Younggon Son

Measurement of interfacial tension by a deformed drop retraction method

This paper describes a technique, which enable one to overcome several difficulties encountered in a conventional deformed drop retraction method. The technique consists of forming deformed drops by the disintegration of a polymer thread and measuring the shape evolution of the drop. It is found that the technique enables one to overcome the difficulties encountered in the conventional deformed drop retraction method. By the optical microscope observation, it was confirmed that the disintegrated drop maintains the axisymmetrical ellipsoidal shape during the retraction process and was parallel to the observation plane. The interfacial tension obtained by the technique was found to be lower than the data from the breaking thread method. This variation was discussed in terms of the interfacial contact time.

Evaluation of polypropylene grafted with maleic anhydride and styrene as a compatibilizer for polypropylene/clay nanocomposites

Among modified Poly(propylene)s (PPs) grafted with polar monomers, PP grafted with maleic anhydride (PP-g-MAH) is known to be the most efficient compatibilizer for PP/clay nanocomposites, since it provides well-dispersed nanostructures and yields optimal physical properties of the nanocomposites. One drawback of this material, however, is that it becomes brittle and its viscosity decreases drastically, leading to nanocomposites with low toughness as the graft degree of MAH increases. Therefore, there is a limitation to increasing both stiffness and toughness of PP/clay nanocomposites with PP-g-MAH. In this study, we investigated the performance of a PP grafted with maleic anhydride and styrene (PP-g-MAH-St) as compatibilizers in PP/clay nanocomposites. It was found that the incorporation of styrene as a comonomer prevents molecular weight reduction of the PP main chain upon high loading of a radical initiator for high graft degree of MAH. The compatibilizers (PP-g-MAH-St) thus obtained show good compatibilizing performance in PP/clay nanocomposites. The PP/clay nanocomposites compatibilized by PP-g-MAH-St show both high stiffness and toughness, which is accomplished by using a compatibilizer of higher viscosity compared with PP-g-MAH.

Preferential positioning of γ-ray treated multi-walled carbon nanotubes in polyamide 6,6/poly( p -phenylene ether) blends

AbstractMorphological characteristics and electrical conductivity of polyamide 6,6/poly(p-phenylene ether)/multi-walled carbon nanotube (PA66/PPE/MWCNT) ternary nanocomposites were investigated. The MWCNTs were modified by 60Co gamma ray (γ-ray) irradiation under a dry condition and O2 atmosphere, which introduces oxygen-containing functional groups on the surfaces of the MWCNTs and thereby provides better compatibility with the hydrophilic PA66 phase. It was observed that the MWCNTs are preferentially positioned in the continuous PA66 matrix, whereas PPE domains are almost free of MWCNTs. Since PA66 consists of a continuous phase and the MWCNTs are preferentially positioned in the PA66 phase, electrical conductivity of PA66/PPE/MWCNT ternary composites is higher than that of PA66/MWCNT binary composites at the same MWCNT content. It was observed that raising the processing temperature and increasing the mixing time were effective means of improving the electrical conductivity of the composites, via enhancement of MWCNT dispersion.

Influence of acrylonitrile content in styrene-acrylonitrile copolymer on the phase morphology and interfacial tension in blends of polycarbonate/styrene-acrylonitrile copolymer

AbstractWe have studied the phase morphology and interfacial tension in blends of PC/styrene-acrylonitrile copolymer (SAN) as representatives of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blends. To confirm how the acrylonitrile (AN) content of the SAN polymer influences the phase morphology and rheology, PC/SAN (90/10) blends with varying AN content ranging from 24 to 41 wt% with respect to the SAN were prepared using a twin-screw extruder. The interfacial tension of the blends was determined from the measured average particle radius and the relaxation time of the interface using Palierne’s emulsion model. The minimum interfacial tension and domain size occurred in the blend containing AN 28.5 wt% versus SAN. The interfacial tension results were consistent with the observed morphology and rheology of the blends. Because the viscosity of SAN polymers varied with the AN content and molecular weight, the effect of the viscosity ratio was also examined by Wu’s empirical expression.

Estimation of viscosity of by comparing the simulated pressure profile from CAE analysis with the Long Fiber Thermoplastic(LFT) measuring cavity pressure

In this study, we proposed a new method that can estimate viscosity curves of unknown samples or high viscous resins like LFT(Long Fiber Thermoplastics). First, we built the system that could detect the pressure of melt during filling the cavity in a mold. It consists of both pressure sensors which are installed in a mold and the Kit which can convert analog signal to digital signal. The kit measures the melt pressure in mold cavity. We could also simulate the cavity pressure during filling process with commercialized CAE softwares(ex, Moldflow). If the viscosity data in CAE Database were correct, the simulated pressure profile coincided with the measured one. According to our proposed algorithm, we obtained correct viscosity data by iterating the process of comparing the simulated profile with the measured one until both coincided each other. In order to verify this algorithm, we selected well-defined PP resin and concluded that the experimental profile comply with the CAE profile. We could also estimate the optimized viscosity curves for PP-LFT by applying our method.

Measurement of Interface Free Energy in Polypropylene/Ethylene–Propylene Rubber Blends

Measurement of between ethylene–propylene rubber (EPR) and polypropylene (PP) is an important research subject in the study of rubber toughened PP. When the ethylene content in EPR is low, the EPR and the PP phases become optically indistinguishable due to their similar refractive indexes, and thus the measurements of interface free energy by conventional methods are impossible. In this study, we devised a new experimental technique that enables measurement of the interface free energy between two polymers having similar refractive indexes. When small amount of inorganic additives are incorporated to the PP phase, interface between PP and EPR phases are clearly seen and the measurements become attainable. Using the suggested method, the interface free energy between EPR and PPs were obtained and presented. Four different PPs were investigated, homo PP and three random PPs that contain small amounts of ethylene unit ranging from 1 to 3 wt%. It was found that the interface free energy decrease as the ethylene content in the PPs increases and the effect of the ethylene content on the interface free energy is unexpectedly large.

Effect of Aspect Ratio on Electrical, Rheological and Glass Transition Properties of PC/MWCNT Nanocomposites

Since the discovery of carbon nanotubes (CNT), significant research works have focused on the application of CNT as conductive filler to polymer nanocomposites which can be used in several fields such as electrostatic dissipation (ESD), electrostatic painting and electromagnetic interference shielding (EMI-shielding). However, the main challenge in the large-scale manufacturing of this technology is the poor electrical conductivity of polymer nanocomposites produced by injection molding process. This study aims to investigate the effect of CNT aspect ratio in improving the electrical conductivity of injection molded nanocomposites. In this work, three types of multiwall carbon nanotubes with different lengths were melt-mixed with polycarbonate in a twin screw extruder followed by injection and compression molding. Results show that nanocomposites with higher CNT aspect ratio exhibit higher electrical conductivity. Longer nanotubes form a stronger conductive network during secondary agglomeration which can withstand the high shear forces during injection molding. Higher melt viscosity and storage modulus were observed in nanocomposites with higher CNT aspect ratio which is attributed to the effective constriction of polymer chains by longer nanotubes. It was also found that Tg of the composites increased with nanotube aspect ratio and the addition of CNT causes degradation which leads to the general Tg depression of polycarbonate.

Reactive compatibilization of liquid crystalline polymer/ethylene-acrylic acid ionomer blends

This paper describes the reactive compatibilization of blends of a wholly aromatic thermotropic copolyester liquid crystalline polymer (TLCP) with random copolymers of ethylene and acrylic acid (EAA) and their salts. Blends were prepared by melt mixing in an intensive batch mixer, and the formation of a graft copolymer due to acidolysis between the TLCP and the acrylic acid group of the ionomer was evaluated. Chemical reaction was assessed by torque measurement during melt mixing and by thermal analysis and morphological observation. The Na-salt of the EAA ionomers was especially effective at promoting a grafting reaction. The extent of reaction depended not only on the cation, but also composition of the ionomer and reaction time. The product of the grafting reaction between the TLCP and a sodium-neutralized ionomer proved to be an effective compatibilizer for TLCP and EAA ionomers.

Crystallization Behavior and Mechanical Properties of High Density Polyethylene/metallocene catalyzed Poly(ethylene-co-octene) Blends

Compatibility between mLLDPE and HDPE was investigated by observing the crystallization behavior and mechanical properties of their blends. HDPE and mLLDPE blends were prepared by a melt-blending with compositions of 100/0, 80/20, 60/40, 40/60/ 20/80 and 0/100. Four different mLLDPEs containing various octene contents (4.1, 6.8, 9.8 및 12.5 mol.%) were investigated. The melting temperature and crystallization peak temperature of the blends were measured by DSC and the mechanical properties were measured in an universal testing machine. By observation that the melting and crystallization peak temperatures of one component were affected by its counterparts, it was revealed that HDPE and mLLDPE are miscible or at leat partially miscible at molten state. It was also found that the crystalline phase of mLLDPE contains HDPE crystals. However. it was not clear that mLLDPE was cocrystalized in the crystalline phase of HDPE. By various investigation with DSC and mechanical properties, it was concluded that the compatibility between mLLDPE and HDPE decreases with the octene content in the mLLDPE.

Study on Rheological Properties of HBA/HNA Thermotropic Liquid Crystalline Polymer

Rheological measurement of a thermotropic liquid crystalline poymer (TLCP) is not an easy task since their rheological responses are strongly influenced by a thermal history during a processing and thus the reproducibility of the measurement is poor. In order to find out a cause for the strong influence of the thermal history, rheological measurements and DSC observations of the TLCP having various thermal histories were carried out. It was observed that the TLCP used in this study shows liquid-like behavior at a temperature above a crystal-nematic transition temperature (), but at the same time crystallization can occur at this temperature range and as a consequence the viscosity of the polymer continuously increases. When the samples are heated beyond the , all crystals thus formed and the thermal histories were observed to disappear. Crystallization rate of the samples annealed above was very low at even the lowed temperature (). Therefore, it is concluded that rheological measurements of TLCP used in this study must be performed after annealed above the nematic-isotropic transition temperature for better reproducibility.