Evaluation of different restoration techniques on fracture resistance of teeth with palatinal cusp fracture

We evaluated reattached tooth fragments in terms of fracture resistance in endodontically treated maxillary premolars with one remaining wall. In total, 60 double-rooted, mature, human maxillary premolars with double canals were used. Ten intact teeth were served as a control group without any application. After endodontic treatment, the palatal wall of the teeth was cut parallel to the horizontal axis on the cementoenamel junction using a diamond disc. The teeth were randomly divided into five groups (n = 10) and were restored as follows. Group 1: restored with composite resin; Group 2: palatal wall bonded to the teeth using adhesive resin, then restored with composite resin; Group 3: teeth restored as in Group 2, plus a post space prepared below 2 mm from the palatinal cusp horizontally, then fibre post bonded using adhesive resin cement; Group 4: cavity enlarged to a depth of 2 mm in the cusp of the palatal wall, then restoration performed as in Group 2; and Group 5: fibre post placed in the root canal and then restoration performed as in Group 1. Failure load testing was performed with a universal testing machine. Kruskal–Wallis and Conover’s multiple comparison tests were used to analyse the data. In the restoration groups the highest median load at failure was observed in Group 4, in which cusp capping was used; the lowest was found in Group 3, in which a horizontal fibre post was applied with the reattached tooth fragments.     

Synthesis and characterization of pyrrole and thiophene functional polystyrenes via “click chemistry”

Novel side-chain pyrrole or thiophene functional polystyrenes (PS-Py and PS-Th) were synthesized by using ‘‘click chemistry’’ strategy. First, approximately 40% of chloro groups of poly(styrene-co-chloromethylstyrene) P(S-co-CMS), prepared by nitroxide mediated radical polymerization (NMRP), were converted to azido groups by using NaN₃ in N,N-dimethylformamide. Propargyl pyrrole was prepared by etherification of 4-(1H-pyrrol-1-yl)phenol prepared by Clauson-Kaas reaction using propargylbromide. Propargyl thiophene was synthesized by heterogeneous esterification reaction between 3-thiophenecarboxylic acid and propargylbromide. Finally, azido-functionalized polystyrene was coupled to these propargyl functional heterocyclics with high efficiency by click chemistry. The intermediates at various stages and final polymers were characterized by spectral analysis and cyclic voltammetry.     

From Metalloligand to Extended 3D Network: Synthesis, Crystal Structure and Magnetic Property of {[Cu(en)2][Cu(μ3-pydc)2]·6H2O}n

A novel 2D coordination polymer, {[Cu(en)₂][Cu(μ₃-pydc)₂]·6H₂O} _n (1) pyridine-2,3-dicarboxylic acid (pydcH₂); ethylenediamine (en), based on the metalloligand [Cu(μ-pydcH)₂] _n , has been prepared and characterized by IR, UV–Vis and ESR spectroscopy, thermal analysis, differential scanning calorimetry and single crystal X-ray diffraction techniques. The temperature dependent magnetic properties have also been studied. The pydc ligand exhibits tetradentate-μ₃ bridging mode, being coordinated through three carboxylate oxygens and one nitrogen atom. The complex contains two copper(II) ions that exhibit two different coordination environment with two en and two pydc ligands. The single crystal structure shows that the complex forms a 3D framework with 2D layers along the c-axis. Van der Waals interactions are responsible for the self-assembly of the layer into a 3D network.     

Treatment of dairy industry wastewater by EC and EF processes using hybrid Fe?Al plate electrodes

BACKGROUND: In this study electrochemical treatment of dairy industry wastewater (DW) was investigated using a combined electrode system consisting of iron and aluminum as sacrificial electrodes. The dairy industry generates strong wastewaters characterized by high biological oxygen demand and chemical oxygen demand concentrations. Dairy industry waste effluents are concentrated in nature, and the main contributors of organic load to these effluents are carbohydrates, proteins and fats originating from the milk. Since dairy waste streams contain high concentrations of organic matter, these effluents may cause serious environmental problems. RESULTS: A pole changer device was employed to change polarization in given time intervals to generate iron and aluminum based coagulants respectively. The effects of current density, initial pH, sodium sulfate (Na₂SO₄) and H₂O₂ concentrations on the removal efficiency were investigated. The best experimental conditions obtained in electrochemical studies were as follows: current density = 15 mA cm^?2, natural pH, without supporting electrolyte addition, H₂O₂ concentration = 3 × 1000 mg L^?1. Under these conditions, 79.2% COD removal from DW was achieved. CONCLUSION: According to the results, 20 min electrolysis is enough, since insignificant variations in COD removal were observed after this time. These methods were found to be successful for the treatment of DW. Copyright © 2011 Society of Chemical Industry     

Electrochemical oxidation of Basic Blue 3 dye using a diamond anode: evaluation of colour,COD and toxicity removal

BACKGROUND: Textile industries generate considerable amounts of waste‐water, which may contain strong colour, suspended particles, salts, high pH and high chemical oxygen demand (COD) concentration. The disposal of these coloured wastewaters poses a major problem for the industry as well as a threat to the environment. In this study, electrochemical oxidation of Basic Blue 3 (BB3) dye was studied in a bipolar trickle tower (BTT) reactor using Raschig ring shaped boron‐doped diamond (BDD) electrodes in recirculated batch mode. The effects of current density, temperature, flow rate, sodium sulfate concentration (Na₂SO₄) as supporting electrolyte, and initial dye concentration were investigated. RESULTS: The best experimental conditions obtained were as follows: current density 0.875 mA cm^?2, temperature 30 °C, flow rate 109.5 mL min^?1, Na₂SO₄ concentration 0.01 mol L^?1. Under these conditions, 99% colour and 86.7% COD removal were achieved. Toxicity tests were also performed on BB3 solutions under the best experimental conditions. CONCLUSION: Based on these results, the BDD anode was found to be very successful for the simultaneous degradation of BB3 and removal of COD. Additional toxicity test results also showed that electrochemical treatment using a BDD Raschig ring anode in a BTT reactor is an effective way of reducing toxicity as well as removing colour and COD. Copyright © 2010 Society of Chemical Industry     

Structure and performance of electroblown PVDF-based nanofibrous electret filters

Poly(vinylidene fluoride) (PVDF)-based nanofibrous mats were produced via electrically assisted solution blowing (electroblowing). Morphology and filtration properties of the nanofibrous mats were investigated as a function of polymer concentration and applied voltage. The average fiber diameter was reduced from 727 ± 366 nm to 408 ± 143 nm and from 424 ± 233 nm to 328 ± 105 nm, using 16 wt% and 12 wt% concentrations, respectively, with an increase of electric voltage from 0 to 30 kV. In addition, the pore size of the mats produced from 12 wt% concentration decreases with the increase of electric voltage. Results showed that electroblown mats possess high filtration properties and performance. Enhancement of mechanical capturing efficiency is attributed to the reduction in fiber diameter and pore size. The enhancement of electrostatic capturing efficiency is thought to be from the improved electret property of the mats, which eliminates the need for a second step to polarize nanofibrous mats. As a result, both mechanical and electrostatic capture efficiency of the mats is enhanced compared to solution blown PVDF mats. The emerging electret property might be due to the accumulation of the electrostatic charges at high voltage and the enhanced polarized β phase, which is the result of the high drawing ratio applied to the polymer jet during the spinning process.     

Photoinitiation of cationic polymerization by visible light activated titanocene in the presence of onium salts

Summary A visible light photoinitiating system for cationic polymerization of cyclic ethers such as cyclohexene oxide (CHO) and vinyl monomers such as n-butyl vinyl ether (BVE) and N-vinyl carbazole (NVC) has been developed, using a fluorinated titanocene free radical photoinitiator, Irgacure 784, together with an onium salt, such as diphenyl iodonium hexafluoro antimonate and N-ethoxy-2-methyl-pyridinium hexafluoro-antimonate. Based on the reported photochemistry of fluorinated titanocenes, a mechanism for generating cationic species is proposed based on electron transfer between photoproducts of titanocene and onium salt. Evidence against the incorporation of an aromatic titanocene moiety in the resulting polymers is presented. Inhibition by a specific proton scavenger suggests that protons may initiate the polymerization. Received: 26 April 2001/Revised version: 6 June 2001/Accepted: 6 June 2001     

New photoinitiating systems designed for polymer/inorganic hybrid nanocoatings

Conventional UV-curable formulations consist of photoinitiators, multifunctional monomers and oligomers, reactive diluents, pigments, and additives. While photoinitiators are the key components of the formulations and responsible for the absorption of light and relevant performances (e.g., cure speed, high-percent conversion, etc.), the final properties of the cured coating are governed by the other high-volume components. With recent advances in the use of nanomaterials like metals, metal oxides, and silicates in coatings, it is now possible to prepare nanocoatings with enhanced physical, chemical, and biological properties. This is due, in part, to the difference in surface area per unit of volume at the nanoscale. Nanocoatings are usually prepared by UV irradiation of formulations containing dispersed nanoparticles. However, the homogeneous dispersion of these nanoparticles is a key challenge due to their easy agglomeration arising from their high surface-free energy. It is often difficult to obtain well-dispersed formulations providing good transmission of light for a complete cure. In this article, we report several synthetic methodologies for the preparation of epoxy and (meth)acrylate-based nanocoatings containing clay or metal nanoparticles. In the former case, photolysis of intercalated photoinitiator within the layers of montmorillonite clay in the presence of monomers resulted in the in situ formation of exfoliated structures. For the preparation of metal nanocoatings, the formation of silver or gold nanoparticles and crosslinking are accomplished simultaneously by photoinduced electron transfer and polymerization processes. The nanoparticles are homogenously distributed in the network without macroscopic agglomeration. Applicability to both free radical and cationic systems is demonstrated. Moreover, a novel photochemical route for grafting from the self-assembled monolayers on gold is presented.     

Investigation of milling characteristics of alumina powders milled with a newly designed vibratory horizontal attritor

In this study, a vibratory horizontal attritor was designed, constructed and used to produce alumina powders. The effects of process parameters, such as milling time, ball-powder weight ratio (BPR) and rotational speed (RS) of the attritor on the mean particle size and particle size distribution have been investigated. Milling times of 1, 5, 10 and 15 h and ball-powder weight ratios of 5:1, 10:1, 20:1 and 40:1 were considered in the present study. Rotational speeds of the attritor were selected as 500, 700 and 900 rpm and distilled water was used as milling media.The experimental results show that increasing milling time and ball-powder weight ratio resulted in finer particles. Optimum rotational speed of the attritor was found as 700 rpm. The mean particle size of attrited powders were in the range of 2.05-6.82 μm, depending on process parameters.     

The effect of zinc oxide nanoparticles on the weathering performance of wood-plastic composites

In recent years, wood-plastic composites (WPCs) have become among the most popular engineering materials. Most of their usage areas are outdoors, where they encounter various damaging factors. The weathering conditions cause significant deterioration to WPC surfaces, which negatively influences their service life. In this study, zinc oxide nanoparticles at different concentrations (1%, 3%, 5%, 10%) were added to a high-density polyethylene-based WPC matrix. The effect of zinc oxide nanoparticles on the weathering performance of WPC was evaluated after 840 hours of an artificial weathering test. The highest colour changes (∆E*) were monitored with control samples exposed for 840 hours. Adding zinc oxide nanoparticles improved the ultraviolet (UV) resistance and decreased the colour changes. The wood flour content also affected the colour changes on the WPC surface. A combination of 10% zinc oxide nanoparticles and 50% wood flour content provided the lowest colour changes. The barrier effect of nanoparticles protected the WPC surfaces from UV light. Zinc oxide nanoparticles also positively affected the load transfer, which restricted the reduction in mechanical properties after the weathering test. The degradation on the surface of WPCs was also investigated using attenuated total reflectance-Fourier Transform–infrared analysis. The changes in the characteristic bands of polymer and wood indicated that surface degradation was inevitable. Light and scanning electron microscopy images also demonstrated micro-cracks and roughness on the surface of WPCs. It is concluded that UV degradation is unavoidable, but zinc oxide nanoparticles can improve surface resistance against weathering conditions.