• Journal of the Korean Applied Science and Technology
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• v.36 no.2
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• pp.645-655
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• 2019

In this study, colloidal microgel with viscoelasticity were prepared by using dispersion containing physical crosslinking agents and microgels with various strengths depending on the degree of cross-links.As the chemical crosslinking agent PEGDA400 content increased, hydrogels have various physical properties the swelling ratio decreased from $2.0{\times}10^4%$ to $6.0{\times}10^3%$ and increased viscosity by about 60%. The colloidal microgel was prepared with micro hydrogel grinded to $100{\mu}m$ size and the rheological behavior was confirmed with physical cross linking agent. A colloidal microgel having various viscosities was prepared by controlling starch and alginate based on micro-hydrogel containing 0.75% (w/v) of PEGDA400. In conclusion, these results would be highly useful for applying as a product that can give various physical properties to the colloidal suspensions, cosmetics, paint, and food industry.

• Journal of Adhesion and Interface
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• v.9 no.4
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• pp.24-29
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• 2008

Polypropylene-natural fiber composites have been prepared and their rheological properties during mixing and thermal properties were investigated. Two types of natural fibers (cotton fiber and wood fiber) were compared. On increasing fiber contents, the torque values of composites were increased, where the cotton fiber exhibited higher increase in torques. The torque values of composites were higher as the MI of PP decreased. X-ray diffraction and differential scanning calorimetry results showed an increase in the crystallization temperature but a decrease of crystallinity of the PP/natural fiber composites on increasing fiber contents.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.85-91
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• 2011

Computational results with pseudoplastic fluid flows for fully developed non-Newtonian laminar flows have been obtained. Those consist of the product of friction factor and Modified Reynolds number and Nusselt numbers with respect to the shear rate parameter in an annular pipe. The numerical results of the product of friction factor and Reynolds numbers and the Nusselt numbers for both Newtonian region and the power law region were compared with previously published asymptotic results, respectively. In the present calculations, the product of friction factor and Newtonian Reynolds numbers for pseudoplastic fluid at power law region in annular pipe is 180% less than that for Newtonian fluid. For power law fluids with different power law flow indices, the difference of the product of friction factor and power law Reynolds number between previous and the present results at the power law region is within 0.20%. The solutions also show the effect of the shear rate parameter on the Nusselt number and about 11% increase of Nusselt number at the power region.

• Journal of Adhesion and Interface
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• v.10 no.1
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• pp.23-29
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• 2009

We investigated effects of a compatibilizer on the rheological properties during mixing and thermal properties of polypropylene (PP)-natural fiber composites. Two types of natural fibers (cotton fiber and wood fiber) were compared. maleic anhydride grafted PP was used for a compatibilizer. On increasing the amounts of the compatibilizer, the torque values of composites were increased, regardless of the kind of fibers. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results showed a slight increase in the degree of crystallinity with adding the compaibilizing agent, while the effects of the kind of fibers were marginal. It may be considered, however, the cotton fiber exhibits better interaction with PP-g-MAH than the natural fiber based on the rheographs, DSC, and XRD results.

• Polymer(Korea)
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• v.38 no.2
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• pp.213-219
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• 2014

The rheological characteristics of highly concentrated polymer bonded explosive simulant were studied. Hydroxyl terminated polybutadiene (HTPB) and polyethylene plastomer (Exact) were used as binders. Sugar and Dechlorane particles whose physical properties are similar to research department explosive (RDX) were used as fillers. When HTPB was used, diethyl hexyl adipate (DEHA or DOA) was used as a plasticizer together for some cases. Highly concentrated suspensions were mixed in a batch melt mixer (Rheomixer 600, Haake) and rheological properties were measured by plate-plate and capillary rheometers. Wall slip phenomena, thixotropy with shear hysteresis, and flow instability were investigated as shear rate and amount of fillers changed.

• Polymer(Korea)
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• v.28 no.6
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• pp.460-467
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• 2004

The polymer blends of waste poly(vinyl chloride) (RPVC) and waste polyethylene (RPE) were prepared by melt mixing. Their morphologies and rheological properties were investigated and torque changes were also measured. Comparing the torques calculated by the log additivity rule with measured torque changes, the polymer blends showed the large negative deviation behavior (NDB) due to their incompatibility. The shear viscosities of the blends decreased with increasing shear rates, showing shear thinning behavior. The shear viscosity of the blends with compatibilizer was larger than that of the blends without compatibilizer. SEM micrographs of the strands after measurement showed that the domain size of the blends was slightly enlarged with increasing the shear rate. Also, RPVC domain size was larger in the core-sections of the strands from capillary viscometer than in the surface region.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3990-3996
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• 2014

Because the physical properties can be decreased when a Nylon 66/glass fiber composite is injected into a mold over $300^{\circ}C$, a systematic study of the thermal history in the case of re-use is needed. Nylon 66/glass fiber extrudates as a function of the extrusion number were prepared using a twin screw extruder at 305/290/273/268/265/$260^{\circ}C$. The chemical structure, thermal properties, melt index, crystal structure, Izod impact strength, and rheological properties were measured by Fourier transform infra-red (FT-IR), melt indexer, DSC, TGA, XRD, Izod impact tester, and dynamic rheometer. The FT-IR spectra indicated that the number of extrusions did not affect the chemical structure. The decrease in molecular weight with increasing extrusion number was confirmed by the melt index and the complex viscosity of extrudates. Based on the DSC and TGA results, the thermal history had no effect on the melting temperature, regardless of the number of extrusions, but the degradation temperature decreased up to $20^{\circ}C$ with increasing extrusion number. The Izod impact strengths of the extrudates were found to decrease with increasing extrusion number. No structural change after extrusion was also confirmed because there was no change in the slope and shape of the G'-G" plot.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.90-95
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• 2014

Nylon66 extrudates as a function of the extrusion number were prepared by a twin screw extruder. Chemical structures, thermal properties, melt index, crystal structures, mechanical properties such as the tensile strength, elongation at break and impact strength, and rheological property were measured by FT-IR, $^1H$-NMR, melt indexer, DSC, TGA, XRD, universal tensile tester, Izod impact tester, and rheometer. FT-IR and $^1H$-NMR characterizations indicated that the number of extrusions did not affect the chemical structure. The decrease in the molecular weight was checked by the melt index of extrudates. There were no effects of the thermal history on the melting and degradation temperature. The tensile and impact strength and modulus were found to be similar, regardless of the number of extrusions, but the elongation decreased significantly. The complex viscosity of extrudates at low frequencies decreased with the extrusion number. No structural changes after extrusion were confirmed from the fact that there was no change in the slope and shape of G'-G" plot.

• Elastomers and Composites
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• v.44 no.1
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• pp.63-68
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• 2009

Recently, much attention has focused on the permanent deformation of roads in hot summer and cracks in cold winter, which are detrimental to safe driving. This leads to necessity of modification of asphalt to resist those deformation. In this study, a type of modified asphalt was prepared by addition of a photoinitiator which is activated by ultraviolet lay. The mechanical and rheololgical properties of photoinitiator-modified asphalt were examined using UTM and rheometer. Results showed that the modified asphalt was effected by ultraviolet and thus tensile strength and storage modulus increased, due to molecular attraction, with initiator content and irradiation dose. Thermal analysis showed less weight loss upon photoinitiator-modification and this indicated that the molecular attraction is the result of cross linking reaction between asphalt molecules induced by photoinitiator. According to long term ultraviolet curing test, properties of the photoinitiator-modified asphalt did not decrease or even increase for 20 years. This indicates that useful life of the asphalt could be extended by addition of photoinitiator.

• Polymer(Korea)
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• v.37 no.4
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• pp.500-506
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• 2013

The effect of compatibilizer types on the properties of polyphenylene sulfide (PPS)/polyethylene terephthalate (PET) blends was investigated. The blends were extruded by a single screw extruder attached with a Maddock mixing zone and their molded properties were examined. As a basic blend composition, a linear PPS/PET (40/60) blend was selected based on cost efficiency. Three types of compatibilizer, SEBS, modified SEBS, and modified PS were added to the basic blend to improve the properties. The thermal, rheological, mechanical properties and the morphology of the ternary blends were analyzed. The maximum mechanical properties of blends was found at 1 phr of m-SEBS or m-PS content, whose values were almost the same as the theoretical values of miscible blend system. It seemed to by the case that the partial reaction between compatibilizer and the basic blend caused the enhancement of compatibility between linear PPS and PET phases. These ternary blends would be applicable as economic linear PPS alloys.