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In the present study, exfoliated graphite nanoplatelets (EGN) were chemically modified with carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) liquid rubber via carboxylation, acylation, and subsequently esterification. Multiple characterizations by means of attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction spectroscopy, thermogravimetric analysis, and scanning electron microscopy demonstrated the chemical modification. For comparison, neat vinyl ester resin (VE), EGN/VE and CTBN-EGN/VE composites were prepared by using a free-standing Teflon mold to avoid pressure during curing. The amounts of EGN and CTBN-grafted EGN containing in EGN/VE and CTBN-EGN/VE composites were 1, 3, and 5 wt%, respectively. The impact strength of EGN/VE and CTBN-EGN/VE composites was strongly dependent upon the CTBN-grafted EGN concentration incorporated into neat VE. It was remarkably enhanced up to 220–240% even with low contents (5 wt%) of CTBN-grafted EGN in comparison to neat VE and unmodified EGN/VE. The result revealed that a small amount of EGN chemically modified with liquid rubber CTBN played an important role in increasing the impact toughness of thermosetting resin.

Chopped kenaf fibers, poly(lactic acid) (PLA), and ammonium polyphosphate (APP) were uniformly compounded by twin-screw extrusion process, and then kenaf/PLA biocomposites with various APP loadings were fabricated by compression molding. The effects of APP on the flame retardant, tensile, dynamic mechanical, and thermo-dimensional properties were investigated. The biocomposites exhibit highly increased flame resistance, showing the limiting oxygen index increased with increasing the APP loading and the UL-94 V-0 level with 20 wt.% and higher APP loadings. The thermal stability of the biocomposites was increased, whereas the thermal expansion behavior was decreased with increasing the APP loading. The incorporation of APP into the PLA matrix contributed to simultaneously enhancing not only the flame retardancy, thermal stability, and thermo-dimensional stability, but also to enhancing the tensile and storage moduli of kenaf fiber/PLA biocomposites.

The effect of multi-walled carbon nanotubes (MWCNT) coating in the presence of polyethyleneimine (PEI) of different molecular weights (MW) on the interfacial shear strength (IFSS) of carbon fiber/acrylonitrile–butadiene–styrene (ABS) and carbon fiber/epoxy composites was investigated. The IFSS between the carbon fiber and the polymer was evaluated by means of single fiber microbonding test. The results indicated that uses of the carbon fibers uncoated and coated with pristine, low MW PEI-treated, and high MW PEI-treated MWCNT significantly influenced the IFSS of both thermoplastic and thermosetting carbon fiber composites as well as the carbon fiber surface topography. The incorporation of low MW (about 1300) PEI into the carboxylated MWCNT was more effective not only to uniformly coat the carbon fiber with the MWCNT but also to improve the interfacial bonding strength between the carbon fiber and the polymer than that of high MW (about 25,000) PEI. In addition, carbon fiber/epoxy composite exhibited the IFSS much higher than carbon fiber/ABS composite due to the chemical interactions between the epoxy resin and amine groups existing in the PEI-treated MWCNT.

In the present study, how side-feeding of NiCF during twin-screw extrusion processing influences the fiber aspect ratio and thermal, mechanical, electrical, and electromagnetic properties of nickel-coated carbon fiber (NiCF)-reinforced polyamide 6 (PA6) composites was explored. For this, the fiber length distribution, thermal stability, heat deflection temperature, dynamic mechanical property, tensile, flexural, electrical resistivity, and electromagnetic interference shielding effectiveness (EMI SE) properties of NiCF/PA6 composites were extensively investigated. Chopped NiCF was regularly fed via either a main feeder or a side feeder and NiCF/PA6 pellets with different fiber-feeding pathways were prepared. The side-feeding effect of NiCF on the fiber length distribution and the composite properties was studied. The thermal stability, heat deflection temperature, storage modulus, tensile, flexural, and surface resistivity, and EMI SE properties of the NiCF/PA6 composites strongly depended not only on the NiCF content but also on the feeding method (main-feeding or side-feeding) upon extrusion processing, indicating that the fiber length distribution relevant to the fiber aspect ratio was critically important to enhance the composites’ properties. As a result, the NiCF/PA6 composites produced via side-feeding of NiCF exhibited an NiCF distribution longer than that produced via main-feeding, leading to enhancement of the thermal stability, heat deflection temperature, storage modulus, tensile, flexural, and EMI SE properties, strongly depending on the NiCF content.

With the wide spread of IT outsourcing, internal IT personnel have been required to change their roles from system development to organizational change agents such as securing software development outsourcing (SDO) success. Conflict resolution is critical to secure the SDO success, but the understanding of how IT personnel facilitate conflict resolution as change agents is limited. The purpose of this study is to understand the negative impact of conflicts on SDO outcomes and to investigate the moderating effect of IT personnel's conflict resolution facilitation (process facilitation, content facilitation) between conflicts and two SDO outcome dimensions (project efficiency and system effectiveness). In order to test the model, data was collected through a cross-sectional field survey using questionnaires, and a total of 144 SDO projects were used in the final analysis. Research results show that conflicts have a negative impact on both of the SDO outcome dimensions, and the effect of conflict resolution facilitation by IT personnel is contingent on the dimensions of SDO outcomes.

The present study explores the effect of the aspect ratio of carbon fiber on the mechanical, thermal, and impact properties of carbon fiber-reinforced acrylonitrile-butadiene-styrene (ABS) matrix composites, which were produced using: (1) chopped carbon fibers with different lengths by means of twin-screw extrusion followed by injection molding; and (2) long fiber thermoplastic (LFT) pellets with different lengths by means of LFT followed by injection molding. The results revealed that the carbon fiber/ABS composites made by using carbon fiber/ABS LFT pellets exhibited the tensile, flexural, dynamic mechanical thermal, heat deflection temperature, and impact properties higher than those by using conventionally extruded carbon fiber/ABS pellets. It is noted that 12-mm-long LFT pellets contributed most to improving the mechanical and thermal properties of carbon fiber/ABS composites, compared to 6- and 24-mm-long LFT pellets. Meanwhile, the Izod impact strength of the composites was highest in the case of 24-mm-long LFT pellets. The improvements in the mechanical and thermal properties of carbon fiber/ABS composites were explained by different length distribution and aspect ratio of carbon fibers existing in the composites produced via conventional twin-screw extrusion and LFT processes, respectively.

Silk fibroin fabrics (SFF) were irradiated at various electron beam absorption doses. The irradiation effect on the breaking properties of SFF, the fiber topography, and the tensile, flexural and dynamic mechanical properties of 2-directional SFF/poly(lactic acid) (PLA) biocomposites were explored. The irradiation at 10 kGy was most effective not only to increase the SFF breaking properties, but also to enhance the mechanical and thermal properties of SFF/PLA biocomposites. The microscopic analysis of fractured surfaces supported the irradiation dependence of the mechanical and thermal data, showing the increased interfacial bonding between the silk fiber and the PLA, particularly at 10 kGy.

Dual-sizing effects with either epoxy or polyurethane (PU) on the thermal, mechanical, and impact properties of carbon fiber/acrylonitrile-butadiene-styrene (ABS) composites produced by extrusion and injection molding processes were investigated. The heat deflection temperature, dynamic mechanical, tensile, flexural, and impact properties of the composites reinforced with either (epoxy + epoxy) or (epoxy + PU) dual-sized carbon fiber were higher than those commercially single-sized with epoxy. The result indicated that the dual-sized carbon fiber significantly contributed not only to improving the heat deflection temperature and the storage modulus, but also to improving the tensile, flexural, and impact properties of carbon fiber/ABS composites. The highest improvement of the composite properties was obtained from the composite with (epoxy + PU) dual-sized carbon fiber. The improvement of the mechanical and impact properties was explained by the enhanced interfacial bonding between carbon fiber and ABS matrix and by the length distribution analysis of carbon fibers present in the resulting composites. The fiber–matrix interfacial behavior was qualitatively well-supported in terms of fiber pull-out, fiber breaking pattern, and debonding gaps between the fiber and the matrix, as observed from the fracture surface topography. This study revealed that the properties of carbon fiber/ABS composites prepared by extrusion and injection molding processes were improved by dual-sizing carbon fiber, which was performed after a commercial epoxy sizing process, and further improved by using PU as an additional sizing material.

Waste Expanded polypropylene (EPP) was utilized as recycled matrix for kenaf fiber-reinforced polypropylene (PP) composites produced using chopped kenaf fibers and crushed EPP waste. The flexural properties, impact strength, and heat deflection temperature (HDT) of kenaf fiber/PP composites were highly enhanced by using waste EPP, compared to those by using virgin PP. The flexural modulus and strength of the composites with waste EPP were 98% and 55% higher than those with virgin PP at the same kenaf contents, respectively. The Izod impact strength and HDT were 31% and 12% higher with waste EPP than with virgin PP, respectively. The present study indicates that waste EPP would be feasible as recycled matrix for replacing conventional PP matrix in natural fiber composites.

In the present study, the activated carbon composites containing silver (Ag) nanoparticles (Acc-Ag composites) for the production of highly functional wound-dressing additives were fabricated using a thermal treatment under an inert argon (Ar) atmosphere. During the thermal treatment, Ag+ was successfully changed to metallic Ag nanoparticles, and NO3− with a potential cytotoxicity was simultaneously eliminated. The reduction of the Ag+ was confirmed using the XRD and XPS analyses. The optimal manufacturing condition of the Acc-Ag composites was examined with various Acc/Ag ratios, and the Acc-Ag composites still maintained superior pore properties. The deodorizing activity of the Acc-Ag composites was evaluated with the use of the NH3 gas as the deodorization test gas; compared with the pure Acc, the Acc-Ag composites showed an excellent deodorant effect. Furthermore, the antibacterial activity of the Acc-Ag composites was tested against three types of bacterial strain, and the results indicated that the Acc-Ag composites showed an enhanced antibacterial activity. Therefore, the Acc-Ag composites with excellent antimicrobial and deodorant properties have great potential for the functional wound dressings.

To maintain the original function of a specific tissue for therapeutic tissue engineering, an advanced cell culture surface for repeat cell proliferation is necessary. We designed a novel cell proliferation and rapid harvesting surface by combining nonwoven nanofiber mat and a thermo-responsive polymer. Nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) mats were fabricated by the electrospinning technique. A poly(N-isopropylacrylamide) (PNIPAM) thermo-responsive layer was grafted on the PHBV nanofiber mat by electron beam irradiation. The average diameter of the PNIPAM-grafted PHBV nanofibers was determined by SEM. ATR-FTIR and ESCA were used to confirm the grafting of PNIPAM onto the PHBV nanofiber surface. Water contact angles on the mats were measured in response to temperature changes. Human adipose-derived stem cells (ADSCs) were cultured on the PNIPAM-grafted PHBV nanofiber mat to investigate cell proliferation, harvesting, and functionality during repeat subculture. Detached ADSCs from each surface by low temperature treatment and trypsin-EDTA were compared by a fluorescence-activated cell sorter (FACS) using expression of stem cell membrane-specific markers such as CD-13 PE, CD-29 PE, and CD-90 FITC. The mass cultivation and intact harvesting of stem cells by low temperature treatment using a thermo-responsive PHBV nanofiber mat is a promising technique for use in regenerative medicine and stem cell therapy.

분쇄형 탄소섬유(MCF)를 함유한 열전도성 고분자복합체를 제조한 후 열전도도를 측정하였고 매트릭스 내에 분포되어 있는 MCF를 관찰하였다. 매트릭스 수지로는 endo-dicyclopentadiene(endo-DCPD)를 사용하였으며, 수지경화반응 초기에 자기밀도가 0.47 Tesla인 영구자석으로 자기장을 인가하여 MCF를 자기장 방향으로 배열하였다. 수지 내에 소량의 산화철(III)을 첨가하여 인가된 자기장에 의하여 발생되는 액상 수지의 흐름에 통하여 MCF를 배열하였다. 자기장을 인가하지 않은 복합체와 비교하였을 때 8 vol% MCF 함량에서 열전도도가 약 210% 가량 크게 향상되었다. 이러한 향상효과는 자기장 방향으로 MCF의 배열에 기인한 것이며, MCF 배열현상을 광학현미경 관찰을 통해 규명하였다. 본 연구결과는 다른 연구에 비해 영구자석을 사용하여 낮은 자기력에서 매우 간단하면서도 효과적으로 복합체에 높은 열전도도를 부여할 수 있음을 제시하여 준다.

Biocompatible barrier membranes with both hydrophobic and hydrophilic surface properties provide critical backup for guided regeneration at localized bone defects without soft tissue invasion. As a surface modified functional barrier, saturated fluorocarbon (CF4)-immobilized nanofibrous silk fibroin (SF) membranes were fabricated by electrospinning for a fibrous non-woven mat, water vapor treatment for insolubilization, and followed by CF4 gas plasma treatment for top surface hydrophobization. Plasma-treated SF nanofiber membranes maintained a non-woven mat structure without shrinkage and deformation in a five-month biodegradation test. From in vivo rabbit cranium perforation model, nanofibrous SF membranes prevented soft tissue invasion and facilitated volumetric bone regeneration compared with the control groups. New bone ingrowth in bone defects at 4 and 8 weeks after surgery was visualized by trichrome staining. Medical application of fluorocarbon-immobilized nanofibrous SF barrier membranes could be one of the practical approaches for guided bone regeneration. Open image in new window

In efforts to characterize and understand the properties and processing of phenylethynyl-terminated imide (LaRC PETI-5, simply referred to as PETI-5) oligomers and polymers as a high-temperature sizing material for carbon fiber-reinforced polymer matrix composites, PETI-5 imidization and thermal curing behaviors have been extensively investigated based on the phenylethynyl end-group reaction. These studies are reviewed here. In addition, the use of PETI-5 to enhance interfacial adhesion between carbon fibers and a bismaleimide (BMI) matrix, as well as the dynamic mechanical properties of carbon/BMI composites, are discussed. Reports on the thermal expansion behavior of intercalated graphite flake, and the effects of exfoliated graphite nanoplatelets (xGnP) on the properties of PETI-5 matrix composites are also reviewed. The dynamic mechanical and thermal properties and the electrical resistivity of xGnP/PETI-5 composites are characterized. The effect of liquid rubber amine-terminated poly(butadiene-co-acrylonitrile) (ATBN)-coated xGnP particles incorporated into epoxy resin on the toughness of xGnP/epoxy composites is examined in terms of its impact on Izod strength. This paper provides an extensive overview from fundamental studies on PETI-5 and xGnP, as well as applied studies on relevant composite materials.

Extrusion processing and properties of fiber-reinforced polymer matrix composites may be influenced by the fiber feeding route upon extrusion. The purpose of the present study was to investigate the effect of fiber feeding route on the fiber length distribution, electromagnetic interference shielding effectiveness (EMI SE), tensile, and flexural properties and heat deflection temperature of resulting composites with different fiber contents. H–NiCF/polypropylene and S–NiCF/polypropylene pellets were produced through two different feeding routes of nickel-coated carbon fiber (NiCF), hopper feeding (H) and side feeding (S) upon extrusion process, respectively. NiCF-reinforced polypropylene (PP) composites were fabricated by means of compression molding using each pellet, respectively. The effect of fiber feeding route on the electromagnetic, mechanical, and thermal properties of the composites with various NiCF contents was studied. S–NiCF/PP composites exhibited the EMI SE, tensile, and flexural properties and heat deflection temperature higher than H–NiCF/PP composites. The improved properties of S–NiCF/PP composites were ascribed to higher aspect ratio and longer fiber distribution of NiCF remaining in the composite than H–NiCF/PP counterparts, due to less shearing and fiber damages during extrusion.

In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flex-ural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron mi-croscopic observations. The results were compared with a phenolic matrix composite coun-terpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.

In the present work, a multi-functional monomer triallyl isocyanurate (TAIC) of 4 wt.% is incorporated into neat poly(butylene succinate) (PBS) by twin screw extrusion technique and the PBS sheets are irradiated at various electron beam absorption doses. It has been found that electron beam irradiation at an appropriate absorption dose plays an effective role in crosslinking the PBS molecules in the presence of TAIC. As a result, the irradiation influences the gel fraction, glass transition temperature, thermal stability, thermo-dimensional stability, dynamic storage modulus, and tensile properties of PBS, depending on the electron beam absorption dose applied. The improvement of the thermal and mechanical properties of PBS is most significant in the range of 50 to 70 kGy. The results are consistent with each other, supporting the electron beam irradiation effect on the property improvement of PBS. Keywords: Poly(butylene succinate), Multi-functional monomer, Extrusion, Electron beam irradiation, Crosslinking, Properties

To improve photocatalytic efficiency, graphene/Ag/TiO₂ nanotube catalyst was synthesized, and its surface characteristics and photocatalytic activity investigated. For deposition of Ag nanoparticles on the TiO₂ nanotubes, a polymer compound containing CH₃COOAg/poly(Llactide) was utilized, and the silver particles were precipitated by reducing the silver ions during the annealing process. Graphene deposition on the Ag/TiO₂ nanotubes was achieved using an electrophoretic deposition process. Based on the dye degradation results, it was determined that the photocatalytic efficiency was significantly affected by deposition of silver particles and graphene on the TiO₂ catalyst. Highly efficient destruction of the dye was obtained with the new graphene/Ag/TiO₂ nanotube photocatalyst. This may be attributed to a synergistic effect of the graphene and Ag nanoparticles on the TiO₂ nanotubes.

Surface modified carbon felts were utilized as an electrode for the removal of inorganic ions from seawater. The surfaces of the carbon felts were chemically modified by alkaline and acidic solutions, respectively. The potassium hydroxide (KOH) modified carbon felt exhibited high Brunauer-Emmett-Teller (BET) surface areas and large pore volume, and oxygencontaining functional groups were increased during KOH chemical modification. However, the BET surface area significantly decreased by nitric acid (HNO3) chemical modification due to severe chemical dissolution of the pore structure. The capability of electrosorption by an electrical double-layer and the efficiency of capacitive deionization (CDI) thus showed the greatest enhancement by chemical KOH modification due to the appropriate increase of carboxyl and hydroxyl functional groups and the enlargement of the specific surface area.

Background In this study, silk fibroin (SF) composite hydrogels containing hydroxyapatite (HAP) nanoparticles (NPs) for bone tissue engineering were fabricated using gamma-ray (γ-ray) irradiation treatment. During the irradiation, the HAP dispersed SF solution was changed to the chemically crosslinked SF hydrogel. Methods Distribution of HAP NPs in the SF hydrogel was examined by SEM imagery and energy dispersive X-ray spectrophotometry, and the crystalline structure of SF composite hydrogels was also confirmed by X-ray diffractometry. An optimum preparation condition of the SF/HAP composite hydrogels was determined with various HAP contents. For evaluation of the osteogenic differentiation of human mesenchymal stem cells (hMSCs), alkaline phosphatase activity (ALP), HAP nucleation in SBF and in vitro calcium accumulation were measured. Results The results revealed that compared with the pure SF hydrogels, the SF/HAP composite hydrogels improved osteogenic differentiation. Conclusion This paper demonstrates the great potential of the SF/HAP composite hydrogels in terms of the production of the bone tissue engineering scaffolds for which osteogenesis is required.

An injectable adhesive hydrogel composed of carboxymethyl cellulose (CMC) and pullulan is developed and evaluated as a postoperative anti-adhesion barrier. CMC was modified with tyramine to introduce crosslinking site via an EDC-NHS reaction. The in situ hydrogel was prepared by an enzyme-mediated reaction of tyramine-immobilized CMC with horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). Pullulan was added to the hydrogel solution to improve adhesiveness to the wound area and accelerate biodegradation. The modified CMC was confirmed by ATR-FTIR spectroscopy. The gelation time, storage modulus (G'), and weight loss of the hydrogels were measured as functions of the amounts of HRP and H2O2. The hydrogel group showed negligible cell proliferation and cytotoxicity, compared to that shown by the control group. The in vivo animal test demonstrated that significant decrease of postoperative tissue adhesion by applying the hydrogels. The CMC-pullulan hydrogel could be a useful treatment as an injectable in situ anti-adhesive agent.

Silk Fibroin (SF) nanofibers containing various silver compounds, such as silver tetrafluoroborate, silver phosphate, silver sulfadiazine, and silver acetate, were prepared by electrospinning. Silver compounds were dissolved into SF solution in 98% formic acid. In this system, the formic acid was used both as a co-solvent of SF and silver compounds, and as a reducing agent for silver ions in solution. The average diameters of SF nanofibers varied depending on the type of silver compounds added. The Ag element in the SF nanofibers was confirmed to be mainly Ag nanoparticles by XPS results. The in vitro cytotoxicity of silver compounds in SF nanofibers on normal human keratinocytes and fibroblasts was examined. Overall, the silver compounds in SF nanofibers are cytotoxic to both normal human epidermal keratinocytes (NHEK) and normal human epidermal fibroblasts (NHEF) cells. Open image in new window

Saturated fluorocarbon (CF4) immobilized silk fibroin (SF) nanofibrous membranes were prepared and characterized for biomedical applications. Biocompatible barrier membranes that provide both hydrophobic and hydrophilic surface properties on each side are critical to prohibit soft tissue invasion into localized bone defect. As a barrier membrane, SF nanofibrous mat was fabricated by electrospinning method, and then subsequently modified with water vapor treatment for insolubilization in water and CF4 gas plasma treatment for surface hydrophobization. Morphology of SF nanofibrous mats were observed by scanning electron microscopy. Conformational change of insolubilized SF nanofibers was confirmed by attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and 13C nuclear magnetic resonance (NMR) spectroscopy. Immobilized fluorine atoms on CF4 plasma treated SF nanofibrous membranes were detected using electron spectroscopy for chemical analysis (ESCA). Water contact angle of the SF nanofiber membrane surface was analyzed by varying plasma input power and time. Insolubilized SF nanofibrous membrane maintained nonwoven mat structure without deformation after water immersion. SF nanofibrous membranes showed significant increment of water contact angle from 99.7° to 141.2° by CF4 gas plasma treatment. Fibroblasts on plasma untreated SF nanofibrous membranes were well attached and spread than a control tissue culture polystyrene dish. Fibroblasts on the CF4 gas plasma treated SF nanofibrous membrane showed significantly lower proliferation behavior than plasma untreated SF nanofibrous membranes. Fluorocarbon immobilized SF nanofibrous barrier membrane will be useful for biomedical applications such as a guided bone regeneration. Open image in new window