this study was to conducted acoustic analysis of A vowel in patients with vocal fold nodules before and after vocal therapy in order to get quantitative confirmation of success of the vocal therapy. We examined female 37 patients, 34.6±6.69 years old with vocal fold nodules. In all patients vowel A was recorded and analyzed before and one month after vocal treatment. Success of vocal therapy was followed-up through the computed acoustic analysis of vowel A. We analyzed parameters of the voice signal, noise, and tremor. Eleven out from Fourtheen analysed parameters showed significant improvement. It is suggested that the phonopedical therapy should be continue up to final stabilization of the voice

Acoustic voice analysis before and after voice therapy

Postoji više načina da se ispitaju efekti vokalne terapije kod poremećaja glasa. Najprecizniji način je primena kompjuterske analize glasa. Cilj ovog istraživanja je bio da se izvrši detaljna analiza akustičke strukture vokala A pre i posle terapije glasa kod pacijenata sa čvorićima na glasnicama, da bi dobili kvantitativnu verifikaciju uspeha vokalne rehabilitacije. Ispitano je 37 pacijenata ženskog pola, starosti 34,6±6,69 godina sa čvorićima na glasnicama. Kod svih je sniman i analiziran vokal A pre i posle jednomesečne vokalne terapije. Uspeh vokalne terapije je bio praćen kompjuterskom analizom akustičke strukture vokala. Obrađeni su parametri signala, šuma i tremora. Od analiziranih parametara vokala A, jedanaest je imalo poboljšanje (p<0,05, i p<0,01). Tri parametra su imala promene u smislu poboljšanja ali uočene razlike nisu bile statistički značajne (p>0,05). Na osnovu dobijenih rezultata konstatovano je da je vokalna terapija dala zadovoljavajuće rezultate ali da se sa vokalnom terapijom treba nastaviti do potpune stabilizacije glasa.We showed multidimensional acoustic analysis of A vowel sound in disorder speech state in patients with vocal fold nodules before and after voice therapy. The aim of this study was to conducted acoustic analysis of A vowel in patients with vocal fold nodules before and after vocal therapy in order to get quantitative confirmation of success of the vocal therapy. We examined female 37 patients, 34.6±6.69 years old with vocal fold nodules. In all patients vowel A was recorded and analyzed before and one month after vocal treatment. Success of vocal therapy was followed-up through the computed acoustic analysis of vowel A. We analyzed parameters of the voice signal, noise, and tremor. Eleven out from Fourtheen analysed parameters showed significant improvement. It is suggested that the phonopedical therapy should be continue up to final stabilization of the voice

The contact and compacting pressures influences on the quality of the friction welded joint

The theoretical and experimental analyses of the friction welding pressure influence on the plastic deformation level and the quality of the friction welded joint are presented in this paper. The joint of the tempering and the High-Speed steel was realized by the friction welding. The objective was to relate the two basic process parameters - the friction and compacting pressures - to plastic deformation parameters during the friction welding of two the steels. The fact that materials are dissimilar additionally complicates the welding procedure and its analysis. The friction welding is a specific and complex process, since in the joint zone material is heated and plasticized with necessary action of the multi-step pressure to realize the joint. The total deformations in the axial and radial directions are directly dependent on the applied welding pressure. Considering that geometry and shape of the friction welded joint directly depend on the friction pressure, some welded joints' basic shapes obtained with various pressures are presented. The experimental investigation was conducted on cylindrical samples made of the two steels and the analysis of results served for establishing the influences of the friction and compacting pressures on changes of the steel samples dimensions and shapes.

The contact and compacting pressures influences on the quality of the friction welded joint

The theoretical and experimental analyses of the friction welding pressure influence on the plastic deformation level and the quality of the friction welded joint are presented in this paper. The joint of the tempering and the High-Speed steel was realized by the friction welding. The objective was to relate the two basic process parameters - the friction and compacting pressures - to plastic deformation parameters during the friction welding of two the steels. The fact that materials are dissimilar additionally complicates the welding procedure and its analysis. The friction welding is a specific and complex process, since in the joint zone material is heated and plasticized with necessary action of the multi-step pressure to realize the joint. The total deformations in the axial and radial directions are directly dependent on the applied welding pressure. Considering that geometry and shape of the friction welded joint directly depend on the friction pressure, some welded joints' basic shapes obtained with various pressures are presented. The experimental investigation was conducted on cylindrical samples made of the two steels and the analysis of results served for establishing the influences of the friction and compacting pressures on changes of the steel samples dimensions and shapes.

Analiza kvalitete Al-Cu spoja ostvarenog zavarivanjem trenjem

This paper outlines the bases of the friction welding process, especially when it comes to friction welding of different materials. This was illustrated on an example of friction welding of aluminum and copper, which is often applied in electrical engineering. The analysis of influential parameters was conducted based on the data obtained by an experiment, since the data on this topic are very seldom in the available literature.Ovaj članak daje osnove procesa zavarivanja trenjem, naročito kada je u pitanju zavarivanje trenjem različitih materijala. To je ilustrirano na primjeru zavarivanja trenjem aluminija i bakra, koji se često primjenjuje u elektrotehnici. Analiza utjecajnih parametara provedena je na temelju podataka dobivenih eksperimentom jer su podaci o ovoj temi vrlo rijetko u dostupnoj literaturi

Fizikalne i metalurške promjene tijekom zavarivanja trenjem brzoreznog i kaljenog čelika

This paper outlines the basic principles of welding by friction of high-speed cutting steel and tempered steel from the viewpoint of metallurgic processes that are going on in the material. The bases of welding by friction of different materials are outlined in a theoretical way. The experimental part of the paper also relates to friction welding of samples made of different metals: high-speed cutting steel (HS 6-5-2-5) on one hand and the tempered steel (C60) on the other.Ovaj rad daje osnovne principe zavarivanja trenjem brzoreznog čelika i kaljenog čelika s motrišta metalurškog procesa koji se odvija u materijalu. Osnove zavarivanja trenjem različitih materijala navedene su teorijski. Eksperimentalni dio rada odnosi se na zavarivanje trenjem uzoraka izrađenih od različitih metala: brzoreznog čelika (HS 6-5-2-5) s jedne i kaljenog čelika (C60) s druge strane