Vilko Mandić

Properties and Antimicrobial Activity of Nanosilver Deposited Cotton Fabric Coated with γ-Methacryloxypropyl Trimethoxysilane

The simple and industrially adjustable process of silver nanoparticles deposition on cotton fabric followed by coating with γ-methacryloxypropyl trimethoxysilane (MPS), as well as the properties of obtained nanocomposite has been investigated. Silver nanoparticles were prepared through the reduction of silver nitrate with sodium borohydrate and deposited on cellulose fabric. In order to stabilize obtained nanostructured material and improve its properties, the fabric was treated by immersion in cross linkable MPS. The morphology of the finished fabrics was characterized by Scanning Electron Microscopy (SEM). It has been determined that process does not impair nanocharacter of silver particles and yield uniform distribution throughout the fabric surface. The concentration of Ag in the fabric samples was determined by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The average deposited amount of nanoparticles was found to be 63 ppm and 48 ppm for samples without and those with MPS, respectively. The character of obtained polysiloxane coating was examined using Fourier Transform Infrared (FTIR) spectroscopy. The presence of SiOSi bonds on the cellulose surface pointed out to self-condensation between silanol groups. Differential Thermal and Thermo-Gravimetric Analysis (DTA/TGA) revealed that MPS deposited on fabric provided modification of thermal properties. The change of the surface properties after the modification was ascertained by contact angle measurements. The antimicrobial activity of the antibacterial finish on the cotton fabric, expressed as bacterial reduction efficiency, has been determined. Bacterial reduction of at least 88.5% against both, Staphylococcus aureus and Escherichia coli, has been obtained.

Corrosion Protection of AISI 316L Stainless Steel with the Sol-Gel Yttria Stabilized ZrO2 Films: Effects of Sintering Temperature and Doping

Nanostructured sol–gel zirconia (ZrO2) films containing 3, 5 and 7 mol % Y2O3 of one and three layers were prepared on stainless steel X2CrNiMo17-12-2 (AISI 316L) surface by the dip coating method. Yttria stabilized zirconia (YSZ) deposited films were sintered at 400 and 600 °C. For the preparation of sol zirconium(IV) butoxide was used as precursor, i-propyl alcohol as a solvent with addition of nitric acid as a catalyst, acetylacetone as chelating agent and water for hydrolysis. Thickness of sol-gel YSZ films deposited on stainless steel was determined by glow- discharge optical emission spectrometry (GD- OES). It was found that thickness of deposited films is barely affected by yttria content while increases by increasing the number of layers and temperature of sintering. The crystal structure of films was determined by X- ray diffraction. The corrosion resistances of uncoated and coated specimens were studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated marine environment (3.5 wt. % NaCl aqueous solution) at room temperature. The influence of yttria stabilized zirconia (YSZ) layers number and temperature of sintering on the corrosion protection was examined as well. Sol-gel derived YSZ films are capable of appreciable improvement in corrosion resistance of stainless steel in the investigated corrosive medium.

The influence of filler treatment on the mechanical properties and phase behavior of thermoplastic polyurethane/polypropylene blends

Thermoplastic polyurethane (TPU) and isotactic polypropylene (iPP) composites and their talc reinforced blends containing untreated and silane treated talc were investigated. The talc surface was modified with organosilane coupling agent in order to improve the polymer–filler interface interaction. TPU has been blended with iPP in a twin screw extruder and samples for investigation were prepared by injection moulding at different concentrations. The neat polymers, composites and blends were characterized with DMA, XRD, FTIR and tensile testing. The obtained results showed that mechanical properties of the talc filled TPU and iPP composites and TPU/iPP blends were improved with the addition of untreated and silane treated talc. The storage modulus of the TPU/iPP blends increased with the addition of untreated and silane treated talc, due to a stiffer interface which talc generated in the polymer matrix. The comparison among samples filled with untreated and silane treated talc filler showed that the polymer composites and TPU/iPP blends filled with silane treated talc displayed better mechanical properties. Silane addition improves the adhesion between the filler and the polymer matrix.

Influence of various fluoride agents on working properties and surface characteristics of uncoated, rhodium coated and nitrified nickel-titanium orthodontic wires

Abstract Objective. To analyze the effect of various fluoride formulations in commercially available agents on working properties of various nickel-titanium orthodontic wires. Materials and methods. Uncoated (NiTi), rhodium coated (RhNiTi) and nitrified (NNiTi) wires were immersed to dH2O, MiPaste, Elmex and Mirafluor for 1 h. Unloading slope characteristics (average force, bending action of the force and average plateau length) and the percentage of useable constant force during unloading were observed. Surface roughness (Ra) was measured. SEM and EDS were used for observation of the surface. Results. NiTi had decreased loading and unloading elastic modulus (E) and yield strength (YS) after immersion to MIPaste and Mirafluor. The unloading YS decreased in the RhNiTi by the MIPaste. The loading and unloading YS of the NNiTi increased in Elmex and increased average plateau force. RhNiTi showed higher average plateau length and the percentage of useful constant force during unloading in Mirafluor and the average plateau force lowered after immersion to MIPaste. The unloading slope characteristics for NiTi were affected by all three prophylactic agents, mostly by Mirafluor, and produced significantly lower forces during both loading and unloading, similarly to the NNiTi wires. The RhNiTi had the lowest forces during both loading and unloading in MIPaste. All results were at significance; p < 0.05. Difference in Ra was observed for RhNiTi after immersion to the MI Paste (p < 0.001; η2 = 0.761). Conclusion. The NiTi and NNiTi wires lose less working force when combined with Elmex. The RhNiTi improve their working properties with Mirafluor and deteriorate when combined with MiPaste.

A structural investigation of tris(ethyl acetoacetate)aluminium (III)

Aluminium tris(ethyl acetoacetate), Al(C6H9O3)3 has been prepared and characterized by means of 1H and 13C nuclear magnetic resonance spectroscopy, scanning electron microscopy and X-ray powder diffraction (XRPD). It was determined that two stereoisomeric complexes can be distinguished in the solution: meridional and facial. The crystal structure of Al(C6H9O3)3 has been determined from XRPD data. The compound crystallizes in the monoclinic space group P21/n.

Sol-Gel Derived Mullite-Gahnite Composite

Mullite-gahnite composites with different phase-proportions were prepared using sol-gel process. Crystallization path was determined using differential thermal analysis (DTA). X-ray powder diffraction (XRD) was used to study the crystal phases development. The course of the thermal reactions is dominated by the intermediate formation of two spinel phases. The former phase was attributed to gahnite, while the latter to Al-Si spinel. Zn loading decreases amounts of mullite and α-alumina, while increases gahnite and amorphous phase. The observed microstructure of sintered bodies is characterized by fine gahnite particles distributed among larger mullite grains, which is highly favourable for ceramics with high mechanical requirements.

The Isothermal and Non-Isothermal Crystallization Kinetics La2O3 Doped, Sol-Gel Derived Mullite

The crystallization kinetic parameters of mullite formation from gels doped with La2O3 in 0.99, 1.96 and 2.91 mol% were determined by differential thermal analysis (DTA) under isothermal and non-isothermal conditions. The gels were prepared by sol-gel process from aluminum and lanthanum nitrate precursors and TEOS dissolved in ethanol (molar ratio Al/Si=3:1) Powder X-ray diffraction (XRD) and electron microscopy analysis methods (SEM, EDS) were used to characterize the present phases. Lanthanum forms no separate crystal phases and its incorporation ability in mullite lattice is neglectable, yet by promoting amorphous phase formation lanthanum evidently influences the mullite composition by making it rich in Al2O3. The obtained activation energies for the mullite crystallization process in non-doped sample are higher than 1300 kJmol-1. The increase of doping level brings the activation energies below 1100 kJmol-1 for the sample with highest amount of lanthanum, i.e. with the greatest deviation from stoichiometric mullite composition.