• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.761-766
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• 2006

Polymer composite are increasingly considered as structural components for use in civil engineering, on account of their enhanced strength-to-weight ratios. Unsaturated polyester (UP) resin have been widely used for the matrix of composites such as FRP and polymer composite, due to its excellent adhesive. Polymer nanocomposites are new class of composites derived from the nano scale inorganic particles with dimensions typically in the range of 1 to 1000 nm that are dispersed in the polymer matrix homogeneously. Owing to the high aspect ratio of the fillers, mechanical, thermal, flame, retardant and barrier properties are enhanced without significant loss of clarity, toughness or impact strength. To prepare the MMT (Montmorillonite)-UP exfoliated nanocomposites, UP was mixed with MMT at $60^{\circ}C$ for 3 hours by using pan mixer. XRD (X-ray diffraction) pattern of the composites and TEM (Transmission Electron Micrographs) showed that the interlayer spacing of the modified MMT were exfoliated in polymer matrix. The mechanical properties also supported these findings, since in general, tensile strength, modulus with modified MMT were higher than those of the composites with unmodified MMT. The thermal stability of MMT-UP nanocomposite is better than that of pure UP, and its glass transition temperature is higher than that of pure UP. The polymer concrete made with MMT-UP nanocomposite has better mechanical properties than of pure UP. Therefore, it is suggested that strength and elastic modulus of polymer concrete was found to be positively tensile strength and tensile modulus of the MMT-UP nanocomposites.

• Restorative Dentistry and Endodontics
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• v.12 no.2
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• pp.45-53
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• 1987

The purpose of this study was to evaluate the tensile bond strength between composite resin and the human enamel. Three composite resin systems, two chemical (Clearfil Posterior, and Clearfil Posterior-3) and one light cure (Photo Clearfil-A), used with and without an intermediate resin (clearfil bonding agent), were evaluated under different amounts of load (10g, 200g and 200g for a moment) for in vitro tensile bond strength to acid-eched human enamel. Clinically intact buccal or lingual surfaces of 144 freshly extracted human permanent molars, embedded in acrylic were flattened with No #600 carborundum discs. Samples were randomly assigned to the different materials and treatments using a table of random numbers. Eight samples were thus prepared for each group(Table 2) these surfaces were etched with an acid etchant (Kurarey Co. Japan) in a mode of etching for 30 seconds, washing for 15 seconds, and drying for 30-seconds. During the polymerization of composite resin on the acid-etched enamel surfaces with and without bonding agent 10-gram, 200 gram and temporary 200 gram of load were applied. The specimens were stored in 50% relation humidity at $37^{\circ}C$ for 24 hours before testing. An universal Testing machine (Intesco model No. 2010, Tokyo, Japan) was used to apply tensile loads in the vertical directed (fig 5), and the force required for separation was recorded with a cross head speed of 0.25 mm/min and 20 kg in full scale. The results were as follow: 1. The tensile bond strength was much greater in applying a bonding agent than in not doing that. 2. The tensile bond strength of chemical cure composite resin was higher than that of light cure composite resin with applying on bonding agent on the acid-etched enamel. 3. In case of not applying a bonding agents on the acid-etching enamel, the highest tensile bond strength under 200 gram of load was measured in light cure composite resin. 4. The tensile bond strength under 200-gram of load has no relation with applying the bonding agent. 5. Under the load of 10-gram, There was significant difference in tensile bond strength as applying the bonding agent.

• Elastomers and Composites
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• v.43 no.1
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• pp.39-48
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• 2008

Peel strength of epoxy adhesives can be increased by adding some amounts of XNBR. In this case, thermal resistance of the adhesive will be decreased by decrease of glass transition temperature of the adhesive. Epoxy resin modified with siloxane-imide was synthesized to improve thermal resistance and peel strength of the adhesive, after that the properties of modified epoxy resin were compared with the commercial epoxy resin. When 5% XNBR was added to 30% modified epoxy resin, this adhesive showed 0.42 N/mm of peel strength and $155^{\circ}C$ of glass transition temperature. These properties are enough compared to the required properties by the industry, i.e., 0.3 N/mm and $150^{\circ}C$, respectively. Weight loss of the modified epoxy resin by the treatment of nitric acid and 0.1N NaOH was reduced, but weight gain by the humid condition was increased by the presence of benzene ring and imide ring. 30% modified epoxy resin blended with 5% XNBR showed 220% improvement in tensile strength and elongation compared to the case of common epoxy resin. This is due to the flexibility of the siloxane in the modified epoxy resin.

• Composites Research
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• v.12 no.3
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• pp.75-83
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• 1999

The thermal properties of carbon/phenolic and silica/phenolic ablative composites were investigated by measuring the heat capacity, thermal diffusivity and thermal conductivity. The heat capacities of carbon/ phenolic and silica/phenolic composites were calculated from differential scanning calorimeter curve. The thermal diffusivities of carbon/phenolic and silica/phenolic composites were measured by the laser flash method with varying laminated direction, i.e., with laminar direction and across laminar direction. The thermal diffusivities decreased with increasing temperature. The thermal conductivities of carbon/phenolic and silica/phenolic composites were calculated using the heat capacity, density and thermal diffusivity. The thermal conductivities increased with increasing temperature. The thermal conductivity of with laminar direction is two times higher than that of across-laminar direction in carbon/phenolic composite due to the directionality of thermal conductivity of carbon fiber. The thermal conductivities of two dimensional fiber reinforced composites were analyzed using the conductivities of constituents and volume fraction of each constituent. The thermal conductivities of carbon fiber and silica fiber were calculated from thermal conductivities of carbon/phenolic and silica/phenolic composites. The thermal conductivities of carbon/phenolic and silica/phenolic composites at RT were predicted from thermal conductivities of fiber and resin with varying the volume fraction of fiber.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.621-626
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• 2012

In this study, the composite coating materials with improved thermal insulation property were prepared by incorporating the hollow micro-spheres with high heat transfer resistance. The UV curable resin system consisting of hexa aliphatic urethane acrylate (UP118), trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), and photoinitiator (Irgacure184) was employed as an organic binder. The glass substrates were coated by the prepared composites via bar coating method and cured under UV radiation. The optical transparency, thermal insulation property, adhesion, and surface hardness of the glass coated with composites containing different type of micro-spheres were investigated. The incorporation of micro-spheres with only 20 vol% of content resulted in remarkable improvement in the thermal insulation property of the coated glass. In addition, the transparent coated glass with light transmittance of about 80% could be obtained when silica micro-sphere (SP) was used as a thermal barrier.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.2
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• pp.56-65
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• 1999

The relationship of the winding process variables and the mechanical properties of filament wound composites is investigated experimentally. The winding process variables considered are the fiber tensions and the fiber ends. The filament wound ring specimens are fabricated using 3-axis controlled filament winding machine. Two types of carbon fibers, TZ-507 and IZ-40, are used as reinforcements and epoxy for filament winding is used as resin. During the winding process, the fiber tensions are varied from 0.5kgf to 3.0kgf, and the number of the fiber ends are varied from 1 to 6. The fiber volume fractions and the void contents for the ring specimens are measured through the resin digestion. The mechanical properties of the ring specimens are also evaluated by the split disk test. The test results show that the winding process variables affect the fiber volume fractions and the void contents of the ring specimens, which result in the variation of the tensile properties of the ring specimens. Therefore, suitable winding process variables should be applied to maximize the structural performance and the productivity for filament wound structures.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.1
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• pp.53-58
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• 2000

In this paper, the variable mechanical strength and dielectric breakdown strength of epoxy composites were measured at boiling absorption condition in order to observe the influences of moisture in out door use. Also, in order to improve water resistance of matrix resin, IPN(interpenetrating polymer network) method which had been already reported, was introduced and the influence was investigated. As Adding filter(SiO2) classified by o[phr], 50[phr] and 100[phr] to two kinds of matrix resin, six kinds of specimens were manufactured. As a result, it was confirmed that the moisture absorption rate was increased and mechanical strength and dielectric breakdown strength were degraded with boiling time and filler content increasing. On the other hand, it was confirmed that moisture absorption rates were decreased and the degrading rates of mechanical strength and dielectric breakdown strength were lowered according to improvement of adhesion strength in case of IPN specimens.

• The Journal of Advanced Prosthodontics
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• v.10 no.4
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• pp.308-314
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• 2018

PURPOSE. Plasma activation of hydrophobic zirconia surfaces might be suitable to improve the bond strength of luting materials. The aim of this study was to analyze the influence of nonthermal argon-plasma on the shear bond strength (SBS) between zirconia and different combinations of 10-MDP adhesive systems and luting composites after artificial aging. MATERIALS AND METHODS. Two hundred forty Y-TZP specimens were ground automatically with $165{\mu}m$ grit and water cooling. Half of the specimens received surface activation with nonthermal argon-plasma. The specimens were evenly distributed into three groups according to the adhesive systems ([Futurabond U, Futurabond M, Futurabond M + DCA], VOCO GmbH, Germany, Cuxhaven) and into further two subgroups according to the luting materials ([Bifix SE, Bifix QM], VOCO GmbH). Each specimen underwent artificial aging by thermocycling and water storage. SBS was measured in a universal testing machine. Statistical analysis was performed using ANOVA and $Scheff{\grave{e}}$ procedure with the level of significance set to 0.05. RESULTS. Surface activation with nonthermal plasma did not improve the bond strength between zirconia and the tested combinations of adhesive systems and luting materials. The plasma-activation trended to reveal higher bond strength if the self-etch luting material (Bifix SE) was used, irrespective of the adhesive system. CONCLUSION. Plasma-activation seems to be suitable to improve bond strength between zirconia and self-etch resin materials. However, further research is necessary to identify the influence of varying plasma-parameters.

• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.459-464
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• 2016

In this study, the electrochemical characteristics of porous silicon/carbon composite anode were investigated to improve the cycle stability and rate performance in lithium ion batteries. In this study, the effect of TEOS and $NH_3$ concentration, mixing speed and temperature on particle size of nano silica was investigated using $St{\ddot{o}}ber$ method. Nano porous Si/C composites were prepared by the fabrication processes including the synthesis of nano $SiO_2$, magnesiothermic reduction of nano $SiO_2$ to obtain nano porous Si by HCl etching, and carbonization of phenolic resin. Also the electrochemical performances of nano porous Si/C composites as the anode were performed by constant current charge/discharge test, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DMC:EMC=1:1:1vol%). It is found that the coin cell using nano porous Si/C composite has the capacity of 2,006 mAh/g and the capacity retention ratio was 55.4% after 40 cycle.

• Restorative Dentistry and Endodontics
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• v.40 no.3
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• pp.188-194
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• 2015

Objectives: This study evaluated the effect of lactic acid and acetic acid on the microhardness of a silorane-based composite compared to two methacrylate-based composite resins. Materials and Methods: Thirty disc-shaped specimens each were fabricated of Filtek P90, Filtek Z250 and Filtek Z350XT. After measuring of Vickers microhardness, they were randomly divided into 3 subgroups (n = 10) and immersed in lactic acid, acetic acid or distilled water. Microhardness was measured after 48 hr and 7 day of immersion. Data were analyzed using repeated measures ANOVA (p < 0.05). The surfaces of two additional specimens were evaluated using a scanning electron microscope (SEM) before and after immersion. Results: All groups showed a reduction in microhardness after 7 day of immersion (p < 0.001). At baseline and 7 day, the microhardness of Z250 was the greatest, followed by Z350 and P90 (p < 0.001). At 48 hr, the microhardness values of Z250 and Z350 were greater than P90 (p < 0.001 for both), but those of Z250 and Z350 were not significantly different (p = 0.095). Also, the effect of storage media on microhardness was not significant at baseline, but significant at 48 hr and after 7 day (p = 0.001 and p < 0.001, respectively). Lactic acid had the greatest effect. Conclusions: The microhardness of composites decreased after 7 day of immersion. The microhardness of P90 was lower than that of other composites. Lactic acid caused a greater reduction in microhardness compared to other solutions.