• Clean Technology
• /
• v.15 no.2
• /
• pp.102-108
• /
• 2009

In this study, poly(lactic acid) (PLA) was modified by reactive extrusion with a functional monomer GMA(glycidyl methacrylate), MMT(montmorillonite), and initiator to enhance the melt strength. Each modified PLA was prepared with different amounts of GMA and MMT and was characterized by measuring thennal- and melt-viscoelastic properties. The degree of dispersion of MMT was measured by X-ray diffraction(XRD) and transmission electron microscopy(TEM). The glass transition temperature($T_g$) of modified PLA-GMA-MMT nanocomposite decreased with increasing GMA content, but was a little affected by the amount of MMT. Surface analysis showed that the nanocomposite became more intercalated than exfoliated as the amount of MMT increases. The complex viscosity and storage modulus of the nano-composite were greatly increased by addition of MMT.

• Applied Chemistry for Engineering
• /
• v.25 no.3
• /
• pp.318-323
• /
• 2014

In order to analyze the effect of maleic anhydride (MAH) content and styrene monomer (SM)/MAH mole ratio on reactive extrusion of maleic anhydride grafted random polypropylenes (MAH-g-rPP), MAH-g-rPPs were prepared by using a twin screw extruder. MAH contents were 0.5, 1.0, 3.0, and 5.0 phr and SM/initiator mole ratio was 0.0, 1.0, and 2.0. Dicumyl peroxide (DCP) was used as an initiator. The graft degree of MAH was confirmed by the existence of carbonyl group (C = O) stretching peak at $1700cm^{-1}$ from FT-IR spectrum. The degree of graft reaction increased up to 3.0 phr MAH and showed the optimum value at 1.0 SM/MAH mole ratio from the area ratio of C = O and C-H stretching peak. Thermal and crystallization properties of MAH-g-rPP and PP/MAH-g-rPP/pulp composites were investigated by DSC, TGA, XRD, and POM. There was a decrease in non-isothermal crystallization temperature of PP/MAH-g-PP/pulp composites. Based on tensile properties and SEM pictures for the fractured surface of PP/MAH-g-PP/pulp composites, MAH content of 1.0 wt% and SM/MAH mole ratio of 1.0 were the optimum formulation as the compatibilizer. The rheological properties of the composites were measured by dynamic Rheometer to compare the processability of the composites with and without compatibilizer. The power law index showed slightly low value at the composites with compatibilizer.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1294-1295
• /
• 2006

Various reactions and the in-situ formation of new phases can occur during the mechanical alloying process. In the present study, Al powders were strengthened by AlN, using the in-situ processing technique during mechanical alloying. Differential thermal analysis and X-ray diffraction studies were carried out in order to examine the formation behavior of AlN. It was found that the precursors of AlN were formed in the Al powders and transformed to AlN at temperatures above $600^{\circ}C$. The hot extrusion process was utilized to consolidate the composite powders. The microstructure of the extrusions was examined by SEM and TEM. In order to investigate the mechanical properties of the extrusions, compression tests and hardness measurements were carried out. It was found that the mechanical properties and the thermal stability of the Al/AlN composites were significantly greater than those of conventional Al matrix composites.

• The Korean Journal of Physiology and Pharmacology
• /
• v.21 no.2
• /
• pp.233-239
• /
• 2017

Intracellular calcium ($Ca^{2+}$) oscillation is an initial event in digestive enzyme secretion of pancreatic acinar cells. Reactive oxygen species are known to be associated with a variety of oxidative stress-induced cellular disorders including pancreatitis. In this study, we investigated the effect of hydrogen peroxide ($H_2O_2$) on intracellular $Ca^{2+}$ accumulation in mouse pancreatic acinar cells. Perfusion of $H_2O_2$ at $300{\mu}M$ resulted in additional elevation of intracellular $Ca^{2+}$ levels and termination of oscillatory $Ca^{2+}$ signals induced by carbamylcholine (CCh) in the presence of normal extracellular $Ca^{2+}$. Antioxidants, catalase or DTT, completely prevented $H_2O_2$-induced additional $Ca^{2+}$ increase and termination of $Ca^{2+}$ oscillation. In $Ca^{2+}$-free medium, $H_2O_2$ still enhanced CCh-induced intracellular $Ca^{2+}$ levels and thapsigargin (TG) mimicked $H_2O_2$-induced cytosolic $Ca^{2+}$ increase. Furthermore, $H_2O_2$-induced elevation of intracellular $Ca^{2+}$ levels was abolished under sarco/endoplasmic reticulum $Ca^{2+}$ ATPase-inactivated condition by TG pretreatment with CCh. $H_2O_2$ at $300{\mu}M$ failed to affect store-operated $Ca^{2+}$ entry or $Ca^{2+}$ extrusion through plasma membrane. Additionally, ruthenium red, a mitochondrial $Ca^{2+}$ uniporter blocker, failed to attenuate $H_2O_2$-induced intracellular $Ca^{2+}$ elevation. These results provide evidence that excessive generation of $H_2O_2$ in pathological conditions could accumulate intracellular $Ca^{2+}$ by attenuating refilling of internal $Ca^{2+}$ stores rather than by inhibiting $Ca^{2+}$ extrusion to extracellular fluid or enhancing $Ca^{2+}$ mobilization from extracellular medium in mouse pancreatic acinar cells.

• Polymer(Korea)
• /
• v.31 no.4
• /
• pp.283-288
• /
• 2007

Polymer blends containing poly(acrylonitrile-butadiene-styrene) (ABS) and polycarbonate(PC) (70/30, wt%) with compatibilizer were prepared using twin screw extruder. Compatibilizers were prepared by reactive extrusion with the ABS, maleic anhydride(MAH) and dicumyl peroxide(DCP) using twin screw extruder In the ABS/PC (70/30) blends, tensile strength did not change significantly, but increased from 52.25 to 55.03 MPa when the ABS-g-MAH was added in the amount of 5 phr. From the results of rheological properties, storage modulus of the ABS/PC/ABS-g-MAH blends at low frequencies showed lager value than that of the ABS/PC(70/30) blend. From the results of the morphological properties of the ABS/PC(70/30) blend, it was observed that the drop size of the PC ranged from 1.2 to $1.5\;{\mu}m$ and did not change significantly with the addition of the ABS-g-MAH($1{\sim}10\;phr$). From the results of the storage modulus, complex viscosity, and tensile strength of the ABS/PC (70/30) blends, it is found that the ABS-g-MAH is an effective compatibilizer in the ABS/PC (70/30) blends when the ABS-g-MAH is added in the amount of 5 phr.

• Applied Chemistry for Engineering
• /
• v.10 no.4
• /
• pp.497-501
• /
• 1999

The changes of properties were studied for the polypropylene(PP)/Nylon6 blends containing different kinds of compatibilizer made by either reactive extrusion of solution reaction. The compatibilizers were PP grafted with maleic anhydride (MAH) made by reactive extrusion and solution reaction. The grafted MAH contents were 0.3 wt %, and 2.7 wt %, respectively. The composition of the PP/nylon6 blend was fixed at 75/25 by weight. Blending was carried out with twin-screw extruder (L/D=30, ${\psi}=30$) at 300 rpm. As the content of PP-g-MAH was increased, the crystallization peak of Nylon6 decreased gradually then finally disappeared. Disappearance of crystallization peak of Nylon6 was mostly affected by grafted MAH content rather than the preparation method and the amount of compatibilizer. The portion of Nylon6 that could not crystallize in its normal crystallization temperature crystallized together with PP at the crystallization temperature of PP. So called concurrent crystallization was observed. Meanwhile two more peaks were observed during heating cycle. One was exothermic peak at $193^{\circ}C$ near to crystallization temperature of Nylon6, the other was endothermic peak at $215^{\circ}C$ that was $5^{\circ}C$ lower than normal endothermic peak of Nylon6. To analyze the peaks, nylon6 was annealed in the differential scanning calorimeter. As a result, the peak at $193^{\circ}C$ was crystallization peak of imperfect crystalline of Nylon6 and the other peak at $215^{\circ}C$ was melting peak of imperfect crystalline of nylon6.

• Asian-Australasian Journal of Animal Sciences
• /
• v.29 no.3
• /
• pp.352-358
• /
• 2016

Quercetin (QT) and taxifolin (TF) are structurally similar plant-derived flavonoids that have antioxidant properties and act as free radical scavengers. The objective of this study was to investigate effects of QT and TF on nuclear maturation of porcine oocytes. Effects of TF at 0, 1, 10, and $50{\mu}g/mL$ on oocyte nuclear maturation (polar body extrusion) were investigated. After incubation for 44 h, there were no significant differences between the treatment and control groups except in the $50{\mu}g/mL$ group which was significantly lower (59.2%, p<0.05) than the other groups (control: >80%). After parthenogenetic activation, further in vitro development of QT- or TF-treated vs control oocytes was investigated. A significantly higher proportion of QT-treated ($1{\mu}g/mL$) oocytes developed into blastocysts compared to controls (24.3% vs 16.8%, respectively); however, cleavage rate and blastocyst cell number were not affected. The TF-treated group was not significantly different from controls. Levels of reactive oxygen species (ROS) and intracellular glutathione (GSH) in oocytes and embryos in a culture medium supplemented with QT or TF were measured. Both treatment groups had significantly lower (p<0.05) levels of ROS than controls, however GSH levels were different only in QT-treated oocytes. We conclude that exogenous flavonoids such as QT and TF reduce ROS levels in oocytes. Although at high concentration ($50{\mu}g/mL$) both QT and TF appear to be toxic to oocytes.

• Polymer(Korea)
• /
• v.26 no.1
• /
• pp.139-144
• /
• 2002

In this study, the PPS/ABS blend system was investigated in order to identify the relationship between the incorporation of compatabilizing moieties and the mechanical properties. ABS resin was chemically modified by the incorporation of maleic anhydride using reactive extrusion method to yield MABS resin, and PPS/MABS blend was prepared by a twin screw extruder. Single glass transition behavior was observed in the various compositions of PPS/MABS blend by dynamic mechanical analysis study. Upon the examination of the mechanical properties, the PPS/MABS blend exhibited an enhanced tensile, flexural and impact strength, which might be due to the better chemical compatibilization to result in the reduced interfacial tension between each components.

• Macromolecular Research
• /
• v.13 no.5
• /
• pp.367-372
• /
• 2005

As a preliminary work for the preparation of nylon 6/c1ay nanocomposites by reactive extrusion, nylon 6/c1ay nanocomposites were prepared by anionic polymerization in a flask. In order to investigate the effect of the intercalation of clay layers, the clay feeding times, such as in pre-mixing where the clay was fed before initiation of polymerization and in after-mixing method where the clay was fed after initiation of polymerization, were changed. The appearance of the WAXD peak of nanocomposites prepared by the pre-mixing method was obvious and the tensile strength was decreased compared with that of pure nylon 6, which indicates that the clay layers were not dispersed and distributed. During the preparation of the nanocomposites by the after-mixing method, disordering of the clay layers was observed with increasing clay addition time and was suspected to result from the rapid polymerization of nylon 6 within the clay layers.

• Polymer(Korea)
• /
• v.24 no.3
• /
• pp.366-373
• /
• 2000

In this study, the PPS/ABS blend system was investigated in order to collectively identify the relationship among blend morphology, chemical compatibilization and thermal property. ABS resin was chemically modified by the incorporation of maleic anhydride through reactive extrusion for enhanced compatibilization, and PPS, ABS and the modified ABS were blend by a sing twin screw extruder. The effect of chemical modification of ABS on the morphological, mechanical, and thermal properities of the resulting blend was examined. A strong interaction was observed between PPS and MABS by optical microsopy as well as scanning electron microscopy, exhibiting a well-dispersed morphological feature. The PPS/MABS blend showing a single glass transition temperature was observed in dynamic mechanical analysis, demonstrating a pseudo-homogeneous phase morphology induced by chemical compatibilization. PPS/MABS blend also exhibited an enhanced thermal stability and heat distortion temperature compared with modified PPS/ABS blend.