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The development of active edible coatings with improved mechanical and barrier properties is a huge challenge. In this study, active edible coatings for sliced cheese have been developed using pullulan (Pull) in combination with two different biopolymers, chitosan (CS) and gelatine (Gel), and a combination of hydrolats as a source of active compounds with antimicrobial effects. In comparison to the monolayer coating, the bilayer coating system demonstrates improved barrier and mechanical properties. A preliminary assessment of the antimicrobial effect of lemongrass and curry plant hydrolats has revealed that both hydrolats exhibited antimicrobial activity against the targeted bacterium Staphylococcus aureus, albeit at different levels. The obtained results suggest that a mixture of 1.56% lemongrass and 12.5% curry plant hydrolats yielded a lower fractional inhibitory concentration (FIC) value. Bilayer coating systems (Pull/CS and Pull/Gel) with an incorporated mixture of hydrolats have demonstrated effectiveness in both cases: artificial contamination before application of the coating system and after application of the coating system. In both contamination scenarios, the coating systems consistently effectively limited bacterial proliferation, indicating the antimicrobial effect of the hydrolat mixture in the coating layers. In the case of artificial contamination before applying the coating system, both coatings demonstrated antimicrobial effectiveness, but the formulation with chitosan had a biocide effect, while the other, with gelatine, had only a bacteriostatic effect in a long-term setting. In the second case, both Pull/CS and Pull/Gel coatings demonstrated effectiveness in inhibiting bacterial growth regardless of the moment of contamination of the sample; the Pull/CS coating showed slightly better antimicrobial activity, achieving complete elimination of bacteria earlier compared with the Pull/Gel coating system.

In this paper, the microstructural damage evolution of a steel with a ferrite-pearlite microstructure (C45E) was investigated during the process of cold upsetting. The development and the accumulation of microstructural damage were analyzed in different areas of samples that were deformed at different strain levels. The scanning electron microscopy (SEM) results showed that various mechanisms of nucleation of microcavities occurred during the upsetting process. In quantitative terms, microcavities were predominantly generated in pearlite colonies due to the fracture of cementite lamellae. In addition, the mechanism of decohesion had a significant influence on the development of a macroscopic crack, since a high level of microcracks, especially at higher degrees of deformation, was observed at the ferrite/pearlite or ferrite/ferrite interfaces. It was found that the distribution of microcavities along the equatorial plane of the sample was not uniform, as the density of microcavities increased with increasing strain level. The influence of stress state, i.e., stress triaxiality, on the nucleation and distribution of microcracks, was also analyzed.

Dual-phase ADI material microstructure consists of different amounts and morphologies of ausferrite and free ferrite, obtained by subjecting ductile iron to specific heat treatment. Its strength is lower compared to comparable ADI materials but exhibits a higher ductility, the major disadvantage of ADI. In the current study, an unalloyed ductile iron was intercritical austenitized in two-phase regions (??+??) at four temperatures from 840 to 780 ??C for 2 h and austempered at 400 ??C for 1 h to obtain dual-phase ADI with different percentages of free ferrite and ausferrite. Light and scanning electron microscopy was performed for the metallographic and fracture studies, respectively. Microscopy results were correlated to tensile testing results. The results indicated that, as the amount of ausferrite present in the matrix increases, higher values of strength and lower ductility are obtained. The fracture surfaces of dual-phase ADI microstructures with 22.8% of ausferrite in their matrix have regions of quasi-cleavage fracture around last-to-freeze zones, related to the presence of ausferrite in those areas. The specimens with the highest values of ausferrite of 86.8% among the dual-phase microstructure have a dominant quasi-cleavage type of fracture.

Biodegradable active packaging films based on a cellulose acetate and poly(caprolactone diol) blend with incorporated lemongrass oil were developed. Films were prepared using a novel bio-based plasticizer, glycerol tritartarate, synthesized using the principles of green chemistry. The influence of the plasticizer, as well as the essential oil amount, on the structural, surface, mechanical, and thermal properties of the blend was investigated. The plasticizer was shown to work as a compatibilizer for two polymers, according to the results of scanning electron microscopy and surface energy analysis. Blends with a greater amount of plasticizer possessed better mechanical properties but showed worse resistance to water. The antimicrobial property of the blend with lemongrass oil was found to be superior to that of the blend without essential oil. The incorporation of lemongrass oil into the polymer blend resulted in one more step longer thermal degradation process. The optimal film properties, biodegradability, cost-effective preparation method, and additional functions made these films suitable for the production of packaging for grapefruit.

In this paper, selective laser melting fabricated specimens in non-heat-treated and heat-treated conditions were subjected to Vickers microhardness testing, by using a full range of loadings: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Microhardness of longitudinal sections and cross-sections were correlated and the obtained values were plotted against loadings and indentation size effect was studied, in order to find the optimal loading range, that gives the material true microhardness, or load-independent hardness. The load dependence of the measured Vickers hardness values was described quantitatively through the application of the Meyer's law, proportional specimen resistance, and the modified proportional specimen resistance model. It was found that the microhardness rises as the loading is higher, causing a reversed indentation size effect, clearly indicating the range of true hardnesses of the tested material. Also, proportional specimen resistance and modified proportional specimen resistance models were found to have the highest correlation factors indicating their higher adequacy compared to Meyer's prediction model.

Within the framework of presented PhD, friction stir spot welding (FSSW) of multiple ultrathin sheets of AA 5754 – H111 (AlMg3) alloy 0.3 mm thick, was studied. The influence of tool geometry and process parameters such as rotational speed and axial load have been analysed using numerous techniques. It has been understood that during the welding at low rotational speeds weld zone undergoes strain hardening, while at high rotational speeds weld zone undergoes thermal softening. It was observed that during FSSW at low rotational speeds a complex layer at weld interface is present, which causes delamination when welded samples are subjected to load., У оквиру ове докторске дисертације испитивано је тачкасто заваривање трењем са мешањем ултратанких лимова дебљине 0.3 mm од легуре АА 5754 – H111 (AlMg3). Утицај геометрије алата и параметара као што су угаона брзина и аксијално оптерећење су детаљно анализирани уз помоћ бројних техника. Установљено је да приликом заваривања ниским угаоним брзинама долази до деформационог ојачавања, док на високим угаоним брзинама долази до термичког омекшавања зоне завара. Код узорка завареног са најмањим бројем обртаја долази до формирања комплексног слоја на међуконтактној површини који изазива деламинацију приликом испитивања механичких особина., U okviru ove doktorske disertacije ispitivano je tačkasto zavarivanje trenjem sa mešanjem ultratankih limova debljine 0.3 mm od legure AA 5754 – H111 (AlMg3). Uticaj geometrije alata i parametara kao što su ugaona brzina i aksijalno opterećenje su detaljno analizirani uz pomoć brojnih tehnika. Ustanovljeno je da prilikom zavarivanja niskim ugaonim brzinama dolazi do deformacionog ojačavanja, dok na visokim ugaonim brzinama dolazi do termičkog omekšavanja zone zavara. Kod uzorka zavarenog sa najmanjim brojem obrtaja dolazi do formiranja kompleksnog sloja na međukontaktnoj površini koji izaziva delaminaciju prilikom ispitivanja mehaničkih osobina.

During the last few years, there has been an increased interest in improving the strength of ductile iron by means of heat-treating to obtain dual phase microstructures that enhance the properties found in the Austempered Ductile Irons (ADI). Therefore, additional research int this field is well motivated. An example of this is the innovative dual phase austempered irons - DP-ADI, that has a greater ductility than the conventionally heat treated ADI, due to its microstructure composed of ausferrite (regular ADI microstructure) and free (proeutectoid) allotriomorphic ferrite. Additionally, dual phase ADI could provide a wide range of mechanical properties as a function of the relative proportion of proeutectoid ferrite and ausferrite constituents, thereby replacing conventional ductile iron. Hence, dual phase ADI will be appropriate for new applications in the critical parts, where a combination of high strength and ductility is a pressing requirement. Furthermore, with the introduction of free ferrite into the matrix increased machinability of ADI could be achieved. The aim of this paper was to review works that have been published over the past years on the effects of process variables, mechanical properties, microstructure and applications of Dual phase Austempered Ductile Iron and to present some own results. This review is an attempt to assemble the results of the worldwide sudden increase in research and development that followed the announcement of the first production of the DP-ADI material.

U ovom radu, izvršena je sinteza i karakterizacija bionanokompozitnih materijala na osnovu poli(laktida) i višeslojnih ugljeničnih nanocevi. Ispitivan je uticaj različitih tehnika funkcionalizacije nanocevi, kao i izbor uslova sinteze i odnosa polaznih komponenti sistema, na svojstva dobijenih kompozitnih materijala na osnovu poli(L-laktida). Radi postizanja uniformne raspodele nanopunila u kompozitima, višeslojne ugljenične nanocevi su modifikovane hemijskom i radijacionom funkcionalizacijom. Izvršena je karakterizacija ugljeničnih nanocevi, sa ciljem utvrđivanja uspešnosti primenjenih tehnika modifikacije na njihova svojstva i stepen funkcionalizacije. Metodom in situ polimerizacije L-laktida sa površina modifikovanih nanocevi, pripremljene su serije uzoraka kompozitnih materijala sa različitim sadrţajem funkcionalizovanih nanocevi. Detaljno je ispitan uticaj funkcionalizovanih nanocevi na toplotna, kristalna, morfološka, mehanička i električna svojstva sintetisanih kompozitnih materijala. Postignuta homogena disperzija nanocevi unutar biorazgradive, biokompatibilne matrice polimera koji se dobija iz obnovljivih sirovina, uticala je na poboljšanje svojstava, kao i na uspostavljanje novih funkcionalnosti dobijenih materijala. Značajno poboljšanje toplotnih i mehaničkih svojstva sintetisanih materijala, zajedno sa postignutom električnom provodljivošću, omogućava proširenje oblasti primene kompozita na osnovu poli(laktida) i ugljeničnih nanocevi., In this thesis, bionanocomposites based on poly(lactide) and multi-walled carbon nanotubes were synthesized and characterised. Poly(L-lactide) was used as a matrix for the composite synthesis; the influence of nanofillers content, the methods of their functionalization, as well as the synthesis parameters, on the properties of obtained materials were investigated. In order to achieve a uniform dispersion of nanofillers in composite materials, multi-walled carbon nanotubes were modified using chemical and radiation functionalization. Characterization of carbon nanotubes was performed in order to determine the influence of applied modification techniques on their properties and degree of functionalization. A series of composite materials with different content of modified nanotubes were prepared by in situ polymerization of L-lactide from the surface of functionalized nanotubes. The influence of functionalized nanotubes on the thermal, crystal, morphological, mechanical and electrical properties of synthesized composites was investigated in detail. The homogeneous dispersion of carbon nanotubes within the biodegradable, biocompatible, biobased polymer matrix, has influenced the improvement of the properties, as well as the acquiring of new functionalities of synthesized materials. The significant improvement of thermal and mechanical properties of composites, and the achievement of its electrical conductivity, allow the field of application of composites based on poly(lactide) and carbon nanotubes to be expanded.

U ovoj doktorskoj disertaciji je ispitan uticaj montmorilonita i termoplastičnih segmentiranih poliuretana na kinetiku reakcija umrežavanja, strukturu i svojstva funkcionalnih hibridnih materijala na osnovu epoksidnih smola. Pripremljene su dve serije uzoraka hibridnih materijala: prva na osnovu epoksidne smole sa različitim sadržajem organski modifikovanog montmorilonita (0, 1, 3, 5 i 10 mas.%) umrežene sa umreživačem Jeffamine D-230; druga serija je sintetisana na osnovu epoksidne smole, sa različitim sadržajem (10, 15 i 20 mas.%) termoplastičnog poliuretanskog elastomera sa različitim sadržajem tvrdih segmenata (20, 25 i 30 mas.%) sintetisanih na osnovu alifatičnog polikarbonatnog diola i heksametilendiizocijanata i produživača lanca butandiola, kao i katalizatora dibutiltin dilaurata; kao i bez dodatog elastomera umrežene sa diaminom Jeffamine D-2000. Umrežavanje reaktivnih sistema sa projektovanim sirovinskim sastavom je praćeno diferencijalnom skenirajućom kalorimetrijom (DSC). Modeli izokonverzije primenjeni su da se ustanovi da li dodatak punila utiče na reakciju umrežavanja hibridnih materijala. Sintetisani materijali su analizirani dinamičkomehaničkom analizom (DMA), mikroskopijom atomskih sila (AFM), kao i TG-DSC i TG-MS metodama i određena su mehanička svojstva (zatezna čvrstoća, prekidno izduženje i tvrdoća po Šoru A). Epoksidni materijal sa 10 mas.% organski modifikovanog montmorilonita ima značajno niže vrednosti energija aktivacije za definisane stepene reagovanja, čime je potvrđen katalitički efekat gline sa slojevitom strukturom kada je prisutna u reakcionoj smeši u dovoljnoj količini. Uticaj otežane difuzije pri kraju reakcije je izraženiji u prisustvu montmorilonita, čime je pokazano da njegovo prisustvo utiče na ceo mehanizam umrežavanja. Utvrđeno je da na vrednosti G', pored udela montmorilonita, utiče i stepen dispergovanja čestica unutar polimerne matrice. Zaključeno je da dodatak punila do 3 mas. % utiče povoljno na ispitana mehanička svojst, In this thesis the influence of clay fillers and thermoplastic segmented polyurethanes on the curing kinetics, structure and properties of functional hybrid materials based on epoxy resins was assessed. Two sets of hybrid material samples were prepared. First type of samples was based on epoxy resin with a different content of organically modified montmorillonite (0, 1, 3, 5 and 10 wt. %) and crosslinking with hardener Jeffamine D-230. Second type of samples was based on epoxy resin, having different content (10, 15 and 20 wt. %) of thermoplastic segmented polyurethane with different content of hard segments (20, 25 and 30 wt. %) based on aliphatic polycarbonate macrodiols and hexamethylene diisocyanate, with chain extender 1,4-butanediol and the catalyst, dibutyltin dilaurate, and also a sample without added elastomeric polyurethane and crosslinking with hardener Jeffamine D- 2000. The curing of the hybrid materials based on epoxy resins systems were investigated by non-isothermal differential scanning calorimetry (DSC). The kinetic study by isoconversion models has been carried out using data from DSC. The synthesized materials were analyzed by dynamicmechanical analysis (DMA), atomic force microscopy (AFM) as well as TG-DSC and TG-MS methods and mechanical properties (tensile strength, elongation and hardness at Shore A) were determined. Epoxy based hybrid material with 10 wt. % of the organically modified montmorillonite has significantly lower activation energy values for the defined reaction rates, thereby confirming the catalytic effect of the clay with the layered structure when present in the reaction mixture in sufficient quantity. The diffusion effects at the end of the reaction are more pronounced in the presence of montmorillonite, which indicates that its presence affects the entire curing mechanism. It was found that G', along with montmorillonite content, is affected by the degree of particle dispersion inside the polymer matrix. It was concluded tha

U disertaciji je prikazan odabir rastvarača, veličine, vrste i udela čestica za aktivni premaz namenjen postizanju povećane dubine uvara na austenitnom nerđajućem čeliku pri zavarivanju netopljivom elektrodom u zaštiti inertnog gasa. Pored sastava aktivnog premaza, u disertaciji je izvršena optimizacija: geometrije elektrode, jačine struje i brzine zavarivanja. Nakon odabira perspektivnih tipova sastava premaza i parametara zavarivanja, na zavarenim uzorcima izvršena je karakterizacija mehaničkih osobina, hemijskog sastava i mikrostrukture., In this doctoral thesis, the selection of solvent, size, type and the content of oxide particles in activated flux aimed at increasing the penetration on austenitic stainless steel in gas tungsten arc welding is presented. Besides activated flux composition, the optimization of welding parameters such as electrode geometry, welding current and welding speed was done. After the selection of successful activated flux formulations and welding parameters, the characterization of mechanical properties, chemical composition and microstructure was determined.