Nanocomposites of epoxy with 3 and 5 wt% graphene nanoplatelets (GnPs) were fabricated with GnP sizes of ~5 and <1 μm dispersed within an epoxy resin using a sonication process followed by three-roll ...milling. The morphology, mechanical, and thermal properties of the composites were investigated. Tensile and flexural properties measurements of these nanocomposites indicated higher modulus and strength with increasing concentration of small GnPs sizes (<1 μm, GnP-C750). The incorporation of larger GnPs sizes (~5 μm, GnP-5) significantly improved the tensile and flexural modulus but reduced the strength of the resulting composites. At 35 °C, the dynamic storage modulus of GnP-5/epoxy composites increased with increasing platelet concentration, and improved by 12 % at 3 wt% and 23 % at 5 wt%. The smaller GnP-C750 increased the storage modulus by 5 % at 3 wt% loading but only 2 % at 5 wt% loading. The glass transition temperatures of the composites increased with increasing platelet concentration regardless of the GnP particle size. A marked improvement in thermal conductivity was measured with the incorporation of the larger GnP size reaching 115 % at 5 wt% loading. The effects of different platelet sizes of the GnP reinforcement on the damage mechanisms of these nanocomposites were studied by scanning electron microscopy.
Carboxyl terminated butadiene acrylonitrile (CTBN) was added to epoxy resins to improve the fracture toughness, and then two different lateral dimensions of graphene nanoplatelets (GnPs), nominally ...<1μm (GnP-C750) and 5μm (GnP-5) in diameter, were individually incorporated into the CTBN/epoxy to fabricate multi-phase composites. The study showed that GnP-5 is more favorable for enhancing the properties of CTBN/epoxy. GnPs/CTBN/epoxy ternary composites with significant toughness and thermal conductivity enhancements combined with comparable stiffness to that of the neat resin were successfully achieved by incorporating 3wt.% GnP-5 into 10wt.% CTBN modified epoxy resins. According to the SEM investigations, GnP-5 debonding from the matrix is suppressed due to the presence of CTBN. Nevertheless, apart from rubber cavitation and matrix shear banding, additional active toughening mechanisms induced by GnP-5, such as crack deflection, layer breakage and separation/delamination of GnP-5 layers contributed to the enhanced fracture toughness of the hybrid composites.
The difficulty of dispersing cellulose nanofibers (CNFs) in hydrophobic polymers such as poly(lactic acid) (PLA) remains a major obstacle to the expansion of cellulose nanocomposite applications. In ...this work, we employed the solvent evaporation technique commonly used for drug microencapsulation to suspend PLA in water as microparticles. The suspension of the microparticles was easily mixed with the CNFs prepared by high-pressure homogenization. Water removal by membrane filtration produced CNF sheets filled with the particles. Compression molding of the stacked sheets resulted in nanocomposites with good CNF dispersions. Increases in the modulus and strength (up to 58% and 210%, respectively) demonstrated the load-bearing capability of the CNF network in the composites.
This work reports the preparation of MFC–PVA composite films, and the thermal and mechanical properties of these films. Microfibrillated cellulose (MFC), which was separated from kraft pulp by a ...mechanical process, was used as the reinforcement in polyvinyl alcohol (PVA) matrix. This MFC reinforcement has an interconnected web-like structure with fibrils having a diameter in the range of 10–100nm, as observed by TEM. MFC–PVA composite films were created by casting from a water suspension to produce a homogeneous dispersion of MFC in the polymer matrix. DMA shows an increase of the storage modulus in the glassy state with increasing MFC content, but a more significant increase in modulus is detectable above the glass transition temperature. There is a steady increase in both the modulus and strength of the composite films until a plateau is reached at 10wt% MFC. The thermal stability of the PVA composite films is slightly increased with the addition of MFC.
As a result of this research, it has been shown that MFC is an excellent reinforcement comparable to cellulose nanowhiskers. Furthermore, by combining MFC with PVA in addition to good mechanical properties, this composite has good chemical resistance and biodegradability. The water soluble characteristics of PVA combined with a water dispersion of MFC are also easily processable.
We investigated the effect of graphene nanoplatelets (GnPs) with two different lateral dimensions on the morphology, flexural, and thermo-mechanical properties of multiscale GnPs/glass fiber/epoxy ...composites. First, 3 and 5 wt% of GnP-C750 (<1 µm in diameter) and GnP-5 (5 µm in diameter) were individually integrated into epoxy suspension through a combination of calendaring and sonication processes. The GnPs/glass fiber/epoxy composites were then fabricated by incorporating glass fibers into the GnPs/epoxy mixture. Results showed that the flexural modulus of the GnPs/glass fiber/epoxy composites was improved by 11.5 and 26.3 % with the addition of 5 wt% GnP-C750 and GnP-5, respectively. At the same filler content, the storage modulus of the glass/epoxy composites incorporated with GnP-C750 and GnP-5 at 30 °C was enhanced by 10.2 and 28.2 %, respectively. The flexural strength of the 3 wt% GnP-5-reinforced glass fiber/epoxy composite is 16.2 % higher than that of the glass fiber/epoxy composite. The dispersion results of GnPs in the composites and the interfacial interactions between fibers and modified matrix were evaluated by scanning electron microscopy.
Rare and potent monoclonal antibodies (mAbs) against the Plasmodium falciparum (Pf) circumsporozoite protein (CSP) on infective sporozoites (SPZ) preferentially bind the PfCSP junctional tetrapeptide ...NPDP or NVDP minor repeats while cross-reacting with NANP central repeats in vitro. The extent to which each of these epitopes is required for protection in vivo is unknown. Here, we assessed whether junction-, minor repeat- and central repeat-preferring human mAbs (CIS43, L9 and 317 respectively) bound and protected against in vivo challenge with transgenic P. berghei (Pb) SPZ expressing either PfCSP with the junction and minor repeats knocked out (KO), or PbCSP with the junction and minor repeats knocked in (KI). In vivo protection studies showed that the junction and minor repeats are necessary and sufficient for CIS43 and L9 to neutralize KO and KI SPZ, respectively. In contrast, 317 required major repeats for in vivo protection. These data establish that human mAbs can prevent malaria infection by targeting three different protective epitopes (NPDP, NVDP, NANP) in the PfCSP repeat region. This report will inform vaccine development and the use of mAbs to passively prevent malaria.
In this study, polyethersulfone (PES) was blended into epoxy resins to improve the fracture toughness of the epoxy resin without loss of mechanical properties, and then two grades of pristine ...graphene nanoplatelets (GnPs) were separately introduced into the PES/epoxy system to fabricate thermally conductive GnPs/PES/epoxy composites with high toughness as well as high stiffness. It was observed that the addition of GnPs obviously affected the final phase morphology by suppressing the phase separation process of the PES modified epoxy due to the increased viscosity and cure-reaction rate of PES/epoxy. The GnPs with a larger lateral dimension revealed a greater reinforcing effect, and the inclusion of 3 wt % GnPs (~5 μm in diameter) endowed the PES/epoxy matrix with a good thermal conductivity and improved the tensile, flexural, and storage modulus by 27.1%, 17.5%, and 15.6% (at 30 °С), respectively. Meanwhile, the fracture toughness was further enhanced by about 29.5% relative to the PES modified epoxy at the same GnPs concentration. The positive results suggest that the modification of epoxy resins using the PES and GnPs is an attractive approach for fabricating tougher and stiffer epoxy-based nanocomposites with multifunctional properties, which could widen the industrial applications of the epoxy resins.
This first part of a two-part review of pheochromocytoma and paragangliomas (PPGLs) addresses clinical presentation, diagnosis, management, treatment, and outcomes. In this first part, the ...epidemiology, prevalence, genetic etiology, clinical presentation, and biochemical and radiologic workup are discussed. In particular, recent advances in the genetics underlying PPGLs and the recommendation for genetic testing of all patients with PPGL are emphasized. Finally, the newer imaging methods for evaluating of PPGLs are discussed and highlighted.
We demonstrate a water-based method to fabricate strong, electrically and thermally conductive hybrid thin films (papers) made from the combination of graphene nanoplatelets (GnP) and cellulose ...nanocrystals (CNC). Unpressed and hot-pressed GnP papers containing CNC ranging from 0 wt% to 25 wt% were prepared. It is found that the GnP is well aligned within the hybrid paper, and a higher degree of alignment is induced by the hot-pressing process. The mechanical properties of the resulting papers increased with increasing content of CNC. The hot-pressed 25 wt% CNC hybrid paper showed the best mechanical properties among all the papers studied and improved the tensile strength by 33% and the modulus by 57% compared to neat GnP paper. Both the highest in-plane and though-plane thermal conductivity of 41 W/m K and 1.2 W/m K were measured respectively for the hot-pressed 15 wt% CNC hybrid paper. The electrical conductivity decreased continuously with increasing content of CNC but the thin film was still conductive at the highest CNC content in this study. The low-cost, environmental-friendly, thermally and electrically conductive flexible GnP/CNC hybrid papers have a set of properties making them suitable for many potential applications.
•Cellulose nanofibrils(CNF)/graphene nanoplatelets(GnP) hybrid papers were prepared with a simple water-based method.•CNF and hot-pressing efficiently enhance the mechanical properties of the GnP ...paper.•The CNF reinforced GnP paper demonstrates high electrical conductivity.•Mechanical flexibility and electrical conductivity of the papers are controllable.
Mechanically flexible and high electrically conductive multilayered graphene nanoplatelets (GnP)/cellulose nanofibrils (CNF) composite papers were successfully fabricated through a vacuum-assisted self-assembly technique. The morphology observation showed that highly disassembled CNF were achieved by high-pressure homogenization of water-based cellulose slurry, and the homogenized CNF uniformly interpenetrated within the microporous GnP paper network. The analyses of mechanical properties and morphology suggest that the CNF effectively bridged the adjacent GnP sheets and efficiently strengthened the GnP papers by producing strong GnP/CNF interfacial interactions resulting from mechanical interlocking, van der Waals forces and hydrogen bonds between the GnP and the CNF. Moreover, it was noticed that hot-pressing pressure is necessary to be applied on samples to produce stronger papers with higher electrical conductivity. As the CNF loading reached 60 wt%, the Young’s modulus and tensile strength of the hot-pressed GnP/CNF hybrid paper were significantly increased to 9.1 GPa and 57.7 MPa, respectively. In addition, a high electrical conductivity of 26.8 S/cm was retained for the paper with 30 wt% CNF. Our approach provides a facial and eco-friendly fabrication route to produce strong and highly conductive GnP/CNF papers which are of great practical appeal as a new type of nanomaterials in various fields.
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