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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: poly-methyl methacrylate, PMMA, zinc-oxide nanoparticles, composite, resin teeth
Objavljeno: 12.12.2017; Ogledov: 43; Prenosov: 2
.pdf Celotno besedilo (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, izvirni znanstveni članek

Opis: 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%).
Ključne besede: textile waste, waste recycling
Objavljeno: 16.11.2017; Ogledov: 88; Prenosov: 1
.pdf Celotno besedilo (304,48 KB)

Semi-analytical method for solving Fokker-Planck's equations
Majeed Ahmed Al-Jawary, Ghassan Hasan Radhi, Jure Ravnik, 2017, izvirni znanstveni članek

Opis: 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.
Ključne besede: Fokker-Planck's equation, semi-analytical method, analytic solution, Brownian motion, Kolmogorov's equation
Objavljeno: 03.11.2017; Ogledov: 47; Prenosov: 3
.pdf Celotno besedilo (476,67 KB)

Polyurethanes for medical use
Tanja Pivec, Majda Sfiligoj-Smole, Petra Gašparič, Karin Stana-Kleinschek, 2017, pregledni znanstveni članek

Opis: 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.
Ključne besede: segmented polyurethanes, chemical structure, reactants, medical applications
Objavljeno: 03.10.2017; Ogledov: 80; Prenosov: 2
.pdf Celotno besedilo (383,90 KB)

Conference proceedings
2017, zbornik

Objavljeno: 13.09.2017; Ogledov: 85; Prenosov: 12
.pdf Celotno besedilo (19,00 MB)

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