Gue-Hyun Kim

Preparation and characterization of biodegradable aliphatic polyester/thermoplastic starch/organoclay ternary hybrid nanocomposites

Biodegradable aliphatic polyester (APES)/thermoplastic starch (TPS)/Cloisite 30B ternary hybrid nanocomposites were prepared via melt intercalation. The dispersion of the silicate layers in the APES/TPS hybrids were characterized by using X-ray diffraction and transmission electron microscopy. Tensile and barrier properties of the APES/TPS/Cloisite 30B hybrids were also studied. Adding APES to the TPS/Cloisite 30B hybrids leads to higher tensile strength and improved barrier property.

Structure-Property Relationship of a Thermoplastic Vulcanizate (Tpv)/Layered Silicate Nanocomposites Prepared Using Maleic Anhydride Modified Polypropylene as a Compatibilizer

Abstract Thermoplastic vulcanizate(TPV)/organoclay nanocomposites have been successfully prepared by melt intercalation method. Maleic anhydride modified polypropylene has been used as a compatibil...

Effects of Multi-Walled Carbon Nanotube (MWCNT) Content on Physical Properties and Cell Structure in Ethylene Vinyl Acetate Copolymer (EVA)/MWCNT Nanocomposite Foams

Melt compounding is used to mix ethylene-vinyl acetate copolymer (EVA) and multi-walled carbon nanotube (MWCNT). Then the obtained EVA/MWCNT mixtures were foamed using a chemical blowing agent. Without any modification of MWCNT, a significant improvement of the tensile properties was observed for the EVA/MWCNT foams. With increasing the MWCNT content to 10 phr, the average cell size decreases to 36 µm due to the higher melt viscosity and the average cell density increases to 10.5 × 106 cell/cm3 due the heterogeneous nucleation. To investigate the possible applications for static dissipative purpose, the surface resistivity of EVA/MWCNT foams was also investigated.

Effect of rubber content on abrasion resistance and tensile properties of thermoplastic polyurethane (TPU)/rubber blends

Thermoplastic polyurethane (TPU) with more rigid hard segments and more flexible soft segments exhibits stronger microphase separation and stronger microphase separation leads to the better mechanical properties in general. In this study, to obtain TPU with low hardness without sacrificing abrasion resistance and tensile properties, TPU was blended with ethylene-propylene-diene monomer rubber (EPDM) or polybutadiene rubber (BR), which have more flexibility than the soft segments in TPU. Also, more rigid nitrile butadiene rubber (NBR) than the soft segments in TPU was blended with TPU for comparison. Even though NBS abrasion resistance, tensile strength and tensile modulus of TPU are much higher than those of EPDM and BR, TPU/EPDM (90/10) and TPU/BR (90/10) blends exhibit the higher NBS abrasion resistance, tensile strength and tensile modulus, than does of TPU. For TPU/NBR blends, the mechanical properties of the blends continuously decrease with increasing content of NBR. Since Tg of EPDM (or BR) is lower than that of the soft segments in TPU used in this study, TPU/EPDM (90/10) and TPU/BR (90/10) blends may result in the increase of flexibility of the soft segments in TPU, and show the stronger microphase separation, which is confirmed by the dynamic mechanical analyzer (DMA) results.

Thermoplastic Polyurethane (TPU)/Ethylene-Propylene-Diene Monomer Rubber (EPDM) and TPU/Polybutadiene Rubber (BR) Blends for the Application of Footwear Outsole Materials

The main objective of this study is to improve abrasion resistance and wet slip resistance of thermoplastic polyurethane (TPU) by blending with ethylene-propylene-diene monomer rubber (EPDM) or polybutadiene rubber (BR) for the application of the footwear outsole materials. With addition of 10 wt% of EPDM or BR, TPU/EPDM and TPU/BR blends exhibited higher NBS abrasion resistance, tensile properties and wet slip resistance than TPU. However, with further increasing content of EPDM and BR, abrasion resistance and tensile properties of the blends decreased. Improvement in abrasion resistance and tensile properties with 10 wt% of addition of EPDM or BR may be due to better microphase separation of TPU.

Effect of Rubber Content of ABS on the Mechanical Properties of ABS/Clay Nanocomposites

One approach to improve the impact strength of acrylonitrile–butadiene–styrene (ABS)/clay nanocomposites is to increase rubber content. To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, other parameters were fixed and ABS/clay nanocomposites containing various rubber contents were prepared in this study. Also the effect of the UV stabilizer on the mechanical properties of ABS/clay nanocomposite was studied. For addition of 3 wt% clay, ABS nanocomposite with 35 wt% content of rubber displayed the highest reinforcement ratio for tensile properties and impact strength.

MOLECULAR DYNAMICS INTERPRETATION OF THE STRUCTURES OF POLYIMIDES FOR ORGANIC ELECTROLUMINESCENT DEVICES

In this work, we discuss the relative efficiency of the organic electroluminescent devices (OELDs) utilizing various fluorine-containing polyimides in hole transporting layer (HTL) in terms of the structure of the polyimides (PI) by molecular dynamics estimation. Materials for polyimides investigated in this study are; 1,2,4,5-benzentetracarboxylic dianhydride (PMDA), 4,4′-(hexafluoroisopropylidene) diphtalic anhydride (6FDA), 4,4′-oxydianiline (ODA), and 4,4′-(hexafluoroisopropylidene) dianiline (6FDAm). The devices used in this study consist of two organic layers, i.e. ITO-coated glass/TPD-dispersed polyimide/Alq3/Al devices. It was found that the EL efficiency of the OELDs is significantly affected by the molecular structure of polyimides as well as the contents of fluorine atoms in the PI. Molecular dynamics calculation proved that PMDA-6FDAm PI exhibits largest steric hindrance among the four PIs used in this work, due to the largest torsion of benzene rings.

Layer-by-layer assembly of graphene on polyimide films via thermal imidization and synchronous reduction of graphene oxide

To investigate the effects of holding time after deposition of polyethylenimine (PEI) solution and molecular weight of PEI on the surface morphology of multi-layer films prepared by layer-by-layer (LbL) method, polyamic acid (PAA)/PEI/graphene oxide (GO) films were prepared using different holding times and different molecular weights of PEI. To convert PAA into polyimide (PI), the films were thermally imidized after film deposition. In this process, GO was also converted into partially reduced GO (rGO). The effects of holding time and molecular weight of PEI on the surface morphology and the sheet resistance of PI/PEI/rGO films were investigated. Also, to investigate the effect of rGO on the barrier properties of PI based multilayer films, (PI/PEI/rGO/PEI)6 films were prepared by LbL method. Longer holding time (10 min) and smaller molecular weight (25,000) of PEI lead to relatively flat surfaces, but shorter holding time (5 min) and larger molecular weight (75,000) result in wrinkled and overlapped surfaces. The sheet resistance of PI/PEI25K/rGO films prepared with holding time 10 and 5 min is 502.1 kΩ/sq and out of range (> 2000 kΩ/sq), respectively. The sheet resistance of PI/PEI75K/rGO films prepared with holding time 10 min is out of range (> 2000 kΩ/sq). Gas transmission rate (GTR) and permeability coefficient of (PI/PEI25K/rGO/PEI25K)6 are lower than those of (PI/PEI75K/rGO/PEI75K)6, respectively.

Effect of acrylic block copolymer on the fracture toughness and glass transition temperature of carbon fabric reinforced 180°C cure-epoxy composites

ABSTRACT In this study, carbon fabric (CF)/180°C cure-epoxy composite laminates were prepared with an acrylic block copolymer as a toughner. The acrylic block copolymer is known to be self-assembled into nanostructures such as micells and vesicles in epoxy resin. The Mode I interlaminar fracture toughness of CF/180°C-cure epoxy composite laminates was evaluated by the double cantilever beam (DCB) test. The fractured surface and glass transition temperature of the composite were investigated by scanning electron microscopy (SEM) and dynamic mechanical analyzer (DMA), respectively. With increasing content of the acrylic block copolymer from 2.5 to 10 phr, the Mode I interlaminar fracture toughness continuously increases. Addition of the acrylic block copolymer (2.5–10 phr) makes little change in Tg of the CF/180°C-cure epoxy composites.

Effect of Organoclay and Blends on the Abrasion Resistance and Mechanical Properties of Poly(styrene-block-butadiene-block-styrene)

To investigate organoclay, high styrene resin masterbatch (HSR), high impact polystyrene (HIPS), and polystyrene (PS) as reinforcing materials for the improvement of the abrasion resistance of poly(styrene-block-butadiene-block-styrene) (SBS), SBS/organoclay nanocomposites, SBS/HSR, SBS/HIPS, and SBS/PS blends were prepared. The effect of organoclay and blends on the abrasion resistance and mechanical properties of SBS was investigated. Even though intercalations of organoclay are observed for SBS/Cloisite 20A nanocomposites and not for SBS/Cloisite 30B composites, the abrasion resistance of SBS/Cloisite 20A nanocomposites is worse than that of SBS/Cloisite 30B composites. When SBS was blended with HSR, HIPS and PS, the abrasion resistance of the blends increases with increasing of HSR, HIPS and PS content from 0 to 20 wt%.