• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.280-286
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• 2015

Two series of unsymmetric dimesogenic compounds containing a butylene or pentamethylene group as the flexible spacer were synthesized and their thermal and mesomorphic properties were studied. Mesogenic groups of the synthesized compounds consisted of a cholesteryl and an azobenzene group with lateral substituent. Chemical structures and mesomorphic properties of the synthesized compounds were investigated by FT-IR, $^1H$-NMR, differential scanning calorimeter (DSC), and polarizing optical microscope (POM). All synthesized compounds, apart from $D5-OCH_3$, showed enantiotropic liquid crystal phases. Compounds having an even number of carbon atoms in the flexible spacer exhibited wide mesophase temperature ranges and high isotropic transition temperatures. Regarding the effect of lateral substituents, compounds with bulky substituents exhibited decreased mesophase temperature ranges and isotropic transition temperatures, while those with polar substituents showed the increased thermal stability of the smectic phase.

• Polymer(Korea)
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• v.39 no.3
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• pp.426-432
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• 2015

Poly(ether sulfone) (PES) embedded diglycidylether of bisphenol-A (DGEBA) epoxy composites were fabricated for improving its mechanical properties and thermal stability. The mechanical properties such as tensile, flexural and impact strength of the composites changed significantly with the introduction of PES. The value of the fracture toughness of this composite also was increased remarkably about 24%. Thermal stability of PES/epoxy composites also improved 12%, which was calculated with integral procedural decomposition temperature (IPDT). From the differential scanning calorimeter (DSC) result, the curing temperature and curing heat decreased according to the increase of PES contents. These were attributed to the good distribution and the formation of the semi-interpenetrating polymer networks (semi-IPNs) composed of the epoxy network and linear PES.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.629-637
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• 2017

Severe dust explosions occurred frequently in food processing industries and explosion damage increase by flame propagation in pipes or plants. However there are few fire explosion data available due to various powder characteristics. We investigated the characteristics of ignition and explosion on sugar, cornstarch and flour dust with high frequency accidents and high social demand. The measurements showed the median diameter of 27.56, 14.76, $138.5{\mu}m$ and ignition temperature has been investigated using by thermo-gravimetric analysis (TGA) and differential scanning calorimeter (DSC). The maximum explosion pressure ($P_m$) and dust explosion index ($K_{st}$) of sugar, cornstarch and flour are 7.6, 7.6, 6.1 bar and 153, 133, 61 [$m{\cdot}bar/s$], respectively. The flame propagation time in duct was calculated in order to evaluate the damage increase due to flame propagation during dust explosion. The explosion hazard increase due to flame propagation was higher in the order of sugar, flour and cornstarch dust.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.445-451
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• 2015

Semi-flexible liquid crystalline polymers containing a mesogenic group and an octamethylene flexible spacer in the main chain were synthesized by solution polycondensation. The mesogenic group in the polymer consists of four aromatic rings connected by ester and ketone, ether, sulfide, methylene, sulfone, or isopropylidene linkage groups. This paper discusses effects of the central linker of the mesogenic group on polymer properties. The structures and properties of synthesized polymers were investigated by $^1H$-NMR, FT-IR, differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), X-ray diffractometer (XRD), and polarizing optical microscope (POM). Polymers having bent linkage groups exhibited low thermal transition temperatures, narrow mesophase temperature ranges, low liquid crystallinity, and good solubilities in organic solvents, while those having bulky linkage groups were amorphous and exhibited high glass transition temperatures.

• Composites Research
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• v.24 no.2
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• pp.30-37
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• 2011

Analysis of wettability between epoxy resin and glass fabric was studied. The mixing ratios of epoxy resin and anhydride hardener were varied as 1:0.5, l:l and l:1.2. Catalyst content was fixed as 0.1wt% of the mixed resin. A curing analysis by differential scanning calorimeter(DSC) showed a possible impregnation of the mixed resin at the room temperature. An effective contact angle of the mixed epoxy resin drop onto the glass fabric being preset on a flat glass plate was measured as a function of time. The wet area of the epoxy resin drop was also measured. Behaviors of the contact angle, the droplet height, the neat wet area and the coefficient of wettability were used to evaluate the wettability of the epoxy resin onto the glass fabric. It was concluded that the equivalent ratio of 1: 1.2 was the most suitable for the wettability.

• Fire Science and Engineering
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• v.14 no.2
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• pp.7-13
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• 2000

We had investigated thermal stability, Ignition temperature and fire gas for polyurethane foams used for manikin, cushion and interior finishing material. Decomposition of polyurethane foams with temperature was investigated using a DSC and the weight loss with temperature increase using a TGA in order to find the thermal hazard of polyurethane foams, and the ignition temperature of polyurethane foams according to species. We studied constant temperature among ignition temperature measuring methods. In addition, noxious gases for polyurethane foams according to combustion condition were analyzed using gas analyzer and GASTEC. As results, initial decomposition temperature of polyurethane foam used for interior finishing material was lower than those for manikin and cushion, and exothermic energy was higher. Ignition temperature of polyurethane foam of interior finishing material was $420^{\circ}$. All of combustion forms at $427^{\circ}$ and under were smoldering combustion, and it was combustion at $500^{\circ}$. As furnace temperature was increased, concentration of noxious gases such as carbon oxide, carbon dioxide, and hydrogen cyanide was increased. And nitrogen oxide at combustion condition($500^{\circ}$) was over 10 ppm.

• Membrane Journal
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• v.24 no.2
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• pp.100-106
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• 2014

In this work, soluble polyimides were synthesized and characterized from 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) and two diamines such as 4,4'-diaminodiphenylether (ODA), 1,4-phenylenediamine (p-PDA). Their thermal properties were analyzed with differential scanning calorimeter (DSC). The gas permeability coefficients (P) and ideal selectivity for $CH_4$ and $CO_2$ of the prepared polyimide membranes were measured with a time-lag apparatus. DOCDA-ODA, DOCDA-p-PDA showed good permeability and selectivity; the permeabilities of $CO_2$ was 6.10, 0.74 barrers and the selectivity of $CO_2/CH_4$ were 67.03, 46.25, respectively. Therefore, DOCDA-ODA showed good possibility as gas separation membrane.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2550-2558
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• 2013

Poly(o-hydroxyamides)(PHAs) copolymers having oligo(oxy ethylene) pendant in the main chain were synthesized by solution polycondensation reaction at low temperature. Copolymer precursors were studied by fourier transform infrared(FT-IR), differential scanning calorimeter(DSC), thermogravimetric analyzer(TGA), universal testing machine(UTM) and limited oxygen index(LOI). The inherent viscosities of the PHAs measured at $35^{\circ}C$ in DMAc or DMAc/LiCl solution were in the range of 0.74~1.42 dL/g. Solubility of the precursors with higher oligo(oxy ethylene) unit was increased, but the PBOs were nearly insoluble in a variety of solvents. The degradation temperature of the copolymer precursors was recorded in the ranges of $408{\sim}664^{\circ}C$ in nitrogen and char yields showed 13~59% values at $900^{\circ}C$. The mechanical properties and flame retardancy of copolymer precursors decreased with higher oligo(oxy ethylene) unit.

• Journal of the Korean Society of Clothing and Textiles
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• v.41 no.1
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• pp.131-140
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• 2017

Uniform nanofibers of polyurethane with different content of Juniperus Chinensis extracts (JCE) were successfully prepared by the electrospinning method. We investigated physiochemical properties of prepared compound nanoweb according to various concentrations of Juniperus Chinensis extracts using a Fourier transform infrared (FT-IR) spectrometer, X-ray diffractometer (XRD), thermogravimeter (TGA), and differential scanning calorimeter (DSC). The antibacterial activity of the JCE loaded PU nanofiber was conducted using the disk diffusion test against Gram-positive and Gram-negative bacteria. JCE was induced in the infrared spectra in the absorption band of PU/JCE nanowebs at $3,300cm^{-1}$, $2,960cm^{-1}$, $1,400-1,600cm^{-1}$, and $1,050cm^{-1}$. Thermal stability decreased with increasing JCE content in the PU/JCE nanowebs. The DSC curve of the PU nanoweb shows an endotherm peak at $420^{\circ}C$; in addition, the peak also became smaller and broader with increasing JCE content. The diffraction intensities of PU observed at 2 theta of $20^{\circ}$ decreased with the increasing amount of JCE in the compound nanoweb. In addition, the crystal intensities of the compound nanowebs also decreased along with the JCE content. Structural analysis indicates that JCE and PU are miscible. Juniperus Chinensis incorporated PU nanofibers demonstrated excellent antibacterial properties against both Gram-positive and Gram-negative bacteria.

• Journal of Powder Materials
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• v.9 no.5
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• pp.359-364
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• 2002

We report the structure, thermal and magnetic properties of a non-equilibrium $Al_{0.6}(Fe_{50}Cu_{50})_{0.4}$ alloy powder produced by rod milling and chemical leaching. An X-ray diffractometry(XRD), a transmission electron microscope(TEM), a differential scanning calorimeter(DSC), a vibrating sample magnetometer(VSM), and superconducting quantum interference device(SQUID) were utilized to characterize the as-milled and leaching specimens. The crystallite size reached a value of about 8.82 nm. In the DSC experiment, the peak temperatures and crystallization temperatures decreased with increasing milling time. The activation energy of crystallization is 200.5 kJ/mole for as-milled alloy powder. The intensities of the XRD peaks of as-milled powders associated with the bcc type $Al_{0.5}Fe_{0.5}$ structure formative at $350^{\circ}C$ sharply increase with increasing annealing temperature. Above $400^{\circ}C$, peaks alloted to $Al_{0.5}Fe_{0.5}$ and $Al_{5}Fe_{2}$ are observed. After annealing at $600^{\circ}C$ for 1h, the leached Ll specimen transformed into bcc $\alpha$-Fe and fcc Cu phases, accompanied by a change in the structural and magnetic properties. The saturation magnetization decreased with increasing milling time, and a value of about 8.42 emu/g was reached at 500 h of milling. The coercivity reached a maximum value of about 142.7 Oe after 500 h of milling. The magnetization of leached specimens as function of fields were higher at 5 K, and increased more sharply at 5 K than at 100 K.