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Synthesis of PMMA/ZnO nanoparticles composite used for resin teeth
Danica Popović, Rajko Bobovnik, Silvester Bolka, Miroslav Vukadinovič, Vojkan Lazić, Rebeka Rudolf, 2017, original scientific article

Abstract: Wear resistance is one of the most important physical properties of the artificial teeth used in acrylic dentures. The goal of this research was to synthesize a new composite material made of matrix Poly-(methyl methacrylate)-PMMA with different percentages (2 % and 3 % of volume fractions) of zinc-oxide nanoparticles (ZnO NPs) as reinforcing elements, to improve its mechanical properties. The dynamic mechanical behaviour of this composite was studied through the DMA method in comparison to the pure PMMA supported by the characterization of their microstructures. Then the wear resistance was analysed on the samples, which were prepared in the form of teeth. In this context their vertical height loss was measured after 100,000 chewing cycles on a chewing simulator, before and after the artificial thermal ageing. Investigations showed that the PMMA/ZnO NP composites dampened the vibrations better than the pure PMMA, which could be assigned to the homogenous distribution of ZnO NPs in the PMMA matrix. It was found that the mean vertical height loss for the pure PMMA teeth was significantly higher (more than 4 times) compared to composite teeth made with ZnO NPs. Introducing the thermal artificial ageing led to the finding that there was no effect on the height loss by the composite material with 3 % of volume fractions of ZnO NPs. Based on this it was concluded that PMMA/ZnO NPs composites showed improved in-vitro wear resistance compared to acrylic-resin denture teeth, so this new composite material should be preferred when occlusal stability is considered to be of high priority.
Keywords: poly-methyl methacrylate, PMMA, zinc-oxide nanoparticles, composite, resin teeth
Published: 12.12.2017; Views: 22; Downloads: 1
.pdf Full text (1,55 MB)

Synergistic chemo-enzymatic hydrolysis of poly (ethylene terephthalate) from textile waste
Felice Quartinello, Simona Vajnhandl, Julija Volmajer Valh, Thomas Farmer, Bojana Vončina, Aleksandra Lobnik, Enrique Herrero Acero, Alessandro Pellis, Georg M. Gübitz, 2017, original scientific article

Abstract: Due to the rising global environment protection awareness, recycling strategies that comply with the circular economy principles are needed. Polyesters are among the most used materials in the textile industry; therefore, achieving a complete poly(ethylene terephthalate) (PET) hydrolysis in an environmentally friendly way is a current challenge. In this work, a chemo-enzymatic treatment was developed to recover the PET building blocks, namely terephthalic acid (TA) and ethylene glycol. To monitor the monomer and oligomer content in solid samples, a Fourier-transformed Raman method was successfully developed. A shift of the free carboxylic groups (1632 cm$^{−1}$) of TA into the deprotonated state (1604 and 1398 cm$^{−1}$) was observed and bands at 1728 and 1398 cm$^{−1}$ were used to assess purity of TA after the chemo-enzymatic PET hydrolysis. The chemical treatment, performed under neutral conditions (T = 250 °C, P = 40 bar), led to conversion of PET into 85% TA and small oligomers. The latter were hydrolysed in a second step using the Humicola insolens cutinase (HiC) yielding 97% pure TA, therefore comparable with the commercial synthesis-grade TA (98%).
Keywords: textile waste, waste recycling
Published: 16.11.2017; Views: 53; Downloads: 1
.pdf Full text (304,48 KB)

Semi-analytical method for solving Fokker-Planck's equations
Majeed Ahmed Al-Jawary, Ghassan Hasan Radhi, Jure Ravnik, 2017, original scientific article

Abstract: In this paper, the linear and nonlinear Fokker-Planck equations (FPE) are solved by a semi-analytical iterative technique. This technique was proposed by Temimi and Ansari (TAM) in 2011. It is used to obtain the exact solutions for the 1D, 2D and 3D FPE. We solve several linear and nonlinear examples to show that the method is efficient and applicable. The results demonstrate that the presented method is very effective and reliable and does not require any restrictive assumptions for nonlinear terms. A symbolic manipulator Mathematica®10 was used to evaluate terms in the iterative process.
Keywords: Fokker-Planck's equation, semi-analytical method, analytic solution, Brownian motion, Kolmogorov's equation
Published: 03.11.2017; Views: 28; Downloads: 3
.pdf Full text (476,67 KB)

Polyurethanes for medical use
Tanja Pivec, Majda Sfiligoj-Smole, Petra Gašparič, Karin Stana-Kleinschek, 2017, review article

Abstract: Polyurethanes are synthetic copolymers containing urethane linkages in their complex chemical structure. They consist of three monomers: a diisocyanate, a polyol and a chain extender, which enables the synthesis of an endless number of polyurethanes with different physicochemical and mechanical properties. The physicochemical properties of various polyurethanes are largely dependent on the conformation of polyols, which may contain two or more different polyols, stabilisers, catalysts, liquids or solid additives and, in the case of foams, foaming agents. Depending on the structure of the polyols, i.e. the length of the chain, structure of the units (aliphatic or aromatic), ester or ether groups, or functionalisation by hydroxyl groups, polyurethanes may be flexible or rigid, and therefore suitable for various applications. In addition to the physical and chemical structure of polyurethanes, this review paper specifically addresses their use in medicine, particularly in wound dressings, tissue engineering scaffolds and drug delivery with nanoparticles and nanocapsules, and provides guidelines for the development of new biodegradable polyurethane materials.
Keywords: segmented polyurethanes, chemical structure, reactants, medical applications
Published: 03.10.2017; Views: 44; Downloads: 2
.pdf Full text (383,90 KB)

Conference proceedings
2017, proceedings

Published: 13.09.2017; Views: 59; Downloads: 12
.pdf Full text (19,00 MB)

Zeta potencial PA 6
Robert Šoster, Nika Veronovski, Lidija Tušek, Karin Stana-Kleinschek, Simona Strnad, Volker Ribitsch, 2003, original scientific article

Abstract: V raziskavi smo preučevali elektrokinetične lastnosti poliamida 6 v obliki (a) folije in (b) tekstilnega filamenta ob uporabi dveh merilnih celic. Merili smo potencial zaradi pretoka in iz tega določili zeta potencial (▫$\zeta$▫ v odvisnosti od pH vrednosti medija. Meritve na posameznem materialu smo preučevali s stališča ponovljivosti. S tem namenom smo opravili meritve na 10 preskušancih istega vzorca. Določili smo osnovne statistične pokazatelje ponovljivosti za ▫$\zeta$▫ pri pH 3 in 9 ter izoelektrično tocko. Metodo smo optimirali glede na čas nabrekanja v raztopini elektrolita pred meritvijo in maso materiala v cilindrični celici. Meritve v 0,001 M KCl na obeh vrstah materiala kljub različni nadmolekulski in površinski strukturi dobro sovpadajo. Krivulje ▫$\zeta$▫=▫$\zeta$▫(pH) imajo pričakovan potek. PA 6 kaže amfoterno naravo zaradi vsebnosti amino in karboksilnih skupin. V alkalnem mediju disociirajo karboksilne skupine, kar povzroči negativen ▫$\zeta$▫ (folija: (-32,9▫$\pm$▫ 1,6) mV, filament: (-35,2▫$\pm$▫2,0) mV pri pH 9). V kislem mediju kaže PA kationski značaj zaradi disociacije amino skupin (folija: (24,5▫$\pm$▫1,7) mV, filament: (15,1▫$\pm$▫1,1) mV pri pH 3). Izoelektrična točka, kjer je ▫$\zeta$▫ enak 0, se nahaja za folijo pri pH vrednosti 4,7▫$\pm$▫0,1, za filament pa pri 4,9▫$\pm$▫ 0,1.
Keywords: polimeri, poliamid 6, elektrokinetične lastnosti, potencial zaradi pretoka, zeta potencial, filament, folija
Published: 01.09.2017; Views: 69; Downloads: 3
.pdf Full text (420,18 KB)

Vrednotenje toplotnih lastnosti tekstilij in njihovih kombinacij
Damjana Celcar, Jelka Geršak, Harriet Meinander, 2010, original scientific article

Abstract: V prispevku je predstavljeno vrednotenje toplotnih lastnosti ploskih tekstilij in njihovih kombinacij, namenjenih za poslovna oblačila, ki je potekalo v dveh delih. V prvem delu so bile raziskane toplotne lastnosti ploskih tekstilij ovrednotene na različnih merilnih napravah, ki omogočajo merjenje prehoda toplote in/ali prehoda vodne pare skozi plosko tekstilijo, in sicer s pomočjo toplotne plošče ter merilnih naprav Thermo Labo II in Permetest. V tem delu raziskave so bile raziskane povezave med lastnostmi ploskih tekstilij oziroma odvisnosti med posameznimi parametri toplotnih lastnosti analiziranih ploskih tekstilij, izmerjenimi na različnih merilnih napravah ter odvisnosti med toplotnimi lastnostmi in debelino tekstilije. V drugem delu raziskave so bile raziskane toplotne lastnosti kombinacij posameznih ploskih tekstilij in sicer s pomočjo toplotnega cilindra s simulacijo znojenja, ki omogoča merjenje prehoda toplote in prehoda vodne pare skozi tekstilije ali kombinacijo tekstilij. Za ta namen je bil raziskan vpliv klimatskih razmer in stopnje znojenja na toplo-tne lastnosti posameznih kombinacij ploskih tekstilij. Raziskava je pokazala, da med parametri toplotnega upora, izmerjenega s toplotno ploščo, ter merilnima napravama Permetest in Thermo Labo II, obstajajo statistično pomembne korelacije, in da med toplotnim uporom, določenim iz kvocienta debeline in toplotne prevodnosti, dobljene z merilno napravo Thermo Labo II ter toplotnim uporom, dobljenim s toplotno ploščo in z merilno napravo Permetest prav tako obstaja korelacija. Potrjeno je, da se z naraščajočo debelino materiala vrednosti toplotnega upora in upora proti prehodu vodne pare ploskih tekstilij povečujejo. Hkrati je bilo ugotovljeno, da različne klimatske razmere in stopnje znojenja vplivajo na toplotne lastnosti kombinacij ploskih tekstilij. Ugotovljeno je bilo, da so toplotne lastnosti, tj. suhi in evaporativni toplotni tok ter sposobnost prehoda vodne pare odvisne od klimatskih razmer oziroma temperaturnega gradienta med površino cilindra in temperaturo zraka, in da se z različno stopnjo znojenja, vrednosti evaporativnega toplotnega toka, korigiranega toplotnega upora in sposobnosti prehoda vodne pare spremenijo.
Keywords: ploske tekstilije, toplotne lastnosti, toplotno udobje, toplotna plošča, Thermo Labo II, Permetest, toplotni cilinder s simulacijo znojenja
Published: 01.09.2017; Views: 52; Downloads: 6
.pdf Full text (544,95 KB)

Vplivi in tveganja nanotehnologij in nanomaterialov na okolje in zdravje ljudi
Aljoša Košak, Marijana Lakić, Aleksandra Lobnik, 2015, original scientific article

Abstract: Razvoj nanomaterialov in njihova uporaba v tekstilstvu sta velika priložnost za izdelavo novih izdelkov z različnimi funkcionalnimi in tehnološkimi lastnostmi, vendar razvoj poleg priložnosti pomeni tveganja za okolje in zdravje ljudi v obliki nanoonesnaževanja ter toksičnih vplivov na žive organizme. V prispevku so obravnavani okoljski vplivi in zdravstvena tveganja nanomaterialov, ki se najpogosteje uporabljajo v tekstilstvu, kot npr. nanodelci srebra ($Ag$), silicijevega dioksida ($SiO_2$), titanovega dioksida ($TiO_2$), cinkovega oksida ($ZnO$), aluminijevega oksida ($Al_2O_3$), aktivnega oglja, nanoglina in ogljikove nanocevke (CNT).
Keywords: nanotehnologija, nanomateriali, življenjski cikel izdelka, nanodelci srebra, nanodelci silicijevega dioksida, nanodelci titanovega dioksida, nanodelci cinkovega oksida, nanodelci aluminijevega oksida, nanoglina, ogljikove nanocevke, toksičnost
Published: 01.09.2017; Views: 57; Downloads: 7
.pdf Full text (513,85 KB)

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