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U ovom radu ispitivane su mješavine poli(metil-metakrilata) i celuloznog acetata, PMMA/CA. Pripremljeni su tanki filmovi čistih komponenata PMMA i CA te polimerne mješavine PMMA/CA sa različitim masenim udjelima CA: 5 % CA (CA5), 10 % CA (CA10) i 20 % (CA20) kako bi se ispitao utjecaj dodatka određene količine CA na svojstva dobivenih uzoraka. Korištene tehnike karakterizacije su termogravimetrijska analiza, diferencijalna pretražna kalorimetrija, infracrvena spektroskopija, pretražna elektronska mikroskopija; određen je kontaktni kut te barijerna i mehanička svojstva uzoraka. Rezultati su pokazali bolja toplinska i mehanička svojstva čistog CA u odnosu na PMMA, međutim, dodatak određene količine CA u polimerne mješavine nije pridonio značajnijem poboljšanju toplinskih i mehaničkih svojstava mješavina. Priređene folije pokazuju porast hidrofilnosti s porastom udjela CA što je vjerojatno posljedica razlika u hrapavosti površine, s obzirom da istovremeno folije mješavina ne pokazuju povećanje propusnost spram vodene pare. In this study, blends of poly(methyl methacrylate) and cellulose acetate, PMMA/CA were tested. Thin films of pure PMMA, CA and PMMA/CA polymeric blends with different mass ratio of CA: 5 % CA (CA5), 10 % CA (CA10) and 20 % (CA20) were prepared to test the effect of adding a certain amount of CA on properties obtained samples. The used characterization techniques are thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy; the contact angle and the barrier and mechanical properties. The results showed better thermal and mechanical properties of pure CA compared to PMMA, however, the addition of certain amount of CA into polymer blends had no a significant effect on improving the thermal and mechanical properties of the blends. The hydrophilicity of blends increased with increasing ratio of CA, which most likely resulted from the difference regarding the surface smoothness, having in mind that foils prepared from blends did not show better barrier properties against water vapor, at the same time.

Vitrimerni materijali su nova klasa polimernih materijala, građom su organske mreže čiji se razmještaj veza može promijeniti temperaturno aktiviranim reverzibilnim reakcijama preslagivanja veza. Mehanizam preslagivanja je asocijativan pa ne dolazi do depolimerizacije pri višim temperaturama te gustoća mreže i broj veza ostaju nepromijenjeni. Cilj ovoga rada bio je dati uvid u strukturu i svojstva vitrimera te mogućnosti njihove primjene. Viskoelastično ponašanje vitrimera opisuju dvije temperature prijelaza: temperatura staklastog prijelaza (označava prijelaz između staklastog i gumastog stanja mreže) i temperatura vitrifikacije (označava prijelaz iz viskoelastične krutine u viskofluid pri čemu dolazi do kidanja i formiranja veza). Iznad temperature vitrifikacije dolazi do postepenog smanjenja viskoznosti u skladu s Arrheniusovim zakonom, a to ponašanje je karakteristično za staklastu siliku prema kojoj su, upravo zbog tog svojstva, dobili ime (lat. vitreus- staklast, transparentan). Osim smanjenja viskoznosti s temperaturom, karakteristike vitrimernih materijala su relaksacija naprezanja, mogućnost reprocesiranja, preoblikovanja, recikliranja, prisjetljivost oblika, samoobnova i otpornost na otapala. Svojim ponašanjem obuhvaćaju karakteristike termoseta i termoplasta i stoga predstavljaju idealnu ekološku zamjenu za plastiku. Vitrimer materials are a new class of polymer materials which consist of organic networks whose topology can be rearranged by thermally activated bond exchange reactions. The exchange mechanism is associative, therefore no depolymerization occurs upon heating and the cross-link density and number of bonds are both preserved. The aim of this work was to give insight into the vitrimer structure and its properties along with their application possibilities. Viscoelastic behaviour of vitrimers can be described by two transition temperatures: the glass-transition temperature (describing the transition between glassy and rubbery state of network) and the vitrification temperature (describing the transition between viscoelastic solid and viscoelastic liquid while bonds are being broken and formed). Above the vitrification temperature, a gradual decrease in viscosity following Arrhenius law can be observed, which is a behavioral characteristic of silica by which Vitrimers were named after (lat. vitreus - glassy, vitreous). Besides the Arrhenius gradual viscosity decrease, vitrimers are characterized by stress relaxation, reprocessing, remoulding, recycling, memory shape effect, self-healing and insolubility. Since their behaviour reflects both thermoset and thermoplast behaviours, they represent an ideal ecological replacement for plastics.

Cilj ovog rada bio je pripremiti fizikalno modificiranu celulozu-FMC i odrediti masu adsorbiranog polimera u ovisnosti o vremenu adsorpcije. Fizikalnom modifikacijom želi se postići promjena svojstava površine čime bi se omogućilo korištenje celuloze kao aditiva u polimernim matricama. Jedan od načina promjene svojstava površine je adsorpcija polimera koji ima tražena hidrofobna svojstva. U ovom radu radikalskom polimerizacijom u toluenu sintetizirani su polimeri homopolimer, poli(dodecil-metakrilat)-PDDMA i kopolimer, poli(dodecil-metakrilat-ko-dimetilaminoetil-metakrilat)-PDMAEMA-30. Sastav kopolimera određen je primjenom NMR-spektroskopije i utvrđeno je da je maseni udio DMAEMA u polimeru 33,69 mas.%. Za pripremu suspenzija korištena je mikroceluloza i polimeri otopljeni u toluenu. Stabilnost pripremljenih suspenzija određena je sedimentacijskim testom a vizualno je utvrđeno da su suspenzije mikroceluloze sa PDMAEMA-30 stabilnije od suspenzija sa PDDMA. Masa adsorbiranog polimera pokušala se odrediti mjerenjem viskoznosti polimernih otopina prije i nakon kontakta sa mikrocelulozom. FMC je dobivena filtriranjem mikroceluloze iz polimerne otopine i sušenjem u vakuum sušioniku. Infracrvenom i NMR spektroskopijom dokazana je prisutnost polimera u uzorcima FMC. The aim of this work was to prepare the physically modified cellulose and determine the mass of the adsorbed polymer depending on the adsorption time. With physical modification it is possible to alter the properties of the cellulose surface so it could be used as an additive in polymer matrices. One way to modify surface properties is to adsorp a polymer that has the required hydrophobic properties. In this paper, homopolymer, poly(docecyl-methacrylate) -PDDMA and copolymer, poly(dodecyl methacrylate-co-dimethylaminoethyl methacrylate) -PDMAEMA-30 are synthesized by the free radical polymerization in toluene. The composition of the copolymer was determined by NMR spectroscopy and was found to contain 33,69 mass.% DMAEMA. For the preparation of the suspensions, microcellulose and polymers were dissolved in toluene. The stability of the prepared suspensions was determined by a sedimentation test and it was visually determined that the suspension of microcellulose with PDMAEMA-30 is more stable than the suspension with PDDMA. The weight of the adsorbed polymer could not be determined by measuring viscosity of polymer solutions before and after the contact with microcellulose. Physically modified cellulose was obtained by filtering the microcellulose from the polymer solution and drying in a vacuum drier. Infrared and NMR spectroscopy demonstrated the presence of polymers in FMC samples.

Celuloza posjeduje tri hidroksilne skupine na svakom glukopiranoznom prstenu na kojima se u povoljnim uvjetima može odviti kemijska reakcija. Naime, intramolekulske i intermolekulske vodikove veze treba dovesti do pucanja, što može omogućiti otapanje celuloze i vođenje željene reakcije. Celuloza je u ovome radu funkcionalizirana s oleinskom kiselinom u homogenim i heterogenim uvjetima, uz promjenjive omjere reaktanata. Za postizanje homogenih uvjeta kao otapalo celuloze korišten je N,N-dimetilacetamid i litijev klorid. FTIR karakterizacijom je potvrđena esterifikacija, a TGA karakterizacijom je utvrđeno da se termička stabilnost više smanjuje graftiranjem oleinskom kiselinom u heterogenim uvjetima. Pokazano je da uzorci bubre u kloroformu i DMAc/LiCl-u. Apsorpcija dieselskog goriva je graftiranjem oleinske kiseline poboljšana, bez obzira na način dobivanja uzoraka. Cellulose has a pyranose ring containing three hydroxyl groups, enabling chemical reactions in favorable conditions. Intramolecular and intermolecular hydrogen bonds have to break to enable dissolving of cellulose and conducting of desirable chemical reactions. In this research cellulose was functionalized with oleic acid in homogeneous and heterogeneous conditions, with varying reactant ratios. To achieve homogeneous conditions, cellulose was disolved using N,N-dimethylacetamid and lythium chloride. FTIR characterization confirmed esterification reaction and TGA characterization determined that thermic stability of cellulose becomes worse by oleic acid grafting in heterogeneous conditions. All of the samples displayed swelling in chloroform and DMAc/LiCl. Apsorption of diesel fuel was improved by oleic acid grafting.

Izolacijska ulja koja se koriste u transformatorima često se nazivaju transformatorska ulja ili trafo ulja, a proizvedena su s ciljem osiguranja sigurnog rada tijekom radnog vijeka transformatora. Primjenjuju se u dvije osnovne svrhe, kao izolacijski materijal i medij za hlađenje. Danas se za izoliranje dijelova pod naponom najčešće koristi mineralno ulje kojem se već dugi niz godina, zbog dobrih toplinskih i električnih svojstava, daje prednost u primjeni. Međutim, kako ono ima i svoje nedostatke kao što su zapaljivost i korozivno djelovanje, transformatorsko izolacijsko ulje na osnovi estera se sve više koristi kao zamjena za mineralno ulje zbog visoke otpornosti na temperaturu, povećane sigurnosti od požara i visokog stupnja biorazgradivosti. U ovom radu korištene su dvije vrste transformatorskog ulja, i to mineralno transformatorsko ulje HyVolt III (Ergon), HIII i sintetsko estersko ulje Midel® 7131 (M&I Materials), M7131, ustupljeno od Končar - Distributivnih i specijalnih transformatora u različitim volumnim omjerima. Pripravljenim smjesama različitih volumnih omjera u rasponu od 1 do 50 vol.% HIII mjerena je viskoznost nakon 30 dana te se pokazalo kako se radi o homogenim mješavinama. Ostale metode kojima su karakterizirane pripravljene smjese i čisti uzorci transformatorskog ulja su toplinska vodljivost, infracrvena spektroskopija, termogravimetrijska analiza, probojni napon, ispitivanje sadržaja vode, faktor dielektričnog gubitka i specifični električni otpor. Termogravimetrijskom analizom utvrđena je bolja toplinska stabilnost sintetskog estera u odnosu na mineralno ulje. Kod svih smjesa dobiven je stabilan probojni napon unatoč porastu sadržaja vode. Također, sve pripravljene mješavine različitih volumnih udjela mineralnog i esterskog ulja pokazuju viši probojni napon u odnosu na probojni napon čistog mineralnog transformatorskog ulja. Zaključno, prema svim praćenim svojstvima, dobiveni rezultati ispitivanih smjesa mineralnog i esterskog ulja pokazuju zadovoljavajuću međusobnu kompatibilnost dielektrika. Insulating oils used in transformers, often referred to as transformer oils, are designed to ensure safe operation during the transformer's working life. They are used for two basic purposes: as an insulating material and a cooling media. Today, mineral insulating oil, which has been used over past year due to its good thermal and electrical properties, is most preferred for isolating. However, as mineral oil it has its shortcomings such as flammability and corrosivity, ester-based transformer oil is increasingly used as a substitute for mineral oil due to high temperature resistance, increased fire safety and high biodegradability. Two types of transformer oils were used in this work: Mineral Transformer Oil HyVolt III (Ergon), HIII and Synthetic Ester Oil Midel® 7131 (M & I Materials), M7131, provided by Končar - Distributive and Special Transformers in different volumetric ratios. Prepared mixtures of different volume ratios ranging from 1 to 50 vol% of HIII were characterized by viscosity measurement after 30 days and it was found that mixtures are homogeneous. In addition prepared mixtures and pure transformer oil sample were characterized by thermal conductivity measurement, infrared spectroscopy, thermogravimetric analysis, breakdown voltage, water content test, dielectric dissipation factor and specific electrical resistivity. Thermal stability of synthetic ester is higher than thermal stability of mineral oil which was shown by thermogravimetric analysis. A stable breakdown voltage was obtained in all mixtures despite increasing water content. Also, all prepared mixtures of transformer oil exhibits higher breakdown voltage versus the breakdown voltage of pure mineral transformer oil. In conclusion, according to all observed properties, the obtained results for the tested mixtures of mineral and ester oil show satisfactory mutual compatibility of dielectrics.

U ovom radu istraživala su se svojstva celuloznih hidrogelova dobivenih iz mikrokristalične celuloze. Hidrogelovi su trodimenzionalne polimerne mreže nabubrene s velikom količinom vode, a mogu se pripraviti fizikalnim ili kemijskim umreživanjem. Otapanje mikrokristalične celuloze provedeno je u vodenoj otopini NaOH/urea. Pripremljene su otopine s masenim udjelom celuloze od 1, 3, 5 i 7 mas.%. Metoda umreživanja celuloze bila je fizikalna što znači da se među molekulama celuloze stvaraju intramolekularne vodikove veze. Bilo je potrebno utvrditi koji maseni postotak celuloze u otopini daje optimalnu poroznost celuloznog hidrogela. Poroznost je vrlo bitno svojstvo hidrogelova pošto ona određuje kapacitet kapljevine koju hidrogel može primiti. Priređeni hidrogelovi karakterizirani su infracrvenom spektroskopijom (FTIR), pretražnom elektronskom mikroskopijom (SEM), rendgenskom difrakcijom (XRD) te bubrenjem. Ustanovljeno je da hidrogel dobiven iz 3%-tne otopine celuloze metodom pretaloživanja ima najviši kapacitet bubrenja što se očitava u najvišim vrijednostima stupnja bubrenja. This work investigates properties of cellulose hydrogels made from microcrystalline cellulose. Hydrogels are three-dimensional polymer networks swollen with water which can be synthetized either by chemical or physical crosslinking. Microcrystalline cellulose was disolved in aqueous sloution of NaOH/urea. Solutions with 1, 3, 5 and 7 mass percentages of cellulose were obitained. It was necessary to determine which mass percentage of cellulose in the solution will give the optimal porosity of the cellulose hydrogel. Porosity is a very important feature of hydrogels as it determines the capacity of solvent that the hydrogel can absorb. Prepared hydrogels were characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and swelling method. It has been found that the hydrogel obtained from 3 mass.% cellulose solution which was prepared by precipitation method has the highest swelling degree.

Cilj ovog rada jest istraživanje utjecaja duljine nanocijevi na toplinsku vodljivost nanofluida na osnovi PAO 4 i YUBASE 4 ulja s višestjenčanim ugljikovim nanocijevima (MWCNT). Eksperimentalni dio podijeljen je u dvije faze. U prvoj fazi pripremljeni su nanofluidi s ugljikovim nanocijevima duljine 50 μm, te različitim surfaktantima (PAT). Ispitana je stabilnost pripremljenih nanofluida, s ciljem utvrđivanja najkompatibilnijih sustava. U drugoj fazi pripremljeni su nanofluidi s ugljikovim nanocijevima duljine u rasponu od 0,5 do 2 μm, te različitim surfaktantima. Također je ispitana stabilnost pripremljenih nanofluida. Najstabilniji nanofluidi iz obje faze ponovo su pripremljeni s ciljem određivanja toplinske vodljivosti. Stabilnost nanofluida ispitana je sedimentacijskim testom vizualnom i instrumentalnom metodom (UV/VIS spektrofotometrija). Vizualna metoda sastoji se od slikanja uzoraka nanofluida i analize slike. Snimljeni su UV/VIS apsorpcijski spektri uzoraka kako bi se odredila stabilnost nanofluida. Stabilnost je prikazana u obliku raspršenosti MWCNT-a u baznom fluidu. Određen je utjecaj surfaktanata na viskoznost baznih fluida, te je izmjerena toplinska vodljivost uzoraka metodom toplinskog impulsa. The aim of this paper was to study the impact of the carbon nanotubes length on the thermal conductivity of nanofluids based on PAO 4 and YUBASE 4 oil with multiwalled carbon nanotubes (MWCNT). Experimental section was divided into two phases. In the first phase nanofluids with carbon nanotubes length of 50 μm, and different surfactants were prepared, as the aim was to explore compatibility of various surfactants with base oils oil and MWCNT. In the second phase nanofluids with carbon nanotubes length in the range from 0.5 to 2 μm, and different surfactants were prepared to explore compatibility of various surfactant and base oil combinations as well. Lastly, the most stabile nanofluids from both phases were prepared in order to test the thermal properties. Sedimentation rate was examined visually and using instrumental method in order to test the nanofluid stability. Visual method includes photographing nanofluid samples, and analysis of the photograph. UV/VIS absorption specters were measured, and the nanofluid stability was presented as a dispersion of the MWCNTs in base fluid. Effect of various surfactants on the base oil viscosity was examined, as well as thermal conductivity of prepared nanofluids.

Dvadeseto stoljeće naziva se i „polimerno doba“. Industrija polimera naglo se razvijala zbog brzog razvoja petrokemije, jeftinih sirovina i energije. Sa stalnim istraživanjem na području polimera, njihova je primjena u suvremenom društvu sve šira. Polimeri su velika skupina materijala. To su makromolekule koje imaju različita mehanička, toplinska, električna, magnetska i optička svojstva. Pri proizvodnji im se dodaju aditivi koji utječu na konačna svojstva proizvoda. Biorazgradljive plastike su polimeri dobiveni iz obnovljivih ili fosilnih izvora. Takav biorazgradljiv materijal može se kompostirati i vratiti u zemlju kao korisna sirovina. Predstavnik biorazgradljive plastike je i poli(etilen-furanoat) (PEF), koji je u potpunosti načinjen od prirodnih sirovina. Kao zamjena za PET, PEF ima bolja mehanička svojstva te svojstvo propusnosti plinova. Kao takav, vjerojatno će u budućnosti potpuno zamijeniti PET, koji je danas u uporabi. The 20th century is called the "Polymer Age". Polymer industry grew rapidly due to the swift development of petrochemistry, cheap raw materials and energy. With continued research into the science and applications of polymers, they play an ever increasing role in society. Polymers are a large class of materials. They are macromolecules which have different mechanical, thermal, electrical, magnetic and optical properties. In the production, additives are added to it to affect the final properties of the products. Biodegradable plastics are polymers which are derived from fossils or renewable sources. Such biodegradable materials can be composted, broken down and returned to the ground as useful nutrients. A representative of biodegradable plastic is polyethylene furanoate (PEF), which is fully made of natural raw materials. As a replacement for PET, PEF has better mechanical properties and gas permeability barrier properties. As such, it will probably completely replace plastics which are in use today.

Kompoziti s obnavljanjem svojstava su kompozitni materijali koji imaju mogućnost automatskog obnavljanja svojih svojstava pri raznim oštećenjima. Razvijeni su u posljednjih petnaest godina inspirirani dizajnom prirodnih sustava (ljudi, životinje, biljke) koji pokazuju sposobnost samoobnavljanja odnosno zacjeljivanja. Ovaj se rad temelji na dvije vrste samoobnovljivih kompozita: kapsulirani i vaskularni samoobnovljivi kompoziti te prikazuje pregled najbitnijih dostignuća i napretka u ovom polju. Uspoređeni su također mehanizmi obnavljanja kompozitnih materijala i procesi izrade mikro kapsula i vaskularnih mreža. Na temelju predstavljene analize ovih vrsta materijala, prezentirani su faktori koji utječu na izvedbu obnavljanja u svrhu otkrivanja ključnih prepreka i potencijalnih istraživanja kompozita s obnavljanjem svojstava. Self-healing composites are composite materials capable of automatic recovery of their properties under various damage. They were developed in the last fifteen years inspired by natural systems such as humans, animals or plants that are capable of self-healing. This paper is based on two types of self-healing composites: capsule-based and vascular self-healing composites, and provides an overview of the most important achievements and advancements in this field. Also, comparison between healing mechanisms and fabrication processes of micro capsules and vascular networks has been made. Based on the analysis of these types of materials, factors that influence healing performance are presented to reveal the key barriers and potential research directions in field of self-healing composites.

Polilaktid (PLA) je termoplastični biorazgradivi polimer, pri čemu se proizvodnja PLA temelji na prirodnim izvorima kao što su kukuruz ili šećerna trska. Zbog dobrih mehaničkih i drugih svojstava (gustoća, prozirnost, barijerna svojstva) PLA je našao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posvećen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najčešće provodi pomoću fizikalnih ekspandirajućih agensa kao što su CO2, N2 ili i–butan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograničena je zbog loših reoloških svojstava taline PLA. U ovom radu kao ekspandirajući agens korištene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoću mlina, a zatim su priređene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoć tresilice. Homogena smjesa prešana je u hidrauličkoj preši na temperaturi od 190 °C u vremenu 8 minuta. Nakon optimizacije uvjeta prešanja, prešanje je provođeno na 180 °C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena prešanja smanjena je degradacija uzoraka prilikom prešanja. Kod pripreme ekspandiranih uzoraka ispitivan je i utjecaj punjenja kalupa na strukturu i svojstva ekspandiranog materijala. Jednoliko popunjavanje kalupa postignuto je za uzorke sa 16 g i 18 g PLA, dok uzorci s 12 g PLA nisu u potpunosti popunili kalup. Polylactide (PLA) is a biodegradable thermoplastic polyester, wherein the production of PLA is based on natural sources such as corn or sugarcane. PLA has found application in the packaging industry (bottles, rigid plastic, foil) due to mechanical and other properties (density, transparency, barrier properties). In addition, a considerable number of papers is devoted to the study of expanded PLA which is an alternative for replacement of the expanded poly(styrene) (E-PS). Expanding of PLA is most commonly achieved by physical blowing agents such as CO2, N2 or i-butane. The use of those physical blowing agents for expanding PLA is limited due to poor rheological properties of PLA melt. Expancel microspheres were used as an expanding agent in this work. PLA granules were grinded with mill and then the mixtures were prepared by adding 3, 5 or 7 wt % of Expancel to grinded PLA granules. Mixtures were additionally homogenized with vortex. The homogeneous mixtures were compressed in a hydraulic press at a temperature of 190 °C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 °C for 6 minutes. Furthermore, by optimizing the temperature and the pressing time during the pressing process, degradation of samples is reduced. During the preparation of expanded test samples, impact of mold filling on the structure and properties of the expanded material was investigated. Uniform filling of mold was achieved for samples with 16 and 18 g of PLA, while the samples with 12 g of PLA did not completely fill the mold.

U ovom su radu provedena istraživanja utjecaja dodatka kalcij karbonata kao punila u polimernu matricu polilaktida. Pritom su korištena dva oblika kalcij karbonata: Socal (S) i Solvay (U). Uzorci su pripremljeni umiešavanjem u Brabender gnjetalici (masenih udjela punila 0,1; 0,5; 1 i 5 %) i umješavanjem u otopini (0,1 i 1 mas. %). Ispitivana su mehanička i toplinska svojstva dobivenih kompozita koristeći dinamičko mehaničku analizu, diferencijalno pretražnu kalorimetriju, termogravimetrijsku analizu, univerzalnu kidalicu, te goniometar za mjerenja kontaktnog kuta. Rezultati su pokazali poboljšanje svojstava s dodatkom kalcij karbonata kao punila u polimernu matricu. Rezultati DMA analize dali su uvid u primarne viskoelastične funkcije materijala. Moduli pohrane dobiveni DMA analizom viši su kod kompozita u odnosu na čisti polilaktid što pokazuje veću mogućnost materijala da podnese opterećenja. Iz DSC analize dobivene temperature i iznosi entalpije faznih prijelaza: staklišta, kristalizacije i taljenja pokazuju pomake prema višim temperaturama. TGA analiza pokazala je kako dodatak punila poboljšava toplinsku stabilnost materijala, a najbolje je rezultate imao kompozit s 0,1 mas. % oba punila. Također, znatno su poboljšana mehaniča svojstva za sve udjele punila. Ispitivanja goniometrom nisu dala jasne rezultate kako dodatak punila utječe na kontaknti kut kompozita i testnih kapljevina (voda, formamid i dijodometan). In this study the addition of calcium carbonate as filler in PLA matrix was investigated. Two kinds of calcium carbonate were used: Socal (S) and Solvay (U). Samples were prepared by melt mixing in Brabender plasticoder (share of filler 0.1, 0.5, 1 and 5 wt. %) and in solution mixing (0.1 and 1 wt. %). Mechanical and thermal properties were investigated using dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, universal testing machine as well as surface properties by measuring contact angle with goniometer. The results showed increased performance with the addition of calcium carbonate as filler in a polymeric matrix. DMA analysis results gave an insight into the primary viscoelastic material functions. Storage modules obtained are higher in the composite compared to pure polylactide indicating a greater ability of materials to withstand the load. The temperatures and enthalpy of phase transitions: glass transition, crystallization and melting obtained by DSC analysis show shifts towards higher temperatures. TGA analysis showed that the addition of filler improves the thermal stability of the materials, whereat the best results showed both composites containing 0.1 wt. % filler. Also, mechanical properties have been significantly improved for all shares of fillers. The results obtained on goniometer didn't give any clear conclusion on influence of added fillers on contact angle of composite and test liquids (water, formamide and diiodomethane).

Unutarnji dijelovi energetskog transformatora koji su pod naponom, izolirani su pomoću papirne izolacije i uronjeni su u izolacijsko ulje. Stoga se izolacijsko ulje i papirna izolacija ispituju prvi kad se jave problemi u radu energetskog transformatora. Stanje izolacije u energetskom transformatoru važan je pokazatelj preostalog životnog vijeka. Poboljšanja u obliku toplinski otpornijeg papira i uporaba biljnog ulja kao alternativa mineralnom, nose probleme vezane za praćenje sustava postojećim uhodanim metodama. Koristi se nekoliko kemijskih tehnika kojima se može utvrditi stanje izolacijskog papira, a to su određivanje stupnja polimerizacije, koncentracija ugljikovih oksida, analiza furana i metanola, te metoda pranja sa organskim spojevima. Pored kemijskih metoda postoje i dielektrične metode: PDC (metoda mjerenja struja polarizacije i depolarizacije), FDS (frekventno zavisna spektroskopija) i RVM (metoda mjerenja povratnog napona). Internal parts of the power transformer are isolated using paper insulation and are immersed in insulating oil. Hence, transformer oil and paper insulation are first to be examined when problems and faults occur related to the work of power transformator. Insulation condition of a power transformer largely determines its remaining lifetime. Improvements in the form of more heat-resistant paper and use vegetable oil as an alternative to mineral bring problems associated with the monitoring of the system with common methods. Several chemical diagnoses techniques are developed to examine the condition of paper insulation such as degree of polymerization, carbon oxides, furanic compounds, methanol, and washing with surface-active substances. in addition to chemical methods there are also dielectric methods: PDC (Polarization and Depolarization Current Method), FDS (Frequency Domain Spectroscopy) and RVM (Recovery Voltage Measurement).

U ovom radu istraživali su se kompozitni materijali na osnovi biorazgradivog polilaktida (PLA) ojačani grafitnim punilima: grafitne pahulje (A) i amorfni grafit (B). Kompoziti su se pripremali umješavanjem na Brabender gnjetalici (udio punila: 0,1, 0,5, 1 i 5 mas. %) i iz otopine (udio punila: 0,1 i 1 mas. %). Ispitivala su se i uspoređivala mehanička i toplinska svojstva čistog PLA i pripravljenih kompozita. Diferencijalnom pretražnom kalorimetrijom ispitivani su fazni prijelazi. Termogravimetrijskom analizom se ispitivala termička stabilnost uzoraka. Goniometrom se određivao kontaktni kut uzoraka sa vodom, formamidom i dijodometanom kao testnim kapljevinama, te je računata površinska energija pripravljenih materijala. Univerzalnom mehaničkom kidalicom su se određivala mehanička svojstva uzoraka. Određivana su vlačna čvrstoća, Youngov modul, te prekidno istezanje. Karakterizacijom kompozitnih materijala ustanovljeno je da dodatkom punila u polilaktid možemo utjecati na njegova svojstva. DSC analizom je zabilježen utjecaj različitih metoda priprave i različitih punila na temperature staklastih prijelaza. Termogravimetrijska analiza je pokazala da dodatkom punila možemo poboljšati termičku stabilnost polilaktida. Mehanička svojstva kompozita bolja su u usporedbi s čistim PLA, zabilježene su veće vrijednosti Youngovog modula, naprezanja i prekidnog istezanja. Iz rezultata ispitivanja na goniometru nije se moglo dobiti jasno pravilo po kojem se mijenja kontaktni kut materijala, odnosno površinska svojstva materijala. This work investigates composites of biodegradeable polylactide (PLA) reinforced with graphite fillers: graphite flakes (A) and amorphus graphite (B). Composites were prepared in a Brabender mixer (filler concetration: 0.1, 0.5, 1 and 5 wt. %) and by solution mixing (with 0.1and 1 wt. % of filler). Mechanical and thermal properties of pure polylactide and its composites were investigated. An insight into phase transition temperature and phase transition of the polymer were obtained by differental scanning calorimetry. The thermal stability of the samples was monitored by thermogravimetry. The contact angles of test liquids (water, formamied and diiodomethane) were determined by a goniometer after which the free surface energy was calculated. The universal testing machine was used to determine mechanical propertise of PLA and prepared composites. The tensile strenght, Young's modulus and elongation at break of the materials were determined. Characterization of composite materials revealed that the addition of fillers to polylactide has different influence on some of its properties. The DSC method has shown influence of various preparation methods and different fillers on the glass transition temperature, which did not change significantly, though. Thermogravimetry has showed that the composites are more thermally stable than pure PLA. Composites have better mechanical properties such as higher Young's modulus, tensile strenght as well as elongation at break. Studies on the goniometer did not give a clear correlation between the type and concentration of filler in the composite and its surface properties.

Cilj ovog rada je priprava i karakterizacija nanofluida koji posjeduju dva najpoželjnija svojstva što se tiče prijenosa topline: dugotrajnu stabilnost i visoku toplinsku vodljivost. U tu svrhu su pripravljene suspenzije višestjenčanih ugljikovih nanocijevi (MWCNT), odnosno grafita u baznom fluidu PAO 8 ulju uz dodatak površinski aktivne tvari (PAT). U prvoj fazi eksperimentalnog rada određeno je koja od površinski aktivnih tvari, za PAO 8 ulje, omogućava najveću stabilnost nanofluida. U drugoj fazi je istraživan utjecaj različitih koncentracija punila i odabrane površinski aktivne tvari (DPS) na stabilnost sustava. Stabilnost pripravljenih nanofluida određivana je pomoću sedimentacijskog testa (vizualno) to pomoću UVVis spektrofotometrije. Karakterizacija nanofluida je provedena određivanjem viskoznosti, toplinske vodljivosti, otpornosti na trošenje i kontaktnog kuta na granici faza čvrsto-kapljevito plinovito. Površinski aktivna tvar s kojom je postignuta najveća stabilnost nanofluida je disperzantni polimerni aditiv na osnovi stirena i metakrilata (DPS). Povećanjem njegove koncentracije dolazi do porasta viskoznosti nanofluida, a time i do veće stabilnosti sustava (Stokesov zakon). Jedini porast toplinske vodljivosti zabilježen je kod nanofluida koji sadrži 2600 mg MWCNT, a razlog tome je što se prijenos topline odvija samo preko nanočestica u kontaktu. Rezultati testa trošenja ukazuju na smanjenje srednjeg promjera istrošenja svih uzoraka, što ukazuje na bolja svojstva podmazivanja. Iz rezultata mjerenja kontaktnog kuta zaključeno je da interakcije između uzoraka i teflonske površine nisu povoljne, dok su staklena i metalna površina zatvarale manji kontaktni kut sa uzorcima. Kod rezultata za metalnu površinu se opaža trend opadanja kontaktnog kuta s povećanjem količine ugljikovih nanocijevi. Iz standardnih devijacija kod sva tri slučaja, vidi se da metoda ima velika odstupanja te zbog toga nije moguće izvesti valjane zaključke. The aim of this work is preparation and characterization of nanofluids with two features most desired for heat transfer systems: long term stability and high thermal conductivity. For this purpose, suspensions of multi-wall carbon nanotubes (MWCNTs) / graphite were prepared in a base oil fluid PAO 8 with the addition of surface-active substances (surfactants). In the first phase of the experimental work, it was determined which of surfactants, for PAO 8 oil, provides the greatest stability of nanofluids. In the second phase, the effect of different concentrations of filler and selected surfactant (DPS) on system stability was studied. Stability of prepared nanofluids was determined by sedimentation test (visually) and by UV-Vis spectrophotometry. Characterization of nanofluids is accomplished by determining the viscosity, thermal conductivity, wear resistance and the contact angle at the solid-liquid-gas interface. The surfactant, that had enabled the greatest stability of nanofluids, was dispersant polymer additive based on styrene and methacrylate (DPS). By increasing its concentration there was an increase in viscosity of nanofluids, and thus greater system stability (Stokes' law) was accomplished. The only increase in thermal conductivity was noted in nanofluid containing 2600 mg of MWCNTs, because the heat transfer takes place only via nanoparticles in touch. The wearing test results indicate a reduction of mean wear diameter of all nanofluids, which indicates better lubricating properties. The results of the contact angle measurement indicate that the interaction between the sample and teflon surfaces are not favorable, while glass and metal surfaces had lower contact angle with samples. Results for metal surface indicate decreasing trend of the contact angle with the increase of carbon nanotubes. From the standard deviations for all three cases, it can be seen that the method has a big deviation and it is not possible to draw valid conclusions.

U ovom radu istraživali su se kompozitni materijali biorazgradivog polilaktida (PLA) ojačani s mineralnim punilima - Schwerspatom (S) i Glimmerom POS (GL). Umješavanjem u Brabender gnjetalici i prešanjem pripremili su se kompoziti s 0,1; 0,5; 1 i 5 mas. % punila, a iz otopine i prešanjem s 0,1 i 1 mas. % punila. Određivala su se i uspoređivala mehanička i toplinska svojstva dobivenih materijala i čistog polimera. Ispitivanjima univerzalnom kidalicom dobiven je uvid u mehanička svojstva pripravljenih kompozita i PLA. Određivana su vlačna čvrstoća, Young-ov modul i prekidno rastezanje. Dinamičko mehaničkom analizom ispitivana su primarna viskoelastična svojstva materijala kao i utjecaj punila na temperaturu staklastog prijelaza polimerne matrice. Toplinska stabilnost uzoraka određivana je termogravimetrijskom metodom, a uvid u fazne prijelaze i temperature faznih prijelaza polimera (matrice) dobiven je diferencijalnom pretražnom kalorimetrijom. Također se određivao kontaktni kut uzoraka s vodom, formamidom i dijodometanom kao testnim kapljevinama, te je računata površinska energija pripravljenih materijala. Karakterizacijom kopompozitnih materijala ustanovljeno je da se dodatkom punila u polilaktid poboljšavaju njegova svojstva. U prisustvu punila polimernoj matrici potrebno je dulje vrijeme za fazne prijelaze što se očitava u pomaku temperatura staklišta, kristališta i tališta na više vrijednosti. DSC analizom ustanovljeno je i smanjenje udjela kristalinične faze dodatkom punila. Punilo povećava nosivost opterećenja polimerne matrice, vidljivo iz porasta modula pohrane. Kompozitni materijali također imaju bolja mehanička svojstva, tj. veći Young-ov modul, rasteznu i prekidnu čvrstoću kao i prekidno rastezanje. Kompozitni materijali toplinski su stabilniji od čistog polimera. Toplinska degradacija počinje na 50 °C višoj temperaturi od čistog polilaktida. This work investigates composites of biodegradable polylactide (PLA) reinforced with mineral fillers - Schwerspat (S) and Glimmer POS (GL). Composites with 0.1; 0.5; 1 and 5 weight % filler were prepared in a Brabender mixer and molded under pressure. Composites with 0.1 and 1 weight % Schwerspat and Glimmer were prepared by solution mixing and molded under pressure. The mechanical and thermal properties of the composites and pure polymer were investigated and compared to each other. An overview of the mechanical properties of PLA and prepared composites was achieved through experiments with an universla testing machine. The tensile strenght, Young's modulus and elongation of the materials were determined. Dynamic mechanical analysis was used to investigate the primary viscoelastic properties of the materials and the effect of fillers on the glass transition temperature of the polymer matrix. The thermal stability of the samples was monitored by thermogravimetric method and insights into phase transition temperature of the phase transition of the polymer (matrix) obtained by differential scanning calorimetry. The contact angles of test liquids (water, formamide and diiodomethane) and free surface energy were also determined. Characterization of the composite materials revealed that the addition of fillers to polylactide improves its properties. In the presence of fillers the polymer matrix needs more time for phase transitions which can be seen in the shift of glass transition, christalization and melting temperatures to higher values. DSC analysis also showed that by the addition of fillers the cristalinity of the polymer lowers. The filler increases the load carrying capacity of the polymer matrix, evident from the increase in storage modulus. Composite materials also have better mechanical properties, ie. higher Young's modulus, tensile and breaking strength as well as elongation. Composite materials are thermally more stable than the pure polymer. Thermal degradation starts at 50 °C higher temperature than the pure polylactide.

Primjena biogoriva sve se intenzivnije istražuje i širi zahvaljujući europskoj i međunarodnoj politici zaštite okoliša. Biogoriva mogu pridonijeti cilju smanjenja emisija CO2 koje su postavljene Kyotskim protokolom. Biobutanol je interesantna opcija kao gorivo za dizelske motore zbog dobre mješljivosti s dizelskim gorivom te smanjenja emisija stakleničkih plinova što se postiže namješavanjem u dizelsko gorivo. U ovom radu ispitana su niskotemperaturna svojstva mješavina n-butanola i dizelskog goriva u udjelima od 0 do 15 % vol. te utjecaj komercijalnih aditiva za dizelsko gorivo, poboljšivača tečenja poli(etilen-vinil acetata) (EVA) i aditiva koji spriječava taloženje parafina (WASA), na niskotemperaturna svojstva mješavina. Diferencijalnom pretražnom kalorimetrijom (DSC) su ispitani fenomeni kristalizacije. Rezultati ispitivanja pokazuju da dodatak n-butanola nema utjecaja na gustoću, točku zamućenja, točku filtrabilnosti i točku tečenja neaditiviranog dizelskog goriva. n-Butanol u koncentraciji od 2,5 % i 5 % vol. uz dodatak EVA i WASA aditiva ima pozitivan učinak na točku filtrabilnosti. Porastom udjela n-butanola aditiviranih mješavina ne dolazi do promjene točke zamućenja i točke tečenja. Kratki sedimentacijski test (Aral test) pokazuje da dodatak n-butanola u dizelskom gorivu uz aditive znatno pogoršava operabilnost dizelskog goriva. DSC krivulje pokazuju da mješavine s nižim udjelima n-butanola (2,5 % i 5 % vol.) imaju izražene interakcije s n-parafinima viših molekulskih masa, dok su pri višim udjelima n-butanola izraženije interakcije n-butanola s parafinima nižih molekulskih masa. n-Butanol djeluje na povišenje temperature početka kristalizacije n-parafina. Dodatak EVA i WASA aditiva djeluje na interakcije molekula parafina i n-butanola čime utječe na promjenu tijeka kristalizacije parafina. The use of biofuels has been intensively investigated thanks to European and international environmental policy. Biofuels can help reduce CO2 emissions set up under the Kyoto Protocol. Biobutanol is an interesting option as a fuel for diesel engines due to its good miscibility with diesel fuel and reduced emissions of greenhouse gases when blended in diesel. In this paper, the low temperature properties of blends of n-butanol and diesel fuel in ratios from 0 to 15 % vol., and the impact of commercial additives for diesel, flow improver poly (ethylene-vinyl acetate) (EVA) and dispersant additves, on the low temperature properties of the mixtures was investigated. In order to examine crystallization of paraffins differential scanning calorimetry was used. The results show that the addition of n-butanol has no effect on density, cloud point, cold filter plugging point and pour point of diesel fuel. n-Butanol/diesel ratios blend with 2.5% and 5% butanol with the addition of EVA and WASA additives have a positive effect on the cold filter plugging point. Increase of the concentrations of n-butanol in blends with additives has no impact on the cloud point and pour point. Aral test shows that the addition of n-butanol in diesel fuel significantly deteriorates operability of diesel fuel. DSC curves show that lower concentrations of n-butanol (2,5% and 5%), act in interaction with the higher molecular weight paraffins while higher concentrations of n-butanol result in higher interactions with the low-molecular-weight paraffins. Addition of n-butanol increases the start temperature of the paraffin crystallization. Addition of EVA and WASA additive effects the interaction of paraffin and butanol molecules resulting in changing the course of paraffin crystallization.