Totally found 622 items.

  • [资讯] A sulfonated PEEK/PCL composite nanofibrous membrane for periosteum tissue engineering application
    The favorable mechanical property and regenerative capacity of bone graft are extremely important for the reconstruction of the large bone defect. Polyetheretherketone (PEEK) has tailored elastic modulus to natural cortical bone, while its application is limited by bioinert surface. Tissueengineered periosteum exhibits improved osteogenesisinducing capacity. However, the present artificial periosteum is difficult to effectively anchor to bone grafts. The use of PEEKbased nanomembrane may be a promising candidate to integrate with PEEK bone graft without anchor problem, which has not been reported until now. In this work, a series of fluorinated PEEK polymers were successfully synthesized and electrospun into nanofibers. The chemical structure, morphology, thermal stability, wettability and mechanical strength of sPEEK membranes were investigated. Then, a novel flexible nanocomposite membrane for tissueengineered periosteum based on fibrous sulfonated PEEK (sPEEK) and polycaprolactone (PCL) was prepared. The functional properties were evaluated accordingly. The sPEEKPCL composite membranes showed superior hydrophilic and better ductility than pure sPEEK film. The capacity of protein adsorption was also evaluated, suggesting the elevated bioactivity of sPEEKPCL composite membranes. Finally, the composite membranes were successfully mineralized by a homogenous and thinner calcium phosphate layer, indicating its potential to improve the osteogenic response.
  • [资讯] Novel lignocellulose based gel polymer electrolyte with higher comprehensive performances for rechargeable lithium–sulfur battery
    For the first time the most abundant natural biomass lignocellulose (LC) on earth is exploited as the matrix of gel polymer electrolyte (GPE) in lithium-sulfur (Li-S) batteries. The prepared GPE based on LC fiber length range (150–300 µm) presents extremely excellent comprehensive performances: high enough liquid electrolyte uptake of 428 wt%, satisfying tensile strength of 3.89 MPa, outstanding ionic conductivity of 4.52 mS cm−1 at room temperature, excellent lithium ion transference number of 0.79, electrochemical stability window of 5.3 V, good compatibility with lithium electrode and thermal stability. The assembled lithium sulfur cell using obtained GPE of G2 shows excellent rate and cycling performance compared to corresponding cell with commercial liquid electrolyte with separator, which is attributed to the successfully suppressed “shuttle effect” in the cell with GPE. What is more important, the LC based GPE is prepared with simple process and biodegradable, which endow the corresponding Li-S batteries with application possibility.
  • [资讯] Borocarbonitride, (BN)X(C)1-X nanosheet-reinforced polymer nanocomposites for high mechanical performance
    The enhancement in mechanical and thermal properties of polymer matrices upon reinforcing with nanoparticles strongly depends on the extent of molecular-level interactions and interfacial adhesion between the nanofiller and the matrix material, which are, in turn, governed by the surface functionalities on the nanofiller. Herein, we examine the reinforcing effect of nanosheets of borocarbonitide, (BN)x(C)1-x, which are analogues to graphene (x = 0) and boron nitride sheets (x = 1), whose surface functional groups vary with the composition, on the mechanical and thermal properties of poly(vinyl alcohol), PVA. Results show that substantial improvement in hardness and elastic modulus of PVA is achieved by adding just 0.2 wt% of BCN. A significant enhancement in the thermal stability was also noted. These results are rationalized by recourse to detailed structural characterization, which shows a substantial enhancement in the degree of crystallinity in PVA upon BCN addition, and improved interfacial adhesion between the nanofiller and the polymer matrix via strong intermolecular interactions. Overall, our results show that it is possible to engineer polymer matrix nanocomposites with exceptional mechanical and thermal properties via the addition of a small amount of BCN.
  • [资讯] Self-humidifying novel chitosan-geopolymer hybrid membrane for fuel cell applications
    Novel, ecofriendly organicinorganic hybrid, selfhumidifying proton exchange membrane (PEM) series from chitosan (CS) were prepared by solventcasting technique wherein heptanedioic acid (HA) is used as crosslinker and geopolymer (GP), an inorganic aluminosilicate material as the filler. FTIR, solid state NMR, SEM and XRD analysis revealed the formation of supercompatible CSHAGP hybrid membranes. Good selfhumidification, appreciable proton conductivity, thermal stability and porosity were exhibited by the membranes. Thermokinetic behaviour of the membranes was studied using Broidos approximation method and the activation energy for different thermal degradation stages was deduced. The hybrid membrane with a concentration of 1.5 wt% of the crosslinker and 0.5 wt% of the filler showed excellent water retention, considerable porosity, highest proton conductivity of 4.12 10 3 Scm 1 , appreciable thermal, mechanical as well as oxidative stability and high activation energy, is considered as the optimum composition. The above results suggest the suitability of these novel hybrid membranes as substitutes for Nafion in fuel cells.
  • [资讯] Synthesis and properties of polydimethylsiloxane/graphene oxide modified, water-based polyurethane/polyacrylate
    In this study, we prepared polydimethylsiloxanegraphene oxide (PG) modified waterborne polyurethane acrylate (WPUA) films and enhanced their hydrophobicity, thermal stability, and mechanical properties. The prepared films were characterized by Fourier transform infrared and energy spectroscopy analysis this confirmed the successful incorporation of PG into WPUA. As shown by scanning electron microscopy and atomic force microscopy analysis, the surfaces of the WPUA films were confirmed to have turned smoother and more compact after PG addition. With an optimized amount of PG (0.1%) incorporated into the WPUA film, it exhibited a contact angle improvement of 21.9 degrees, an enhanced decomposition temperature at 5% weight losses of 25 degrees C, and an elongation at break improvement of 482.92% over those of pure WPUA. The newly synthesized PGWPUA showed considerable enhancements in its hydrophobicity and thermal and mechanical properties and could be deemed to have potential value as an alternative contender for practical applications in coatings painted on tunnels and highways. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47926.
  • [资讯] Morphologies and properties of epoxy/multi-walled carbon nanotube nanocomposite foams prepared through the free-foaming and limited-foaming process
    Microcellular epoxymultiwalled carbon nanotube (EPMWCNT) composite foams loaded with 2 wt% (mass fraction) of MWCNT were prepared through the freefoaming process (Frefoam) and limitedfoaming process (Limfoam) using chemical foaming agent (CFA), respectively. The morphologies of EPMWCNT composite foams with different densities were analyzed by scanning electron microscopy (SEM). It was found that the cell size of both Frefoam and Limfoam decreased with increasing the density, while Limfoam exhibited a smaller cell size and a higher cell density in contrast to those of Frefoam at similar density. In addition, the dynamic mechanical properties, thermal stability, and electrically and thermal conductive properties of the EPMWCNT foams in the density range of 0.278 gcm 3 1.108 gcm 3 were investigated and the difference in performances between Frefoam and Limfoam was analyzed. Limfoam had an obviously lower crosslink density than that of Frefoam due to the effect of compressed gas, which was clearly reflected in the results of gel fraction, glass transition temperature (T g ), molecular weight between crosslinks (M c ), and initial thermal decomposition temperature. Compared with Frefoam, Limfoam had superior thermal conductive property and exhibited weak electrically conductive property, indicating the conductive pathway was affected by the foaming process.
  • [资讯] Electrical conductivity studies on Ammonium bromide incorporated with Zwitterionic polymer blend electrolyte for battery application
    Solid polymer blend electrolytes are widely studied due to their extensive applications particularly in electrochemical devices. Blending polymer makes the thermal stability, higher mechanical strength and inorganic salt provide ionic charge carrier to enhance the conductivity. In these studies, 50% polyvinyl alcohol (PVA), 50% poly (N-vinyl pyrrolidone) (PVP) and 2.5% L-Asparagine mixed with different ratio of the Ammonium bromide (NH4Br), have been synthesized using solution casting technique. The prepared PVA/PVP/L-Asparagine/doped-NH4Br polymer blend electrolyte films have been characterized by various analytical methods such as FT-IR, XRD, impedance spectroscopy, TG-DSC and scanning electron microscopy. FT-IR, XRD and TG/DSC analysis revealed the structural and thermal behavior of the complex formation between PVA/PVP/L-Asparagine/doped-NH4Br. The ionic conductivity and the dielectric properties of PVA/PVP/L-Asparagine/doped-NH4Br polymer blend electrolyte films were examined using impedance analysis. The highest ionic conductivity was found to be 2.34×10−4 S cm−1 for the m.wt. composition of 50%PVA:50%PVP:2.5%L-Asparagine:doped 0.15 g NH4Br at ambient temperature. Solid state proton battery is fabricated and the observed open circuit voltage is 1.1 V and its performance has been studied.
  • [资讯] Determination of J-R curves by load separation criterion in highly ductile TP-based composites under high temperature conditions
    This work was aimed at determining the J-integral in 5-harness satin weave carbon fabrics reinforced PolyPhenylene Sulphide (PPS) structures at 120 °C > Tg (glass transition temperature). The use of the linear elastic fracture mechanics (LEFM) framework to investigate the fracture behavior is not relevant in C/PPS laminates whose angle-ply stacking sequence is characterized by a highly ductile behavior. Thus the corresponding strain energy release rate (denoted J) in angle-ply laminates can be evaluated by means of the J-integral to account for the elastic-plastic fracture mechanics (EPFM). To this aim, a particular attention was paid to determine ηel- and ηpl-factors which are key points in the evaluation of J. ηel is classically evaluated using the compliance method, whereas, ηpl is determined by means of the load separation method applied to both elastic and total displacements. The comparison between initial crack length calculated using plastic and total displacement allows us to conclude that ηpl-factor based on total displacement leads to more accurate results. Using the Sij parameter, it is therefore possible to estimate transverse crack growths for different initial notch lengths. The predicted crack growth is in a good agreement with the experimental evolution obtained using Digital Image Correlation (DIC). Finally, the present work provides the J-R curves of highly ductile composite systems for different initial crack length over width ratios (a/w).
  • [资讯] Greatly improved thermal properties of polybenzoxazine via modification by acetylene/aldehyde groups
    A novel benzoxazine resin (PHB-apa) with low curing temperature, high Tg and excellent thermal stability was developed. Be different from other benzoxazines, PHB-apa contains both aldehyde group and acetylene group on the phenol ring and the aniline ring, respectively. Other benzoxazine monomers contain only one aldehyde group or one acetylene group were chosen for comparison. Their chemical structures were proved by 1H and 13C Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The polymerization reaction monitored by Differential Scanning Calorimetry (DSC) and FTIR suggests that the presence of the aldehyde group in PHB-apa leads to a low curing temperature that is benefit for processing. Besides, it is noticeable that this new polybenzoxazine has outstanding thermal property due to the cooperative reaction of the aldehyde group and the acetylene group. Its Tg from Dynamic thermo mechanical analysis (DMA) and char yield at 800 °C under N2 from Thermogravimetric Analysis (TGA) are as high as 459 °C and 77.2%, respectively. Such kind of high values is a breakthrough for thermosetting resins, which will allow its application as a heat-resistant material at a much high temperature.
  • [资讯] Vitrification of PLA by fast scanning calorimetry: Towards unique glass above critical cooling rate?
    In this work, glass transition temperature of polylactide obtained over a wide range of cooling rates is investigated. The kinetics associated with the glass transition measured upon cooling and the devitrification measured upon heating are discussed. Thermal lag corrections of the glass transition temperatures are detailed. A verification of thermal lag correction values is also proposed based on structural relaxation phenomena. The glass transition is characterized in terms of fictive temperature, fragility and structural relaxation in order to discuss the intriguing non-dependency of the polylactide fictive temperatures upon cooling for high cooling rates. To our knowledge, this intriguing phenomenon is reported and detailed for the first time by fast scanning calorimetry.
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