A new method for fabrication of thin film nanofibrous composite (TFNC) ultrafiltration (UF) membrane consisting of an ultrathin poly(acrylonitrile-co-acrylic acid) (PAN-AA) barrier layer based on a polyacrylonitrile (PAN) nanofibrous support layer was proposed in this study. First, a thin PAN-AA nanofibrous layer was electrospun and deposited on a thicker PAN nanofibrous substrate. Then, the as-prepared PAN-AA nanofibers were swollen in the alkaline buffer solution and merged imperceptibly as an integrated nonporous hydrogel layer on the PAN substrate. The PAN-AA hydrogel layer was cross-linked with different bivalent metal cations (Ca2+, Mg2+) to form an ultrathin barrier layer, of which the thickness and porosity were optimized by controlling the depositing time of PAN-AA nanofibers and pH value of buffer solution. Proteins with different molecular weights were used to evaluate the ultrafiltration performance of the resultant composite membranes. Due to its hydrophilic and negative charged barrier layer, the PAN-AA-Mg and PAN-AA-Ca TFNC UF composite membranes exhibited excellent permeate flux (221.2 and 219.2 L/m2 h) and rejection efficiency (97.8% and 95.6%) for bovine serum albumin (BSA) aqueous solution (1 g/L) at 0.3 MPa. The PAN-AA TFNC UF membranes could be used to retain solutes, of which the radius was larger than 4.6 nm.

A simple approach was developed to prepare carboxycellulose nanofibers directly from untreated biomass using nitric acid or nitric acid-sodium nitrite mixtures. Experiments indicated that this approach greatly reduced the need for multichemicals, and offered significant benefits in lowering the consumption of water and electric energy, when compared with conventional multiple-step processes at bench scale (e.g., TEMPO oxidation). Additionally, the effluent produced by this approach could be efficaciously neutralized using base to produce nitrogen-rich salts as fertilizers. TEM measurements of resulting nanofibers from different biomasses, possessed dimensions in the range of 190–370 and 4–5 nm, having PDI = 0.29–0.38. These nanofibers exhibited lower crystallinity than untreated jute fibers as determined by TEM diffraction, WAXD and 13C CPMAS NMR (e.g., WAXD crystallinity index was ∼35% for nanofibers vs 62% for jute). Nanofibers with low crystallinity were found to be effective for removal of heavy metal ions for drinking water purification.

Nanocellulose extracted from wood pulps using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation and sulfuric acid hydrolysis methods was characterized by small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) techniques. The dimensions of this nanocellulose (TEMPO-oxidized cellulose nanofiber (TOCN) and sulfuric acid hydrolyzed cellulose nanocrystal (SACN)) revealed by the different scattering methods were compared with those characterized by transmission electron microscopy (TEM). The SANS and SAXS data were analyzed using a parallelepiped-based form factor. The width and thickness of the nanocellulose cross section were ∼8 and ∼2 nm for TOCN and ∼20 and ∼3 nm for SACN, respectively, where the fitting results from SANS and SAXS profiles were consistent with each other. DLS was carried out under both the VV mode with the polarizer and analyzer parallel to each other and the HV mode having them perpendicular to each other. Using rotational and translational diffusion coefficients obtained under the HV mode yielded a nanocellulose length qualitatively consistent with that observed by TEM, whereas the length derived by the translational diffusion coefficient under the VV mode appeared to be overestimated.

ABSTRACTUltrafiltration membranes containing a cellulose nanofiber barrier layer were fabricated by the spray coating method, where the thickness and uniformity of the barrier layer were systematically investigated as a function of air pressure, flow rate and concentration of the cellulose nanofiber suspension. In specific, the surface morphology of the barrier layer was studied by scanning electron microscopy and its uniformity was examined by the fluorescence dye imaging method. The ultrafiltration performance of the membranes fabricated by the spray coating method was also compared with that of the membranes made by the knife coating approach using dextran molecules as probe, where the former consistently exhibited significantly higher permeation flux while remaining the same rejection ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44583.

•Luffa sponge with super-hydrophobicity was prepared by surface modification with POSS.•The luffa sponge can absorb 8 to 12 times of its weight for different types of oils.•Both mean pore size and oil viscosity affect the absorption capacity of the sponge.•The sponge exhibits high oil absorption capacity, reusability, and cost-effectiveness.A super-hydrophobic porous material with high absorption capability, suitable for oil spill cleanup, was demonstrated using a natural luffa sponge modified by a polyhedral oligomeric silsesquioxane (POSS)-based compound. Through facile treatments of surface roughing and POSS coating, the initial hydrophilic luffa sponge was transformed to super-hydrophobic having a water contact angle of 155°. The modified luffa sponge could absorb 8 to 12 times of its weight for different types of oils and could be recycled for many times in use. The effects of oil viscosity and sponge pore size on the absorption capacity were investigated; where the absorption selectivity tests revealed that the modified luffa sponge could essentially take up all the components of the oil during the absorption process.Download high-res image (275KB)Download full-size image

•Electrospun & UCN-based nanofibrous membranes were used as substrates of RO membranes.•Thin-film nanofibrous composite RO membranes were fabricated by spray coating approach.•Different additives can affect on the filtration performance of the RO membranes.•The RO membranes exhibited significantly enhanced permeation flux and rejection ratio.Interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) was carried out on top of the highly permeable nanofibrous ultrafiltration (UF) membrane substrates to create thin-film nanofibrous composite (TFNC) reverse osmosis (RO) membranes for desalination. The UF substrates contained distinct fibrous layers: poly(ethylene terephthalate) (PET) non-woven mat as the mechanical support, electrospun polyacrylonitrile (PAN) nanofibrous scaffold as the mid-layer or barrier layer, and ultra-fine cellulose nanofibers (CNs) as the barrier layer. An aliphatic co-monomer, piperazine (PIP) and different additives (e.g. an ionic liquid 1-octyl-3-methylimidazolium chloride, OMIC) were included in interfacial polymerization to improve the permeation flux for RO operations. To further increase the membrane permeability, a spray coating method was also used to control the barrier layer thickness by adjusting the load of the aqueous solution in polymerization. The optimized RO membrane exhibited a rejection ratio of 96.5% against NaCl (500 ppm) and a flux of 28.6 L/m2 h at 0.7 MPa, approaching the performance of a high-flux commercial RO membrane (DOW FILMTEC™ XLE). We believe higher permeation flux can be achieved using nanocomposite barrier layer with the CN-based UF substrate, while still maintaining high salt rejection ratio.Download high-res image (126KB)Download full-size image

A novel kind of thin-film nanofibrous composite (TFNC) nanofiltration membrane consisting of a polypiperazine amide (PPA) barrier layer, an ultrathin electrospun poly(acrylonitrile-co-acrylic acid) (PAN–AA) transitional mid-layer and an electrospun polyacrylonitrile (PAN) nanofibrous supporting layer, was successfully fabricated by interfacial polymerization with piperazine (PIP) and trimesoyl chloride (TMC) onto the PAN–AA/PAN double-layer substrate. The PAN–AA nanofibrous mid-layer played two important roles between the PPA barrier layer and the PAN nanofibrous supporting layer. It could be swollen in the alkaline aqueous monomer (PIP) solution to form an intermediate hydrogel film, which acted as the transitional mid-layer to cover the majority of the large surface pores of the electrospun PAN nanofibrous substrate. On the other hand, the hydrophilic PAN–AA hydrogel film could capture and reserve abundant PIP monomer to facilitate interfacial polymerization with TMC to form an endurable ultrathin PPA barrier layer, resulting in an integrated composite membrane confirmed by the mechanical properties. The resultant TFNC membranes demonstrated a high rejection rate (98.2%) and high permeate flux (64.4 L m−2 h−1) for MgSO4 aqueous solution (2.0 g L−1), and also exhibited excellent structural stability due to the strong interactions between the barrier layer and the nanofibrous support that were enhanced by the transitional PAN–AA mid-layer.

•Synchrotron SAXS/WAXS methods are powerful tools for polymers/biopolymers research.•Geometrical information of cellulose nanofiber can be examined using solution-SAXS.•2D pattern analysis helps to understand polymorphism, orientation, and morphology.Synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) techniques are frequently used to study hierarchical structure and preferred orientation in polymers and biopolymers. In this article, two examples based on materials showing preferred orientation at different length scales are given. In the first example, cellulose fibers/nanofibers were investigated from the perspectives of crystal polymorphism, preferred orientation and nanoscale morphology. In the second example, a time-resolved SAXS/WAXS study was carried out to investigate the melting and recrystallization processes of a pre-stretched random co-polymer, poly(propylene-ran-1-butylene) (PB).Illustration of spherical trigonometric relationship in fiber diffraction geometry, in reciprocal space (left); and a comparison of simulated and experimental fiber diffraction patterns of jute cellulose fibers (right).Figure optionsDownload full-size imageDownload as PowerPoint slide

•Adhesion of PE substrate to e-spun PES increased 10-fold after chromic acid treatment.•Bonding strength of PES nanofibers to PE film increased with increasing spinning rate.•The MDT of PES/PE/PES membrane is much higher than that of PE or commercial separator.Polyethersulfone (PES) electrospun nanofibrous membranes have been prepared and deposited on both sides of a microporous polyethylene (PE) substrate to fabricate a nanocomposite separator, which exhibits a high meltdown temperature (MDT) to prevent the thermal runaway within the battery under the condition of overcharging or abuse. To improve adhesion to electrospun PES nanofibrous membranes, the PE substrate with low surface energy and hydrophobic nature was etched with chromic acid and characterized with atomic force microscopy (AFM) and infrared spectroscopy (FTIR) techniques as well as the water contact angle test. Compared to the original film, the modified PE substrate showed a nearly 10-times increase in adhesive strength to the electrospun PES membrane. The morphology of the electrospun PES membrane, controlled by different electrospinning flow rates, was also demonstrated to have a substantial impact on adhesion, where a 5-fold increase of the adhesive strength was observed when the flow rate increased from 20 μL/min to 60 μL/min. The composite PES/PE/PES separator, structured as a PE substrate sandwiched in 2 electrospun PES membranes, maintained the low shutdown temperature (SDT) of 131 °C but achieved a significantly higher MDT of 221 °C. Furthermore, the high porosity of the electrospun PES membrane ensured that the air permeability of the separator was not sacrificed when compared with the original PE separator.

Highly anisotropic organoclays and relatively isotropic carbon black particles are both nanoscale fillers widely used to enhance polymer properties. Nanocomposites formed through incorporation of organoclay can result in various morphologies including intercalated and exfoliated structures, while carbon black can also be dispersed in polymeric material and form a network structure. In this study, we illustrate a synergistic effect of having both organoclay and carbon black dispersed in the polymer matrix with different functionality. To evaluate the structure and property (permeability) relationships in these nanocomposites, multi-directional small-angle X-ray scattering (SAXS) and complementary transmission electron microscopy (TEM) measurements were carried out to characterize the organoclay structure and orientation. It was found that the addition of carbon black greatly enhances the tortuosity by the joining of carbon black and organoclays leading to reduced permeability and enhanced barrier properties.

Ultrathin cellulose microfibril fractions were extracted from spruce wood powder using combined delignification, TEMPO-catalyzed oxidation, and sonication processes. Small-angle X-ray scattering of these microfibril fractions in a “dilute” aqueous suspension (concentration 0.077 wt %) revealed that their shape was in the form of nanostrip with 4 nm width and only about 0.5 nm thicknesses. These dimensions were further confirmed by TEM and AFM measurements. The 0.5 nm thickness implied that the nanostrip could contain only a single layer of cellulose chains. At a higher concentration (0.15 wt %), SAXS analysis indicated that these nanostrips aggregated into a layered structure. The X-ray diffraction of samples collected at different preparation stages suggested that microfibrils were delaminated along the (11̅0) planes from the Iβ cellulose crystals. The degree of oxidation and solid-state 13C NMR characterizations indicated that, in addition to the surface molecules, some inner molecules of microfibrils were also oxidized, facilitating the delamination into cellulose nanostrips.

Oxidized cellulose nanofibers (CNF), embedded in an electrospun polyacrylonitrile (PAN) nanofibrous scaffold, were grafted with cysteine to increase the adsorption capability for chromium (VI) and lead (II). Thiol-modified cellulose nanofibers (m-CNF) were characterized by titration, FT-IR, energy dispersive spectroscopy (EDS) and SEM techniques. Static and dynamic Cr(VI) and Pb(II) adsorption studies of m-CNF nanofibrous composite membranes were carried out as a function of pH and of contact time. The results indicated these membranes exhibited high adsorption capacities for both Cr(VI) (87.5 mg/g) and Pb(II) (137.7 mg/g) due to the large surface area and high concentration of thiol groups (0.9 mmol of –SH/gram m-CNF). The morphology and property of m-CNF nanofibrous composite membranes was found to be stable, and they could be used and regenerated multiple times with high recovery efficiency.

Ionic liquids (ILs) with long alkyl substituted groups, including 1-docosanyl-3-methylimidazolium bromide (IL-1) and 1-docosanyl-3-methylimidazolium hexafluorophosphate (IL-2), were synthesized and used to modify the surface of carbon nanofibers (CNF). The nanocomposite film prepared by solution-blending of ionic liquid modified CNF (i-CNF) and ultrahigh molecular weight polyethylene (UHMWPE) displayed better toughness when compared with pure UHMWPE even at very low concentrations (e.g. 0.4 wt%). The effect of ionic liquids on the elongation-to-break ratio of this nanocomposite system was investigated. The ionic liquid with hexafluorophosphate as the anion was more efficient to increase the toughness of UHMWPE due to the improved compatibility of IL with UHMWPE in the polymer matrix than that of the bromide. The rheological behavior of molten nanocomposites revealed that the storage modulus and the complex viscosity decreased with increasing ionic liquid content in the high frequency region. However, a reverse trend was observed when the frequency was less than 0.05 s−1. In-situ monitoring in the change of crystallinity of the nanocomposite during tensile deformation suggested a mechanism of sliding between UHMWPE crystal regions and the surface of carbon nanofibers.

Nanofiltration (NF) membranes, consisting of a composite barrier layer prepared by interfacial polymerization of polyamide around the ultra-fine cellulose nanofibers (CN) layer in a thin-film nanofibrous composite (TFNC) scaffold, were demonstrated. Two interfacial polymerization pathways (termed IP and IP-R), regarding the arrangement of the aqueous and organic phases, were investigated. It was found that interfacial polymerization with the aqueous phase above the organic phase (IP-R) yielded better filtration performance, i.e., IP-R based membranes exhibited a higher MgCl2 rejection than IP based membranes. Transmission electron microscopy (TEM) observation indicated that the denser part of the barrier layer was on the CN layer surface of IP-R based membranes, whereas this portion was deeply immersed in the CN layer of IP based membranes. To investigate the structure and property relationship of the composite barrier layer, both IP and IP-R based membranes were treated with 1% trimesoyl chloride (TMC) in hexane. After treatment, the rejection of NaCl was found to increase from 74% to 91% for IP-R based membranes, while remained unchanged (∼75%) for IP based membranes. This behavior can be explained by the decrease in pore size due to the cross-linking of TMC and secondary amino groups in the barrier layer of IP-R based membranes, while the permeability in IP based membranes was probably mainly controlled by the water passage through channels formed at the interface between CN and polymer matrix in the barrier layer of IP based membranes, which is not dependent of the cross-linking reaction.

The structure and property relationships of propylene-1-octene random copolymer having different octene comonomer concentrations were investigated. In specific, the crystal structure evolution in these copolymers during uniaxial stretching at 60 °C was characterized by in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. With high octene content, the copolymer behaved like an elastomer with small elastic modulus and yield stress, low crystallinity and low crystal orientation under stretching. Furthermore, step-cycle tensile test showed that the copolymer with high octene content had a high recovery ratio. With low octene content, the copolymer behaved like a plastomer with large elastic modulus and yield stress, high crystallinity and high crystal orientation under stretching. From 2D SAXS results, it was found that in low octene content sample, lamellar fragmentation occurred resulting in a significant decrease in lamellar lateral size. In contrast, in high octene content sample, stress might be mainly concentrated on the amorphous matrix, leading to an inter-lamellar slip and a small decrease in lamellar lateral size. Schematic structural changes of propylene-1-octene copolymer under tensile deformation were illustrated to explain the different elasticity behavior in these copolymers.

A novel class of high-flux microfiltration filters consisting of an electrospun nanofibrous membrane and a conventional non-woven microfibrous support is being presented. The nanofibrous non-woven layer was fabricated by electrospinning of polyvinylalcohol (PVA) directly onto the microfibrous support and then followed by chemical cross-linking with glutaraldehyde (GA) in acetone. By altering the processing parameters, such as the applied voltage and the distance between the spinneret and the collector, as well as the concentration of PVA solution, electrospun PVA membranes with an average fiber diameter of 100 ± 19 nm were obtained. Characterizations revealed that the mean pore size of the electrospun PVA membranes ranged from 0.30 μm to 0.21 μm with the electrospun PVA membrane thickness varying from 10 m to 100 μm. Due to the high porosity, microfiltration filters based on these electrospun membranes showed 3–7 times higher pure water flux than the Millipore GSWP 0.22 μm membrane. The nanofibrous PVA membranes with an average thickness of 20 μm could successfully reject more than 98% of the polycarboxylate microsphere particles with a diameter of 0.209 ± 0.011 μm, and still maintain 1.5–6 times higher permeate flux than that of the Millipore GSWP 0.22 μm membrane.

⿢Overview of the fabrication and applications of electrospun nanofiber membranes.⿢Recent advances in nanofiber-based membranes for water filtration.⿢Recent development of nanofibrous affinity membranes for adsorption.The development of nanofiber technology offers viable means to produce nanofibrous articles, useful for many health, energy and environmental applications. In specific, polymeric nanofibers fabricated by electrospinning can be used as effective membrane materials for environmental remediation due to the light weight, high surface area, and interconnected porous structure. In this paper, we review some recent advances in electrospinning for mass production of nanofiber membranes, especially suitable for water purification. These electrospun nanofibers not only can form highly porous membranes with controlled pore size, but also can be functionalized to enhance the separation performance. Various composite membrane formats containing different arrangements of nanofibers have been demonstrated for many sorts of water applications, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, and adsorption.Download high-res image (309KB)Download full-size image

•Fluorinated ionic liquid had been successfully prepared and employed to modify MWCNTs.•Modified MWCNTs dispersed well in FEP matrix can improved its mechanical properties.•F-IL-MWCNTs serve as both of plasticizer and reinforcing reagent in FEP nanocomposite.Fluorinated ionic liquid (F-IL), 1-(3-perfluorooctylpropyl)-3-methylimidazolium bis(perfluoroethylsufonyl)amine, had been successfully prepared and employed to modify multi-wall carbon nanotubes (MWCNTs) for improving the processability of fluoro-ethylene-propylene (FEP). The thermally decomposed temperature of F-IL was higher than 350 °C measured by thermal gravimetric analysis (TGA) which indicated that the fluorinated ionic liquid could be suitable for melting blend with FEP (blending at 290 °C) by a twin-screw extruder. Through “cation-π” interaction between the imidazolium cation of F-IL and the graphene surface of MWCNTs, MWCNTs can be modified with F-IL and used as nanofillers to improve the dispersity of MWCNTs in fluorocopolymer FEP verified by SEM images of the FEP nanocomposite. The structural characterization and mechanical property of FEP nanocomposite during the deformation were investigated by tensile experiments and simultaneous time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques.