• Applied Chemistry for Engineering
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• v.22 no.5
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• pp.467-472
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• 2011

This study investigated illite/polypropylene (PP) composite filament formation via melt-spinning and evaluated their physical properties to prepare functional fibers using natural materials. When composite filaments were formed, the composite filaments exhibited smaller fiber diameters compared to that of neat PP filament because of the lubricant effect of illite induced by its layered structure. Moreover, fluorination effect increased interfacial affinity and dispersion in the polymer, resulting in smaller diameter of fluorinated illite/PP composite filament, which was 2/3 of the neat PP filament diameter. Addition of raw and fluorinated illite improved thermal stability of illite/PP composite filament. Raw illite/PP composite filament cannot be used for a practical application, because it broke during drawing process, whereas the fluorinated illite/PP composite filament can be used for a practical application, because it exhibited similar tensile strength of the neat PP filament and 50% increased modulus. Even with improved illite/PP interfacial affinity and illite dispersion in the polymer, illite/PP composite filament formed microcomposite, because non-expandable illite had strongly bound layers, resulting in only a little illite exfoliation and PP intercalation into illite.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.173-181
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• 2021

Reinforced concrete structures are exposed to various environments, resulting in reinforcement corrosion due to moisture and ions penetration. Reinforced concrete corrosion causes a decrease in the durability performance of reinforced concrete structures. One solution to mitigate such issues is using FRP rebars, which offer several advantages such as high tensile strength, corrosion resistance, and light-weight than conventional rebars, in reinforced concrete instead of conventional steel rebars. The FRP rebar used should be examined at the limit state because FRP reinforced concrete has linear behavior until its fracture and can generate excessive deflection due to the low elastic modulus. It should be considered while designing FRP reinforced concrete for flexure. In the ultimate limit state, the flexural strength of FRP reinforced concrete as per ACI 440.1R is significantly lower than the flexural strength by applying both the environmental reduction and strength reduction factors accounting for the material uncertainty of FRP rebar. Therefore, in this study, the experimental results were compared with the deflection of the proposed effective moment of inertia referring to the local and international standards. The experimental results of GFRP and BFRP reinforced concrete were compared with the flexural strength as determined by ACI 440.1R and Fib bulletin 40. The flexural strength obtained by the experimental results was more similar to that obtained by Fib bulletin 40 than ACI 440.1R. The flexural strength of ACI 440.1R was conservatively evaluated in the tension-controlled section.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.553-564
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• 2022

Concrete is a representative composite material that shows excellent performance in the construction field. However, it is a brittle and nonhomogeneous material and exhibits weak behavior against bending and tensile forces. To compensate for such weakens, fiber reinforcement has been utilized, and steel fiber has been recognized as one of the best material for such purpose. However, steel fiber can seriously affect the durability of concrete exposed to the marine environment due to the corrosion caused by chlorine ions. This study intended to evaluate the mechanical performance of steel fiber reinforce concrete during and after repeated wet/dry cycles in salt solution. According to the experimental results, there was no reduction in the relative dynamic modulus of concrete during the repeated wet/dry cycles in salt solution for 37 weeks. Flexural strength was not decreased after completion of repeated wet/dry cycles in salt solution. There was no sign of corrosion in steel fibers after visual observation of fractured surface. However, the flexural toughness was decreased, and this is because about half of the concrete specimen showed failure before reaching the maximum displacement of 3 mm. Although repeated wet/dry cycles in salt solution did not cause cracks in concrete through corrosion of steel fibers, specific attention is required because it can reduce flexural toughness of steel fiber reinforced concrete.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.28 no.2
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• pp.97-104
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• 2022

This study investigated the characteristics for the optimal concentration of addition of the mixing solution through the corn husk pulverization and surface modification of biomass byproducts adding mixed solution between ESO and silane. And surveyed the specific surface area, water absorption, particle size and physical properties of bio- degradable plastic sheet. The specific surface area was 1.105 m²/g, particle size was the highest at 19 ㎛. The impact strength, tensile strength, elongation and hardness of plastic sheet showed the highest at the 1% concentration among the mixing solutions. The flexural strength and modulus was high according to the increasing the mixing solution. The results above showed that it was the best the adding 1% of mixed solution after silane treatment of corn husks for its manufacture as a bio-based plastic sheet.

• Composites Research
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• v.20 no.1
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• pp.23-31
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• 2007

In order to improve the mechanical properties of jute fiber/polypropylene(PP) composites, the property change with the addition of a coupling agent, maleic anhydride polypropylene(MAPP) was examined experimentally. The maleated coupler acts as an intermediate to chemically connect the polar nature of the fiber and non-polar nature of the polyolefin polymer resin. Furthermore, the decrease in viscosity of the resin which results from the melting point reduction by the MAPP, leads to an increase of contact area with the fiber interface. We discussed the improvement of the PP composite blend of the maleated coupler with the 80mm jute long fiber mat in conjunction with the change of physical parameters in the thermoplastic resin. We confirmed the extent of contribution to the mechanical physical enhancement by using the following parameters: melting flow index(MI) and viscosity, contact angle, thickness of the composite, interfacial shear strength and morphology observation etc. Especially it was observed that the MI and viscosity, MAPP mixture had a very strong relationship with the tensile and flexural strength and modulus, and interfacial shear strength(IFSS).

• Tunnel and Underground Space
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• v.33 no.3
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• pp.109-125
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• 2023

Disposal repository for high-level radioactive waste secures its safety by means of engineered and natural barriers. The performance of these barriers should be tested and verified through various aspects in terms of short and/or long-term. KAERI has been conducting various in-situ demonstrations in KURT (KAERI Underground Research Tunnel). After completing previous experiment, a conceptual design of an improved in-situ experiment, i.e. K-COIN (KURT experiment of THMC COupled and INteraction), was established and detailed planning for the experiment is underway. Preliminary characterizations were conducted in KURT for siting a K-COIN test site. 15 boreholes with a depth of about 20 m were drilled in three research galleries in KURT and intact rock specimens were prepared for laboratory tests. Using the specimens, physical measurements, uniaxial compression, indirect tension, and triaxial compression tests were conducted. As a result, specific gravity, porosity, elastic wave velocities, uniaxial compressive strength, Young's modulus, Poisson's ratio, Brazilian tensile strength, cohesion, and internal friction angle were estimated. Statistical analyses revealed that there did not exist meaningful differences in intact rock properties according to the drilled sites and the depth. Judging from the uniaxial compressive strength, which is one of the most important properties, all the specimens were classified as very strong rock so that mechanical safety was secured in all the regions.

• Elastomers and Composites
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• v.37 no.4
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• pp.244-257
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• 2002

A thermotropic liquid crystalline polymer(TLCP) which has flexible butylene/hexylene spacers in the main chain and a triad aromatic ester type mesogenic unit containing a naphthyl group was prepared by solution polycondensation. The in-situ composites based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystalline polymer(TLCP) were prepared and melt spun at different TLCP contents and different draw ratios to produce monofilaments. Blends of the TLCP with PEN were investigated in terms of thermal, mechanical properties and morphology. The TLCP synthesized showed nematic mesophasic behavior and its transition temperature to isotropic melt from mesophase was 249℃. The blends showed well dispersed TLCP phases in the PEN matrix without macroscopic phase separation. Inclusion of TLCP in the blends decreased the cold crystallization temperature of PEN in the blend, therefore, the TLCP acts as a nucleating agent in the blend and showed good interfacial adhesion between the dispersed LCP phases and PEN matrix with domain sizes 40~50 nm in diameter and well developed fibrillation in the monofilaments. The TLCP acted effectively as a reinforcing material in the PEN matrix at the 10wt% level, it led to an increase of initial modulus up to 270% and tensile strength by 235%, while the elongation rate increasing with higher draw ratios.

• Journal of the Korean Chemical Society
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• v.67 no.6
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• pp.420-428
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• 2023

Crosslinking was introduced into vinylized-mesoporous silica and recycled polyethylene. By introducing a vinyl group into the mesoporous silica, it becomes a material capable of inducing cross-linking with non-polar polyethylene. By synthesizing vinylized-mesoporous silica and inducing crosslinking with recycled polyethylene, a recycled polyethylene composite with improved physical properties than existing recycled polyethylene was synthesized. In addition, even when a small amount is added according to the grade of recycled polyethylene using vinylized-mesoporous silica, the crosslinking reaction proceeds and all physical properties are improved. Four types of vinylized-mesoporous silica were synthesized, and the shape, microstructure, and functional groups were analyzed by TEM, BET, FT-IR, and XRD. Using vinylized-mesoporous silica, three types of compounds were blended by crosslinking reaction with recycled polyethylene. In order to confirm the presence or absence of crosslinking, analysis was performed using XPS and FT-IR, and physical properties such as tensile strength, elongation, flexural strength, and flexural modulus were confirmed using a universal testing machine. As a result, by applying vinylized-mesoporous silica to recycled polyethylene in various grades, the weak physical properties of existing recycled polyethylene were overcome. By applying the vinylized-mesoporous silica, recycled polyethylene composite material that overcomes the weak physical properties to the normal polyethylene, it shows the optimal physical property index that can be used commercially. Therefore, it is expected that it can potentially increase the use of recycled polyethylene and recycle resources.

• Food Science and Preservation
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• v.31 no.1
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• pp.126-137
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• 2024

In this study, zinc oxide nanoparticles (ZnONPs) were synthesized using three distinct zinc salts: zinc acetate, zinc chloride, and zinc nitrate. These ZnONPs were subsequently utilized in the fabrication of carrageenan-ZnONPs (Car-ZnONPs) composite films. The study assessed influence of the various ZnONPs on the morphological, water vapor barrier, color, optical, and antimicrobial properties of the Car-ZnONPs composite films. The surface morphology and UV-blocking attributes of the composite films were affected by the type of ZnONPs used, but their surface color, transparency, and chemical structure remained unaltered. The composite film's thickness and elongation at break (EB) significantly increased, while the tensile strength significantly decreased. In contrast, film's elastic modulus (EM) and water vapor permeability coefficient (WVP) showed no significant difference. All the composite films with added ZnONPs demonstrated potent antibacterial activity against Escherichia coli O157:H7 and Listeria monocytogenes . Among the carrageenan-based composite films, Car-ZnONPs^ZC showed the highest antibacterial and UV-blocking properties, and its elongation at break was significantly higher than that of the pure carrageenan films. This suggests that ZnONPs composite films have the potential to be used as an active packaging film, preserve the safety of the packaged food and extend shelf life.

• Composites Research
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• v.12 no.4
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• pp.71-78
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with diaminodiphenyl methane (DDM), diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work, the effect of aromatic amine curing agents. In contrast, the results show that the DGEBA/DDS cure system having the sulfone structure between the benzene rings had higher values in the conversion of epoxide, density, shrinkage (%), glass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBA/DDM cure system having methylene structure between the benzene rings, whereas the DGEBA/DDM cure system presented higher values in the maximum exothermic temperature, thermal expansion coefficient, and thermal stability. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property and stem from the effect of the conversion ratio of epoxide group. The result of fractography shows that the each grain size of the DDM/DGEBA system with feather-like structure is larger than that of the DDS/DGEBA system.