Repository of Faculty of Chemical Engineering and Technology University of Zagreb
Not a member yet
2768 research outputs found
Sort by
Phosphonic acids as adhesion promoters of water-based coating
No full textPremazi na bazi organskih otapala često se koriste u zaštiti metala od korozije, međutim otkriveno je da oni predstavljaju rizik za zdravlje ljudi i okoliš zbog isparavanja toksičnih hlapljivih organskih spojeva. Stoga su ekološki prihvatljivi vodorazrjedivi premazi danas stekli značajnu pažnju zbog njihovog smanjenog udjela hlapljivih organskih spojeva. Problem sa čistim vodorazrjedivim premazima je što oni sadrže hidrofilne skupine i surfaktante zbog čega korozivni ioni i molekule vode mogu lako prolaziti kroz premaz, što onda uzrokuje slaba barijerna svojstva tih premaza. Dodavanje zaštitnih punila ili inhibitora korozije u takve premaze se pokazalo dobrim načinom poboljšanja barijernih svojstava. Primjer takvih spojeva su fosfonske kiseline koje mogu imati ulogu inhibitora korozije i promotora adhezije premaza. U ovom radu su ispitane dvije vrste dugolančanih kiselina, hidroklorid
12-aminododecilfosfonske kiseline i 12-fosfonododecilfosfonska kiselina u kombinaciji sa vodorazrjedivim akrilatnim premazom. Korištene su CuSn12 brončane elektrode čija je površina oksidirana. Ispitivane kiseline nanošene su na površinu bronce metodom uranjana i metodom kista. Elektrode su izlagane otopini kisele kiše (pH = 5) te su u periodu od 10 dana provedena EIS mjerenja, a potom se površina elektroda analizirala optičkim mikroskopom. Također je provedena pull-off metoda za određivanje adhezije premaza.Organic solvent based coatings are often used for corrosion protection of metals, however they have been found to pose a risk to human health and the environment due to the evaporation of toxic volatile organic compounds. Therefore, eco-friendly water-based coatings have attracted increasing attention in recent years. Unfortunately, water-based coatings contain hydrophilic groups and surfactants, so that corrosive ions and water molecules can easily pass through the coating, leading to poorer barrier properties. Incorporation of protective fillers into these coatings was shown as a viable way to address this issue. An example of compounds commonly used as fillers are phosphonic acids, which could act as corrosion inhibitors and adhesion promoters. In this study, two types of long chain acids, 12-aminododecylphosphonic acid hydrochloride and
(12-phosphonododecyl)phosphonic acid in combination with a water-borne acrylic coating, were examined. As electrodes were used CuSn12 bronze electrodes whose surface was oxidized. Examined acids were applied on the surface of bronze by immersion method and brush method. The electrodes were exposed to a solution of acid rain (pH = 5) and
EIS measurements were performed over a period of 10 days, and then the surface of the electrodes was analyzed with optical microscope. The pull-off test was also performed to determine the coating adhesion
Crystallization of thin manganite coatings using intense pulsed light
No full textCilj ovog rada bio je sintetizirati tanke filmove lantanovog manganita (LaMnO3) i proučiti njihova svojstva za primjenu u perovskitnim solarnim ćelijama koje se sve više proučavaju kao alternativa silicijevim solarnim ćelijama. Solarne ćelije predstavljaju zeleni izvor energije te su građene od više slojeva, a upravo su slojevita struktura i sastavi slojeva na bazi perovskita glavni predmeti istraživanja zbog velike učinkovitosti i potencijala za raznovrsnu primjenu. Karakteristični LaMnO3 tanki filmovi pripremljeni su iz viskozne otopine metalnih nitrata kompleksiranih dodatkom limunske kiseline. Sinteza je provedena prema postupku samozapaljenja, ali je prekidana u trenutku geliranja. Viskozna otopina prekursora je na staklene podloge nanošena postupkom prevlačenja rotacijom, a kristalizacija otopine prekursora u manganitnu fazu provedena je koristeći novoproučavanu tehniku intenzivne pulsirajuće svjetlosti (IPL). IPL fototretman pokazao se kao prikladan, ekonomičan i djelotvoran postupak za stvaranje potrebnih tankih filmova. Kao rezultat pripreme dobiveni su tanki filmovi hrapave površine s kristaliziranom LaMnO3 strukturnom fazom te popratnim nusproduktima. Mjerenjem optičkih svojstava pripremljenih materijala otkriveno je kako uzorci posjeduju optički procjep između 1,3 i 1,5 eV. Dobivene vrijednosti slažu se s ostalim proučavanim materijalima koji svoju uporabu pronalaze u strukturi solarnih ćelija. Tanke filmove LaMnO3 koji su dobiveni izlaganjem intenzivnoj pulsirajućoj svjetlosti potrebno je detaljnije proučavati i optimirati njihova svojstva kako bi imali mogućnost uporabe kao aktivni sloj u anorganskim perovskitnim solarnim ćelijama.The aim of this work was to synthesize lanthanum manganite (LaMnO3) thin films and study their properties for application in perovskite solar cells, which are increasingly being studied as an alternative to silicon solar cells. Solar cells represent a green source of energy and have a structure of several layers, and precisely the layered structure and composition of layers based on perovskite are the main subjects of research due to their high efficiency and potential for various applications. Characteristic LaMnO3 thin films were prepared from a viscous solution of metal nitrates complexed with the addition of citric acid. The synthesis was carried out using autocombustion process, but it was interrupted at the moment of gelation. The viscous precursor solution was applied to the glass substrates by spin coating method, and the crystallization of the precursor solution into the manganite phase was carried out using the newly studied technique of intense pulsed light (IPL). IPL phototreatment has proven to be a suitable, economical and effective procedure for creating the necessary thin films. As a result of the preparation, thin films with a rough surface and with a crystallized LaMnO3 structural phase and accompanying byproducts were obtained. By measuring the optical properties of the prepared materials, it was revealed that the samples had an optical gap between 1.3 and 1.5 eV. The obtained values agreed with other studied materials that found their use in the structure of solar cells. LaMnO3 thin films obtained by exposure to intense pulsed light need to be studied in more detail and their properties need to be optimized in order to have the possibility of being used as an active layer in inorganic perovskite solar cells
Development and optimization of biflavonoids extraction from Ginkgo biloba L. leaves using deep eutectic solvents
No full textBiljni svijet je prirodno skladište bioaktivnih tvari. Jedna od najviše istraženih skupina svakako su flavonoidi koji imaju višestruku funkciju u biljkama, ali i pozitivan utjecaj na ljudsko zdravlje. Flavonoidi u biljkama mogu postojati u slobodnom obliku, ali najčešće su glikolizirani, metilirani, acetilirani, prenilirani ili polimerizirani, što utječe i na njihovu bioaktivnost. Flavonoidni dimeri, poznatiji pod nazivom biflavonoidi, se sastoje od dva identična ili različita flavonoidna monomera. U odnosu na monomere značajno su manje istraženi iako pokazuju bolju biološku aktivnost od njih i nedavno je prepoznat njihov farmakološki potencijal, ponajviše zbog antivirusne, antikancerogene i antifungalne aktivnosti. Biflavonoidi su prisutni u biljkama koje se koriste u tradicionalnoj medicini poput ginka (Ginkgo biloba L.). Kako bi se biflavonoidi mogli koristiti, potrebno ih je izolirati iz prirodnih izvora. Ovaj proces obično uključuje korištenje raznih organskih otapala, koja mogu biti opasna za okoliš i ljude stoga se u zadnje vrijeme sve više koriste eutektična otapala (engl. Deep Eutectic Solvent, DES) koja su prepoznata kao zelena i jeftina ekstrakcijska sredstva, a dodatna prednost im je izražena fleksibilnost. Osim toga, zbog svoje netoksičnosti i biorazgradivosti odgovaraju svim zahtjevima i principima zelene kemije. Zbog svega navedenog, DES se smatraju vrlo pogodnima za izolaciju biomolekula kao što su biflavonoidi. U sklopu ovog rada, prirodna eutektička otapala (engl. Natural Deep Eutectic Solvent, NADES) korištena su za ekstrakciju biološki aktivnih molekula iz listova ginka. Pomoću računalnog modela COSMO-RS ispitana je topljivost ginkgetina, najčešćeg predstavnika biflavonoida u listovima ginka, i amentoflavona, najpolarnijeg biflavonoida u ginku. Na temelju topljivosti procijenjeno je kako bi 15 od 250 ispitanih NADES moglo biti dobro ekstrakcijsko sredstvo. Odabrani NADES su u sljedećem koraku sintetizirani i karakterizirani (gustoća, viskoznosti, pH-vrijednost). U slijedu šaržnih ekstrakcija pomoću odabranih 15 otapala pri istim procesnim uvjetima (temperatura, vrijeme ekstrakcije i omjer početne mase usitnjenog lišća ginka i volumena otapala) ispitana je učinkovitost ekstrakcije biflavonoida, ukupnih flavonoida, polifenola i fenolnih kiselina. Najveća učinkovitost ekstrakcije ukupnih flavonoida postignuta je pomoću NADES betain:etilen glikol (B:EG) 1:2 s 30 % H2O (w/w). Dobiveni rezultati uspoređeni su s ekstrakcijom provedenom pod istim uvjetima korištenjem 80 % metanola kao otapala, pri čemu je korištenjem odabranog NADES postignuta veća učinkovitost ekstrakcije za 24 %.
U sljedećem koraku, ekstrakcija s odabranim NADES je dodatno optimirana korištenjem eksperimentalnog Box-Behnken dizajna na tri razine s tri faktora: vrijeme ekstrakcije, omjer početne mase usitnjenog lišća i volumena NADES-a i temperatura. Dobiveni rezultati pokazali su da su optimalni uvjeti ekstrakcije korištenjem odabranog NADES: vrijeme ekstrakcije
45 min, omjer početne mase usitnjenog lišća i volumena NADES 20 mg/mL, te temperatura 20 ºC. Naposljetku, korištenjem HPLC-DAD metode u ekstraktima su određene koncentracije 5 najzastupljenijih biflavonoida u lišću ginku (amentoflavon, ginkgetin, izoginkgetin, bilobetin i sciadopitisin).The plant kingdom is a known reservoir of bioactive natural products. The best-studied group to date is flavonoids, which perform multiple functions in plants and have positive impact on human health. Flavonoids can occur in free form in plants, but are more commonly glycosylated, methylated, acetylated, prenylated, or polymerized, which affects their bioactivity. Flavonoid dimers, known as biflavonoids, are consist of two identical or different flavonoid units. They are a less-studied subgroup of flavonoids, although they have bigger bioactivity, and they have recently been recognized as potential pharmaceutical agents, particularly because of their antiviral, anticancer, antifungal, and other bioactivities. They are commonly found in plants used in traditional medicine, such as ginkgo (Ginkgo biloba L.). The crucial step for the pharmaceutical use of any natural product is its isolation from the natural matrix. This process usually involves the use of various organic solvents, which can be hazardous to the environment and humans. Therefore, deep eutectic solvents (DES) have recently been recognized as environmentally friendly and cheap extraction agents, whose additional advantage is their pronounced flexibility. Besides that, there are non-toxic and biodegradable, so they satisfy all the requirements and principles of green chemistry. Due to all of the above, DES are considered very suitable for the isolation of biomolecules such as biflavonoids. As part of this work, natural deep eutectic solvents (NADES) were used to extract biologically active molecules from ginkgo leaves. To select the best NADES for efficient extraction of biflavonoids from ginkgo, COSMOtherm software was used, and solubility of ginkgetin, as the most common biflavonoid in ginkgo leaves, and amentoflavone, as the most polar, was calculated. Based on the obtained solubility predictions, 15 of 250 tested NADES could be effective in extraction of biflavonoids. In the next step, those 15 NADES were synthesized, and characterized (density, viscosity, and pH). After synthesis, the extraction of biflavonoids, total phenols, flavonoids and phenolic acids was performed in a series of batch experiments with the same process conditions (temperature, extraction time and ratio of initial mass of shredded leaves and mass of NADES) where the extraction efficiency of total flavonoids was defined as a criterion for the selection of the best NADES. The highest extraction efficiency was obtained with Betaine:Ethylene Glycol (B:EG) 1:2 NADES with 30 % H2O (w/w). Compared to extraction with 80 % methanol, 24 % higher extraction efficiency was obtained using B:EG 1:2 with 30 % H2O (w/w) NADES under the same process conditions. In addition, extraction with that solvent was optimized using the experimental Box-Behnken design at three levels with three factors: extraction time, ratio of initial mass of shredded leaves and mass of NADES, and temperature. It was concluded that the optimal extraction conditions are: extraction time of 45 min, the ratio of the initial mass of shredded leaves and mass of NADES 20 mg/mL, and temperature 20 ºC. Finally, the concentrations of the 5 most abundant biflavonoids in ginkgo (amentoflavone, ginkgetin, isoginkgetin, bilobetin and sciadopitisin) were determined using HPLC-DAD method
Characterization and preparation of pH sensor films by the sol-gel method for application in the microreactors
No full textCilj ovog rada bio je pripremiti pH-senzorske filmove na bazi indikatora lakmusa imobiliziranog u silanskom filmu na stijenkama kanala mikroreaktora. Za izradu mikroreaktora u ovom radu korištena je tehnologija proizvodnje rastaljenim filamentom (engl. Fused Filament Fabrication – FFF), a kao materijal filamenta korištenog za 3D-ispis upotrjebljen je poli(etilen-tereftalat) obogaćen glikolom (PETG). Na stijenke kanala 3D-ispisanih mikroreaktora potom je nanesen pH-senzorski film. Za pripremu pH-senzorskih filmova odabrana je sol-gel metoda zato što omogućava pripravu senzora u obliku tankih filmova. Kao prekursori za sol-gel metodu odabrani su tetraetoksisilan (TEOS) i feniltrimetoksisilan (FTMS), a u silanski film imobiliziran je indikator lakmus. Promjena boje filma na stijenkama kanala mikroreaktora u određenim je slučajevima bila teško uočljiva okom pa je za analizu promjene boje korišten RGB softver za analizu boje. Pripremljeni filmovi karakterizirani su metodom kontaktnog kuta gdje su kao testne kapljevine korišteni voda i dijodometan te je provedena infracrvena spektroskopija s Fourierovom transformacijom (FTIR). Analizom RGB vrijednosti zaključeno je kako senzorski film pripremljen dodatkom uparene indikatorske otopine i nano-titanijevog dioksida daje najintenzivniju promjenu boje pa je taj film korišten i na stijenkama kanala mikroreaktora.
pH-senzorski film uspješno je nanesen na stijenke kanala mikroreaktora.
Promjenom pH-vrijednosti kapljevine u mikroreaktoru dolazi do promjene boje filmova na stijenkama kanala mikroreaktora unutar jedne minute, a brzina ovisi o pH-vrijednosti otopine. Potvrđeno je da se senzorski filmovi mogu višekratno koristiti.The aim of this work was to prepare and characterise pH sensor films based on litmus indicator immobilized in a silane film in the microreactor channels. The microreactors were made using fused filament fabrication technology (FFF) and polyethylene terephthalate glycol (PETG) filament. The pH-sensor film was then applied inside the channels of the
3D-printed microreactor. The sol-gel method was chosen for the preparation of the
pH sensor films because it enables the preparation of the sensor films in the form of thin films. Tetraethoxysilane (TEOS) and phenyltrimethoxysilane (FTMS) were selected as precursors for the sol-gel method and litmus indicator was immobilized in the silane film.
The colour change of the film in the channels of the microreactor was difficult to see with the naked eye in certain cases, so an RGB analysis software was used to analyse the colour change of the sensor films. The prepared films were characterized by the contact angle method, where water and diiodomethane were used as test liquids, and Fourier-transform infrared spectroscopy was performed. The analysis of the RGB values showed that the sensor film prepared with the addition of vaporized indicator solution and nano-titanium dioxide gives the most intense colour change, so this film was used in the channels of the microreactor. The pH sensor film was successfully applied to the surface of the microreactor channels. Due to the change in the pH of the solution inside the microreactor, the colour of the pH senor film changes within one minute, and rate of change depends on the pH of the solution. It was confirmed that the pH sensor films can be used multiple times
Polyhydroxyalkanoates as sustainable future materials
No full textU današnje vrijeme sve je veći naglasak na promicanju svijesti o zaštiti okoliša i pronalasku novih materijala koji bi doprinijeli smanjenju onečišćenja istog. Jedan od glavnih krivaca za onečišćenje okoliša je konvencionalna plastika koja nema sposobnost biorazgradnje te na taj način ima negativan utjecaj na kvalitetu života ljudi u današnje vrijeme. Onečišćenje uzrokovano nagomilavanjem plastike doseglo je alarmantne razine te je sve veća potreba za rješenjem nastalih problema. U potrazi za novim materijalima koji prilikom svoje razgradnje ne stvaraju otpad, veliki potencijal pokazuju upravo polihidroksialkanoati (PHA). PHA spadaju ugrupu mikrobnih poliestera koje sintetiziraju mikroorganizmi. Istraživanja usmjerena naprocjenu okoliša pokazala su kako su PHA potencijalni kandidati koji bi doprinijeli smanjenju emisije stakleničkih plinova i gomilanju otpada kao i razvijanju brojnih inovacijama na polju biotehnologije, medicine te industrije općenito. Na taj način se promiče politika održivog razvoja kojom teži većina zemalja današnjice. Biorazgradljivost i biokompatibilnost čine ovu vrstu materijala održivim rješenjem. Glavnu prepreku u globalizaciji proizvodnje PHA predstavljaju troškovi proizvodnje te slaba fizikalna svojstva. Iz navedenih razloga, potrebno je staviti težište na promicanje istraživanja proizvodnog procesa ove vrste poliestera kako bi se postigla ekonomičnost procesa proizvodnje. Istraživanja je potrebno usmjeriti na razvijanje i poboljšanje fizikalnih i mehaničkih svojstava PHA kako bi materijal postao konkurentan konvencionalnoj plastici. U ovom istraživanju cilj je bio analizirati svojstva biorazgradljivih polimera; PHA, termoplastičnog škroba (TPS), polilaktida (PLA) i polikaprolaktona (PCL), te njihovih polimernih mješavina s PHA. Ispitana su toplinska, mehanička i površinska svojstva materijala, kao i promjene u kemijskom sastavu, kako bismo bolje razumjeli njihovu primjenu u kontekstu ekološki prihvatljivih polimernih materijala.Nowadays, more and more emphasis is being placed on raising awareness of environmental protection and finding new materials that can help reduce pollution. One of the main causes of environmental pollution is conventional plastic, which is not biodegradable and therefore has a negative impact on people's quality of life. The pollution caused by the accumulation of plastics has reached alarming levels, and there is an increasing need to solve the problems that have arisen. In the search for new materials that do not produce waste when they decompose, polyhydroxyalkanoates (PHA) show great potential. PHA belongs to the group of microbial polyesters synthesized by microorganisms. Research focused on environmental assessment has shown that PHAs are potential candidates that would contribute to the reduction of greenhouse gas emissions and waste generation, as well as to the development of numerous innovations in the field of biotechnology, medicine and industry in general. In this way, most countries' sustainable development policy is promoted today.
The biodegradability and biocompatibility make this type of material a sustainable solution. The main obstacle to the globalization of PHA production is the production cost and the weak physical properties of PHA. For the above reasons, research on the production process of this kind of polyester needs to be promoted to achieve the economic efficiency of the production process. Research should focus on developing and improving PHA's physical and mechanical properties to make the material competitive with conventional plastics. In this study, the properties of the biodegradable polymers PHA, thermoplastic starch (TPS), polylactide (PLA), and polycaprolactone (PCL) and their polymer blends with PHA were investigated. The materials' thermal, mechanical and surface properties, as well as the changes in chemical composition, were investigated to better understand their application in the context of environmentally friendly polymer materials
F-gas Directive for working media
No full textU prvom dijelu rada opisuje se problem globalnog zagrijavanja koji se odvija već dugi niz godina. Negativan utjecaj na okoliš od strane čovjeka popraćen emisijama raznih stakleničkih plinova neke su od pojava koje doprinose globalnom zatopljenju. Ideja o smanjenju posljedica provedena je od strane Europske unije kroz F – gas regulativu. Kroz rad opisani su ciljevi i zahtjevi regulative koji bi pridonijeli poboljšanju situacije u budućnosti. Uredbom se propisuje postupno smanjivanje i ukidanje štetnih tvari, a odnosi se na radne tvari u rashladnoj tehnici o kojima je riječ u drugom dijelu rada.The first part of the paper describes the problem of global warming, which has been going on for many years. Negative impact on the environment by people accompanied by emissions of various greenhouse gases are some of the things that contribute to global warming. The idea of reducing the consequences was implemented by the European Union through the F-gas regulation. This paper describes the goals and requirements of the regulation that would have a good impact on improving the situation in the future. The regulation establishes the gradual reduction and elimination of harmful substances, and it refers to working substances in refrigeration technology, which are discussed in the second part of the paper
Application of magnetic resonance in chemistry and medicine
No full textMagnetska rezonancija je metoda oslikavanja koja se koristi u dijagnostici, najčešće kako bi se otkrili patološki procesi u tkivima. Koristi se i u istraživačke svrhe kako bi se proučila struktura promatranog uzorka. Djeluje na način da se promatrani uzorak postavlja u vanjsko magnetsko polje, dolazi do interakcije između vanjskog magnetskog polja i protona, te se javlja longitudinalna magnetizacija. Na promatrani uzorak djeluje se radiofrekventnim pulsom, koji uzrokuje rotaciju vektora rezultantne magnetizacije u ravninu koja je okomita na smjer djelovanja vanjskog magnetskog polja, te se kao posljedica toga javlja transverzalna magnetizacija. Prestankom djelovanja RF pulsa sustav se relaksira, što znači da se vraća u ravnotežno stanje. Razlikuju se dvije vrste relaksacija, longitudinalna relaksacija, 1, i transverzalna relaksacija, 2. Vremena relaksacije bitni su parametri koji utječu na oslikavanje magnetskom rezonancijom, te na kvalitetu dobivene slike. Kako bi se provelo oslikavanje potrebno je emitirani signal prevesti iz domene vremena u domenu frekvencije Fourierovom transformacijom. Oslikavanje magnetskom rezonancijom koristi se i u molekulskoj spektroskopiji. Dobiveni spektar koristi se za određivanje molekulske strukture.Magnetic resonance is a method of countouring which is being used in diagnostics, most frequnetly in disclosing pathological processes inside tissues. It is being used in reserach purposes in order to study the structure of the observed sample. It acts in such a way that the observed sample is set in the external magentic field, interaction occurs between external magnetic field and protons, and longitudinal magnetization occurs. The observed sample is acted upon by a radio frequency pulse, which causes the resultant magnetization vector to rotate in a plane perpendicular to the direction of action of the external magnetic field, and as a consequence transverse magnetization occurs. When the RF pulse stops, the system relaxes, which means that it returns to its equilibrium state. There are two types of relaxation, longitudinal relaxation, 1 , and transverse relaxation, 2. Relaxation times are important parameters that affect the MRI imaging and the quality of the image obtained. In order to carry out imaging, it is necessary to convert the transmitted signal from the time domain to the frequency domain by Fourier transformation. Magnetic resonance imaging is also used in molecular spectroscopy. The resulting spectrum is used to determine the molecular structure
Extraction of bioactive components from chamomile by deep eutectic solvents
No full textNiskotemperaturna eutektička otapala pokazala su se potencijalno dobrim sredstvima za ekstrakciju bioaktivnih komponenti, primjerice polifenola, iz cvijeta, ploda, lista i drugih biljnih dijelova. Pregledom literature ustanovljeno je da je kamilica kao vrlo vrijedna sirovina u tom pogledu dosad razmjerno neistražena. U sklopu ovog diplomskog rada provedene su ekstrakcije polifenolnih spojeva iz suhih usitnjenih cvjetova kamilice pomoću etanola kao konvencionalnog otapala te niskotemperaturnih eutektičkih otapala (DES, engl. deep eutecic solvent) kao zelenih otapala. Upotrebljavali su se DES-ovi na bazi kolin-klorida (ChCl) i etilen-glikola (EG) te betaina (B) i propilen-glikola (PG) u različitim molarnim omjerima. Sadržaj bioaktivnih komponenti određen je farmakopejskim postupkom te UV/VIS spektrofotometrijom. Također su određivani ekstrakcijski kapaciteti DES-ova procesom višestupanjske ekstrakcije. Osim toga, masena koncentracija apigenin-7-O-glukozida, derivata flavona, u ekstraktima određena je tekućinskom kromatografijom visoke djelotvornosti. Na temelju eksperimentalnih podataka o ekstrakciji fenolnih kiselina najboljim se pokazao DES ChCl:EG molarnoga omjera 1:5 i to u ekstraktu sa najvećim omjerom suhe tvari i otapala. U slučaju određivanja flavonoida najboljim se pokazao DES B:PG molarnoga omjera 1:5 i to također u ekstraktu s najvećim omjerom suhe tvari i otapala. Kod ekstrakcije treslovina uočene su velike oscilacije rezultata, no kao najbolja otapala za ekstrakciju treslovina primjetno se izdvajaju DES-ovi B:PG molarnoga omjera 1:5 i ChCl:EG molarnoga omjera 1:5. Većina ispitanih DES-ova bolja su ekstrakcijska sredstva nego etanol.
Pri ispitivanju ekstrakcijskog kapaciteta uočeno je smanjenje sadržaja bioaktivnih komponenti u ekstraktima s povećanjem broja ekstrakcijskih stupnjeva, suprotno od očekivanoga povećanja. Rezultati kromatografskog određivanja apigenin-7-O-glukozida pokazali su da je DES ChCl:EG bolje ekstrakcijsko sredstvo od DES-a B:PG, nasuprot ekstrakciji ukupnih flavonoida. Općenito su bolji rezultati dobiveni s povećanjem udjela HBD-a i omjera suhe tvari i otapala.Deep eutectic solvents were found to be potentially good media for extracting bioactive components, for example polyphenols, from flowers, fruits, leaves and other plant parts.
A review of the literature has shown that chamomile, as a very valuable raw material, has been relatively unexplored in this regard. As part of this thesis, the extraction of polyphenolic compounds from dry ground chamomile flowers was carried out using ethanol as a conventional solvent and deep eutectic solvents (DES) as green solvents. DESs based on choline chloride (ChCl) and ethylene glycol (EG) and betaine (B) and propylene glycol (PG) in different molar ratios were used. The content of bioactive components was determined by the pharmacopoeial procedure and UV/VIS spectrophotometry. The extraction capacities of DESs were also determined by the process of multi-stage extraction. In addition, the mass concentration of apigenin-7-O-glucoside, a flavone derivative, in the extracts was determined using high-performance liquid chromatography. Based on the experimental data on the extraction of phenolic acids, DES ChCl:EG with molar ratio 1:5 proved to be the best, in particular in the extract with the highest ratio of dry matter to solvent. In the case of flavonoids, DES B:PG with molar fraction 1:5 proved to be the best, also in the extract with the highest ratio of dry matter to solvent. Large oscillations of results were observed in the extraction of tannins, but DESs B:PG with molar fraction 1:5 and ChCl:EG with molar fraction 1:5 stand out as the best solvents for tannin extraction. Most of the investigated DESs were found to be better extraction media than ethanol. By examining the extraction capacity, a decrease in the content of bioactive components in the extracts was observed with an increase in the number of extraction stages, contrary to the expected increase. Chromatographic determination of apigenin-7-O-glucoside in the extracts pointed to DES ChCl:EG as a better extraction agent compared to DES B:PG, contrary to the extraction of total flavonoids. In general, better results were obtained with increasing HBD content and dry matter to solvent ratio
State-of-the art of predictive corrosion maintenance
No full textMetali se koriste u razne svrhe poput izrade građevinskih objekta, cjevovoda, prijevoznih sredstva, elektroničke opreme i slično. Metali u rudama se nalaze u stabilnom stanju no prilikom obrade metali prelaze u metastabilno stanje. U tom metastabilnom stanju je podložan kemijskoj reakciji s okolinom koja se zove korozija te takva reakcija rezultira u gubitku mase metalnog materijala i potencijalnoj šteti. Svake godine raste potreba za proizvodnjom zamjenskih metalnih dijelova samo zbog djelovanja korozije, što je jako opterećujući trošak današnje ekonomije. Iz tog razloga, sve više se počelo ulagati u istraživanja za primjenu prediktivnog korozijskog održavanja. Prediktivno korozijsko održavanje je tehnika koja omogućuje predviđanje nastanka korozije na metalnoj površini primjenom simulacija realnih uvjeta korozijskog sustava. Prediktivno korozijsko održavanje uključuje tehnike zaštite metala i legura te tehnike praćenja samog korozijskog sustava. Kako bi se mogao predložiti sustav zaštite metala od korozije, potrebno je primijeniti saznanja iz područja elektrokemije, metalurgije i fizike. U okviru ovog završnog rada je predstavljen kratki pregled oblika korozije te najpoznatije tehnike zaštite. Zatim slijedi literatura koja navodi najnovija saznanja prediktivnog korozijskog održavanja i prijedlog sustava zaštite pomorskih brodova integracijom umjetne inteligencije u sustav.Metals are used for various purposes such as materials in construction, pipelines, transportation vehicles, electrical equipment and more. Metals in nature (ores) are found to be in a stable state, but during processing they transition into a metastable state. In the metastable state, they are susceptible to a chemical reaction with the environment called corrosion, that results in the mass loss of the metal material and potential damage. Each year, the need for producing replacement metal parts due to corrosion-related effects is growing, posing a significant burden on today's economy. As a result, increasing investments have been made for the research and application of predictive corrosion maintenance. Predictive corrosion maintenance is a technique that allows the prediction of corrosion occurence on metal surfaces by simulating real corrosion system conditions. It involves protective techniques for metals and alloys, as well as monitoring techniques for the corrosion system itself. To propose a corrosion protection system for metals, knowledge from fields such as electrochemistry, metallurgy and physics must be applied. This study provides a brief overview of corrosion types and well-known protection techniques. It also reviews the literature on the latest advancements in predictive corrosion maintenance and suggests a protection system for maritime vessels by integrating artificial intelligence into the system
Kinetics of crystallization of poly(ε-caprolactone) - carbon nanotube composites
No full textPodručje nanotehnologije danas je jedno od najvažnijih područja istraživanja u većini tehničkih disciplina. Polimerni nanokompoziti su sustavi koji se sastoje od polimerne matrice (kontinuirana faza) i punila s najmanje jednom dimenzijom reda veličine nanometra (diskontinuirana faza). Na svojstva nanokompozita utječu svojstva polimerne matrice i svojstva punila. Svojstva punila ovise o udjelu i vrsti punila, veličini i raspodjeli punila, specifičnoj površini punila, obliku čestica te o interakcijama koje se uspostavljaju na međupovršini matrica/punilo. Zbog smanjenja dimenzije punila na nanoveličinu omogućeni su novi pomaci u istraživanjima kompozita. Cilj ovog rada je istražiti utjecaj višestjenih ugljikovih nanocjevčica (eng. multiwalled carbon nanotubes, MWCNT) na proces neizotermne kristalizacije nanokompozita (PCL/CNT) s različitim udjelom CNT. Nanokompoziti PCL/CNT s različitim udjelom CNT dobiveni su iz PCL/CNT otopine u THF-u. Toplinska karakterizacija PLC/CNT nanokompozita provedena je tehnikom diferencijalne pretražne kalorimetrije (DSC) u neizotermnim uvjetima. Iz vrijednosti očitanih iz DSC krivulja određena je energija aktivacije (Ea), polovično vrijeme kristalizacije (t1/2) i ukupno vrijeme kristalizacije (tu). Ea je određena prema Kissinger-ovom i Flynn, Wall, Ozawa (FWO) modelu.Today, the field of nanotechnology is one of the most important areas of research in most technical disciplines. Polymer nanocomposites are systems consisting of a polymer matrix (continuous phase) and fillers with at least one nanometer-sized dimension (discontinuous phase). The properties of the nanocomposites are influenced by the properties of the polymer matrix and the properties of the filler. The properties of the filler depend on the content and type of filler, the size and distribution of the filler, the specific surface area of the filler, the shape of the particles and the interactions that are established at the matrix/filler interface. Due to the reduction of the size of the filler to the nanosize, new advances in composite research have been made possible. The aim of this study is the influence of multiwalled carbon nanotubes (MWCNT) on the non-isothermal crystallization process of PCL/CNT nanocomposites with different weight rations of MWCTN. PCL/CNT nanocomposites with different CNT content were obtained from a PCL/CNT solution in THF. The thermal characterization of the PCL/CNT nanocomposite was performed using the differential scanning technology (DSC) technique in non-isothermal conditions. From the DSC values, the activation energy (Ea), the half-time of crystallization (t1/2) and the total time of crystallization (tt) were determined. Ea was determined according to the Kissinger and Flynn, Wall, Ozawa (FWO) models