Youn Cheol Kim

Effects of linear low density polyethylene on physical properties and irradiation effectiveness of polypropylene

Blends of polypropylene (PP)/linear low density polyethylene (LLDPE) were prepared by melt mixing in twin screw extruder at 190 °C. Polyfunctional monomer TMPTMA (trimethylolpropane-trimetacrylate) was added to the mixture as a crosslinking co-agent to improve the crosslinking or branching efficiency of the olefins during irradiation. The effect of LLDPE on the crosslinking or branching effectiveness and physical properties of PP was investigated in conjunction with the monomer content of LLDPE in the blends. Thermal stability, rheological properties and electron beam irradiation effectiveness of PP in presence of LLDPE were analyzed by DSC, TGA and RDS. Solution gel analysis and the presence of −C=O in FT-IR test supported some crosslinking or branching that occurred after irradiation. Certain decrease in melting temperature (Tm) that was noticed after irradiation could have been the result of chain scissioning, which decreases the number of tie molecules in the amorphous region and consequently weakens the lamellar connections. Shear thinning effect and zero shear viscosity were improved by irradiation in the PE incorporated samples.

Effect of electrochemical treatment on pull-out properties of 73/27 HBA/HNA copolyester fibers in thermosetting matrix

The surface of high-strength 73/27 HBA/HNA fibers was electrochemically modified in aqueous sodium hydroxide solution (10 wt %) with the change of the applied current to improve the interfacial shear strength (IFSS) of the fiber in the thermosetting matrix. A sodium component was identified on the surface of the treated fibers by scanning electron microscopy (SEM). The detection of sodium is best interpreted as the existence of a negative charged functional group (COO−Na+) on the surface of the treated fibers. A pull-out test was used to measure the IFSS of the HBA/HNA fibers and epoxy/amine cure system. According to the calculating value from Greszczuks geometrical model, the IFSS increased with the applied current in the range of 50–450 mA. However, no further increase in the IFSS was observed for strong treatment (1500 mA). There was an optimum by applied current to obtain maximum IFSS. The electrochemical treatment of the 73/27 HBA/HNA copolyester fibers was effective in altering their surface chemistry and improving the interfacial adhesion at the moderate treating conditions.

After‐Rinsing Hair Growth Promotions of Hinokitiol‐Containing Vesicles and Emulsions

Two kinds of topical dosage forms of hinokitiol (HKL), namely vesicles and oil‐in‐water (O/W) emulsions, were prepared. Behenyl trimethylammonium chloride (BTMAC) and fatty acids were used as bilayer‐forming materials of the vesicles, and oils were employed as oil phases of the emulsions. The substantivity of HKL in the preparations was evaluated in vitro using hairless mouse skins. After applying the preparations onto the skin and rinsing it, the amount of HKL left on the skin was determined using high performance liquid chromatography (HPLC). It was higher when HKL was encapsulated in cationic vesicles rather than in nonionic vehicles, emulsions. An ionic interaction between the cationic vehicle and negatively charged skin is likely to account for the high substantivity. Among the emulsion preparations, an emulsion having octyl salicylate as oil phase exhibited the highest substantivity of HKL. This is probably because that the oil is a good solvent for HKL and it is skin‐retentive. In vivo hair growth‐promotion effect of each dosage form was investigated, where the sample application onto the clipped backs of female mice (C57BL6) and the subsequent rinsing of the backs were done once a day for 30 days. Only HKL in the cationic vesicles had hair growth promotion effect, possibly due to the significant substantivity.

Substantivity and After‐Rinsing Hair Growth Promotion of Cationic Microparticles of Minoxidil

Cationic minoxidil (MXD) particles were prepared by passing a suspension containing MXD and distearyldimethylammonium chloride (DSDMAC) through a high pressure microfluidizer, operating at 500 bar to 1000 bar. The size of the particles is a few micrometers and the surface charge was+42 mV to+44 mV. The cationic MXD particles were included in a hair cleansing shampoo, of which a major detergent is sodium lauryl ether sulfate (SLES). On an UV spectrophotometer, the turbidity of the cationic MXD particles suspension increased with increasing amount of the anionic surfactant. At the same time, the surface charge of the cationic MXD particles was neutralized around equi‐molar ratio of SLES/DSDMAC, and the value became negative in the excess amount of SLES. These mean that DSDMAC adsorbed on MXD particles is complexed with SLES in the hair shampoo by an ionic interaction. Interestingly, even though the MXD particles contained in a shampoo exhibited negative surface charge, the skin‐retentive amount of MXD was appreciable and the after‐rinsing hair growth promotion effect was remarkable. One of possible mechanisms is that SLES would be desorbed from the complexed MXD particles during the rinsing step, and the charge of the particles might change from a positive value to a negative one, leading to an ionic interaction between the cationic particles and negatively charged skin.

Study on the Melt Flow and Physical Properties of Nylon 66/Carbon Filler Composite with Processing Aid

It is difficult to fabricate the product of the polymer/carbon filler composites with high carbon filler content through the conventional extrusion or injection process due to poor melt flow properties. In this study, the effect of processing aid on the melt flow and physical properties of the nylon66/carbon filer composites was discussed. The carbon fillers such as carbon black (CB), multi-walled carbon nanotube (MWCNT), nickel coated carbon fiber (Ni-CF) were used. Polyethylene-wax (L-C102N, L-C121N) and 2,2,6,6-tetramethyl-4-piperidinyl (BIS) were used as the processing aids. The nylon66/carbon filler composites with different processing aid types and content were fabricated by using a twin-screw extruder at 280 C of die temperature. In case of nylon66/CB/CNT/CF composites with BIS processing aid, an improvement of melt flow properties was certified by the complex viscosities and melt flow index, and there was little change in electrical properties such as surface resistivity.

Effect of Fabrication Methods on the Physical Properties of Nylon 66/Carbon Filler Composite

In this study, the effect of fabrication method on the basic properties and electromagnetic interference (EMI) shielding performance of the nylon66/carbon filler composites was discussed. The carbon fillers such as carbon black (CB), multi-walled carbon nanotube (MWCNT), and nickel coated carbon fiber (Ni-CF) were used. The master-batch (MB) of CB/MWCNT and feeding method of Ni-CF were used as fabrication methods. The concentration of CB and MWCNT in MB was fixed at 20 wt% and MBs were fabricated by using a twin screw extruder at die temperature of 280 C. The composites were prepared with two different feeding methods that Ni-CFs were fed separately at main and side feeder. The improvements of melt flow and electrical properties were confirmed from complex viscosity and surface resistance in the case of nylon 66/CB/CNT/Ni-CF composites fabricated through MB, and EMI shielding performance increased largely when Ni-CF was fed into the composites at side feeder.

Effects of the Carbon Fillers on the EMI Shielding Performance and Physical Properties of Nylon66 Composites

In this study, nylon66/carbon filler composites were prepared according to the type and content of carbon filler, the surface resistivity, electromagnetic interference (EMI) shielding performance, and mechanical properties of the composites were investigated. The carbon fillers such as carbon black (CB), multi-walled carbon nanotube (MWCNT), nickel coated carbon fiber (Ni-CF) were used. The nylon66/carbon filler composites with different filler types and filler content were fabricated by using a twin-screw extruder at 280 C reference of die temperature. Double percolation was certified by surface resistivity when CNT and CB were compounded together in nylon66 matrix. Based on EMI shielding effectiveness, the minimum content of NI-CF was 20 wt% when the EMI shielding effective value has over 40 dB. The complex viscosities of the nylon66/CNT/CB/Ni-CF composites were measured by using a dynamic rheometer to determine the processability of the composite. Also, the morphological properties were investigated by using SEM.

Study on the Physical Properties of the Polypropylene/Kenaf Fiber Felt Treated by Corona or Compatibilizer

In order to improve the interfacial adhesion property between polypropylene (PP)/kenaf fiber (KF) felt and polyurethane (PU) binder, corona discharge treatment and PP-g-MAH grafted maleic anhydride (MAH) were applied as a compatibilizer to PP/KF felt. Isothermal experiments were carried out by using differential scanning calorimetry (DSC) to determine the reaction temperature and time for PU binder. Tensile, flexural and impact properties were evaluated to analyze the mechanical properties of PP/KF/PU treated by corona discharge and PP-g-MAH. In case of modified-PP (mPP)/KF/PU composite treated by corona discharge and PP-g-MAH, the tensile and impact properties were improved. It may be because when the corona discharge was applied to the mPP/KF felt, the compatibilizing ability between the mPP/KF and PU binder increased due to the insertion of oxygen group in PP chain. The interface adhesion properties of the mPP/KF/PU composites were identified by SEM images of the fracture after the tension test.

Effect of irradiation and LDPE content on crystal formation of PP

The crystallization behavior of irradiated polypropylene (PP) and the blend is an important parameter for polymer processing. Blends of PP/low density polyethylene (LDPE) with different LDPE contents were prepared by melt mixing in a twin screw extruder. The effect of the LDPE content on the irradiation effectiveness of the PP/LDPE blend with trimethylolpropane-trimetacrylate (TMPTMA) as a crosslinking co-agent was investigated in conjunction with the LDPE loading in the blend. The non-isothermal crystallization and crystal structure were measured by DSC, X-ray diffraction (XRD), and polarized optical microscopy (POM). A decrease in the melting temperature of PP was observed due to irradiation, which may be due to the PP chain scissioning effect of irradiation. The Ozawa component n represents a rod shaped, disc shaped and sphere-shaped geometry of the crystal if the value corresponds to 2, 3 and 4, respectively. Based on Ozawa analysis, the values of n were 3.8 and 2.3 for the pure PP and PP blends with 30 wt% LDPE, respectively. The fact that the crystal geometry of PP changed from spherical to disc and rod shaped was confirmed by Ozawa analysis and POM. The β form XRD peak of the PP/LDPE blend at 16.1o disappeared after irradiation due to the crosslinking reaction.

Improvement research for impact strength of nylon66/silicate composites

A study of the improvement in the impact strength is required to apply Nylon 66/silicate composites as an automobile material. Nylon 66/silicate composites were prepared using a twin screw extruder in case of a silicate treatment by γ-APS (S-silicate) and the addition of an octene α olefin grafted by maleic anhydride (PE-g-MAH). The chemical structure of the silane treated silicate was measured by Fourier transform infra-red (FT-IR) spectroscopy. The chemical reaction was confirmed by the decrease in the FT-IR intensity of the OH stretching vibration. The thermal properties, intercalation structure, and Izod impact strength were measured by DSC, TGA, XRD, and Izod impact tester. There was no significant effect on the degradation temperature of the Nylon66/silicate composite, but the crystallization temperature and crystallinity increased slightly in the case of the Nylon66/silicate composites. This suggests that the additives act as heterogeneous nuclei on the Nylon 66 matrix. The Izod impact test indicated that S-silicate enhanced the impact performance by up to 24%.