• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.888-894
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• 2015

Inorganic composite particles have excellent physical and chemical characteristics and have been applied in various industries. Recently, many studies have examined the optical properties, such as light scattering, refraction, transmission characteristics, by coating organic-inorganic materials on a substrate, such as mica. Mica is widely applied as a pigment, plastics, painted products, and ceramics because of its high chemical stability, durability and non-toxicity. Magnesium oxide has a range of properties, such as high light transmittance, corrosion resistance and non-toxicity, and it is used as an optical material and polymer additives. To use the optical properties of mica and magnesium oxide, mica was coated with magnesium hydroxide by a dissolution and recrystallization process. In this study, the optimal conditions for the haze value of the particles were found by adjusting the amount of precursors and pH. Magnesium hydroxide layers were formed on the surfaces of mica and converted to MgO after calcination at $400^{\circ}C$ for 4 h. The results showed that the value of MgO-coated mica haze can be controlled easily by the amount of the magnesium hydroxide and pH. The optical properties of the inorganic composite powder were analyzed using a hazemeter and the highest haze value was 85.92 % at pH 9. The physicochemical properties of the synthesized composite was analyzed by SEM, XRD, EDS, and PSA.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.193-199
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• 1998

The mixtures of ultra-high molecular weight polythylene (UHMWPE), high density polyethylene (HDPE), process oil (mineral oil) and potassium hexatitanate whisker were melted and mixed at $150^{\circ}C$ for 30min, and prepared by compression molding to the specimen of separator of about $200{\mu}m$ thickness at the same temperature and 5000 psi. Thereafter the pores were formed by extracting process oil with organic solvents. In this study, the range of PR (the ratio polymer to process oil) was varied from 0.1 to 0.5 because the specimen turned into rubbery phase at which PR was below 0.1 whereas it changed into gel phase at which PR was above 0.5. When the specimen was treated with nonpolar organic solvents, process oil was extracted nearly 98%. Tensile strength was $31kg/cm^2$ at PR = 0.426, and resistance of specimen was $37m{\Omega}/cm^2$ at PR = 0.186, and $53m{\Omega}/cm^2$ at PR = 0.426. The $N_2$ adsorption-desorption isotherm showed a hysteresis representing regions of capillary condensation, and the surface area at PR = 0.186 was relatively large as $130cm^2/g$. Potassium hexatitanate whisker was randomly dispersed in between PE layers. It might be that the whisker is intercalated through the PE thin layers oriented by compression.

• Elastomers and Composites
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• v.48 no.2
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• pp.172-179
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• 2013

Impact modifier reinforced polymers are frequently used. In this study, Izod impact test has been simulated to analyze the mechanism of impact reinforcement of Nylon6 which contains impact modifier. The modeling of rubber particles added to Nylon6 as an impact modifier has been attempted. Based on the modeling, simulation of Izod impact test has been performed to observe the distribution and direction of stress at the cross-section of impact specimen. Three computer simulation models for Nylon6 were investigated. Those were without impact modifier, containing impact modifier without surface treatment, and containing impact modifier with surface treatment in the Nylon6. Simulation results showed that the stress which originated at the notch surface propergated to the inside of specimen round a impact modifier. In addition to that, impact modifier reinforced Nylon6 specimen showed low stress ditribution in the cross-section specially at notch surface. Principal stress in perpendicular direction to crack was also lowered in impact modifier reinforced Nylon6. These enhanced impact resistance reduced and crack propergations. Through this study it was realized that the computer simulation can be utilized to investigate the property enhacement of composite materials.

• Elastomers and Composites
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• v.45 no.1
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• pp.51-57
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• 2010

Cellulose nanowhiskers (CNW) gamered increasing interest for their remarkable reinforcement of polymer composites. In this work, we were to produce cellulose whiskers from commercially available microcrystalline cellulose (MCC) by acid hydrolysis with sulfuric and hydrochloric acids. Electron microscopy found that each acid produced sililar cellulose crystals of diameters ranging from 20 to 30 nm and lengths ranging from 200 to 300 nm. Moreover, all samples showed remarkable flow birefringence through crossed polarization filters. Conductometric titration of CNW suspensions revealed that the sulfuric acid treated sample had a surface charge of between 140.00 mmol/kg and 197.78 mmol/kg due to sulfate groups, while that of the hydrochloric acid treated sample was undetectable. Thermogravimetric analysis showed that the thermal decomposition temperature and apparent activation energy (evaluated by Broido's method at different stages of thermal decomposition.) of H1-CNW - prepared by hydrolysis with hydrochloric acid - was higher than those of S1-CNW and S2-CNW - prepared by hydrolyzing MCC with sulfuric acid.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.423-430
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• 2013

In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.

• Polymer(Korea)
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• v.25 no.3
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• pp.359-366
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• 2001

Isothermal physical aging of a glass fiber/epoxy composite was examined at different aging temperatures ($T_a$) and degrees of conversion (monitored by the glass transition temperature, $T_g$) by means of the TBA torsion pendulum technique. The range of aging temperature was from 10 to $130^{\circ}C$ : the conversion was systematically changed from $T_g$=$76^{\circ}C$ to $T_g$=$177^{\circ}C$ (fully crosslinked). The effect of isothermal physical aging was manifested as perturbations of the modulus and mechanical loss vs. temperature in the vicinity of $T_a$ for all conversions. The rate of isothermal physical aging determined from the change of modulus with aging time at fixed aging temperature decreased and then increased with increasing conversion below T$_{a}$=9$0^{\circ}C$. There exists a superposition in aging rate vs. ($T_g$ -$T_a$) by shifting horizontally and vertically. This implies that the physical aging process is independent of the change of chemical structure as conversion proceeds. It has been found that water absorbed at the aging temperature below $70^{\circ}C$ during isothermal physical aging lowers the apparent aging rate. It is due to the absorbed water molecules forming strong polar interactions with hydroxyl group on network chain and reducing the segmental mobility during the physical aging.g.

• Polymer(Korea)
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• v.31 no.2
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• pp.160-167
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• 2007

This paper proposes a model for the solutions predicting the coefficient of thermal expansion of composites including fiber-like shaped$(a_1>a_2=a_3)$ and disk-like shaped$(a_1=a_2>a_3)$ inclusions like two dimensional geometries, which was analyzed by one axis and a single aspect ratio, $(\rho_\alpha=a_1/a_3)$. The analysis follows the procedure developed for elastic moduli by using the Lee and Paul's approach. The effects of the aspect ratio on the coefficient of thermal expansion of composites containing aligned isotropic inclusions are examined. This model should be limited to analyze the composites with unidirectionally aligned inclusions and with complete binding to each other of both matrix and inclusions having homogeneous properties. The longitudinal coefficients of thermal expansion $\alpha_{11}$ decrease and approach the coefficient of thermal expansion of filler, as the aspect ratios increase. However, the transverse coefficients of thermal expansion $\alpha_{33}$ increase or decrease with the aspect ratios.

• Composites Research
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• v.34 no.3
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• pp.192-198
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• 2021

Due to enormous market growing of electric vehicles without combustion engine, reducing unwanted BSR (buzz, squeak, and rattle) noise is highly demanded for vehicle quality and performance. Particularly, innerbelt weatherstrips which not only block wind noise, rain, and dust from outside, but also reduce noise and vibration of door glass and vehicle are required to exhibit high damping properties for improved BSR performance of the vehicle. Thermoplastic elastomers (TPEs), which can be recycled and have lighter weight than thermoset elastomers, are receiving much attention for weatherstrip material, but TPEs exhibit low material damping and compression set causing frictional noise and vibration between the door glass and the weatherstrip. In this study, high damping EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV) were investigated by varying EPDM/PP ratio and ENB (ethylidene norbornene) fraction in EPDM. Viscoelastic properties of TPV materials were characterized by assuming that the material damping is directly related to the viscoelasticity. The optimum material damping factor (tanδ peak 0.611) was achieved with low PP ratio (14 wt%) and high ENB fraction (8.9 wt%), which was increased by 140% compared to the reference (tanδ 0.254). The improved damping is believed due to high fraction of flexible EPDM chains and higher interfacial slippage area of EPDM particles generated by increasing ENB fraction in EPDM. The stick-slip test was conducted to characterize frictional noise and vibration of the TPV weatherstrip. With improved TPV material damping, the acceleration peak of frictional vibration decreased by about 57.9%. This finding can not only improve BSR performance of electric vehicles by designing material damping of weatherstrips but also contribute to various structural applications such as urban air mobility or aircrafts, which require lightweight and high damping properties.

• Polymer(Korea)
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• v.30 no.4
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• pp.318-325
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• 2006

Polypropylene-clay nanocomposites were studied by the modification of clay with amino silanes to introduce covalent bonds in nanocomposites, and prepared by melt-compounding with polypropylene, clay modified with amino silanes and maleic anhydride grafted polypropylene. The . .structure and surface properties of modified clay were determined by x-ray diffraction, infrared spectrum, and solid-state $^{29}Si$ nuclear magnetic resonance spectrum. The modification of clay with aminosilanes led to the increase of the silicate interlayers to about $19.8{\AA}$, the weakening effects of hydroxy group at $3650cm^{-1}$ and the signal of amine groups at -69 ppm proved that the modification had taken place.

• Composites Research
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• v.29 no.3
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• pp.91-97
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• 2016

In this paper, impulse-momentum theory was coupled to a constitutive equation both for implementing quasi-static and impact characteristics of EPP (Expanded polypropylene). Also, parameters which have physical meanings were expressed as functions of relative density. Simultaneous nonlinear Newton-Raphson method was applied to find the proper values for parameters in the constitutive equation along with quasi-static test data. Results from the impulse-momentum theory coupled constitutive equation showed good agreement with experimental data and the potential to be applied to different material type polymeric foam.