1. Editorial on the special issue entitled “Towards a sustainable and recyclable future with wood and wood-based composites”Klementina Pušnik Črešnar, Olivija Plohl, 2025, other scientific articles Abstract: Water hammer phenomena in pipelines can induce significant transient pressure surges, leading to structural failures and operational inefficiencies. This study presents a comparative analyzis of two numerical approaches for simulating water hammer: a one-dimensional (1D) inviscid model with added friction based on the Euler equations and the method of characteristics, and a three-dimensional (3D) viscous model utilizing the Navier-Stokes equations in OpenFOAM. Benchmarking problems are solved first, then both methods are used to study a 3.4 km long DN400 pipeline subject to sudden pump failure by analyzing pressure surges, cavitation, and water column separation. The 1D model effectively predicts transient pressure waves and cavitation conditions with minimal computational cost, while the 3D model provides a detailed representation of multiphase flow dynamics, including cavitation bubble growth and collapse via the volume of fluid method. To mitigate adverse effects, a dynamic combination air valve is introduced, and its effectiveness in reducing pressure surges and cavitation is demonstrated. The results highlight the trade-offs between computational efficiency and accuracy in modelling water hammer events and underscore the importance of protective measures in pipeline systems.
Keywords: wood-based material, renewable resources, recycling, new materials
Published in DKUM: 09.12.2025; Views: 0; Downloads: 14
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2. Funkcionalizacija tanina kot trajnostnega antioksidanta v recikliranem kompozitu polipropilenaLaura Šantl, 2025, undergraduate thesis Abstract: Potrebe po polimernih materialih, osnovanih iz termoplastov bodisi termosetov, ki jih opredeljujemo kot plastične materiale, naraščajo zaradi njihove vsestranske uporabe. Kljub nenehni rasti proizvodnje se letno reciklira le približno 10 % plastike, 8 % se sežge, preostanek pa konča na odlagališčih, v oceanih in posledično tudi v živih organizmih. To ne povzroča le izčrpavanja neobnovljivih virov energije, temveč tudi vpliva na emisije toplogrednih plinov. Ključna prioriteta EU za doseganje ogljične nevtralnosti do leta 2050 predstavljajo učinkovite strategije za trajnostni razvoj in zmanjšanje CO₂, ki temeljijo na ponovni uporabi recikliranih materialov. Predlagana raziskava obravnava razvoj trajnostnih in reciklirnih kompozitov, katerih glavni izziv je ustvarjanje visoko zmogljivih reciklirnih termoplastičnih kompozitov, ojačanih s polifenoli, kjer naravna polnila nadomeščajo tradicionalna kemična z biološko osnovanimi alternativami.
V sklopu diplomske naloge smo s procesom ekstruzije vroče taline pripravili termoplastični kompozit na osnovi recikliranega polipropilena (PP-r), ojačan z naravnim polnilom taninom (T.P), funkcionaliziranim s citronsko kislino (CA). Preučevali smo vpliv funkcionalizacije T.P na vezavo med polimerno matrico in polnilom ter na fizikalno-kemijske, termične in antioksidativne lastnosti PP-r. Funkcionalizirane delce T.P smo ovrednotili z infrardečo spektroskopijo z oslabljenim popolnim odbojem (ATR-FTIR), termogravimetrično analizo (TGA), dinamičnim sipanjem svetlobe (DLS) in 2,2-difenil-1-pikrilhidrazil (DPPH) metodo, termoplastične kompozite pa z ATR-FTIR spektroskopijo, TGA, diferenčno dinamično kalorimetrijo (DSC) in DPPH metodo. Ugotovili smo, da vzorci z nižjim dodatkom CA izkazujejo najugodnejše ravnovesje lastnosti ter izboljšano kompatibilnost s polimerno matrico. Rezultati potrjujejo potencial funkcionaliziranih naravnih dodatkov pri izboljšavi lastnosti recikliranih polimernih kompozitov, kar predstavlja pomemben korak v smeri razvoja trajnostnih materialov.
Keywords: tanin, citronska kislina, reciklirani polimeri, funkcionalizacija, antioksidativnost, termičnoplastični kompoziti, trajnostni materiali
Published in DKUM: 12.09.2025; Views: 0; Downloads: 14
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3. Koloidna stabilnost delcev tanina mletih v planetarnem mikromlinu : diplomsko delo univerzitetnega študijskega programa I. stopnjeKlara Perčič, 2025, undergraduate thesis Abstract: Tanini so polifenolne spojine, katere uvrščamo med naravne antioksidante in jih pridobivamo iz različnih delov rastlin. Od tega je odvisna tudi sama struktura molekule. Na podlagi strukture ločimo dve vrsti, kondenzirane in hidrolizirane. Tanini so, zaradi svojih lastnosti, zelo aplikativne spojine, katerih uporaba je razširjena na številnih področjih. Pomembni so tako za rastline kot pri ljudeh, saj zavirajo delovanje in razmnoževanje mikroorganizmov, ki povzročajo bolezenska stanja. Za njihovo učinkovito delovanje je stabilnost raztopine koloidov zelo pomemben dejavnik. Da dosežemo koloidno stabilnost, moramo zagotoviti ozko porazdelitev velikosti delcev in nižjo vrednost polidisperznega indeksa (PDI). Ena izmed metod, s katero vplivamo na ozko porazdelitev delcev je mletje. Z mletjem namreč povzročimo nastanek delcev manjšega hidrodinamskega premera mlevnega materiala, v primerjavi z izhodnim.
Diplomsko delo zajema študijo vpliva zmanjšanja velikosti delcev s pomočjo mletja, na koloidno stabilnost delcev tanina v vodnih suspenzijah. Delce smo mleli z uporabo planetarnega mikromlina in planetarnega krogličnega mlina, pri tem pa smo spreminjali procesne parametre, kot so razmerje med mlevnim materialom in mlevnimi kroglicami (1:15 in 1:20), čas mletja in število obratov. Pred izvedbo dela smo referenčni vzorec ovrednotili z uporabo metode dinamičnega sipanja svetlobe (DLS) in zeta potenciala, s termogravimetrično analizo (TGA) ter Fourierjevo transformacijsko infrardečo spektroskopijo (FTIR). Za določanje (končnega) premera zmletih delcev smo ponovno uporabili DLS, merjenje antioksidativnosti pa smo spremljali z UV-Vis spektrofotometrom.
Keywords: tanin, koloidna stabilnost, mletje, hidrodinamski premer delcev, karakterizacija
Published in DKUM: 09.09.2025; Views: 0; Downloads: 0
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4. Green engineering of bio-epoxy resin: functionalized iron-oxide nanoparticles for enhanced thermal, mechanical, surface and magnetic propertiesKlementina Pušnik Črešnar, Julio Vidal, 2025, original scientific article Abstract: In the pursuit of environmental sustainability, reduced emissions, and alignment with circular economy principles, bio-epoxy resin nanocomposites have emerged as a promising alternative to traditional petroleum-based resins. This study investigates the development of novel bio-epoxy nanocomposites incorporating iron-oxide nanoparticles (Fe2O3, MnP) as multifunctional fillers at loadings of 0.5 wt.% and 3.0 wt.%. MnP nanoparticles were synthesized and subsequently functionalized with citric acid (MnP-CA) to enhance their surface properties. Comprehensive characterization of MnP and MnP-CA was performed using X-ray diffraction (XRD) to determine the crystalline structure, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and zeta potential measurements to confirm surface functionalization. The bio-epoxy resins matrix (bio-EP), optimized for compatibility with MnP and MnP-CA, was thoroughly analyzed in terms of chemical structure, thermal stability, curing behavior, dynamic–mechanical properties, and surface characteristics. Non-isothermal differential scanning calorimetry (DSC) was employed to evaluate the curing kinetics of both the neat (bio-EP) and the MnP/MnP-CA-reinforced composites, offering insights into the influence of nanoparticle functionalization on the resin system. Surface zeta potential measurements further elucidated the effect of filler content on the surface charge and hydrophilicity. Magnetic characterization revealed superparamagnetic behavior in all MnP- and MnP-CA-reinforced (bio-EP) composites. This research provides a foundational framework for the design of green bio-epoxy nanocomposites, demonstrating their potential as environmentally friendly materials and representing an emerging class of sustainable alternatives. The results underscore the viability of bio-epoxy systems as a transformative solution for advancing sustainable resin technologies across eco-conscious industries.
Keywords: bio-based epoxy (nano)composites, curing behavior, dynamic mechanical properties, surface properties
Published in DKUM: 06.08.2025; Views: 0; Downloads: 8
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5. Unlocking innovation: Novel films synthesised and structurally analysed from poly (l-lactide-co-ethylene adipate) block copolymers blended with poly(lactic acid)Athira John, Klementina Pušnik Črešnar, Johan Stanley, Sabina Vohl, Damjan Makuc, Dimitrios Bikiaris, Lidija Fras Zemljič, 2025, original scientific article Abstract: This study addresses the inherent shortcomings of poly (lactic acid) (PLA), a biodegradable polymer widely used in industries such as packaging and biomedical applications. The principal challenge of PLA resides in its low crystallinity, which detrimentally affects its mechanical properties and thermal stability. Additionally, PLA is prone to water and hydrolysis, which compromises its chemical resistance and can lead to degradation over time. To overcome surmount these limitations, the study focuses on the development of hybrid films through the blending of PLA with poly (l-lactide-co-ethylene adipate) (pLEA) block copolymers. The objective is to augment the crystallinity, mechanical performance, and chemical resistance of the resulting materials. The study employs a range of analytical techniques, including Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Polarised Light Microscopy (PLM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA), to thoroughly characterize the copolymers and blend films. By systematically selecting blending ratios and processing methodologies, the study demonstrates enhancements in the properties of the resultant hybrid films compared to neat PLA. Specifically, the structure of films significantly changed from amorphous to crystalline in a short duration - 5 min, of annealing., leading to better tensile strength, modulus and reduced wettability, which are crucial for applications requiring durability and resistance to environmental factors. Films made from 30 wt% of pLEA 97.5/2.5 with 70 % of PLA by fast cooling exhibited outstanding mechanical properties, with a tensile strength 20 MPa higher than that of neat PLA films. Additionally, the chemical resistance may be improved, as evidenced by a decrease in wettability by approximately 15° and a reduction in the polar component of the surface free energy by about 7 mN/m. Hydrophobic, water-repellent materials resist penetration by water and other polar solvents, reducing exposure to corrosive substances and enhancing chemical resistance through barrier protection. Overall, this research addresses the limitations of PLA through innovative copolymerization and blending strategies, offering valuable insights into optimizing the material's properties for various practical applications.
Keywords: Poly(lactic acid), Poly(l-lactide-co-ethylene adipate), copolymer, blend, crystallinity
Published in DKUM: 13.03.2025; Views: 0; Downloads: 10
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6. Hybrid nanostructures of ▫$Fe_3O_4$▫ and Au prepared via coprecipitation and ultrasonic spray pyrolysisLan Kresnik, Peter Majerič, Darja Feizpour, Klementina Pušnik Črešnar, Rebeka Rudolf, 2024, original scientific article Abstract: The coupled processes of coprecipitation and ultrasonic spray pyrolysis (USP) were used to synthesize Fe3O4-Au hybrid nanostructures. The first coprecipitation method enabled the synthesis of Fe3O4 nanoparticles by mixing iron salts’ ions (Fe2+ and Fe3+) and ammonia as the base, and USP was used as the coating process of the Fe3O4 nanoparticles with Au. The formatted hybrid nanostructures consist of Fe3O4 nanoparticles that have Au on their surface in the form of gold nanoparticles (AuNPs). AuNPs have a crystalline structure and range in size from 10 to 200 nm. Additional characterization techniques, including ICP-OES, TEM, SEM, EDS, DLS, zeta potential, and room temperature magnetic hysteresis loops, were used to determine the chemical, physical, and magnetic properties of the Fe3O4 nanoparticles and hybrid nanostructures. It was found that USP produces separate AuNPs too (not just on the Fe3O4 surface), suggesting a bimodal formation of AuNPs. The zeta potential of the Fe3O4 nanoparticles showed poor stability (−15 mV), indicating a high tendency to aggregate, and the zeta potential of the hybrid nanostructures was also very low (≅0), which, comparatively means even worse stability. The saturation magnetization of the Fe3O4 nanoparticles was 35 emu/g, which is relatively lower than that of bulk Fe3O4, while the saturation magnetization of the hybrid nanostructures was significantly lower (0.1 emu/g) compared to the Fe3O4 nanoparticles.
Keywords: magnetic NPs, gold NPs, transmission electron microscopy, magnetic properties
Published in DKUM: 29.11.2024; Views: 0; Downloads: 14
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8. Active agents incorporated in polymeric substrates to enhance antibacterial and antioxidant properties in food packaging applicationsJohan Stanley, Athira John, Klementina Pušnik Črešnar, Lidija Fras Zemljič, Dimitra A. Lambropoulou, Dimitrios Bikiaris, 2023, review article Keywords: food packaging, active agents, bulk preparation techniques, antibacterial and antioxidant properties
Published in DKUM: 11.04.2024; Views: 251; Downloads: 38
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9. Determination of shear bond strength between PEEK composites and veneering composites for the production of dental restorationsAnamarija Kuchler, Klementina Pušnik Črešnar, Iztok Švab, Tomaž Vuherer, Majda Žigon, Mihael Brunčko, 2023, original scientific article Abstract: We studied the shear bond strength (SBS) of two PEEK composites (BioHPP, BioHPP plus) with three veneering composites: Visio.lign, SR Nexco and VITA VM LC, depending on the surface treatment: untreated, sandblasted with 110 μm Al2O3, sandblasted and cleaned ultrasonically in 80% ethanol, with or without adhesive Visio.link, with applied Visio.link and MKZ primer. For the BioHPP plus, differential scanning calorimetry (DSC) revealed a slightly lower glass transition temperature (Tg 150.4 ± 0.4 °C) and higher melting temperature (Tm 339.4 ± 0.6 °C) than those of BioHPP (Tg 151.3 ± 1.3 °C, Tm 338.7 ± 0.2 °C). The dynamical mechanical analysis (DMA) revealed a slightly higher storage modulus of BioHPP (E’ 4.258 ± 0.093 GPa) than of BioHPP plus (E′ 4.193 ± 0.09 GPa). The roughness was the highest for the untreated BioHPP plus, and the lowest for the polished BioHPP. The highest hydrophobicity was achieved on the sandblasted BioHPP plus, whereas the highest hydrophilicity was found on the untreated BioHPP. The highest SBSs were determined for BioHPP and Visio.lign, adhesive Visio.link (26.31 ± 4.17 MPa) or MKZ primer (25.59 ± 3.17 MPa), with VITA VM LC, MKZ primer and Visio.link (25.51 ± 1.94 MPa), and ultrasonically cleaned, with Visio.link (26.28 ± 2.94 MPa). For BioHPP plus, the highest SBS was determined for a sandblasted surface, cleaned ultrasonically, with the SR Nexco and Visio.link (23.39 ± 2.80 MPa).
Keywords: BioHPP, CAD/CAM milling, BioHPP plus, pressing, veneering composites, roughness, wettability, shear bond strength
Published in DKUM: 05.04.2024; Views: 213; Downloads: 23
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10. Kraft lignin/tannin as a potential accelerator of antioxidant and antibacterial properties in an active thermoplastic polyester-based multifunctional materialKlementina Pušnik Črešnar, Alexandra Zamboulis, Dimitrios Bikiaris, Alexandra Aulova, Lidija Fras Zemljič, 2022, original scientific article Abstract: This research focuses on key priorities in the field of sustainable plastic composites that will lead to a reduction in CO2 pollution and support the EU’s goal of becoming carbon neutral by 2050. The main challenge is to develop high-performance polyphenol-reinforced thermoplastic composites, where the use of natural fillers replaces the usual chemical additives with non-toxic ones, not only to improve the final performance but also to increase the desired multifunctionalities (structural, antioxidant, and antibacterial). Therefore, poly (lactic acid) (PLA) composites based on Kraft lignin (KL) and tannin (TANN) were investigated. Two series of PLA composites, PLA-KL and PLA-TANN, which contained natural fillers (0.5%, 1.0%, and 2.5% (w/w)) were prepared by hot melt extrusion. The effects of KL and TANN on the PLA matrices were investigated, especially the surface physicochemical properties, mechanical properties, and antioxidant/antimicrobial activity. The surface physicochemical properties were evaluated by measuring the contact angle (CA), roughness, zeta potential, and nanoindentation. The results of the water contact angle showed that neither KL nor TANN caused a significant change in the wettability, but only a slight increase in the hydrophilicity of the PLA composites. The filler loading, the size of the particles with their available functional groups on the surfaces of the PLA composites, and the interaction between the filler and the PLA polymer depend on the roughness and zeta potential behavior of the PLA-KL and PLA-TANN composites and ultimately improve the surface mechanical properties. The antioxidant properties of the PLA-KL and PLA-TANN composites were determined using the DPPH (2,2′-diphenyl-1-picrylhydrazyl) test. The results show an efficient antioxidant behavior of all PLA-KL and PLA-TANN composites, which increases with the filler content. Finally, the KL- and PLA-based TANN have shown resistance to the Gram-negative bacteria, E. coli, but without a correlation trend between polyphenol filler content and structure.
Keywords: poly (lactic acid), Kraft lignin, tannin, multifunctionality of PLA composites, surface mechanical properties, antioxidant/antibacterial activity
Published in DKUM: 18.09.2023; Views: 495; Downloads: 209
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