• Polymer(Korea)
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• v.26 no.2
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• pp.185-192
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• 2002

Rigid polyurethane foams (PUFs) were prepared from polymeric 4.4'-diphenyl-methane diisocyanate (PMDI), polyether polyol, 1,4-butane diol, silicone surfactant, and distilled water. The density of the PUF was decreased from 173.7 to 41.7 kg/㎥ with an increase in distilled water from 0.5 to 3.0 php (parts per hundred polyol by weight), respectively, at the 0 php butane diol. The cell size of the PUF increased from 115 to 258 $mu extrm{m}$ with an increase in the amount of distilled water from 0.5 to 3.0 php, respectively, at the 10 php butane diol. It was found that the compressive strength of the PUF increased with the content of distilled water, at the same density. Out of the study for the surfactant effect on the properties of the PUF, it was observed that the cell site of the PUF decreased from 360 to 146 $mu extrm{m}$ with an increase in the amount of the surfactant from 0 to 0.33 php, respectively, but the tell size did not change significantly when the amount of the surfactant exceeded 0.33 php.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.395-404
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• 2019

In the case of fire, surface treatment agents used in external insulation finishing methods are substances that are vulnerable to fire due to thin finishes and the combustion of polymers. In this study, it was expected that the performance of surface preparation mortars could be improved by using expandable graphite with excellent thermal performance. Experimental results showed that the mechanical properties of surf ace preparation mortar were improved by using the fly ash and silica fume. Surface treatment materials using expanded graphite have a characteristic of expanding when a fire occurs. It has been shown that heat-swellable surface treatment materials can reduce the penetration of heat sources into the surface of synthetic insulation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.5
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• pp.533-549
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• 2024

Soil conditioning is a critical process when tunneling with an earth pressure balance (EPB) shield tunnel boring machine (TBM) to enhance performance. To determine the optimal additive injection conditions, it is important to understand the rheological properties of conditioned soil, which is typically assessed using a rheometer. However, a rheometer cannot simulate the actual process of muck discharge in a TBM. Therefore, in this study, a scaled-down model of an 8-meter-class EPB shield TBM chamber and screw conveyor, reduced by a factor of 1:20, was fabricated and its applicability was evaluated through laboratory experiments. A lab-scale model experiment was conducted on artificial sandy soil using foam and polymer as additives. The experimental results confirmed that screw torque was consistent with trends observed in previous laboratory pressurized vane shear test data, establishing a positive proportional relationship between screw torque and yield stress. The muck discharge efficiency according to foam injection ratio (FIR) showed similar values overall, but decreased slightly at 60% of FIR and when the polymer was added. In addition, the pressure distribution generated along the chamber and screw conveyor was assessed in a manner similar to the actual EPB TBM. This study demonstrates that the lab-scale screw conveyor model can be used to evaluate the shear properties and muck discharge efficiency.

• Transactions of Materials Processing
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• v.11 no.1
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• pp.69-74
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• 2002

In addition to lightweight and moldable characteristics, polymeric foams possess an excellent energy absorbing capability that can be utilize for a wide range of commercial applications, especially in the crashworthiness of the automobiles. The purpose of the present study is to develop experimental methodology to characterize the pressure dependent yield behavior of the energy absorbing polymeric foams. For the compression test in a triaxial stress sate, a specially designed device was placed in a hydraulic press to produce and control oil pressure. For the test material, the polyurethane foams of two different densities were used. The displacement of the specimen, the load subjected to the specimen, and oil pressure applied to the specimen were measured and controlled. Stress strain curves and yield stresses for the four different oil pressure were obtained. It was found from the present experiments that the polyurethane foams exhibited significant increases in yield stress with applied pressure or mean normal stress. Based on this observation, a yield criteria which included the effect of the stress invariant were established for the polymeric foams. The obtained experimental constants which constituted the pressure-dependent yield criterion were verified.

• Polymer(Korea)
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• v.25 no.4
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• pp.528-535
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• 2001

Polyurethane specimens were mainly composed of polyol, MDI, silicone surfactant, and water. The effects of ethylene glycol on the cell size, forming magnification, cream time, gel time, take free time, final free rising height, and reactive temperature were investigated. The cyclopentane was used for PU foam as a physical blowing agent. The components were hand-mixed at about 5000 rpm within 4 seconds at room temperature. The mixtures with various ethylene glycol contents were foamed in the wood mold. When the index of isocyanate was fixed, as the amount of ethylene glycol increased, cell size and thermal conductivity were decreased by about 5.1% and 14%, respectively.

• Fire Science and Engineering
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• v.27 no.4
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• pp.41-46
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• 2013

The present study has been conducted to investigate the reaction kinetics and pyrolysis parameters for flame propagation analysis of furniture material components. TGA measurement for component materials such as MDF (medium density fiberboad) panel including coating material, synthetic leather and foam cushion are performed under maximum temperature of $600^{\circ}C$ and heating rate of $10^{\circ}C/min$. The results of TGA have shown that the peak temperature of MDF panel was $324^{\circ}C$ and the initial peak temperature of coating material decreased by $270{\sim}280^{\circ}C$. In the case of synthetic leather and foam materials, the reference temperature and reference rate depend on the type of polymer consisting the sample, the initial kinetic characteristics was classified into 2 categories of about $270^{\circ}C$ and $420^{\circ}C$ of reference temperature for the tested synthetic materials. The present study showed the pyrolysis parameters of reference temperature and reference rate proposed by Lyon to evaluate the pre-exponential factor and activation energy. The present study can contribute to improve the reliability of computational fire analysis and enhance the understanding of fire propagation phenomena based on the thermal properties study of material.

• Polymer(Korea)
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• v.39 no.2
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• pp.210-218
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• 2015

The reaction behavior of rigid polyurethane foams were studied on the effects of gelling catalysts of amine type, such as; dimethylcyclohexyl amine (DMCHA) and of potassium type, such as; potassium octoate (PO). Rigid polyurethane foams were provided with polymeric 4,4'-diphenylmethane diisocyanate, polyester polyol, silicone surfactant, blowing agent and a few gelling catalysts. As the contents of catalyst, DMCHA increased from 0 to 2.0 g, the reaction time decreased from ca. 330 to ca. 35 sec and due to the exothermic reaction, the maximum temperature increased from ca. 217 to ca. $234^{\circ}C$, respectively. As the contents of PO increased from 0 to 2.5 g, the reaction time decreased from ca. 79 to ca. 38 sec and the maximum temperature increased from ca. 182 to ca. $271^{\circ}C$, respectively. The kinetic parameters were calculated and the conversions were based on the temperature rising method of adiabatic process. As the content of DMCHA increased, the rate constant $k_0$ increased. But in the case of PO catalyst, $k_0$ did hardly depend upon its amount, and showed us similar reaction rate constants.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.355-374
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• 2022

Soil conditioning improves the performance of EPB (earth pressure balance) shield TBMs (tunnel boring machines) by reducing shear strength, enhancing workability of the excavated soil, and supporting the tunnel face during EPB tunnelling. The mechanical and rheological behavior of the excavated muck mixed with additives should be properly evaluated to determine the optimal additive injection condition corresponding to each ground type. In this study, the laboratory pressurized vane test apparatus equipped with a vane-shaped rheometer was developed to reproduce the pressurized condition in the TBM chamber and quantitively evaluate rheological properties of the soil specimens. A series of the pressurized vane tests were performed for an artificial sand soil by changing foam injection ratio (FIR) and polymer injection ratio (PIR), which are the injection parameters of the foam and the polymer, respectively. In addition, the workability of the conditioned soil was evaluated through the slump test. The peak and yield stresses of the conditioned soil with respect to the injection parameters were evaluated through the rheogram, which was derived from the measured torque data in the pressurized vane test. As FIR increased or PIR decreased, the workability of the conditioned soil increased, and the maximum torque, peak stress, and yield stress decreased. The peak stress and yield stress of the specimen from the laboratory pressurized vane test correspond to the workability evaluated by the slump tests, which implies the applicability of the proposed test for evaluating the rheological properties of excavated soil.