A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers

Polyacrylamide (PAM) was used as a matrix material for fabricating novel nanocomposite hydrogels reinforced with natural chitosan nanofibers (CNFs) via in situ free-radical polymerization. The nanocomposite's structure, strength, morphology and rheological properties were investigated. The results showed that the CNFs had a strong interaction with PAM through hydrogen and covalent bondings. The CNFs acted as a multifunctional cross-linker and a reinforcing agent in the hydrogel system. The compression strength and storage modulus of the nanocomposite hydrogels were significantly higher than those of the pure PAM hydrogels and the corresponding PAM/chitosan semi-interpenetrating polymer network (PAM-SIPN) hydrogels. The swelling ratio (SR) of the nanocomposite hydrogels was lower than that of the PAM hydrogel, but was similar to that of the PAM-SIPN hydrogel. Among the CNF contents used, the 1.5 wt% CNF loading level showed the best combined swelling and mechanical properties for the hydrogels.     

Enhanced Conductivity and mechanical properties of polyimide based nanocomposite materials with carbon nanofibers via carbonization of electrospun polyimide fibers

Carbon nanofibers (CNF) have been obtained by the thermal treatment of the electrospun polyimide fibers in our present work. The carbon structure and surface morphology of the as-received CNFs were investigated using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Investigations of the nanocomposite materials fabricated using these CNFs as conductive fillers and polyimide as matrix show that the presence of CNFs can improve both the mechanical and electrical properties of the material. The conductivity of the nanocomposite films increases with increases in the CNF content and a percolation threshold of about 6.3 vol % (0.0785 in weight fraction) is calculated according to percolation theory.     

Decorating silver nanoparticles on electrospun cellulose nanofibers through a facile method by dopamine and ultraviolet irradiation

In this paper, a new method is introduced for producing multi-functional cellulose nanofibers in order to achieve the biodegradable materials for various applications with a minimal amount of potentially toxic materials. Cellulose nanofibers (CNFs) were fabricated by electrospinning cellulose acetate solution followed by deacetylation. The CNFs were then treated with silver nitrate, ammonia, and sodium hydroxide and subsequently with dopamine as reducing and adhesive agent. Ag ions on the CNF surface were photo-reduced to Ag nanoparticles (NPs) using UVA irradiation to produce a dense layer of silver nanoparticles on the nanofibers. This is based on the simultaneous formation of polydopamine and Ag NPs on CNFs. Overall, this is a fast, simple, and efficient procedure that takes place in a conventional method at ambient temperature. The crystalline structure of CNFs decorated with AgNPs was studied by X-ray diffraction. Field-emission scanning electron microscopy and energy-dispersive X-ray patterns showed uniform distribution of silver nanoparticles on the CNF surface. Incorporation of AgNPs on the CNF surface via dopamine improved the electrical conductivity and also the tensile strength of the nanomat. The CNFs decorated with AgNPs exhibited a low electrical resistivity around 35 KΩ/square and a tensile strength of 87% higher than untreated CNFs.     

Electrochemistry of perfluorinated fullerenes: the case of three isomers of C60F36

1-Naphthol has been used as an in situ fluorescent probe to characterize the surface physicochemical properties of carbon nanofibers (CNFs). The fluorescence of 1-naphthol adsorbed on untreated CNFs originates from the ¹L_b state and its peaks are shifted by the polarity of the surrounding media, indicating that there is a relatively non-polar area on the CNF surface. 1-Naphthol interacting with oxidized sites on the surface of nitric acid-treated CNFs exhibited an ion-pair fluorescence. This shows that there are some functional groups, interacting with 1-naphthol, on the treated CNF surface. The surface physicochemical properties of the CNFs can be characterized by this fluorescent probe.     

Dispersion of acid-treated carbon nanofibers into gel matrices prepared by the sol-gel method

1-Naphthol has been used as an in-situ fluorescent probe to characterize the dispersibility of carbon nanofibers (CNFs) into the sol-gel matrix of silicon alkoxide. The ion-pair fluorescence of 1-naphthol was found in the gel dispersing acid-treated CNFs instead of 1Lb fluorescence, which was preferred in the low polar gel matrix. This indicates that 1-naphthol easily interacts with oxidized groups present on the surface of the acid-treated CNFs due to the high dispersibility of the CNFs into the gel matrix. The oxidized groups on the CNF surface are useful for preventing self-assembly and/or aggregation of the CNFs in the gel matrix.     

Effect of pectin extraction method on properties of cellulose nanofibers isolated from sugar beet pulp

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films.

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Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.     

纳米碳纤维的表面性质和微结构对氧还原催化活性的影响

采用超声处理的方法分别对管式纳米碳纤维(t-CNF)和鱼骨式纳米碳纤维(f-CNF)进行了表面化学处理. XPS结果表明, 在混酸(浓硫酸+浓硝酸)和氨水中进行超声化学处理可以在CNF表面分别引入含氧官能团和含氮官能团. 电化学测试结果表明, 2种不同微结构CNF的氧还原催化活性都遵循相同的趋势, 即CNF-P相似文献   

Cellulose nanofibril (CNF) reinforced starch insulating foams

In this study, biodegradable foams were produced using cellulose nanofibrils (CNFs) and starch (S). The availability of high volumes of CNFs at lower costs is rapidly progressing with advances in pilot-scale and commercial facilities. The foams were produced using a freeze-drying process with CNF/S water suspensions ranging from 1 to 7.5 wt% solids content. Microscopic evaluation showed that the foams have a microcellular structure and that the foam walls are covered with CNF’s. The CNF’s had diameters ranging from 30 to 100 nm. Pore sizes within the foam walls ranged from 20 to 100 nm. The materials’ densities ranging from 0.012 to 0.082 g/cm³ with corresponding porosities between 93.46 and 99.10 %. Thermal conductivity ranged from 0.041 to 0.054 W/m-K. The mechanical performance of the foams produced from the starch control was extremely low and the material was very friable. The addition of CNF’s to starch was required to produce foams, which exhibited structural integrity. The mechanical properties of materials were positively correlated with solids content and CNF/S ratios. The mechanical and thermal properties for the foams produced in this study appear promising for applications such as insulation and packaging.     

Toughening Mechanism of Nanocomposite Physical Hydrogels Fabricated by a Single Gel Network with Dual Crosslinking——The Roles of the Dual Crosslinking Points

A facile method to fabricate tough and highly stretchable polyacrylamide (PAM) nanocomposite physical hydrogel (NCP gel) was proposed. The hydrogels are dually crosslinked single network with the PAM grafted vinyl hybrid silica nanoparticles (VSNPs) as the analogous covalent crosslinking points and the reversible hydrogen bonds among the PAM chains as the physical crosslinking points. In order to further elucidate the toughening mechanism of the PAM NCP gel, especially to understand the role of the dual crosslinking points, the PAM hybrid hydrogels (H gels) and a series of poly(acrylamide-co-dimethylacrylamide) (P(AM-co-DMAA)) NCP gels were designed and fabricated. Their mechanical properties were compared with those of the PAM NCP gels. The PAM H gels are prepared by simply mixing the PAM chains with bare silica nanoparticles (SNPs). Relative to the poor mechanical properties of the PAM H gel, the PAM NCP gel is remarkably tough and stretchable and also generates large number of micro-cracks to stop notch propagation, indicating the important role of PAM grafted VSNPs in toughening the NCP gel. In the P(AM-co-DMAA) NCP gels, the P(AM-co-DMAA) chains are grafted on VSNPs and the polydimethylacrylamide (PDMAA) only forms very weak hydrogen bonds between themselves. It is found that mechanical properties of the PAM NCP gel, such as the tensile strength and the elongation at break, are enhanced significantly, but those of the P(AM-co-DMAA) NCP gels decreased rapidly with decreasing AM content. This result reveals the role of the hydrogen bonds among the grafted polymer chains as the physical crosslinking points in toughening the NCP gel.     

Enhanced Electron Transfer Rates by AC Voltammetry for Ferrocenes Attached to the End of Embedded Carbon Nanofiber Nanoelectrode Arrays

The effect of the interior structure of carbon nanomaterials on their electrochemical properties is not well understood. We report here the electron transfer rate (ETR) of ferrocene (Fc) molecules covalently attached to the exposed end of carbon nanofibers (CNFs) in an embedded nanoelectrode array. The ETR in normal DC voltammetry was found to be limited by the conical graphitic stacking structure interior of CNFs. AC voltammetry, however, can cope with this intrinsic materials property and provide over 100 times higher ETR, likely by a new capacitive pathway. This provides a new method for high‐performance electroanalysis using CNF nanoelectrodes.     

Supercritical CO2-driven, periodic patterning on one-dimensionals carbon nanomaterials

One-dimensional carbon nano-materials, in particular carbon nanotubes (CNTs) and carbon nanofibers (CNFs), are of scientific and technological interest due to their satisfactory properties and ability to serve as templates for directed assembly. In this work, linear high density polyethylene (PE) was periodically decorated on CNTs and CNFs using a supercritical carbon dioxide (scCO₂)antisolvent-induced polymer epitaxy (SAIPE) method, leading to nano-hybrid shish-kebab (NHSK) structures. The formation mechanism of different morphologies of PE lamellae on CNTs and CNFs has been discussed. Palladium nanoparticles were synthesized and immobilized on the PE/CNF NHSK structure with the assistance of scCO₂. The obtained hierarchical nano-hybrid architecture may find applications in microfabrication and other related fields.     

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.     

In-Vitro Cytotoxicity Study: Cell Viability and Cell Morphology of Carbon Nanofibrous Scaffold/Hydroxyapatite Nanocomposites

Electrospun carbon nanofibers (CNFs), which were modified with hydroxyapatite, were fabricated to be used as a substrate for bone cell proliferation. The CNFs were derived from electrospun polyacrylonitrile (PAN) nanofibers after two steps of heat treatment: stabilization and carbonization. Carbon nanofibrous (CNF)/hydroxyapatite (HA) nanocomposites were prepared by two different methods; one of them being modification during electrospinning (CNF-8HA) and the second method being hydrothermal modification after carbonization (CNF-8HA; hydrothermally) to be used as a platform for bone tissue engineering. The biological investigations were performed using in-vitro cell counting, WST cell viability and cell morphology after three and seven days. L929 mouse fibroblasts were found to be more viable on the hydrothermally-modified CNF scaffolds than on the unmodified CNF scaffolds. The biological characterizations of the synthesized CNF/HA nanofibrous composites indicated higher capability of bone regeneration.     

Effect of cellulose nanofiber on the dynamically asymmetric phase separation in epoxy/polysulfone blends

Significant effect of cellulose nanofibers (CNFs) on cure‐induced phase separation in dynamically asymmetric system is reported. An epoxy/polysulfone blends with typical layered structure formation was chosen as the polymer matrix, and morphology evolution and rheological behavior of systems with different nano‐size fiber loadings upon curing reaction were investigated using optical microscopy and rheological measurement. CNF distributed uniformly in the polymer matrix and had good interaction with polymer chains. Curing reaction of epoxy was promoted by CNF, making the system gel and phase separate earlier. Meanwhile, system viscosity was increased with CNF addition, and the movement of polymer chains and component diffusion were constrained, as a result, the structure evolution process was slowed down. The CNF altered the final morphologies, resulting in refined structures with smaller characteristic length scales or even completely change the morphologies from the layered structures to a bicontinuous structure when the CNF concentration reached to a relatively high level. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1357–1366     

Reactive Dyeing of Electrospun Cellulose Nanofibers by Pad-steam Method

Based on the functional properties of electrospun cellulose nanofibers(CNF), scientists are showing substantial interest to enhance the aesthetic properties. However, the lower color yield has remained a big challenge due to the higher surface area of nanofibers. In this study, we attempted to improve the color yield properties of CNF by the pad-steam dyeing method. Neat CNF was obtained by deacetylation of electrospun cellulose acetate(CA) nanofibers. Three different kinds of reactive dyes were used and pad-steam dyeing parameters were optimized. SEM images revealed smooth morphology with an increase in the average diameter of nanofibers. FTIR results showed no change in the chemical structure after dyeing of CNF. Color fastness results demonstrated excellent ratings for reactive dyes, which indicate good dye fixation properties and no color loss during the washing process. The results confirm that the pad-steam dyeing method can be potentially considered to improve the aesthetic properties of CNF, which can be utilized for functional garments, such as breathable raincoats and disposable face masks.     

Direct current electrodeposition of carbon nanofibers in DMF

Carbon nanofibers (CNFs) were electrodeposited on indium tin oxide (ITO) electrodes by using a DC electric field from N,N′-dimethylformamide (DMF). An improved dispersion of CNFs has been found in DMF solution compared to ethanol and acetonenitrile. After treated by concentrated H₂SO₄/HNO₃, CNFs were dispersed uniformly and stably in DMF. During the electrodeposition process, CNFs moved towards anode indicating the negative charge of the nanofibers. Effects of electric field strength, CNF concentration in the suspension, and the solvents used for CNF dispersion were examined on the deposition nature of CNFs.     

Growth and characterization of pyrene crystals on carbon nanofibers

Pyrene crystals were grown on carbon nanofibers (CNFs) by dispersing pyrene polycrystals and CNFs in water during ultrasonic irradiation, and they were characterized by scanning electron microscopy, X-ray diffractometry (XRD) and spectroscopy. The XRD measurements indicated that the orientation and size of the pyrene crystals on the CNF aggregates were different from that of the added pyrene polycrystals. Based on the spectroscopic properties of the pyrene crystals on the CNFs, the pyrene crystals on the CNF aggregates and on the individual CNFs were determined to be polycrystals and single crystals, respectively. These results indicate that pyrene crystals are produced on the CNFs by recrystallization of the added pyrene polycrystals and their crystal states depend on the aggregation state of the CNFs.     

Effect of cellulose nanofibers on induced polymerization of aniline and formation of nanostructured conducting composite

Cellulose nanofibers (CNFs), derived from the most abundant and renewable biopolymer, are known as natural one-dimensional nanomaterials because of their high aspect ratio. CNFs also are rich in hydroxyl groups, offering opportunities for functionalization toward development of high-value nanostructured composites. Herein, CNFs were extracted from poplar wood powder by chemical pretreatment combined with high-intensity ultrasonication, and then coated with polyaniline (PANI) through in situ polymerization. The PANI-coated CNFs formed nanostructured frameworks around PANI, thereby conferring the CNF/PANI composite with stability and higher charge transport. The optimum PANI content to achieve maximum conductivity of CNF/PANI composites was determined. The morphology, crystall structure, chemical composition, and conductivity of the samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and four-point probe method, respectivily. Our results demonstrated that CNFs can be effective as a template for a flexible and stable conducting polymer to form higher-order nanostructures.     

Electrochemical capacitances of well-defined carbon surfaces

Reported is the capacitive behavior of homogeneous and well-defined surfaces of pristine carbon nanofibers (CNFs) and surface-modified CNFs. The capacitances of the well-defined CNFs were measured with cyclic voltammetry to correlate the surface structure with capacitance. Among the studied pristine CNFs, the edge surfaces of platelet CNFs (PCNF) and herringbone CNFs were more effective in capacitive charging than the basal plane surface of tubular CNF by a factor of 3-5. Graphitization of PCNF (GPCNF) changed the edge surface of PCNF into a domelike basal plane surface, and the corresponding capacitances decreased from 12.5 to 3.2 F/g. A chemical oxidation of the GPCNF, however, recovered a clear edge surface by removal of the curved basal planes to increase the capacitance to 5.6 F/g. The difference in the contribution of the edge surface and basal-plane surface to the capacitance of CNF was discussed in terms of the anisotropic conductivity of graphitic materials.