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Determination of shear bond strength between PEEK composites and veneering composites for the production of dental restorations
Anamarija 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: 52; Downloads: 4
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Kraft lignin/tannin as a potential accelerator of antioxidant and antibacterial properties in an active thermoplastic polyester-based multifunctional material
Klementina 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: 374; Downloads: 17
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Long-term creep compliance of wood polymer composites: using untreated wood fibers as a filler in recycled and neat polypropylene matrix
Marko Bek, Alexandra Aulova, Klementina Pušnik Črešnar, Sebastjan Matkovič, Mitjan Kalin, Lidija Slemenik Perše, 2022, original scientific article

Abstract: Neat (NPP) and recycled (RPP) polypropylene matrix materials were used to prepare wood–polymer composites with untreated wood fibers up to 40 wt.%. Long-term creep properties obtained through the time-temperature superposition showed superior creep resistance of composites with NPP matrix. In part, this is attributed to their higher crystallinity and better interfacial adhesion caused by the formation of a transcrystalline layer. This difference resulted in up to 25% creep compliance reduction of composites with NPP matrix compared to composites with recycled (RPP) polypropylene matrix, which does not form a transcrystalline layer between the fibers and polymer matrix. Despite the overall inferior creep performance of composites with RPP matrix, from the 20 wt.% on, the creep compliance is comparable and even surpasses the creep performance of unfilled NPP matrix and can be a promising way to promote sustainability.
Keywords: lesno-polimerni kompoziti, lezenje, vzdržljivost, les, recikliranje, wood–polymer composites, creep, durability, wood, recycling
Published in DKUM: 16.08.2023; Views: 241; Downloads: 17
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Razvoj in priprava biorazgradljive aktivne embalaže : magistrsko delo
Žan Jankovič, 2023, master's thesis

Abstract: V magistrskem delu smo razvili biorazgradljivo aktivno embalažo ter fizikalno-kemijsko karakterizirali in ocenili aktivni učinek (antioksidativni in protimikrobni) PLA folij. Nanosi plasti biopolimera hitozana in ekstraktov na PLA folije so bili potrjeni z metodami ATR-FTIR in XPS. Fizikalno-kemijska karakterizacija folij je potekala tudi z določevanjem omočljivosti in prepustnosti kisika. Metode so dokazale, da je z vidika omočljivosti in prepustnosti kisika zelo pomemben premaz iz ekstraktov, ki vpliva na izboljšanje omočljivosti in slabšo prepustnost kisika. Potrdili smo tudi desorpcijo hitozanov in ekstraktov iz površine folij v desorpcijsko kopel. Z analiznima spektrofotometričnima metodama DPPH in ABTS pa smo analizirali antioksidativno aktivnost folij in dokazali, da so vzorci PLA folij premazanih s hitozanoma in ekstraktoma robide ali brina izboljšale antioksidativno aktivnost. Slabše so se odrezale PLA folije premazane s hitozanoma in ekstraktom alge pri obeh metodah. Protimikrobno aktivnost smo določevali na gram pozitivno bakterijo Staphylococcus aureus in gram negativno bakterijo Escherichia coli. Vse testirane folije so imele zelo dobro protimikrobno aktivnost na bakterijo Staphylococcus aureus. Dobro protimikrobno aktivnost na bakterijo Escherichia coli pa je imel le vzorec PLA folije, ki je bil premazan s kvarternim hitozanom in premazom brina. Ker smo v PLA folijah uporabili naravne in okolju prijazne materiale za izdelavo funkcionaliziranih folij prepostavljamo, da so kompozitne folije z okoljskega vidika spremeljive, saj so biorazgradljive.
Keywords: aktivna embalaža, PLA folije, primarni hitozan, kvarterni hitozan, ekstrakti, antioksidativna embalaža, protimikrobna embalaža
Published in DKUM: 12.06.2023; Views: 466; Downloads: 59
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Biorazgradljivost biološko razgradljive plastike v morski vodi : magistrsko delo
Lara Lizzi, 2022, master's thesis

Abstract: Plastika je s svojim pojavom na trgu povzročila pravo revolucijo in predstavlja eno izmed velikih civilizacijskih rešitev. Njene ugodne lastnosti so vplivale na naše vsakodnevno življenje v takšni meri, da si težko predstavljamo življenje brez nje. Plastika je prerasla večino umetnih materialov in je že dolgo pod okoljskim nadzorom, obstojnost plastike v okolju povzroča velike okoljske probleme, saj pogosto konča v ekosistemih, kjer ni zaželena. Posebej kritična so morja iz katerih se plastika težje izloča in negativno vpliva na morske živali, ujete v odpadke, in povzroča problem nano/mikroplastike, ki vstopa v prehranjevalno verigo. V težnji po razvoju podobnemu materialu plastiki, vendar s hitrejšim časom razgradnje in manjšim negativnim vplivom na okolje se je razvila t.i. biorazgradljiva plastika. V raziskovalnem delu smo v obdobju 190 dni spremljali biološko razgradljive (polilaktična kislina, polilaktična kislina premazana s hitozanom in plastika na osnovi škroba) in nerazgradljive vzorce plastik (polipropilen), ki so bili izpostavljeni simuliranem morskem okolju. Metode s katerimi smo analizirali plastične vzorce so gravimetrija, goniometrija, infrardeča spektroskopija s Fourierjevo transformacijo, rentgenska difrakcija, termo-gravimetrična analiza in optična mikroskopija. Rezultati kažejo na stabilnost polipropilena v simuliranem morskem okolju, med tem ko lahko potrdimo degradacijo ostalih preučevanih biološko razgradljivih vzorcev s pomočjo uporabe več analiznih metod. Ob zaključku eksperimentalnega dela smo ugotovili, da je potrebno za določitev biorazgradljivosti uporabiti skupino analiznih tehnik, ki nam podajo vpogled v spremembe preučevanih vzorcev.
Keywords: Biološko razgradljiva plastika, razgradljivost, simulirana morska voda, polilaktična kislina.
Published in DKUM: 29.08.2022; Views: 918; Downloads: 227
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Razvoj biorazgradljivih škrobnih folij z vgrajenimi rastlinskimi ekstrakti : diplomsko delo
Anita Krajnc, 2020, undergraduate thesis

Abstract: V zadnjem desetletju se je pojavilo ponovno zanimanje za pretvorbo škroba v plastični material – termoplastični škrob, ki lahko nadomesti materiale izdelane iz fosilnih virov npr. nafto. V raziskavi v okviru diplomskega dela smo razvili biorazgradljive škrobne folije, katerim smo z dodajanjem različnih naravnih rastlinskih ekstraktov izboljšali njihove lastnosti. Kot osnovno surovino smo uporabili krompirjev škrob. Temu smo v razmerju 10:1 in 1:5, ob prisotnosti glicerola in brez glicerola, dodajali tri vrste naravnih ekstraktov, in sicer rožmarin, timijan in hitozan. Naredili smo tudi kontrolni vzorec brez ekstraktov. Cilj diplomskega dela je ugotoviti, kakšen vpliv imajo različni naravni ekstrakti ter razmerje in dodatek glicerola na končne lastnosti materiala. Pri delu smo uporabili naslednje metode dela: določanje tališča z talilno mizico, stičnega kota z goniometrom, ugotavljanje % antioksidativnosti z ABST metodo in določanje funkcionalnih skupin z ART-FTIR metodo. Ugotovili smo, da rezultati kažejo dobra izhodišča za potencialno in praktično uporabo in da so rezultati v skladu z načeli bioekonomije in krožnega gospodarstva.
Keywords: bioplastika, biorazgradljiva plastika, bioekonomija, škrob, folije
Published in DKUM: 21.12.2020; Views: 925; Downloads: 152
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