Effect of Zirconium Oxide Nano-Fillers Addition on the Flexural Strength, Fracture Toughness, and Hardness of Heat-Polymerized Acrylic Resin

Purpose: The mechanical strength of polymethyl methacrylate (PMMA) remains far from ideal for maintaining the longevity of denture. The purpose of this study was to evaluate the effect of Zirconium oxide (ZrO2) nanofillers powder with different concentration (1.5%, 3%, 5% and 7%) on the flexural strength, fracture toughness, and hardness of heat-polymerized acrylic resin. Materials and methods: Zirconium oxide powders with different concentrations (1.5%, 3%, 5% and 7%) were incorporated into heat-cure acrylic resin (PMMA) and processed with optimal condition (2.5:1 Powder/monomer ratio, conventional packing method and water bath curing for 2 hours at 95。C) to fabricate test specimens of PMMA of dimensions (50 × 30 × 30 mm) for the flexural strength, fracture toughness, and (50 × 30 × 30 mm) were fabricated for measuring hardness. PMMA without additives was prepared as a test control. Three types of mechanical tests;flexural strength, fracture toughness and hardness were carried out on the samples. The recorded values of flexural strength in (MPa), fracture toughness in (MPa.m1/2), and hardness (VHN) were collected, tabulated and statistically analyzed. One way analysis of variance (ANOVA) and Tukey’s tests were used for testing the significance between the means of tested groups which are statistically significant when the P value ≤ 0.05. Results: Addition of Zirconium oxide nanofillers to PMMA significantly increased the flexural strength, fracture toughness and hardness. Conclusion: These results indicate that Zirconium oxide nanofillers added to PMMA has a potential as a reliable denture base material with increased flexural strength, fracture toughness, and hardness. According to the results of the present study, the best mechanical properties were achieved by adding 7%wt ZrO2 concentration.

Effect of Nano-fillers on Conductivity of Polyethylene/Low Melting Point Metal Alloy Composites

A novel method for preparing conductive polyethylene （PE） composites has been developed. In the method, the powder of low melting point metal alloy （LMPA） is filled into the PE matrix by using twin screw extruder at a temperature below the melting point of the LMPA, and followed by a die drawing process at a temperature around the melting point of the metal alloy. It has been found that die drawing process, repeating the die drawing process and adding nano-fillers, such as montmorillonite （MMT） and multi-wall carbon nanotubes （MWCNTs）, all help reduce the metal particle size in the PE matrix, thus improve the conductivity of the composite. The conductivity improvement is attributed to an increased number of the smaller metal particles. Therefore, conductive composites of polymer/metal alloy/nano-filler with high conductivity are possible to be prepared by using the new method.

Effects of Nano-Filler on the Thermal and Fire-Resistant Properties of Ethylene-Vinyl Acetate Copolymer

Sepiolite （S9, B10, B20, B40） and boehmite have been added to an intumecent flame retardant （IFR） system to produce the halogen-free and fire-resistant ethylene-vinyl acetate copolymer （EVM） rubber. The rubber contains ammonium polyphosphate （APP） as acid source, double pentaerythritol （D-PER） as carbon source and melamine （MN） as gas source. The effects of nano-filler sepiolite and boehmite on the fire-resistant property of EVM rubber based on IFR system were investigated. The test results show that the system with nano-filler of sepiolite B10 has the best fire-resistant property. The process of smoke emission and thermal decomposition, the element composition of char surface and the micro morphology of intumecent char layer of the EVM IFR system with nano-filler were also studied by NBS chamber, thermogravimetric （TG） analysis, X- ray photoelectron spectroscopy （XPS） and scanning electron microscope （SEM）.

Effect of Nano-Filler on Structural and Ionic Transport Properties of Plasticized Polymer Electrolyte

Polymer blend electrolytes, where PEO-PMMA polymer blend is used as polymer host matrix, doped with AgNO3 and plasticized with ethylene carbonate (EC) and Al2O3 as nano-filler were synthesized using the solution cast techniques. The polymer films were characterized by impedance spectroscopy, XRD, DSC, SEM, FT-IR and ionic transport mea-surements. The results indicate an enhancement in conductivity of PEO-PMMA-AgNO3-EC polymer electrolytes. The ionic conductivity of the polymer films is also found to increase with temperature. Electrical properties of polymer films in the framework of dielectric and modulus formalism are studied and

纳米填料混合物对低密度聚乙烯基复合材料树老化形态的影响(英文)

This paper deals with a digest on electrical treeing degradation in nanocomposite of magnesium oxide(MgO) added to a low-density polyethylene(LDPE).The objective is to elucidate the"visual"aspects of runaway stage of final treeing breakdown mechanisms,and to ensure that the existence of MgO filler itself is responsible for this aspect instead of voltage application changes.The"visual"aspect of treeing breakdown was investigated by applying ac ramp voltage with continuous rising speed of 0.5 kV/s.As soon as tree had been incepted,the voltage was kept constant to observe the tree propagation until breakdown.The tree propagations were also described by their fractal dimension. To ensure the responsibility of MgO filler on the"visual"aspect results,the experiment was repeated using the same rate of ac ramp voltage.However,as soon as tree had been incepted,the voltage was either increased or decreased to a constant value of mean tree inception voltage obtained from the preceding results to observe its propagation to breakdown. As a result,the tree inception voltage was increased with the filler concentration in LDPE.The filler is considered not only acted as a physical obstacle for tree to propagate,but also as a chemical obstacle in which the free electron might be trapped to cause difficulties for electron avalanche occurrence.This consideration could also be valid for tree propagation up to breakdown.During propagation,due to the filler,the tree structure is accompanied by more branches.Since the branches are closely placed each other,the tree tips become relatively uniform field compares to pure LDPE.This would produce the higher local breakdown strength at the tree tips,leads to the suppression of propagation.The"visual"aspect of breakdown could be achieved by applying voltage exactly at the inception level. After bridging the tree would not breakdown until a short period of time lag.Within this period,the tree channel will be eroded by internal flashover(IFO) and become thicker.MgO filler could still restrain the IFO at the small diameter; however there will be a maximum diameter above which the effect of MgO would be very small.Lastly,it is confirmed that the MgO filler itself excels to suppress the tree degradation instead of the voltage application changes.The polymer nanocomposite appears to be more resistive to treeing degradation than their base material.

The Effect of the Light Intensity and Light Distances of LED and QTH Curing Devices on the Hardness of Two Light-Cured Nano-Resin Composites

Background: Effective polymerization of the composite resin is essential to obtain long term clinical success and has a great importance obtaining improved mechanical properties. The purpose of this study was to measure the effect of the light intensity of LED and QTH curing devices in relation to the light distances, on the hardness (KHN) of two light cure nano-resin composite. Material and Methods: The top and bottom surfaces of the two nanofill composite specimens were evaluated. Two LED and two QTH light curing devices were used at nine different distances. Light intensity was measured with two radiometers placed at these same distances from the curing tip. 360 pvc dies were prepared with circular cavity 3 mm in diameter and 2 mm thick. The tested materials were placed in each cavity. The different light curing distances were standardized by adding pvc spacers dies at different height matching the different distances. Top and bottom surface microhardness were evaluated with a Micro Hardness Tester in knoop hardness numbers (Kg/mm2). Data were statistically analyzed using: Three-way ANOVA, Tukey and Pearsons test. Results: It was revealed that there was a statistically significant difference in microhardness between the composites (p < 0.001), between the nine distances (p < 0.001) and between the four light curing devices (p < 0.001). Increasing the distance of the light source from composite resin, the light intensity and the microhardness values at the top and bottom surface decrease. LED light curing devices produced a greater microhardness results at the bottom surface of the specimens. The Filtek Ultimate nanocomposite (3 m) showed highest microhardness values on the top and bottom surfaces, polymerized with all four curing devices and all nine distances compared to Empress Direct nano composite (Ivoclar vivadent). Clinical significant: Even with high power LED curing light, the distance between the tip of the light source and the restoration surface should be as close as possible. In this study, Filtek Ultimate showed better results (highest microhardness values) than Empress Direct.

Dielectric spectroscopy and structural characterization of nano-filler-loaded epoxy resin

This work outlines the characterization of epoxy resin[Bisphenol A-(epichlorhydrin):epoxy]and hardener[N(3-dimethylaminopropyl)-1,3-propylenediamine]with various inorganic nano-fillers.Dielectric characterizations of epoxy,hardener,neat epoxy(epoxy+hardener)and nano-epoxy(nano-filler+neat epoxy)composites loaded with 1 wt.%of inorganic nano-fillers(SiO_(2),Al_(2)O_(3),TiO_(2)and ZnO)were carried out using precision LCR meter,over the frequency range of 1 kHz-2 MHz at a constant temperature of 300.15 K.The structural information of nano-fillers,neat epoxy and nano-epoxy composites was understood by Fourier transform infrared spectroscopy and by XRD.Moreover,hardness and shear strength(shear punch)were also determined in order to gain additional information about the mechanical properties of epoxy composite.Influence of inorganic nano-fillers on the dielectric properties,structural chemistry and mechanical properties of neat epoxy composite is discussed thoroughly in this study.