• 펄프종이기술
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• 제29권3호
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• pp.17-25
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• 1997

Natural water-soluble polymers such as starch, casein and carboxy methyl cellulose(CMC) have been limited in their uses. However, the proper water retention of coating colors can not be obtained without addition of these polymers. Furthermore, the coating runnability and the physical properties of coated paper were not also satisfied. Therefore, the objective of this study was to synthesize the water retention and flow modifiers which can improve the water retention and flow properties of coating colors. We have measured physical properties of flow modifiers and coating colors which included flow modifiers. The viscosity of flow modifiers was very low at acid pH, and rapidly increased at about pH 7, and gradually reached to equilibrium at alkali pH. Such an increase comes from the molecular weight of flow modifiers and the amount of acrylic and methacrylic acids. The viscosity of coating color containing the flow modifiers was lower than that containing CMC. However, both of them had little difference in water retention. The water-phase viscosity of synthetic modifier containing coating color was either higher or similar compared to that of CMC containing coating color. The high shear viscosity of coating colors was low. Therefore, it can be concluded that the synthetic flow modifiers are very useful for improvement of flow properties and water retentions.

• Macromolecular Research
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• 제15권1호
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• pp.10-16
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• 2007

In this work, we prepared epoxy/BMI composites by using N,N'-bismaleimide-4,4'-diphenylmethane (BMI), epoxy resin (diglycidyl ether of bisphenol-A (DGEBA)), and 4,4'-diamino diphenyl methane (DDM). The thermal properties and water sorption behaviors of the epoxy and BMI composites were investigated. For the epoxy/BMI composites, the glass transition and decomposition temperatures both increased with increasing BMI addition, which indicates the effect of BMI addition on improved thermal stability. The water sorption behaviors were gravi-metrically measured as a function of humidity, temperature, and composition. The diffusion coefficient and water uptake decreased and the activation energy for water diffusion increased with increasing BMI content, indicating that the water sorption in epoxy resin, which causes reliability problems in electronic devices, can be diminished by BMI addition. The water sorption behaviors in the epoxy/BMI composites were interpreted in terms of their chemical and morphological structures.

• 한국주조공학회지
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• 제4권2호
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• pp.89-95
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• 1984

A Study on the Mechanical Properties of Molding Sand with Various Water/Clay Ratio A standard sample of molding sand was prepared by adding a various amount of bentonite, which has water/clay ratio from 0.4 to 0.6, into artificial sand, Hanyoung #6. The results obtained by measuring the room temperature properties of green mold are as follows. 1. This compressive strength of green molds which have 4% and 10% of bentonite decreased with increasing water/clay ratio, but the maximum strengths of 4.3 (psi) and 7.2 (psi) were observed in the samples with 6%, 8% bentonite respectively when the water/clay is 0.45. 2. The optimum water/clay ratio for strength and permeability increased from 0.4 to 0.5 with increasing clay. 3. The green compressive strength was proportional to the hardness. 4. Deformation increased with increasing water/clay ratio. 5. Flowability decreased with increasing water/clay ratio and clay content in molding sand.

• Membrane and Water Treatment
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• 제13권6호
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• pp.259-290
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• 2022

Carbon nanotubes (CNTs), due to their excellent physical, chemical and mechanical properties and their ability to prepare new membranes with attractive properties, have found applications in water and wastewater technology. CNT functionalization, which involves the introduction of different types of functional groups into pure CNTs, improves the capabilities of CNT membranes for water and wastewater treatment. It turns out that CNT-based membranes have many advantages, including enhanced water permeability, high selectivity and anti-fouling properties. However, their full-scale application is still limited by their high cost. With their tremendous separation efficiency, low biofouling potential and ultra-high water flux, CNT membranes have the potential to be a leading technology in water treatment in the future, especially in desalination.

• Geomechanics and Engineering
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• 제36권2호
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• pp.145-156
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• 2024

The mechanical properties of the concrete-frozen soil interface play a significant role in the stability and service performance of construction projects in cold regions. Current research mainly focuses on the precast concrete-frozen soil interface, with limited consideration for the more realistic cast-in-place concrete-frozen soil interface. The two construction methods result in completely different contact surface morphologies and exhibit significant differences in mechanical properties. Therefore, this study selects silty clay as the research object and conducts direct shear tests on the concrete-frozen soil interface under conditions of initial water content ranging from 12% to 24%, normal stress from 50 kPa to 300 kPa, and freezing temperature of -3℃. The results indicate that (1) both interface shear stress-displacement curves can be divided into three stages: rapid growth of shear stress, softening of shear stress after peak, and residual stability; (2) the peak strength of both interfaces increases initially and then decreases with an increase in water content, while residual strength is relatively less affected by water content; (3) peak strength and residual strength are linearly positively correlated with normal stress, and the strength of ice bonding is less affected by normal stress; (4) the mechanical properties of the cast-in-place concrete-frozen soil interface are significantly better than those of the precast concrete-frozen soil interface. However, when the water content is high, the former's mechanical performance deteriorates much more than the latter, leading to severe strength loss. Therefore, in practical engineering, cast-in-place concrete construction is preferred in cases of higher negative temperatures and lower water content, while precast concrete construction is considered in cases of lower negative temperatures and higher water content. This study provides reference for the construction of frozen soil-structure interface in cold regions and basic data support for improving the stability and service performance of cold region engineering.

• 대한금속재료학회지
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• 제50권10호
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• pp.729-734
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• 2012

This study investigated the effect of water absorption on the tensile properties of carbon-glass/epoxy hybrid composites at room temperature and $-30^{\circ}C$. To investigate the effect of the position of glass fabric in the hybrid composite on the tensile properties, the stacking pattern of the fiber fabrics for reinforcing was created in three different ways: (a) glass fabrics sandwiched between carbon fabrics, (b) carbon fabrics sandwiched between glass fabrics and (c) alternative layers of carbon and glass fabrics. They were manufactured by a vacuum-assisted resin transfer molding (VARTM) process. The results showed that there was surprisingly little difference in tensile strength at the two different temperatures with dry and wet conditions. However, the water absorption into the hybrid system affected the tensile properties of the hybrid composites at RT and $-30^{\circ}C$. When the glass fabrics were at the outermost layers, the hybrid composite had the lowest tensile properties. This is attributed to the fact that the composite had a relatively high water absorption rate.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.199-202
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• 1998

In examining application of polymer as electrical insulators, it is very important to perform accelerated aging test substituted the process which polymer insulator is degraded for long-time by the process of short-time. The purpose of this paper is to examine the properties of water degradation which affect on the efficiency of epoxy insulator. To do this, the surface properties on epoxy insulating material have been investigated after long-time accelerated degradation in boiling water condition. The experimental results showed the contact angle and surface resistivity after treatment to decrease the sample of water treatment. In dielectric properties, dielectric constant was increased by the aging development with water treatments.

• 대한기계학회논문집A
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• 제30권7호
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• pp.779-786
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• 2006

Woven sisal textile reinforced composites were manufactured to evaluate fracture toughness, and tensile test. All specimens were immersed in water five times. All specimens are immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surface were investigated to study the failure mechanism and fiber/matrix interfacial adhesion. It is shows that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples observed poor mechanical properties such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrate a decrease in inclination with increasing cyclic times of wetting and drying fur the epoxy and vinyl-ester.

• 한국의류학회지
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• 제41권3호
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• pp.517-526
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• 2017

The biodegradation and water absorption properties of lignin/poly(vinyl alcohol) (PVA) nanofibrous webs are investigated. Lignin/PVA nanofibrous webs containing 0, 50, and 85wt% of lignin were prepared via an electrospinning process to observe the effect of the lignin concentration on the biodegradability and water absorption properties of lignin/PVA nanofibrous webs. The morphology of the materials was examined by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). To understand the wetting behavior and hydrophilic nature of the electrospun lignin/PVA nanofibrous webs, the water absorbency, contact angle, and water uptake were examined. The enzymatic degradation of lignin/PVA nanofibrous webs was investigated using laccase by measuring total organic carbon (TOC) concentration over a course of 50 days. Water drops were absorbed immediately into all of the specimens. The water uptake of lignin/PVA nanofibrous webs increased as the amount of PVA in the lignin/PVA hybrid webs increased. The enzymatic degradation experiment indicated that the inherent biodegradability of lignin was retained after its transformation into nanofibers. Our findings imply that blending these two types of polymers is promising because it can lead to the development of a new range of multifunctional materials such as antimicrobial absorbent nanotextiles based on sustainable biopolymers.

• 한국환경보건학회지
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• 제14권1호
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• pp.33-38
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• 1988

Natural mineral water is generally quite different from ordinary drinking water due to its original nature and various properties. The complexity of natural mineral water requires, therefore, not only to identify its nature and proper characteristics, but also to classify them by a reasonable scientific basis of comparison. The study was concentrated on a possible classification technique to natural mineral waters by their constitutions and physico-ehemical properties. The classification was carried out by the computation of such numerical parameters as ionic equivalent percentage, electrolytic conductance or mobility, ionic molecular weight, molecular concentration, equivalent conductivity and degree of ionization in consideration of the determinative criteria as follows -particular single element or molecule -major components of natural waters as bicarbonate, sulphate, chloride,caloride, calcium, magnesium, and sodium -moleculat concentration related to blood osmotic pressure -water temperature at emergence from spring -contents of free carbon dioxide (CO2) -pH value of water -total dissolved solids or salts (NaCl) The results obtained proved out to be clearly distinguhhable from ordinary drinking water as far as concern natural mineral water as an example on the subject -simple water -bicarbonate-predominating water -cold spring -carbonated-non gaseous water -weak alkaline water -non saline water Putting these various results together, the sample turned out to be a kind of natural mineral water that can be used as a drinking water if microbiologically safe.