• Polymer(Korea)
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• v.24 no.2
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• pp.141-148
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• 2000

Polycaprolactone (PCL) was blended with corn starch to produce biodegradable compost films and the biodegradability and mechanical properties were investigated. As the compatibilizer for the immiscible PCL/starch blend, 2-hydroxyethylmethacrylate (HEMA)-PCL macromer was grafted onto starch by initially grafting HEMA to starch and then grafting of PCL onto HEMA via ring opening polymerization of $\varepsilon$-caprolactone. When biodegradability of the PCL grafted starch-g-DEMA copolymers was compared with that of starch by the modified Sturm test, graft copolymers degraded at much slower rates due to the presence of the non-degradable HEMA. With the addition of the graft copolymer up to 5 wt% to the blend, the elongation-at-break of the starch/PCL blend increased substantially, while the tensile strength and modulus did not change much. SEM observation of the blend containing 2 wt% copolymer clearly indicated that the interfacial adhesion between the starch and PCL was strengthened by the copolymer.

• Advances in materials Research
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• v.7 no.1
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• pp.45-72
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• 2018

In the present study, a special attention has been paid to the effects regarding the use of different superplasticizers in different dosages. To do so, 36 mixes of normal and self-compacting concrete with two water/binder ratios of 0.35 and 0.45, four different types of superplasticizer including melamine-formaldehyde, naphthalene-formaldehyde, carboxylic-ether and poly-carboxylate, four different superplasticizer/cement ratios of 0.4%, 0.8%, 1.2% and 1.6% and two silica fume/cement ratios of 0% and 10% have been cast. Moreover, the initial and final setting time of the pastes have been tested. For self-compacting mixes, flow time, slump flow, V-funnel, J-ring and L-box tests have been carried out as well as testing the compressive strength and rupture modulus. For normal concrete mixes,slump test has been conducted to assess the workability of the mix and then for each mix, the compressive strength and rupture modulus have been determined. The results indicate that in addition to the important role of superplasticizer type and dosage on fresh state properties of concrete, these parameters as well as the use of silica fume could affect the hardened state properties of the mixes. For instance, the mixes whose superplasticizer were poly-carboxylic-ether based showed better compressive and tensile strength than other mixes. Besides, the air contents showed robust dependency to the type of the superplasticizer. However, the use of silica fume decreased the air contents of the mixes.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.10-16
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• 2007

A rubber seal for wheel bearing which has been mainly applied to car wheel supporting device is required to have both high sealing performance and drag torque. Because of severe operational conditions like infiltration of mud or splashed water, the importance of rubber seal which is aimed for leakage prevention of grease and effective blocking of foreign substances has been increasing continuously. The sealing performance of this seal depends on several factors such as materials of seal, friction conditions of contact regions and geometry of seals and so on. We have focused on the effects of geometric characteristics such as the angle of main lip, interference between lip edge and inner metallic ring. In this study, the optimization of geometric variables was performed using the finite element analysis. For the sake of finite element analysis, uniaxial tensile tests were conducted and several constants for Mooney-Rivlin's equation were obtained. According to the results of this study, mock-up bearing was made. To verify this study, drag torque and mud spray test were preformed.

• Composites Research
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• v.18 no.1
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• pp.45-54
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• 2005

The delamination in the filament-wound composite flywheel rotor often lowers the performance of the flywheel energy storage system. A conventional ring type hub usually causes tensile stresses on the inner surface of the composite rotor, resulting in lowering the maximum rotational speed of the rotor. In this work, the stress and strain distributions within a hybrid composite rotor were derived from the two-dimensional governing equation with the specified boundary conditions, and an optimum pressure at the inner surface of the rotor was proposed to minimize the strength ratio and maximize the storage energy. A split type hub was introduced to apply the calculated optimum pressure at the inner surface, and a spin test was performed up to 40,000 rpm to demonstrate the performance of the split type hub with radial and circumferential strains measured using a wireless telemetry system. From the analysis and the test, it was found that the split type hub successfully generates a compressive pressure on the inner surface of the rotor, which can enhance the performance of the composite rotor by lowering the strength ratio within the rotor.

• Journal of Adhesion and Interface
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• v.23 no.2
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• pp.44-52
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• 2022

Epoxy resin has the disadvantage of being easily destroyed by instantaneous impact due to its high crosslinking density despite its high glass transition temperature (T_g) and excellent properties. To compensate for this, in this study, polyol was synthesized by ring opening polymerization of propylene glycol (PPG) diamine, Jeffamine D 2000 and propylene carbonate, and urethane modified epoxy was synthesized using this. The properties of the synthesized urethane modified epoxy were confirmed by FT-IR, H-NMR. To confirm the degree of improvement in impact resistance as an adhesive, a urethane modified epoxy adhesive was prepared by mixing a digylcidyl ether bisphenol A (DGEBA) with curing agent and curing accelerator. Properties test of urethane modified epoxy were shear strength, tensile strength and impact strength. As a result, excellent results were obtained in all test when the ratio of DGEBA : urethane modified epoxy was 8:2.