Nano-epoxy resins containing electrospun carbon nanofibers and the resulting hybrid multi-scale composites

For the first time, electrospun carbon nanofibers (ECNFs, with diameters and lengths of ∼200 nm and ∼15 μm, respectively) were explored for the preparation of nano-epoxy resins; and the prepared resins were further investigated for the fabrication of hybrid multi-scale composites with woven fabrics of conventional carbon fibers via the technique of vacuum assisted resin transfer molding (VARTM). For comparison, vapor growth carbon nanofibers (VGCNFs) and graphite carbon nanofibers (GCNFs) were also studied for making nano-epoxy resins and hybrid multi-scale composites. Unlike VGCNFs and GCNFs that are prepared by bottom-up methods, ECNFs are produced through a top-down approach; hence, ECNFs are more cost-effective than VGCNFs and GCNFs. The results indicated that the incorporation of a small mass fraction (e.g., 0.1% and 0.3%) of ECNFs into epoxy resin would result in substantial improvements on impact absorption energy, inter-laminar shear strength, and flexural properties for both nano-epoxy resins and hybrid multi-scale composites. In general, the reinforcement effect of ECNFs was similar to that of VGCNFs, while it was higher than that of GCNFs.     

Hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing electrospun carbon nanofiber mats

Herein we report the development and evaluation of hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing mats of electrospun carbon nanofibers (ECNs). The results indicated that (1) the interlaminar shear strength and flexural properties of hybrid multi-scale composite were substantially higher than those of control/comparison composite without ECNs; in particular, the interlaminar shear strength was higher by ∼86%; and (2) the electrical conductivities in both in-plane and out-of-plane directions were enhanced through incorporation of ECNs, while the enhancement of out-of-plane conductivity (∼150%) was much larger than that of in-plane conductivity (∼20%). To validate the data reduction procedure, a new shear stress formula was formulated for composite laminates, which took into account the effect of layup and inter-layers. The study suggested that ECNs could be utilized for the development of high-performance composites, particularly with the improved out-of-plan properties (e.g., interlaminar shear strength).     

Hybrid composites made of carbon and glass woven fabrics under quasi-static loading

Experimental studies are presented on in-plane mechanical properties for two types of hybrid composites made using 8H satin weave T300 carbon fabrics and plain weave E-glass fabrics with epoxy resin. Results are also presented for 8H satin weave T300 carbon/epoxy and plain weave E-glass/epoxy. Studies are carried out under both tensile and compressive in-plane quasi-static loading. It is observed that for hybrid composites, placing glass fabric layers in the exterior and carbon fabric layers in the interior gives higher tensile strength and ultimate tensile strain than placing carbon fabric layers in the exterior and glass fabric layers in the interior. Quantitative data is given for different mechanical properties.     

Porous carbon nanofibers with narrow pore size distribution from electrospun phenolic resins

Phenolic resin-based porous carbon nanofibers (PCNFs) with large surface area and narrow pore size distribution have been successfully prepared using novolac-type phenolic resin as precursor. The high molecular weight precursor was first synthesized in this study, then was dissolved in methanol. The PCNFs were finally obtained through electrospinning the phenolic resin polymer solution followed by successive curing and carbonization without activation. The N₂ adsorption/desorption isotherms reveal that the PCNFs have high specific surface area about 812 m²/g, the pore size falls in the range of 0.4-0.7 nm and the pore volume is 0.91 cm³/g. The vapor adsorption testing demonstrated that PCNFs exhibited different adsorption performance for ethanol and water.     

Glassy carbon nanofibers from electrospun cellulose nanofiber

Journal of Materials Science - Glassy carbon nanofibers (g-CNFs) with diameter of ca. 45 nm were prepared from electrospun cellulose nanofibers (CelluNFs) by two sequential steps:...     

Microstructures and mechanical properties of aligned electrospun carbon nanofibers from binary composites of polyacrylonitrile and polyamic acid

High mechanical performance carbon nanofibers are highly required for the carbon nanofiber-reinforced composites, and it is necessary to develop novel precursors for the preparation of carbon nanofibers. In this work, blends of poly(acrylonitrile-butyl acrylate mono-butyl itaconate) (co-PAN) and polyamic acid (PAA) were electrospun into aligned nanofibers and the nanofibers were converted to carbon nanofibers by thermal imidization, pre-oxidation and high-temperature carbonization. FT-IR spectroscopy was applied to monitor the chemical structures of the nanofibers before and after pre-oxidation. Tensile tests were used to characterize the mechanical properties of electrospun carbon nanofibers (ECNFs). The microstructures of ECNFs were investigated by high-resolution TEM and Raman spectroscopy. The results indicated that the ECNFs derived from blend of co-PAN/PAA with molar ratio of 6/4 and with carbonization temperature of 1400 °C possessed the highest tensile strength of 1212 MPa, which could be attributed to the ordered graphitic structures in ECNFs.     

Fabrication and evaluation of polyamide 6 composites with electrospun polyimide nanofibers as skeletal framework

In this study, two types of polyimide (PI) nanofiber mats, including (1) the mats consisting of (almost) randomly overlaid PI nanofibers and (2) the mats consisting of highly aligned PI nanofibers, were prepared by the materials-processing technique of electrospinning. The nanofiber mats were subsequently used to develop composites with polyamide 6 (PA6) via the composites – fabrication method of polymer melt infiltration lamination (PMIL). Owing to superior mechanical properties (i.e., the tensile strength and modulus were 1.7 GPa and 37.0 GPa, respectively) and large specific surface area of electrospun PI nanofibers, the PI/PA6 composites with PI nanofiber mats as skeletal framework demonstrated excellent mechanical properties. In particular, the PI/PA6 composite containing 50 wt.% of aligned PI nanofibers had the tensile strength and modulus of 447 MPa and 3.0 GPa along the longitudinal direction, representing ～700% and ～500% improvements as compared to neat PA6.     

纳米纤维素增强聚乙烯醇/水性聚氨酯静电纺膜的研究

采用TEMPO(2,2,6,6-四甲基哌啶氧化物自由基)氧化纤维素纳米纤维(TOCNs)作为聚乙烯醇(PVA)/水性聚氨酯(WPU)静电纺膜的增强剂。研究中使用拉伸实验研究TOCNs的增强作用,此外还使用扫描电子显微镜、红外光谱仪、热重分析仪及差示扫描量热仪等对静电纺膜进行结构性能表征。扫描电镜观察发现当纳米纤维素加入量为5%(质量分数)时,其在聚合物基质中分散良好,所得静电纺纳米纤维保持了良好的形态。此外,加入5%(质量分数)的纳米纤维素能够将材料的抗张强度提高44%,且纳米纤维素的加入对材料的热稳定性也有一定的改善,纳米纤维素起到一种纳米填料的效果。鉴于PVA、WPU、TOCNs均为亲水性,无毒且具有生物相容性的物质,所得静电纺膜在组织支架及伤口护理材料等方面具有潜在应用。     

Fabrication and characterization of electrospun mullite nanofibers

Continuous mullite (3Al₂O₃·2SiO₂) nanofibers were fabricated by a sol-gel electrospinning technique. The detailed crystallization development and micromorphological evolution of both the as-electrospun nanofibers and the sintered mullite nanofibers were investigated. Results indicated that the spinnability and micromorphological evolution of mullite nanofibers are largely dependent on the viscosity η of the mullite sol, which can be adjusted by polyvinylprrolidone (PVP) content. Mullite nanofibers with common cylindrical morphology and diameters ranging from 400 nm to 800 nm could be obtained easily and rapidly when PVP content is ranged from 5 wt.% to 8 wt.%. High purity polycrystalline mullite nanofibers with diameters of about 200 nm were obtained after sintering at 1200 °C for 2 h. All sintered nanofibers consisted of single crystalline grains with size of approximately 100 nm.     

A review: carbon nanofibers from electrospun polyacrylonitrile and their applications

Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed.     

Hybrid resins from polyisocyanate,epoxy resin and water glass: chemistry,structure and properties

Epoxy resin (EP) was selected as potential reactive emulsifier for polyurea-based thermoset resins produced from polyisocyanate/water glass/emulsifier systems. As emulsifier diphenyl-2-ethylhexylphosphate and/or EP served for the initial water-in-oil type emulsions whereby “water” means water glass, and “oil” the organic phase, composed of polyisocyanate and emulsifier, respectively. The EP content of the systems has been varied from 15 to 35 wt% and from 35 to 45 wt% for the hybrid resins with and without DPO emulsifier, respectively. Effects of EP hybridization on the structure, mechanical, thermal and flammability properties of the final polyurea-based systems were studied. EP proved to be a suitable emulsifier based on the fact that the mean size of the polysilicate, generated from the dispersed WG, was markedly reduced. EP could even fully replace the phosphate emulsifier without sacrificing the mechanical properties of the resulting hybrid thermosets. Moreover, the hybridization with EP was accompanied with improved stiffness and fracture toughness.     

Preparation and mechanical properties of carbon nanotube grafted glass fabric/epoxy multi-scale composites

In the present paper, carbon nanotubes (CNTs) were chemically grafted onto surfaces of the amino silane treated glass fabric by a novel chemical route for the first time to create 3D network on the glass fibers. The chemical bonding process was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The glass fabric/CNT/epoxy multi-scale composite laminates were fabricated with the CNT grafted fabrics using vacuum assisted resin infusion molding. Tensile tests were conducted on fabricated multi-scale composites, indicating the grafting CNTs on glass fabric resulted a decrease (11%) in ultimate tensile strength while toughness of the multi-scale composite laminates were increased up to 57%. Flexural tests revealed that the multi-scale composite laminates prepared with CNT grafted glass fabric represent recovering after first load fall. The interfacial reinforcing mechanisms were discussed based on fracture morphologies of the multi-scale composites.     

静电纺丝法制备聚丙烯腈基纳米炭纤维及其表面结构表征

通过稳定化、炭化静电纺制的聚丙烯腈(PAN)前驱体纤维制备了直径为100nm～300nm的纳米炭纤维.用扫描电镜(SEM)、场发射扫描电镜(FESEM)、扫描隧道显微镜(STM)及扫描量热分析法(DSC)研究了纳米炭纤维及其前驱体纤维的形貌及结构.结果表明:纳米炭纤维及其前驱体纤维的直径表现为对数正态分布.静电纺制纤维的环化放热峰移向低温,表明静电纺制纤维可在较低的温度下引发环化.由于静电纺制纤维的粗糙表面及在热处理过程中的收缩行为,在纳米炭纤维表面形成了长度为10nm宽度为5nm的凹坑.     

LaOCl nanofibers derived from electrospun PVA/Lanthanum chloride composite fibers

Electrospun nanofibers of poly (vinyl alcohol) (PVA)/Lanthanum (Ш) chloride (LaCl₃) composite were employed to prepare the LaOCl nanofibers by calcination. TG-DSC was used to investigate the thermal property of precursor, while FT-IR, XRD, FESEM and TPD were employed to characterize the derived LaOCl nanofibers. Results indicate that the addition of LaCl₃ leads to the formation of fork segments in the structure of electrospun PVA/LaCl₃ composite nanofibers, therefore, changing the decomposition behavior of the fibers. Pure LaOCl fibers with a diameter range of 90-220 nm can be obtained by calcination of electrospun PVA/LaCl₃ composite nanofibers at 700 °C for 7 h. The resultant LaOCl nanofibers show a good sensing behavior for CO₂ gas.     

Strengthening and toughening mechanisms in microfiber reinforced cementitious composites

Materials with quasi-brittle stress strain curves exhibit desirable properties such as enhanced durability, flaw tolerance and toughness. This study reveals that steel microfiber reinforced cement based composites exhibit such quasi-brittle behavior. Mechanical properties of steel microfiber reinforced cement based composites are obtained through flexure and splitting tension tests. The cracking process and crack fiber interactions that lead to the quasi-brittle behavior in these composites were investigated. The strength and toughness enhancement is associated with crack wake mechanisms. Aggregate bridging and pullout and secondary crack formations associated with microfiber bridging sites are predominant during the strain hardening regime. Multiple secondary microcracks perpendicular to the fiber/matrix interface is the dominant failure mode beyond peak load in the strain softening regime.     

Preparation and photoluminescence properties of electrospun nanofibers containing PMO-PPV and Eu(ODBM)3phen

This communication explores a facile approach for fabricating nanofibers containing luminescent conjugated polymer, poly(2-methoxy-5-octoxy)-1,4-phenylene vinylene)-alt-1,4-(phenylene vinylene) (PMO-PPV), and rare earth complex, Eu(ODBM)₃phen (ODBM: 4-n-Octyloxydibenzoylmethanato; phen: 1,10-phenanthroline) via an electrospinning technique. The morphology and photoluminescent properties of the electrospun fibers were characterized by scanning electron microscopy, fluorescence spectrophotometer and UV optical microscopy. The electrospun fibers with diameters ranging from 70 nm to 200 nm as well as parallel orientation show strong green and red photoluminescence. This is the first but important approach towards novel applications of luminescent conjugated polymers and rare earth complex nanofibers. This kind of eletrospun nanofiber is a promising candidate for optical and electrical nanomaterials.     

Comparative performance of collagen nanofibers electrospun from different solvents and stabilized by different crosslinkers

Collagen electrospun scaffolds well reproduce the structure of the extracellular matrix (ECM) of natural tissues by coupling high biomimetism of the biological material with the fibrous morphology of the protein. Structural properties of collagen electrospun fibers are still a debated subject and there are conflicting reports in the literature addressing the presence of ultrastructure of collagen in electrospun fibers. In this work collagen type I was successfully electrospun from two different solvents, trifluoroethanol (TFE) and dilute acetic acid (AcOH). Characterization of collagen fibers was performed by means of SEM, ATR-IR, Circular Dichroism and WAXD. We demonstrated that collagen fibers contained a very low amount of triple helix with respect to pristine collagen (18 and 16 % in fibers electrospun from AcOH and TFE, respectively) and that triple helix denaturation occurred during polymer dissolution. Collagen scaffolds were crosslinked by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), a commonly employed crosslinker for electrospun collagen, and 1,4-butanediol diglycidyl ether (BDDGE), that was tested for the first time in this work as crosslinking agent for collagen in the form of electrospun fibers. We demonstrated that BDDGE successfully crosslinked collagen and preserved at the same time the scaffold fibrous morphology, while scaffolds crosslinked with EDC completely lost their porous structure. Mesenchymal stem cell experiments demonstrated that collagen scaffolds crosslinked with BDDGE are biocompatible and support cell attachment.     

High electrochemical activity from hybrid materials of electrospun tungsten oxide nanofibers and carbon black

Tungsten oxide (WO₃) nanofibers were prepared by oxidizing the electrospun ammonium metatungstate (AMT) and polyvinyl pyrrolidone (PVP) composite fibers. The WO₃ nanofibers with controllable diameters ranging from 80 to 130 nm were obtained by electrospinning different AMT/PVP mixture solutions. Electrochemical activity of the WO₃ nanofibers was measured in 0.5 M sulfuric acid solution. Cyclic voltammetry tests show that the WO₃ nanofibers have electrochemical activity which is closely related to hydrogen oxidation in fuel cells and the electrochemical activity could be greatly enhanced by the addition of carbon black. The hybrid materials of the WO₃ nanofibers and carbon black with the WO₃:C mass ratio of 10:1 possess high electrochemical activity with an anodic peak current density of 11.2 mA/cm², even higher than the commercial 20 wt% Pt/C catalyst. The electrospun WO₃ nanofibers may be promising electrocatalysts or catalyst supports for hydrogen oxidation in fuel cells due to the simplicity in production and high electrochemical activity.     

Hybrid aluminium matrix composites containing boron carbide and quasicrystals: manufacturing and characterisation

Hybrid composites of boron carbide (B₄C) and Al_62.5Cu₂₅Fe_12.5 quasicrystals (QCs) were prepared by ball milling and pressureless sintering in aluminium matrix to investigate their individual and hybrid effects on microstructural and mechanical properties. Hybrid composite contained B₄C and QCs in 3?wt-% each, making a total of 6?wt-%. For reference, specimens of pure aluminium and two composites containing 6?wt-%B₄C and 6?wt-% QCs were prepared. Microstructural characterisation was performed using optical, scanning electron microscopy and X-ray diffraction, while evaluation of mechanical properties was carried out by hardness and compression tests. Uniform dispersion of reinforcements in composites was observed along with significant increase in the mechanical properties. The composite containing 6?wt-% QCs demonstrated the highest hardness, while the hybrid composite showed better compressive properties.