• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.618-624
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• 1989

Ultrasonically induced bubble formation in thermoplastic matrix was investigated experimentally and theoretically. polystyrene was saturated with nitrogen under the pressure of 0.2 to 3.45 MPa in a pressure chamber, followed by pressure release and ultrasonic bubble nucleation. Zinc stearate was added to polystyrene as the nucleating agent to induce heterogeneous nucleation. Various mixture of low density polyethylene and polyethylene wax was also saturated with the gas. The foamed specimens with or without ultrasonically induced bubble nucleation was modeled by modifying the classical nucleation theory. The rate of ultrasonic nucleation was predicted for homogeneous and heterogeneous nucleation at a conical cavity. This study showed that the heterogeneous and heterogeneous nucleation at a conical cavity. This study showed that the heterogeneous nucleation must be employed for ultrasonic production of bubbles in a viscous fluid and the homogeneous nucleation for ultrasonic production of bubbles in a low viscosity fluid.

• Macromolecular Research
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• v.16 no.3
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• pp.218-223
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• 2008

In order to obtain crosslinked poly(butylene succinate) (PBS) foams with a closed-cell structure, a commercial-grade PBS was first modified in the melt using two different branching agents to increase the melt viscosity. The rheological properties of the branched and crosslinked PBS were examined by varying the amount of the branching agents. The complex viscosity of the crosslinked PBS increased with increasing amount of the branching agent. However, it decreased with increasing frequency. When 2 phr of the branching agent was added to PBS, the storage modulus (G') was higher than the loss modulus (G") throughout the entire frequency range, showing that the addition of a branching agent increases the melt viscosity and elasticity of PBS effectively. Closed-cell PBS foams were prepared by mixing the chemical blowing agent with the crosslinked PBS. The effect of the foaming conditions such as temperature and time, and the amount of the crosslinking agent on the structure of the expanded PBS foams were also investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1367-1370
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• 2005

Microcellular foam processing of polymers requires a nucleated cell density greater than $10^9\;cells/cm^3$ so that the fully grown cells are smaller than 10 mm. A microcellular foam can be developed by first saturating a polymer sample with a volatile blowing agent, followed by rapidly decreasing its solubility in the polymer. In general, the cellular structure of crystalline polymer foams is difficult to control, compared to that of amorphous polymer foams. Since the gas does not dissolved in the crystallites, the polymer/gas solution formed during the microcellular processing is nonuniform. Moreover, the bubble nucleation is nonhomogeneous because of the heterogeneous nature of the crystalline polymer. In this paper, the effects of the crystallinity and morphology of crystalline polymers on the microcellular foam processing and on reflectivity of products are investigated. First, polymer specimens with various morphology and amount of solved blowing agent were prepared by varying the saturation pressure, saturation time and foaming condition. Then, cell morphologies according to several conditions were studied. The specimens with differing gas amount of solved and morphologies were foamed and their cellular structures were compared. The experimental results of reflectivity are compared to raw specimen and another specimen of different experimental conditions. After the experiments, recognize whether how reflectivity changes according to solved gas amount. And the effect of cell density and cell size on reflectivity is studied

• Polymer(Korea)
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• v.34 no.1
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• pp.8-13
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• 2010

The physical properties of polymeric foams depend on the density of foams, physical properties of base polymers, the content of open cells, and cell structures including the size and its distribution, the shape of cell, and the thickness of skin layer. The foam density is affected by the chemistry of raw materials, the concentration of crosslinking agent and the blowing agent as well as the operating parameters during production process. In this study, the basic formulations of foams are composed of polyester polyol, MDI, amine catalyst, tin catalyst, silicone surfactant, and water. Cross-linking density of polyurethane was increased by using chain extenders. Also, the mechanical properties of polyurethane foam were improved by using the inorganic fillers (silica 1,2 and talc 1,2) having different $SiO_2$ contents and particle sizes. We investigated the properties of modulus, tensile strength, compressive strength and hardness of foams obtained by changing kind of inorganic filler and chain extender, and observed the distribution of inorganic filler as well as variation of cell size within the foams by electron microscopy.

• Fire Science and Engineering
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• v.21 no.1 s.65
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• pp.69-73
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• 2007

In this research, an environmental-friendly foam extinguisher was newly developed using a natural surfactant as its composition. Two criteria were applied to verify its extinguishing performance and environmental attraction. One is unit 2 model by "Standards of Model Approval and Inspection Technology for Portable Fire Extinguishers" presented in Korea Fire Equipment Inspection Corporation. The other is Terrestrial Plants, Growth Test and Fish, Acute Toxicity Test presented in Korea Institute of Toxicology(Korea Research Institute of Chemical Technology). Test results showed that the extinguishing performance was 5 unit of general fire Class A, the $LC_{50}$ by germination was 75(g/kg) and the $EC_{50}$ by growth was 62(g/kg) through Terrestrial Plants, Growth Test, and also the toxicity was 6658 ppm in Fish, Acute Toxicity Test. The numerical values were highly evaluated than other fire extinguishing agents being commercialized in domestic. The results also showed suitably in basic physical properties and anti-corrosion properties for making use of fire extinguishing agent.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.9-18
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• 2019

Concrete, which is the most widely used building material in modern times, has been improved not only in strength but also in structural performance such as increase in toughness and ductility, weight reduction, and improvement in quality of human life. Due to the surge in demand for the building, there is a tendency to be used variously from architectural panel and architecture to interior accessories. In Korea, a light-transmitting concrete, LEFC(Light Emotion Friendly Concrete), that insert plastic rods to stimulate emotional sensation through the combination of light and concrete has developed. In previous research, it was confirmed that the use of a synthetic foam agent rather than an animal foam agent did not cause a fogging phenomenon. In this study, lightweight by applying foaming agent to LEFC and two types of fiber (Nylon Fiber, Polyvinyl Alcohol) were compared to achieve to investigate the fiber to be applied in future. An equation that can predict the loss and adhesion reduction of the concrete section according to the diameter of the rod (5mm, 10mm) and the interval (10mm, 15mm, 20mm) was proposed.

• Journal of the Korean Institute of Gas
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• v.5 no.4 s.16
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• pp.79-84
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• 2001

In this study, the effect of polyol structure(OH-value, functionality) on the reactivity, mechanical property and cell morphology of polyurethane foam and the possibility of replacing HFC-36smfc was examined by evaluating how each blowing agent(CFC-11, HCFC-l4lb, HFC-36smfc) affects the reactivity, mechanical property and cell morphology. Results of the experiment showed that as the functionality and OH-value of polyol increased, there was an increase in the temperature profile, reaction rate, density and compressive strength. However. as the functionality and OH-value increased. the ceil size became smaller The use of different kinds of blowing agents did not appear to have and significant influence on the temperature profile, reaction rate, density and compressive strength. The foam using HFC-365mfc produced more uniform cells compared to the foam using HCFC-l4lb.

• Journal of the Korean Applied Science and Technology
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• v.28 no.2
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• pp.232-239
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• 2011

Fabric fibrous filter has been used in various industrial applications owing to the low cost and wide generality. However, the basic properties of fabric materials often limit the practical utilization including hot gas cleaning. This study attempts to find new coatings of porous fibrous filter media in order to overcome its insufficient thermal resistance and durability. Teflon was one of the plausible chemicals to supplement the vulnerability against frequent external thermal impacts. A foaming agent composed of Teflon and some organic additives was tentatively coated on the glass fiber mat. The present test Teflon foam coated filter was fount to be useful for hot gas cleaning, up to $250^{\circ}C$-$300^{\circ}C$. Close examination using XPS(X-ray Photoelectron Spectroscopy) and Contact angle proved the binding interactions between carbon and fluorine, which implies coating stability. The PTFE/Glass foam coated filter consisted of more than 95% (C-F)n bond, and showed super-hydrophobic with good-oleophobic characteristics. The contact angle of liquid droplets on the filter surface enabled to find the filter wet-ability against liquid water or oil.

• Elastomers and Composites
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• v.50 no.4
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• pp.297-303
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• 2015

Ammonium polyphosphate-polyurethane foam composite (APP-PUF) was prepared from poly(adipate)diol/ammonium polyphosphate composite (f = 2), polyether polyol (f = 4.6), and PMDI (f = 2.5). As a blowing agent, $H_2O$ was used at various concentrations. The thermal decomposition behavior, morphology, closed-cell content, and density of APP-PUF were characterized. At the $H_2O$ concentrations lower than 3.5 php, the cell size of pure polyurethane foams (PUF) and APP-PUFs were close each other. As the $H_2O$ concentration became greater than 5.0 php, the cell size of the PUFs greatly increased compared to that of APP-PUFs. Addition of 1.5~1.9 wt% ammonium polyphosphate to the PUFs greatly enhanced the thermal stability of the PUFs, so 50 wt% residual temperature of APP-PUFs increased to $380{\sim}488^{\circ}C$, which were $30{\sim}70^{\circ}C$ higher than those of the PUFs. Thermal stability of the PUFs and APP-PUFs increased with $H_2O$ content and then decreased once $H_2O$ content exceeded 5 php.

• Polymer(Korea)
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• v.32 no.5
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• pp.497-500
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• 2008

Polystyrene foam (styrofoam) was treated with low-temperature oxygen plasma by means of immobilization and grafting techniques in order to modify its hydrophobic surface property to hydrophilic one using hydrophilic monomers of acrylic acid and acrylamide, and its surface chemical structure, morphology, and hydrophilicity were examined by ESCA, field emission scanning electron microscope (FESEM), and contactangle meter. The experimental evidences, such as the increases of O/C and N/C ratios in ESCA spectrum, thin film deposition, decrease in contact-angle, strongly suggested that the plasma treatments were useful methods for the preparation of hydrophilic surface. Contact angle diminished drastically from $84^{\circ}$ to $18{\sim}19^{\circ}$. Acrylamide, compared to acrylic acid, appeared to play a decisive role, and to be more powerful agent for improving its surface hydrophilicity.