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Effect of the sizes and shapes of the diverse carbon allotropes such as carbon black, carbon nanotube, graphene nanoplatelet, graphite, pitch-based carbon fiber (PCF), and expanded graphite (EG) on the thermal conductivity of polymer composites is investigated. Effective improvement of the thermal conductivity of composites with microsized one-dimensional (1D) PCF and EG including the intercalation spacing is observed due to efficient formation of thermal transfer networks and little phonon scattering at the interfaces by the reduction of the interfaces. The excellent bulk and in-plane thermal conductivity of the composites with 20 wt% EG fillers of 1.9 and 6.7 Wm−1K−1 is observed.

Thermoplastic carbon fiber fabric reinforced composites (CFFRCs) were prepared using a novel fast manufacturing process with a low viscosity polymerizable cyclic butylene terephthalate (CBT) resin. Structure and properties of the composites altered by thermal annealing were investigated to develop appropriate post processing of the CFFRCs for fast production and lowering the processing cost. Annealing at 200°C for 120 min resulted in improved mechanical properties and thermal stability of the polymerized CBT (pCBT) based on differential scanning calorimetry, wide-angle X-ray diffraction, and thermo gravimetric analysis. The tensile strength of the CFFRC compression molded at 250°C for 2 min was 440 MPa and that of the CFFRC annealed at 200°C for 120 min after compression molding was 500 MPa, which is an improvement of 550 and 625% relative to the pCBT matrix, respectively. In addition, the thermal stability of the CFFRC annealed at 250°C for 120 min improved by 10°C. Therefore, tensile strength and thermal stability of the manufactured CFFRC can be improved by using the appropriate annealing conditions. POLYM. ENG. SCI., 54:2161–2169, 2014. © 2013 Society of Plastics Engineers

The Bcl-2-interacting death suppressor (Bis) protein is involved in antiapoptosis and antistress pathways. However, its roles after neonatal hypoxia-ischemia remain obscure. Therefore, we investigated the effects of Bis deletion on hippocampal cell death following neonatal hypoxia-ischemia. We transected the right common carotid artery of bis(+/+) and bis(-/-) mice at postnatal Day 7 and subjected them to hypoxia for 35 min. Cresyl violet staining showed that hypoxia-ischemia induced progressive cell death in the hippocampi of bis(+/+) mice. Moreover, Bis was expressed in astrocytes, not microglia, in sham-manipulated hippocampi of bis(+/+) mice, and was markedly enhanced after hypoxia-ischemia. Immunoblotting showed that Bis expression significantly increased 3 and 7 days following hypoxia-ischemia. Unexpectedly, 7 days after hypoxia-ischemia, the number of hippocampal NeuN-positive cells was higher in the bis(-/-) mice than in the bis(+/+) mice. We subsequently performed transcriptomic analysis and quantitative real time polymerase chain reaction to search for the underlying genes responsible for resistance to hypoxia-ischemia in the bis(-/-) hippocampus. These studies showed that 6 h after hypoxia-ischemia, galectin 3 and filamin C levels increased to a lesser extent in the bis(-/-) hippocampi compared with the bis(+/+) hippocampi. Finally, our in vitro hypoxia-ischemia model, using A172 glioma cells and primary astrocytes, showed that downregulation of Bis blocked the enhanced expression of galectin 3 after oxygen-glucose deprivation. This study demonstrated that Bis was upregulated in the astrocytes after hypoxia-ischemia. In addition, we showed that hippocampal neurons are less vulnerable to hypoxia-ischemia in mice lacking Bis, possibly because of the modulation of galectin 3 induction.

Residual stresses and thermoviscoelastic deformation of a laminated film utilized for film insert molding was investigated through measurement of thermal expansion coefficient (CTE) and relaxation modulus. Thermoviscoelastic deformation of the film was also analyzed with numerical analysis by applying measured relaxation modulus, CTE, and residual stress to finite element method (FEM). Stress relaxation of the pristine film showed significantly different behavior from that of the unannealed film during annealing. Effects of the CTE and relaxation modulus on the thermoviscoelastic deformation were predicted by considering thermal shrinkage and structural relaxation. Moreover, numerical results on thermoviscoelastic deformation were in good agreement with experiments when initial stress distribution in the solid specimen was applied to the numerical analysis. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Back-injection of polymeric liquid to preformed films, also known as film insert molding (FIM), provides the surface quality of polymeric parts. The back-injection material is responsible for mechanical and thermal properties of the part, especially such as stiffness and thermal expansion. In the back-injection molding it is important to ensure that the inserted films are not wrinkled by the injection of molten polymers. In this study, FIM was carried out with utilizing polycarbonate/acrylonitrile butadiene styrene (PC/ABS) alloy and polymethyl methacrylate/acrylonitrile butadiene styrene (PMMA/ABS) film. The wrinkling of films was observed by the atomic force microscope (AFM). Numerical simulations were performed to understand the mechanism of the film wrinkling and optimize the processing conditions of FIM for high precision parts by using commercial packages including Hypermesh™, Moldflow™, and COMSOL™. A critical shear rate for the film wrinkling of a center garnish part was determined based on the deformation energy of plate. It was found that the critical shear rate calculated numerically was in good agreement with that of the film insert molded parts. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

The dimensional variation of an injection-molded, semicrystalline polymer part is larger than the variation of an amorphous polymer part because the shrinkage of a crystalline polymer is generally greater than the shrinkage of an amorphous one. We investigated the warpage of film-insert-molded (FIM) specimens to determine the effect of the crystallization behavior on the deformation of FIM parts. More perfect crystalline structures and higher crystallinity developed in the core region of the FIM specimens versus other regions. Relatively imperfect crystalline structures and low crystallinity developed in the adjacent regions of the inserted films, whereas a thin, amorphous skin layer developed in the adjacent regions of the metallic mold wall. The crystallizable substrate in the FIM specimens caused very large warpage because nonuniform shrinkage occurred in the thickness direction of the specimens. Therefore, the warpage of an experimentally prepared FIM poly(butylene terephthalate) specimen was greater than that predicted numerically because of its complex crystallization behavior.

Complex automotive parts were produced by film insert molding and the ejected parts were annealed to investigate the viscoelastic deformation. Warpage of the part was predicted by numerical simulation of mold filling, packing, and cooling stages with non-isothermal three-dimensional flow analysis. The flow analysis results were transported to a finite element stress analysis program and the stress analysis was performed by using time-temperature superposition principle to investigate viscoelastic deformation. Predicted residual stresses, viscoelastic deformation, and warpage showed good agreement with experimental results. Thermal shrinkage of the inserted film and relaxation of the residual stress affected the viscoelastic deformation of the part significantly during annealing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Three-dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in-mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in-mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Impregnation of the multi-layered fiber preform with injected resin was analyzed by using the control volume finite element method for three-dimensional mold filling simulation of the resin transfer molding (RTM). Numerically predicted flow fronts were compared with experimental data to validate accuracy of the numerical results and applicability of the numerical code developed in this study. Since isothermal Newtonian flow was assumed, Darcy's law and continuity equation were used as governing equations and permeability tensors employed for each layer. Flow simulation was conducted for the two types of mold geometries, i.e., rectangular plate and hollow cylinder. It was proven by comparing numerical results with experimental data that the simulation code is accurate enough to predict the flow patterns, especially when multi-layered preforms were placed in the cylindrical mold. It was also found that the filling time was reduced by using outer gates compared with the case of inner gates. Three-dimensional numerical simulation provided useful information for mold filling and can be used to design an optimum mold and make the RTM process efficient. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Rheological behaviors of polypropylene/layered silicate nanocomposites were investigated in both shear and uniaxial elongational flows. They were analyzed by using the K-BKZ constitutive equation with two damping functions, for example, the WD-FO and PSM-LT models in transient and steady elongational viscosities. Although pure PP matrix and uncompatibilized nanocomposite did not show the strain hardening, compatibilized nanocomposite showed outstanding strain-hardening behavior due to three-dimensional network structure. Predictions of WD-FO and PSM-LT models gave good agreement with the experimental results at low elongational rate region. However, the elongational viscosity calculated with the WD-FO model did not predict the steady-state value and diverged to infinity when . The PSM-LT model offered good description on transient and steady elongational viscosities even at higher elongational rates as well as on strong strain-hardening behavior of compatibilized nanocomposites. Through the numerical analysis, using the K-BKZ model with two types of damping functions, it was found that the PSM-LT model was superior to that of the WD-FO model in rheological modeling of PP/layered silicate nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

BACKGROUND: The effects of filler geometry are important for understanding the internal structure and physical properties of polymer composites. To investigate the effects of filler geometry on electrical conductivity as well as morphological and rheological properties, three types of polycarbonate (PC) composites were prepared by melt compounding with a twin-screw extruder. RESULTS: The electrical conductivity of PC/carbon black (CB) and PC/graphite (carbon) nanofibre (CNF) composites did not show a percolation threshold through the entire filler loading ranges. However, PC-blend-carbon nanotube (CNT) composites showed a percolation electrical threshold for a filler loading of 1.0 to 3.0 wt% and their maximum electrical conductivity approached 10−3 S m−1. PC-blend-CB and PC-blend-CNF composites showed Newtonian behaviour like pure PC matrix, but PC-blend-CNT composites showed yield stress as well as increased storage modulus and strong shear thinning behaviour at low angular frequency and shear rate due to strong interactions generated between CNT–CNT particles as well as PC molecules and CNT particles on the nanometre scale. CONCLUSIONS: The electrical conductivity of the PC composites with different carbon constituents was well explained by the continuous network structure formed between filler particles. The network structure was confirmed by the good dispersion of fillers as well as by the yield stress and solid-like behaviour observed in steady and dynamic shear flows. Copyright © 2009 Society of Chemical Industry

Film-insert-molded (FIM) tensile specimens were prepared under various molding conditions to investigate the effects of wall temperature and packing pressure on the residual stress distribution and thermoviscoelastic deformation. The warpage of the specimen increased with increasing mold-wall temperature difference and decreased with increasing packing pressure. The FIM specimens produced with unannealed films showed the warpage reversal phenomenon (WRP) during annealing and the degree of WRP was affected significantly by the molding conditions and thermal shrinkage of the film. The warpage of the specimen was predicted by three-dimensional flow and stress analyses and the prediction was in good agreement with the experimental results.

Film insert molding (FIM) has been modeled numerically to predict residual stress and viscoelastic deformation of the part. Nonisothermal three dimensional flow analysis for filling, packing, and cooling stages was carried out by using a commercial software. It was assumed that the inserted film was solid throughout the entire molding procedure although remelting could occur at the interface with the substrate. The flow analysis results, e.g., temperature, stress, and density distribution in the substrate domain, were transported to a finite element stress analysis program for viscoelastic stress analysis. Deflection of the FIM part was obtained as soon as the part was ejected from the mold by assuming isotropic elastic material. The residual stress distribution in the FIM part was acquired by removing the constraints along the boundary of the molded part. Viscoelastic deformation of the FIM part was predicted by performing viscoelastic stress analysis in order to understand long term behavior of the FIM part when exposed to room temperature. Durability of automotive and electronic parts produced by the film injection molding can be predicted by the procedure adopted in this study. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Thermotropic liquid crystal polymer (TLCP)/ poly(ethylene 2,6-naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin-draw process. In this study, we suggest novel drawing technology using the CO2 laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 1358C for 10 min. It was confirmed that the CO2 laser draw- ing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO2 laser-drawing method has a great potential for industrial applications as a novel fiber-drawing process, and it can also be applied con- tinuously to conventional spin-draw system. 2007 Wiley

BACKGROUND: The melt blending of thermotropic liquid crystal polymers (TLCPs) using conventional thermoplastics has attracted much attention due to the improved strength and tensile modulus of the resulting polymer composites. Moreover, because of their low melt viscosity, the addition of small amounts of TLCPs can reduce the melt viscosity of polymer blends, thereby enhancing the processability. RESULTS: In this study, TLCP/poly(ethylene 2,6-naphthalate) (PEN) blend fibers were prepared by melt blending and melt spinning to improve fiber performance and processability. The relation between the structure and the mechanical properties of TLCP/PEN blend fibers and the effect of annealing on these properties were also investigated. The mechanical properties of the blend fibers were improved by increasing the spinning speed and by adding TLCP. These properties of the blend fibers were also improved by annealing. The tensile strength of TLCP5/PEN spun at a spinning speed of 2.0 km h−1 and annealed at 235 °C for 2 h was about three times higher than that of TLCP5/PEN spun at a spinning speed of 0.5 km h−1. The double melting behavior observed in the annealed fibers depended on the annealing temperature and time. CONCLUSION: The improvement of the mechanical properties of the blend fibers with spinning speed, by adding TLCP and by annealing was attributed to an increase in crystallite size, an increase in the degree of crystallinity and an improvement in crystal perfection. The double melting behavior was influenced by the distribution in lamella thickness that occurred because of a melt-reorganization process during differential scanning calorimetry scans. Copyright © 2007 Society of Chemical Industry

White matter lesions are thought to result from chronic cerebral ischemia and constitute a core pathology of subcortical vascular dementia. This rarefaction has been known to be associated with microglial activation. We investigated whether minocycline, a microglial inhibitor, attenuates the white matter damage induced by chronic cerebral hypoperfusion that is used as a model of vascular dementia. Male Wistar rats were subjected to bilateral, permanent occlusion of the common carotid arteries (BCCAO) to induce chronic cerebral hypoperfusion. Minocycline or saline was injected daily for 2 weeks after BCCAO. In the corpus callosum and the optic tract, white matter damage observed with Klüver-Barrera staining was significantly attenuated in the minocycline-treated group compared to saline-treated controls. In control rats, immunoreactivities of major basic protein (MBP), Ox-42 as a microglial marker, and matrix metalloproteinase (MMP)-2 were increased in the corpus callosum. Minocycline significantly reduced these changes. Co-expression of Ox-42 and MMP-2 was confirmed by double immunofluorescence histochemistry. Our results suggest that chronic treatment with minocycline could be protective against at least some ischemic white matter damage, and its mechanism may be related to suppressing microglial activation.

Previous in vitro studies using cell cultures or brain slices have demonstrated that phospholipase D (PLD) in the nervous system is involved in the signaling mechanism in response to a variety of agonists. However, little is known about the pathophysiological role of PLD-mediated signaling in the adult brain. We examined the changes in the expression of a PLD isozyme, PLD1, in the adult rat hippocampus, using immunological approaches and an assay for PLD activity after transient forebrain ischemia (four-vessel occlusion model) that results in the selective delayed death of CA1 pyramidal cells and induces reactive astrocytes in the CA1 subfield. In the control hippocampus, PLD1 the level of immunoreactivity was very low. After ischemia, in parallel with the results of Western blot analysis and the PLD activity assay, immunohistochemical analysis of PLD1 demonstrated that the immunoreactive proteins peaked at 7-14 days and were most prominent in the CA1 and the dentate hilar region. The temporal and spatial patterns of immunoreactivity of both PLD1 and glial fibrillary acidic protein (GFAP) were very similar, indicating that reactive astrocytes express PLD1, confirmed by double staining for PLD1 and GFAP. These results demonstrate that reactive astrocytes upregulate PLD in vivo after injury in the adult rat hippocampus.

Rectangular plates of the size of 1800 × 600 × 12 mm3 and 1200 × 600 × 12 mm3 were selected for injection molding and injection compression molding, respectively, in order to investigate warpage characteristics of the large-sized polymer plates with orthogonal stiffener. To determine the mold system and to reduce warpage of the specimen, numerical analyses for injection molding and injection compression molding were performed by using a commercial simulation code. Experiments were performed to verify the suggested mold system and warpage of the specimen. Relatively large warpage of the injection molded product was observed and small warpage of the injection compression molded product was generated. Compression force of the injection compression molding was only 6% of the clamp force of the injection molding. Warpage of the product was reduced significantly by using the injection compression molding. The injection compression molding will be used to substitute expensive and disused wood forms with inexpensive and recyclable polymer plates for concrete casting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

In this study, experimental and numerical studies were performed to investigate the relationship among the functionalization method, weight fraction of MWCNTs, thermal imidization cycle, and mechanical properties of various PAI/MWCNT composite films. Poly(amide-co-imide)/multiwalled carbon nanotube composite films were prepared by solution mixing and film casting. The effects of chemical functionalization and weight fraction of multiwalled carbon nanotubes on thermal imidization and mechanical properties were investigated through experimental and numerical studies. The time needed to achieve sufficient thermal imidization was reduced with increasing multiwalled carbon nanotube content when compared with that of a pure poly(amide-co-imide) film because multiwalled carbon nanotubes have a higher thermal conductivity than pure poly(amide-co-imide) resin. Mechanical properties of pure poly(amide-co-imide) and poly(amide-co-imide)/multiwalled carbon nanotube composite films were increased with increasing imidization time and were improved significantly in the case of the composite film filled with hydrogen peroxide treated multiwalled carbon nanotubes. Both the tensile strength and strain to failure of the multiwalled carbon nanotube filled poly(amide-co-imide) film were increased substantially because multiwalled carbon nanotube dispersion was improved and covalent bonding was formed between multiwalled carbon nanotubes and poly(amide-co-imide) molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Virgin injection-molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three-dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009