• Elastomers and Composites
• /
• v.37 no.3
• /
• pp.159-169
• /
• 2002

The improvement of flame retardancy of the foams based on NBR/GTR compounds was conducted by formulating various materials i.e. NBR, GTR, inorganic and phosphorus containing flame retardants, foaming agent, cross-linking agent and activator. The foaming properties, morphology, smoke density and flame retardancy of the specimens were investigated using SEM, LOI tester, smoke density control system and cone calorimeter. The phosphorus containing flame retardant reduces heat release rate, increases the limiting oxygen index and a char formation. The inorganic flame retardant increases the limiting oxygen index and reduces heat release rate with an increased CO yield by char formation, and smoke suppressing effect. The formed char seemed to intercept the oxygen transport and heat transfer into the core area. When the composition ratios of the compounds of NBR/GTR were $100{\sim}80/0{\sim}20 wt.%$, and the ratios of the rubbers/flame retardants were $1/1.55{\sim}3.60 wt.%$, we could developed foams with low heat release rate, high limiting oxygen index($28.0{\sim}39.3$), closed or semi-closed cell of uniformity and reasonable expandability($225{\sim}250 %$).

• Membrane Journal
• /
• v.32 no.6
• /
• pp.427-441
• /
• 2022

Polymer electrolyte membrane (PEM) serving as a separator that can prevent the permeation of unreacted fuels as well as an electrolyte that selectively transports protons from the anode to the cathode has been considered a key component of polymer electrolyte membrane fuel cell (PEMFC). The perfluorinated sulfonic acid-based PEMs, represented by Nafion®, have been commercialized in PEMFC systems due to their high proton conductivity and chemical stability. Nevertheless, these PEMs have several inherent drawbacks including high manufacturing costs by the complex synthetic processes and environmental problems caused by producing the toxic gases. Although numerous studies are underway to address these drawbacks including the development of sulfonated hydrocarbon polymer-based PEMs (SHP-PEMs), which can easily control the polymer structures, further improvement of PEM performances and durability is necessary for practical PEMFC applications. Therefore, this study focused on the various strategies for the development of SHP-PEMs with outstanding performance and durability by 1) introducing cross-linked structures, 2) incorporating organic/inorganic composites, and 3) fabricating reinforced-composite membranes using porous substrates.

• Polymer(Korea)
• /
• v.39 no.3
• /
• pp.382-387
• /
• 2015

The dispersion of calcium carbonate ($CaCO_3$) in polypropylene (PP) and the effect of $CaCO_3$ size on the crystallinity of PP were studied. Polymer composite usually suffers from the brittleness when reinforced with inorganic fillers. The problem is generally related to the size and dispersion of fillers. First, the dispersion was studied for the nanosize $CaCO_3$ with 15~40 nm average diameter. To enhance the dispersibility in PP, the surface of the $CaCO_3$ was treated with sodium lignosulfonate (SLS). $CaCO_3$/PP composites were prepared via melt compounding. The $CaCO_3$ coated with more than 3 wt% SLS was uniformly distributed within the PP matrix, while the uncoated $CaCO_3$ formed aggregated structures in the PP. Even with 30 wt%, the SLS-$CaCO_3$ was well dispersed in the PP matrix. Also, the transition enthalpy of $CaCO_3$/PP increased and the full-width of half maximum of the crystallization peak decreased regardless of SLS coating and size of $CaCO_3$. However, the crystallinity of PP was more influenced by nano $CaCO_3$. These results imply that the nano $CaCO_3$ coated with SLS may reduce the brittleness of polymer composites.

• Korean Chemical Engineering Research
• /
• v.47 no.3
• /
• pp.332-336
• /
• 2009

When NCAs(non-conductive adhesives) are used for adhesion of micro-electronic devices, they often show problems such as delamination and cracking, due to the differences of CTE(coefficients of thermal expansion) between NCAs and substrates. Additions of inorganic particles or flexibilizers have been performed to solve those problems. The effects of silica addition on thermal/mechanical properties of amino modified siloxane(AMS)/silica/epoxy-nanocomposites were examined. The silica was treated by 3-glycidoxypropyltrimethoxysilane(GPTMS) for better compatibility between silica and epoxy matrix. AMS/silica/epoxy-nanocomposites filled with various amounts of AMS(1 and 3 phr) and various amounts of silica(3, 5 and 7 phr) were prepared. And Tg, moduli and CTE of nanocomposites were analyzed. Tg of AMS/Aerosil(non-modified silica)/epoxy-nanocomposites decreased from 125 to $118^{\circ}C$ with increasing Aerosil contents and moduli increased from 2,225 to 2,523 MPa with increasing Aerosil contents. Tg of AMS/M-silica (modified silica)/epoxy-nanocomposites decreased from 124 to $120^{\circ}C$ with increasing M-silica contents and moduli increased from 1,981 to 2,743 MPa with increasing M-silica contents. CTE of AMS/Aerosil/epoxy-nanocomposites and AMS/M-silica/epoxy-nanocomposites showed decreasing tendency regardless of the surface treatments.

• Elastomers and Composites
• /
• v.43 no.4
• /
• pp.230-240
• /
• 2008

In order to synthesize polymer particle containing inorganic material, styrene and nbutylmetacrylate were copolymerized with alumina by dispersion polymerization. The ratio in weight of styrene to n-butyl methacrylate was 3:1. Poly(N-vinyl pyrrolidon) and 2,2'-azobis(isobutyronitrile) were added as stabilizer and as initiator, respectively. The change of particle size was investigated with concentration of initiator, the type of medium, the mixed solubility parameter (${\delta}_{mix}$) of medium, and coupling agent. The enhancement in concentration of initiator resulted in slight increase of particle size. The increase of polarizability in medium also yielded the increase of particle size. In case of changing the ratio of isopropanol to distilled water, we could find relationship of $[{\delta}_{mix}]^{-4.01}\;{\propto}$ particle size and $[{\delta}_{mix}]^{-0.83}\;{\propto}$ particle size distribution(PSD). The type and the concentration of coupling agent showed no effect on the particle size and PSD.

• Journal of Microbiology and Biotechnology
• /
• v.22 no.11
• /
• pp.1568-1574
• /
• 2012

Microbiological calcium carbonate precipitation (MCCP) has been investigated for its ability to improve the durability of cement mortar. However, very few strains have been applied to crack remediation and strengthening of cementitious materials. In this study, we report the biodeposition of Bacillus subtilis 168 and its ability to enhance the durability of cement material. B. subtilis 168 was applied to the surface of cement specimens. The results showed a new layer of deposited organic-inorganic composites on the surface of the cement paste. In addition, the water permeability of the cement paste treated with B. subtilis 168 was lower than that of non-treated specimens. Furthermore, artificial cracks in the cement paste were completely remediated by the biodeposition of B. subtilis 168. The compressive strength of cement mortar treated with B. subtilis 168 increased by about 19.5% when compared with samples completed with only B4 medium. Taken together, these findings suggest that the biodeposition of B. subtilis 168 could be used as a sealing and coating agent to improve the strength and water resistance of concrete. This is the first paper to report the application of Bacillus subtilis 168 for its ability to improve the durability of cement mortar through calcium carbonate precipitation.

• Journal of Electrochemical Science and Technology
• /
• v.8 no.3
• /
• pp.183-196
• /
• 2017

The research efforts directed at advancing water electrolysis technology continue to intensify together with the increasing interest in hydrogen as an alternative source of energy to fossil fuels. Among the various water electrolysis systems reported to date, systems employing a solid polymer electrolyte membrane are known to display both improved safety and efficiency as a result of enhanced separation of products: hydrogen and oxygen. Conducting water electrolysis in an alkaline medium lowers the system cost by allowing non-platinum group metals to be used as catalysts for the complex multi-electron transfer reactions involved in water electrolysis, namely the hydrogen and oxygen evolution reactions (HER and OER, respectively). We briefly review the anion exchange membranes (AEMs) and electrocatalysts developed and applied thus far in alkaline AEM water electrolysis (AEMWE) devices. Testing the developed components in AEMWE cells is a key step in maximizing the device performance since cell performance depends strongly on the structure of the electrodes containing the HER and OER catalysts and the polymer membrane under specific cell operating conditions. In this review, we discuss the properties of reported AEMs that have been used to fabricate membrane-electrode assemblies for AEMWE cells, including membranes based on polysulfone, poly(2,6-dimethyl-p-phylene) oxide, polybenzimidazole, and inorganic composite materials. The activities and stabilities of tertiary metal oxides, metal carbon composites, and ultra-low Pt-loading electrodes toward OER and HER in AEMWE cells are also described.

• Composites Research
• /
• v.32 no.6
• /
• pp.388-394
• /
• 2019

Inherited the excellent electrical and mechanical properties based on the low dimensional structure of graphene, three-dimensional graphene nanostructures have gathered great attention as electrochemical energy storage electrodes owing to their high porosity and large specific surface area. Also, having the catecholamine structure, dopamine has been regarded as a multifunctional material to possess high affinity to various organic/inorganic materials and to modify a hydrophobic surface to a hydrophilic one. In this work, through coating dopamine on the three-dimensional graphene nanostructure, we tried to increase the specific capacitance by enhancing the wettability with electrolyte and to improve the mechanical compressive property by strengthening the nano-architecture. As a result, the dopamine-coated nanostructure exhibited significant improvement on the specific capacitance (51.5% increase) and compressive stress (59.6% increase).

• Elastomers and Composites
• /
• v.52 no.1
• /
• pp.22-26
• /
• 2017

The thermal conductivity and the adhesive properties were measured, after synthesis of thermal conductive composite which was obtained as a result of mixing alumina or graphite with acrylic adhesive synthesized by UV polymerization. The adhesive properties of the composite were evaluated measuring the peel strength at 180 degrees, the retention, and the initial tack;the thermal conductivity was estimated using laser flash analysis. As the filler contents increased, a decrease in peel strength and initial tack and an increase in retention and thermal conductivity were observed. When compared to alumina, the adhesion of graphite showed a dramatic decrease, whereas the thermal conductivity was further enhanced. It was found out that the small size of graphite increased the mechanical interlocking between the polymer and the filler, and it was easier for graphite to come into contact with other graphite in the matrix.

• Applied Chemistry for Engineering
• /
• v.23 no.3
• /
• pp.271-278
• /
• 2012

In this work, we have prepared the nanocomposite by the reaction of mica and zinc oxide, and investigated the application of nanocomposite to UV protecting creams. Mica treated with 3-aminopropyltrimethoxysilane (APTMS) reacted with 1,4-phenylenediisothiocyanate (PDC) to give -N=C=S functionalized surface, which was further reacted with zinc oxides coated with APTMS to give mica-zinc oxide nanocomposites. The composites were characterized by EA, EDS, TGA, SEM, zeta potential measurement, powder XRD, and DRS UV/Vis analyses. Finally, we measured transmittances of ultraviolet protection creams manufactured by using mica composite covered with zinc oxides in the range of 280~400 nm. The nanocomposites developed in this work might be applicable as inorganic hybrid materials for UV protecting creams.