Nylon-6 Membranes Research Articles

Primary amide-functionalized cyclotricatechylene covalent organic frameworks membrane for efficient enrichment of melamine and its derivatives in migration solution of food contact materials.

A highly chemically stable primary amide-functionalized cyclotricatechylene covalent organic framework was synthesized by an irreversible reaction and a post-synthetic modification. It possessed a rod-like morphology and exhibited strong solvent stability owing to the polyether bonds. The material showed good adsorption performance for melamine and its derivatives and adsorption mechanism was investigated by molecular simulations. The adsorbent was coated on the nylon-66 membrane to prepare the enrichment membrane. Under optimized conditions, an in-syringe membrane-based extraction method, combined with ultra-high performance liquid chromatography-tandem mass spectrometry was developed for the analysis of melamine and six melamine derivatives in the migration solution. A good linearity was obtained with correlation coefficients ranging from 0.9924 to 0.9995. The limits of detection were 1-200ng/L and the limits of quantification were 3-500ng/L. This method was successfully applied to the migration solution of sushi bamboo rolling mats with spiked recoveries of 73.2%-115% and relative standard deviations of 0.9%-9.9%. This work shows a practical and perspective approach for the efficient enrichment of food contact material hazards.

Separation of used automobile oil/water mixture by Nylon 6/ZnO nanoparticles electrospun membrane

The separation of water from oily wastewater by using membranes is a big challenge because of serious membrane fouling and low separation efficiency. So, for the first time, Nylon 6 (N6) membranes blended with ZnO nanoparticles with a N6 support layer by the electrospinning technique were fabricated, where the N6 layer enhanced the mechanical strength and ZnO NPs formed a strong barrier on the N6 membrane to reduce membrane pore-clogging. The micron pore size membranes created by hydrophilic ZnO NPs on electrospun Nylon 6 fiber–matrix structures contributed to the hydrophilicity and fouling resistance of the membranes. The optimal quantities of ZnO NPs and N6 in the electrospun membranes were 2.5 and 40 w.t%, respectively, for achieving the desired specific flux of 215.14 LMH/bar over 3 h when using a 0.1% v/v oil/water influent. Up to 90% of oil, chemical oxygen demand, turbidity, total dissolved solids, and total suspended solids were removed to fulfill discharge requirements. The presence of ZnO NPs in the N6 membrane also exhibited excellent anti-fouling properties with the flux recovery ratio of 52.5 % and water flux of 405.6 LMH/bar, which was much better than those of a pristine N6 membrane, indicating the microfiltration membranes developed in this study were reasonably resistant to fouling to ensure high effluent water quality and the fabricated N6/ZnO NPs membrane is feasible in treating oil-containing wastewater.

Dummy molecularly imprinted membranes based on an eco-friendly synthesis approach for recognition and extraction of enrofloxacin and ciprofloxacin in egg samples

In this work, novel dummy molecularly imprinted membranes (MIMs) were fabricated using the nylon-66 (NY-66) membranes as the subtracts based on an eco-friendly “sandwich” technology with less consumption of organic reagents at mild conditions for recognition and extraction of enrofloxacin (ENR) and ciprofloxacin (CIP) in egg samples. The prepared MIMs were characterized by SEM, ATR-FTIR and TGA, showing the successful construction of uniform and porous polymers on the surface of membranes. A series of adsorption affinity tests were investigated, indicating the prepared materials had specific recognition capacity and excellent stability as novel sorbents. Furthermore, Box-Benhnken design (BBD) and single factor investigations were applied to optimize pretreatment procedures, coupling with Ultra High Performance Liquid Chromatograph (UHPLC) detection. The method showed a good correlation (r2>0.9999) within the linear range of 5.0~5000.0 µg kg−1, and limit of detection (LOD) of ENR and CIP were 0.3 and 0.7 µg kg−1, respectively. The mean recovery ranged from 84.5% to 97.0% within relative standard deviations (RSDs) of 10.2%. Finally, ENR and CIP were not detected in 3 batches of egg samples. The current study developed the dummy MIMs as sorbents combined with UHPLC analysis for extraction and detection of target analytes in food matrices.

Monitoring the decolourisation efficacy of advanced membrane fabricated phytosilica nanoparticles in textile effluent water treatment

Silica nanoparticles are generally mesoporous that are predominant in the sand and rocks. Silica nanoparticles have a wide range of applications in various fields such as medicine, waste management, effluent treatment and electronics. The present work has explored the synthesis of silica nanoparticles through acid and alkaline leaching method from Pedalium murex which is a common weed that is found in southern parts of Tamil Nadu. Silica nanoparticles (SiNps) and its functional groups were confirmed by EDX and FTIR analysis with their respective energy dispersion levels and wavenumbers. Size, shape and morphological features of SiNps were analysed by PSA, TEM and SAED analysis. Synthesised and characterized nanosilica was crosslinked over nylon-66 and cellulose nitrate membranes and were confirmed by FTIR analysis for their crosslinking with SiNps. Water retention activity of the crosslinked and non crosslinked membranes was analysed by contact angle measurement to ensure the receptability of the membranes to remove contaminants by the adsorption. The decolourisation efficiency of the crosslinked nylon 66 membrane was found as a potential source for the treatment with 65.5% colour reduction when compared with other membranes. A slight reduction of solid profiles and COD ranges were achieved for crosslinked membranes than non crosslinked membranes.

Preparation and Characterization of Chromium(VI) Ion-Imprinted Composite Membranes with a Specifically Designed Functional Monomer

Cr(VI) anion-imprinted composite membranes (Cr(VI)-IICM1∼23) based on a designed functional monomer N,N'-(ethane-1,2-diyl)bis(2-methylacrylamide) (EBMA) were synthesized via surface-grafting. Using nylon-6 membrane for support, the main imprinting parameters, i.e., the functional monomer and crosslinker dosages, membrane soaking times, and porogen solvent ratios were optimized. The morphology and surface area of the optimum imprinted composite membrane (Cr(VI)-IICM11) were characterized by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The effects of the Cr(VI) anion concentration, adsorption time, temperature, and pH on adsorption were investigated. Additionally, the permeation, mass transfer, and adsorption of the Cr(VI)-IICM11 were characterized for aqueous Cr(VI) anions. The adsorption capacity and imprinting factor of the Cr(VI)-IICM11 in the imprinting solution were high, and the membrane had good permeation selectivity for Cr(VI) anions. Additionally, Cr(VI)-IICM11 efficiently adsorbed aqueous Cr(VI) anions. These results suggest that EBMA was a suitable functional monomer for Cr(VI) anions serving as the template. Therefore, Cr(VI)-IICM is a suitable material for adsorbing and separating Cr(VI) anions in complex, aqueous solutions.

A dual-functional membrane for bisphenol A enrichment and resonance amplification by surface-enhanced Raman scattering

Bisphenol A (BPA) was one of the environmental hormones that would cause endocrine and metabolic disorders in human or wildlife. This paper proposed a method to detect the trace amounts of BPA in water samples by fully utilizing the enrichment and resonance amplification functions of a new dual-functional membrane. In this work, gold nanoparticles (AuNPs) modified by 3-amino-5-mercapto-1,2,4-triazole (AMT) were embedded in nylon66 membrane to produce a dual-functional membrane which could carry out sample enrichment by capturing BPA molecules from water and achieve resonance amplification by connecting BPA to the surfaces of AuNPs. By designing an automatic sampler for large-volume enrichment, the SERS enhancement factor (EF) of the method was further improved to 1.2×105. The present method had been successfully applied to detect BPA in drinking water and environmental water by SERS with the detection limit of 0.012μg/L. It had the potential for on-site detecting of BPA in various water samples.

Preparation and Characterisation of Surface Adsorbed Reduced Graphene Oxide/Polyaniline Nanocomposite on Polymer Membrane for Trimethylamine Sensing

A graphene/polyaniline (rGO/PANi) nanocomposite was synthesized by solution blending method and deposited on to a nylon-6 membrane via vacuum assisted self-assembly (VASA) method to fabricate a flexible material applied as a chemoresistive gas sensor for trimethylamine (TMA). The morphological and structural characterization of surfaced adsorbed polymer nanocomposite was carried out by FT-IR, SEM, UV-Vis and surface profilometry. While, electrical property was carried out by four-point probe measurement. Prepared rGO/PANi nanocomposite has a percolation threshold around 0.40% vol. fraction, with a conductivity of 8.28 S/m (rsd = 3.0%, n=3) and thickness around 38.58 μm (rsd = 7.63%, n=3. The composite sensor exhibited linear range from 45 to 230 mg/L (r2= 0.9962) and the calculated limit of detection was 25.30 mg/L. It exhibited a repeatable response to TMA gas.

Studies on Nylon-66 membrane using aqueous solutions of potassium and lead nitrate salts as permeants

Abstract Measurements on hydrodynamic and electro-osmotic permeability of water and aqueous solutions of KNO 3 and Pb(NO 3 ) 2 in the concentration (C) range of 10 - 4 $10^{-4}$ M to 10 - 3 $10^{-3}$ M are made across the Nylon-66 membrane. The data obtained are used to ascertain the form of transport equation using the theory of non-equilibrium thermodynamics. Conductance of membrane equilibrated with water and aqueous solutions are measured and the data are used to estimate phenomenological coefficients. These phenomenological coefficients are used to determine the average pore radius, the average number of pores and the membrane constant. Zeta potentials are evaluated using electro-osmotic permeability and membrane-permeant conductance data to understand the electrical nature of the membrane-permeant interface. It is observed that hydrodynamic permeability and electro-osmotic permeability depend linearly on the applied pressure difference and the potential difference, respectively.

Lipase adsorption on woven nylon-6 membrane: Optimization, kinetic and thermodynamic analyses

Candida rugosa lipase was immobilized on the activated nylon-6 membrane using 0.5% glutaraldehyde as cross-linking agent. The immobilized lipase had an improved temperature and pH stability and exhibited good reusability. The adsorption process followed pseudo-second order rate equation and the biosorption isotherms correlated well with the Langmuir isotherm model. Negative ΔG indicated the adsorption process was spontaneous and the positive ΔH indicated that the adsorption was endothermic. The standard entropy ΔS value was also positive, which suggested an increase in the freedom of the system.

Graphene/Nylon-6 Chemiresistor Sensor for Trimethylamine Gas Sensing

A graphene/nylon-6 nanocomposite was fabricated by incorporating reduced graphene oxide onto a nylon-6 (N6) membrane via vacuum assisted self-assembly (VASA) method. The graphene oxide was synthesised through acid dissolution according to the method of Marcano & Tour and subsequently reduced to graphene using L-ascorbic acid. The surface morphology and electrical characteristic of graphene and its nanocomposites was characterized. The percolation threshold of the prepared nanocomposites was around 1.92% (w/w) with a sheet resistance of 3.839 x 103Ω per square (rsd= 0.22%, n=4). Different weight ratios of the nanocomposite were tested for its sensitivity towards the amine vapour. The final sensor for trimethylamine concentration has a working concentration range between 23 and 230 mg/L. The sensor exhibited linearity between 45 to 230 mg/L (r2= 0.9917) while the detection and quantitation limit was calculated at 0.39 mg/L and 1.30 mg/L, respectively. This nanocomposite demonstrates that it can be used as a chemiresistor gas sensor that is sensitive and selective to trimethylamine vapour.

<i>Candida rugosa</i> Lipase Adsorption on Nylon-6: Optimization, Kinetic and Thermodynamic Analysis

Candida rugosa Lipase was immobilized on the activated nylon-6 membrane using 0.5% glutaraldehyde as cross-linking agent. The immobilized lipase had an improved temperature and pH stability and exhibited good reusability. The adsorption process followed pseudo-second order rate equation and the biosorption isotherms correlated well with the Langmuir isotherm model. Negative ΔG indicated the adsorption process was spontaneous and the positive of ΔH indicated that the adsorption was endothermic.

Development of novel nanocomposite membrane for water purification

In the area of water purification, nanotechnology provides efficient removal of pollutants and germs. Electrospun nanofibers membrane has a potential for water purification due to its high large surface area, and good mechanical strength. In the present study, PAMAM dendrimers composite nylon-6 nanofibers membrane was prepared by crosslinking method using glutaraldehyde. Modified membrane has drastically improved water purification efficiency. Further, the efficacy of the modified membrane can be renewed by mere exposure of the saturated membrane with the solution having acidic pH. The modified membrane can be used as an effective tool for water purification.

Preparation of bi-continuous Nylon-66 porous membranes by coagulation of incipient dopes in soft non-solvent baths

Microporous Nylon-66 membranes were prepared by non-solvent induced phase separation (NIPS) from the Water/1-Butanol/Formic acid/Nylon66 quaternary system. Water, as a strong non-solvent for Nylon-66, was employed to enhance polymer crystal nucleation in the casting dope, while 1-butanol was adopted as a soft coagulant whereby liquid–liquid demixing mechanism can be sufficiently suppressed. By gradually increasing the water content in the dope, the effect of nucleation density on the morphology of the membrane was clearly manifested. While low water content (<2.5%) dopes resulted in membranes consisting of large full spherulites, high water content (>7.5%) dopes gave rise to symmetric bi-continuous membranes composed of small interlocked, stick-like crystallites intertwining with continuous channels of micropores. Water permeation flux and tensile strength of the membranes were measured and correlated with the porosity, pore size, and membrane morphology. In addition, X-ray diffraction (XRD) and Fourier Transform Infrared-Attenuated total reflection (FTIR-ATR) analyses indicate that the membranes contained α-type crystals with a crystallinity of ~38%, consistent with that determined from Differential Scanning Calorimetry (DSC). The later method also showed that all membranes have a similar crystal melting behavior with Tm ~265°C.

Regulation of Critical Ethanol Response Concentrations of Ethanol-Responsive Smart Gating Membranes

Regulation of the critical ethanol response concentration of ethanol-responsive smart gating membranes has been systematically investigated by preparing a series of gating membranes with grafted poly(N-isopropylacrylamide) (PNIPAM) and PNIPAM-based copolymer gates. A porous Nylon-6 (N6) membrane is used as the substrate membrane, and the surface-initiated atom transfer radical polymerization (ATRP) method is employed to graft polymers onto the substrate membrane. Fourier Transform Infrared Spectrometer (FT-IR) is used to determine chemical compositions of the prepared membranes, and Scanning Electron Microscope (SEM) is used to investigate the microstructures of membranes. The fluxes of ethanol solutions across different membranes are studied systematically by changing the ethanol concentration. The results show that the introduction of hydrophilic monomer N,N-dimethylacrylamide (DMAA) or hydrophobic monomer butyl methacrylate (BMA) into the grafted PNIPAM-based gates can effectively regulate the critical...

Effects of APTEOS content and electron beam irradiation on physical and separation properties of hybrid nylon-66 membranes

Nylon-66 contains functional groups which form hydrogen bonds with inorganic silica networks and allow the creation of hybrid membranes. As a typical semicrystalline polymer, nylon-66 can be crosslinked through electron beam (EB) irradiation to form nanofiltration membranes. The effects of γ-aminopropyltriethoxylsilane (APTEOS) and EB irradiation on the physical and separation properties of nylon-66 membranes were studied in this work. Hybrid nylon-66 membranes were prepared by adding an APTEOS solution (5wt%, 10wt% and 20wt%) into nylon-66 which was dissolved in formic acid. Before air drying, membranes were irradiated at 60kGy, 70kGy and 80kGy. More cellular pores were formed in nylon-66 membranes with the addition of APTEOS. However, increased irradiation dose caused the formation of a dense layer in nylon-66 membranes. Crosslinked silica in nylon-66 membranes was confirmed by FT-IR and DMA, while XRD results showed that there was a high degree of crystallinity in some membranes after irradiation. With improvements in membrane pore size and the ratio of membrane thickness to porosity, nylon-66 membrane with 10wt% of APTEOS irradiated at 70kGy exhibited satisfactory permeability, excellent removal of neutral solutes and improved rejection of divalent ions.

Dechlorination of chlorinated hydrocarbons by bimetallic Ni/Fe immobilized on polyethylene glycol-grafted microfiltration membranes under anoxic conditions

In this study, the dechlorination of chlorinated hydrocarbons including trichloroethylene (TCE), tetrachloroethylene (PCE) and carbon tetrachloride (CT) by bimetallic Ni/Fe nanoparticles immobilized on four different membranes was investigated under anoxic conditions. Effects of several parameters including the nature of membrane, initial concentration, pH value, and reaction temperature on the dechlorination efficiency were examined. The scanning electron microscopic images showed that the Ni/Fe nanoparticles were successfully immobilized inside the four membranes using polyethylene glycol as the cross-linker. The agglomeration of Ni/Fe were observed in poly(vinylidene fluoride), Millex GS and mixed cellulose ester membranes, while a relatively uniform distribution of Ni/Fe was found in nylon-66 membrane because of its hydrophilic nature. The immobilized Ni/Fe nanoparticles exhibited good reactivity towards the dechlorination of chlorinated hydrocarbons, and the pseudo-first-order rate constant for TCE dechlorination by Ni/Fe in nylon-66 were 3.7–11.7 times higher than those in other membranes. In addition, the dechlorination efficiency of chlorinated hydrocarbons followed the order TCE > PCE > CT. Ethane was the only end product for TCE and PCE dechlorination, while dichloromethane and methane were found to be the major products for CT dechlorination, clearly indicating the involvement of reactive hydrogen species in dechlorination. In addition, the initial rate constant for TCE dechlorination increased upon increasing initial TCE concentrations and the activation energy for TCE dechlorination by immobilized Ni/Fe was 34.9 kJ mol −1, showing that the dechlorination of TCE by membrane-supported Ni/Fe nanoparticles is a surface-mediated reaction.

Effect of electron beam irradiation on morphology and sieving characteristics of nylon-66 membranes

Nylon-66 is a typical semicrystalline polymer that can be crosslinked through electron beam (EB) irradiation. Crosslinking can dramatically change polymer properties. The objective of this research was to observe how EB irradiation affects morphology and sieving characteristics of nylon-66 membranes. EB irradiation was carried out in air at 60, 70 and 80 kGy doses. Scanning electron microscopy (SEM), swelling and gel content studies evidenced the morphological changes and crosslinking of nylon-66 membranes. Sieving characteristics were also measured using pure water permeation, and rejection of raffinose, vitamin B12, and mono- and divalent salts. These results show that nylon-66 membrane surface and permeation characteristics changed with different irradiation doses. The nylon-66 surface became denser and the gel content increased with increasing irradiation dose. Furthermore, pure water permeation decreased and small molecules were increasingly rejected with greater irradiation doses. The amount of rejection was between 33% and 88.4% for vitamin B12 and between 16% and 83% for raffinose. The highest vitamin B12 and raffinose rejection was seen with a N-80 membrane, and no rejection was measured with N-0 or N-60 membranes. Salt rejection, however, was very low, especially for NaCl, with only 10.51–46% rejected. Based on flux, permeability and uncharged solute (vitamin B12 and raffinose) rejection data, nylon-66 type N-70 and N-80 membranes were estimated to be in the nanofiltration (NF) range.

Enhanced production of a thermostable mannanase by immobilized cells of Bacillus subtilis on various membranes

Cells of the thermophilic Bacillus subtilis WY34 were immobilized on various formaldehyde-activated polymer membranes and the immobilized cells were used for the production of thermostable mannanase in flasks. The results showed that polyethersulfone membranes (PES) and nylon-6 membranes were the most suitable supports for cell immobilization to produce the mannanase. Moreover, PES and nylon-6 membranes immobilized cells provided 1.78- and 1.74-fold higher mannanase activity compared to the control after 4 days of cultivation, respectively. The immobilized cells on PES and nylon-6 membranes had good stability and retained 131.5 and 114.3% of ability of enzyme production even after six cycles of repeated batch fermentation, respectively. Active cell growth was observed by scanning electron microscopy (SEM) after 16 days (four cycles) repeated batch cultivation. Therefore, the membrane-immobilized cells of B. subtilis WY34 can be proposed as an effective biocatalyst for repeated usage for production of the thermostable mannanase.

Preparation of thermo-responsive gating membranes with controllable response temperature

The adjustment or manipulation of response temperature of thermo-responsive membranes was systematically investigated by adding hydrophilic or hydrophobic monomers into N-isopropylacrylamide (NIPAM) monomer solution in the fabrication of thermo-responsive gates for the membranes. Plasma-induced grafting polymerization method was introduced to graft thermo-responsive polymers poly( N-isopropylacrylamide) (PNIPAM), poly( N-isopropyl-acrylamide- co-acrylamide) (PNA) and poly( N-isopropylacrylamide- co-butyl methacrylate) (PNB) as functional gates onto porous polyvinylidene fluoride (PVDF) or Nylon-6 (N 6) membrane substrates. The SEM and XPS characterizations showed that PNIPAM, PNA and PNB were all successfully grafted onto the porous PVDF or N 6 membrane substrates. The water flux experimental results showed that the response temperatures of grafted gating membranes were linearly increased with increasing the molar ratio of hydrophilic monomer acrylamide (AAM) in the NIPAM co-monomer solution, but linearly decreased with increasing the molar ratio of hydrophobic monomer butyl methacrylate (BMA) in the NIPAM co-monomer solution. The response temperature of PNA- g-PVDF membrane was raised to 40 °C when 7 mol% of AAM was added into the NIPAM co-monomer solution, and that of PNB- g-N 6 membrane was reduced to 17.5 °C when 10 mol% of BMA was introduced into the NIPAM co-monomer solution. The relationship between the hydrophobicity and response temperature of grafted membranes was also investigated. The results in this study provided valuable guidance for the design and preparation of thermo-responsive gating membranes with desired response temperatures for different applications.

Thermo-Responsive Membranes with Cross-linked Poly(N-Isopropyl-acrylamide) Hydrogels inside Porous Substrates

Thermo-responsive membranes were prepared by fabricating cross-linked poly(N-isopropylacrylamide) (PNIPAM) hydrogels inside the pores of porous Nylon-6 (N6) membranes by the free radical polymerization method. SEM micrographs of the prepared membranes showed that PNIPAM hydrogels were filled uniformly throughout the entire thickness of the porous N6 membranes. Both PNIPAM-filled N6 membranes prepared at 60 °C and at 25 °C exhibited significant reversible and reproducible thermo-responsive diffusional permeability. When the environmental temperature remained constant, the diffusional coefficient of vitamin B12 (VB12) across the PNIPAM-filled N6 membrane prepared at 25 °C was ca. twice the value of that prepared at 60 °C due to different filling yields. The thermo-response factor of the membrane prepared at 25 °C was higher than that prepared at 60 °C. The 3-dimensional interpenetrating network structure of the cross-linked PNIPAM hydrogels inside the N6 porous substrates could effectively ensure a repeatable thermo-responsive permeation performance.