Woong-Ki Choi

Effects of comonomer with carboxylic group on stabilization of high molecular weight polyacrylonitrile nanofibrous copolymers

New precursors, poly(acrylonitrile-co-crotonic acid) (poly(AN-CA)) and poly(acrylonitrileco-itaconic acid-co-crotonic acid) (poly(AN-IA-CA)) copolymers, for the preparation of carbon fibers, were explored in this study. The effects of comonomers with acidic groups, such as crotonic acid (CA) and/or itaconic acid (IA), on the stabilization of nanofibrous polyacrylonitrile (PAN) copolymers were studied. The extent of stabilization, evaluated by Fourier transform infrared spectroscopy, revealed that the CA comonomer could retard/control the stabilization rate of PAN, in contrast to the IA comonomer, which accelerated the stabilization process. Moreover, the synthesized PAN copolymers containing CA possessed higher Mv than those of the IA copolymers and also showed outstanding dimension stability of nanofibers during the stabilization, which may be a useful property for improving the dimensional stability of polymer composites during manufacturing.

Mechanical interfacial adhesion of carbon fibers-reinforced polarized-polypropylene matrix composites: effects of silane coupling agents

Thermoplastic composites are used in a variety of applications such as mass transit, auto-motive parts, and military structures [1-6]. Their appeal compared to conventional materials such as aluminum, steel, and thermoset composites for these applications lies in their high specific strength, corrosion resistance, superior impact resistance, high toughness, and ease of recycling [1-7].In recent years, carbon fibers (CF) have been widely used as reinforcing materials in high performance composites. CF present several advantages, including high modulus and strength, good stiffness, and creep resistance [8-10]. Despite these advantages, the CF/ther-moplastic composites have unsatisfactory mechanical properties because CF have poor in-terfacial adhesion with most thermoplastic polymers due to their non-polar surface.The interfacial adhesion between reinforcing fibers and polymer matrices in composites is the controlling factor in obtaining optimum mechanical properties of composites [11-13]. To achieve good interfacial adhesion between CF and thermoplastic matrices, it is necessary to increase the surface polarity. In this light, increasing the surface polarity for van der Waals forces and hydrogen bonding can improve the interfacial adhesion. In efforts to increase the surface polarity of CF, various surface treatment techniques have been applied, including plasma treatment, anodic oxidation, metal plating, and cou-pling treatment [14,15]. Among the various treatments, coupling treatment is known to be a very effective method for improving the interfacial adhesion between the fibers and the thermoplastic matrices [16].The role of coupling agents in improving the interfacial adhesion between polymers and inorganic surfaces has been widely documented [17,18]. However, the effects of different coupling agents on interfacial adhesion between CF and polar-modified thermoplastic matri-ces have yet to be explicitly identified. Therefore, the first objective of this study is to evaluate the influence of sizing treatments by silane-based coupling agents on the interfacial adhesion properties between the fibers and the thermoplastic matrix. Another objective is to investigate the effects of the presence of surface functional groups containing silane-oxygen groups on the mechanical properties of carbon fiber-reinforced maleic anhydride-grafted polypropylene.The CF used in this work were polyacrylonitrile based high strength fibers, T-700SC-13000 (12K unidirectional fabric; Toray, Tokyo, Japan). The average diameter of these CF was around 7 μm. A highly polarized polypropylene sheet prepared by maleic anhydride grafting (Homan Petrochemical Co, Seoul, Korea) was used as a matrix. The reagents used for the coupling treatments were vinyltriethoxy silane (VTES), 3-ami-no propyl triethoxy silane (APS), and 3-methacryloxy propyl trimethoxy silane (MPTS; Aldrich, St. Louis, MO, USA), denoted as VTES, APS, and MPTS, respectively. The acid and silane treatments of the CF were carried out by the following procedure. For the acid

Fiber surface and electrical conductivity of electroless Ni-plated PET ultra-fine fibers

In this work, electroless Ni-plating on polyethylene terephthalate (PET) ultra-fine fibers surfaces was carried out to improve the electric conductivity of the fiber. The surface properties of PET ultra-fine fibers were characterized using scanning electron microscopy, X-ray diffraction, and contact angle analyses. The electric conductivity of the fibers was measured using a 4-point testing method. The experimental results revealed the presence of island-like nickel clusters on the PET ultra-fine fibers surfaces in the initial plating state, and the electric conductivity of the Ni-plated fibers was enhanced with increasing plating time and thickness of the Ni-layers on the PET ultra-fine fibers.

Effects of maleic anhydride content on mechanical properties of carbon fibers-reinforced maleic anhydride-grafted-poly-propylene matrix composites

In this work, the effects of maleic anhydride (MA) content on mechanical properties of chopped carbon fibers (CFs)-reinforced MA-grafted-polypropylene (MAPP) matrix composites. A direct oxyfluorination on CF surfaces was applied to increase the interfacial strength between the CFs and MAPP matrix. The mechanical properties of the CFs/MAPP composites are likely to be different in terms of MA content. Surface characteristics were observed by scanning electron microscope, Fourier transform infrared spectroscopy, and single fiber contact angle method. The mechanical properties of the composites were also measured by a critical stress intensity factor (KIC). From the KIC test results, the KIC values were increased to a maximum value of 3.4 MPa with the 0.1 % of MA in the PP, and then decreased with higher MA content.

Preparation and Characterization of Highly Conductive Nickel-coated Glass Fibers

In this work, we employed an electroless nickel plating on glass fibers in order to enhance the electric conductivity of fibers. And the effects of metal content and plating time on the conductivity of fibers were investigated. From the results, island-like metal clusters were found on the fiber surfaces in initial plating state, and perfect metallic layers were observed after 10 min of plating time. The thickness of metallic layers on fiber surfaces was proportion to plating time, and the electric conductivity showed similar trends. The nickel cluster sizes on fibers decreased with increasing plating time, indicating that surface energetics of the fibers could become more homogeneous and make well-packed metallic layers, resulting in the high conductivity of Ni/glass fibers.

One-Pot Synthesis of Ag-TiO2/Nitrogen-Doped Graphene Oxide Nanocomposites and Its Photocatalytic Degradation of Methylene Blue

In this study, we report Ag-TiO2/graphene oxide (GO) nanocomposites prepared by a simple one-pot synthesis using TiO2, AgNO3, and N-doped graphene (NDG). The NDG was synthesized using a microwave-assisted hydrothermal (MHT) method as a function of MHT time. The morphology and structure of Ag-TiO2/GO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Raman, and Fourier-transform infrared spectroscopy (FTIR). The photocatalytic activity of Ag-TiO2/GO nanocomposites in visible light was explored using the degradation, of methylene blue (MB) dye under the ultraviolet (UV) light. The result showed that Ag-TiO2/GO-3 was very efficient for the degradation of MB with nitrogen doping time. The degradation efficiency of the photocatalytic nanoparticles after 6 h of irradiation was about 80%. Increasing the N-doping time increased their hydrophilicity, thereby improving the photocatalytic performance of Ag-TiO2/GO nanocomposites.

Effect of Silane Coupling Agent on the Creep Behavior and Mechanical Properties of Carbon Fibers/Acrylonitrile Butadiene Rubber Composites

In this study, we investigated the effect of the silane coupling agent on the relationship between the surface free energy of carbon fibers (CFs) and the mechanical strength of CFs/acrylonitrile butadiene rubber (NBR) composites. Moreover, the creep behavior of the CF/NBR composites at surface energetic point of view were studied. The specific component of the surface free energy of the carbon fibers was found to increase upon grafting of the silane coupling agent, resulting in an increase in the tensile strength of the CF/NBR composites. On the other hand, the compressive creep strength was found to follow a slightly different trend. These results indicate the possible formation of a complex interpenetrating polymer network depending on the molecular size of the organic functional groups of the silane coupling agent.