Preparation and characterization of polyamide-urethane thin-film composite membranes

We attempted to produce reverse osmosis membranes with 5-chloroformloxy-isophthaloyl chloride (CFIC) and m-phenylenediamine (MPD) with an interfacial polymerization technique on the polysulphone supporting film. The membranes produced were characterized using permeation experiments with salt water. Attenuated total reflectance infrared (ATR-IR), X-ray photoelectronic spectroscopy (XPS), as well as imaging using scanning electronic microscopy (SEM) were used. The results show that the active layer of a CFIC/MPD TFC membrane is polyamideurethane, including an amide functional group (-CONH-), urethane functional group (-OCONH-) and hydroxyl functional group (-OH). The flux and rejection of a CFIC/MPD TFC membrane are better than a TMC/MPD TFC membrane in the same condition (concentrations of CFIC = 0.15 wt% and contact time with the organic solution is 20 s, which is the best preparation parameter) and the surface of the CFIC/MPD TFC membrane is a dense, finely dispersed grainy structure.     

Bilayer thin-film composite membranes for air separation

Bilayer composite membranes suitable for separating air, consisting of poly(4-methylpentene-1) (PMP) thin film as a selective top layer, an ethylcellulose–heptycellulose (ECHC) blend thin film as a selective sublayer, and polysulfone as a porous support, were investigated using a constant pressure–variable volume method. By varying operating temperature, pressure, time, as well as stage cut, the membranes were characterized for their oxygen enriched air (OEA) flux and oxygen concentration in the OEA permeated in a single step. The results show that both the OEA flux and oxygen concentration through the membranes increase with increasing operating pressure. With the increase of operating temperature, the OEA flux increases largely but the oxygen concentration decreases slightly. The oxygen concentration also decreases slightly with the stage cut. On the contrary, the OEA flux decreases and oxygen concentration increases slightly with operating time. It is found that a PMP thin film plays an important role in enhancing the air-separation capability of the membrane. The PMP/ECHC bilayer thin-film composite membrane could enrich the OEA containing 43.6% oxygen at the OEA flux of 5.06 × 10^?4 cm³ (STP)/s cm² with a good performance stability. © 1995 John Wiley & Sons, Inc.     

Cross-linked PAN-based thin-film composite membranes for non-aqueous nanofiltration

A new approach on the development of cross-linked PAN based thin film composite (TFC) membranes for non-aqueous application is presented in this work. Polypropylene backed neat PAN membranes fabricated by phase inversion process were cross-linked with hydrazine to get excellent solvent stability toward dimethylformamide (DMF). By interfacial polymerization a selective polyamide active layer was coated over the cross-linked PAN using N,N′-diamino piperazine (DAP) and trimesoyl chloride (TMC) as monomers. Permeation and molecular weight cut off (MWCO) experiments using various dyes were done to evaluate the performance of the membranes. Membranes developed by such method show excellent solvent stability toward DMF with a permeance of 1.7 L/m² h bar and a molecular weight cut-off of less than 600 Da.     

Novel thin-film composite membranes containing photoreactive groups part I: Choosing the photoreactive group

Thin-film composite membranes containing photoreactive groups have been developed. The presence of these groups facilitates the subsequent photochemical conversion of the membrane to include a range of different chemical moieties. For example, a cationic or an anionic membrane can be made from the same initial composite membrane. In this paper the selection of an appropriate photolabile group is investigated.     

A polyamide thin-film composite membrane modified by Michael addition grafting of hyperbranched poly(amine ester)

In this work polyamide thin-film composite membrane (TFC) surface modified via Michael addition grafting of a hydrophilic hyperbranched poly(amine ester). For this purpose, amine-rich polyamide layer formed by interfacial polymerization on a polyethersulfone support, and then acrylated hyperbranched poly(amine ester) (AC-HBPAE) was used as grafting moiety. The membrane surface was characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM) and water contact angle techniques. Field emission scanning electron microscopy (FE-SEM) was used to evaluate surface and cross-section morphology of samples. Filtration performances and bio-fouling resistance were also studied using a nanofiltration cell. Surface chemical composition and contact angle indicated the successful grafting of acrylated poly(amine ester) to the membrane surface. The results also indicated there is a solid relationship between acrylation percentage of hyperbranched polymer and membrane properties such as fouling resistance. A uniform and hydrophilic surface observed for TFC membrane modified with 5% acrylated hyperbranched poly(amine ester).     

New thin-film composite reverse osmosis membranes and spiral wound modules

Two new series of thin-film composite reverse osmosis membranes have been developed and fabricated into spiral wound modules. The NTR-7100 series membrane is able to desalt sea and brackish water. The NTR-7250 membrane is designed for use at pressures below 20 kg/cm². The membrane has a very high water permeability and is resistant to chemical and microbiological attack. In particular, the membrane is stable to chlorine, as shown by long-term reverse osmosis tests with tap water containing about 1 ppm of residual chlorine. The membrane has an unusual pattern of solute rejection. Salts containing divalent anions, such as sodium sulphate or magnesium sulfate, are rejected more than 98%; while salts with monovalent anions and bivalent cations, such as magnesium chloride, are rejected about 90% and salts with monovalent anions and cations, such as sodium chloride, are rejected 30–50%. Neutral solutes have relatively high rejection; for example, glucose, 90% and sucrose, <99%.     

Vapor-phase polymerization of high-performance thin-film composite membranes for nanofiltration

Thin-film composite (TFC) membranes are commendable semipermeable barriers for water treatment. Although conventionally immiscible interfaces between aqueous and organic solutions are widely utilized for obtaining TFC membranes, interfacial polymerization still suffers from the issues of harmful solvents, complex diffusion/reaction of the reactants, and thermodynamic and kinetic instability of interfaces. In this study, vapor-phase polymerization with no requirements for organic solvent and immiscible interface is utilized for processing TFC nanofiltration membranes. Through cross-linking of β-cyclodextrin and piperazine layers by trimesoyl chloride vapor, polyester and polyamide TFC membranes with high cross-linking degree are simply prepared in a scalable and reproducible manner. The prepared TFC membranes exhibit stable nanofiltration and desalination performance for all water, organic solvent, and water–organic mixture systems, with permeance up to an order of magnitude higher than that of commercial membranes.     

Chitosan and modified chitosan membranes I. Preparation and characterisation

Chitosan has been prepared from prawn shell and crab shell chitin. The molecular weight of the material derived from prawn shells is higher than that obtained from crab shell. The molecular weight, tensile strength, elongation at the break, and hydrophilic properties of chitosan are extremely dependent on the degree of deacetylation achieved when chitin is hydrolyzed to chitosan. Graft copolymers have been prepared with chitosan and a series of vinyl monomers using both heterogeneous and homogeneous reaction conditions. The hydrophilic properties of chitosan can be modified by blending with poly(vinyl alcohol).     

Fabrication of thin-film composite membranes with pendant,photoreactive diazoketone functionality

A disulfonyl chloride monomer having a pendent photoreactive diazoketone functional group has been synthesized in high overall yield (>90%). The synthesis involves a convenient two-step reaction sequence starting from commercially available 6-diazo-5-oxo-5,6-dihydro-1-naphthalenesulfonyl chloride, which was reacted with piperazine then 1,3,6-naphthalenetrisulfonyl chloride to give the disulfonyl chloride diazoketone. Thin-film composite membranes having photoreactive diazoketone moieties as side chains of a polysulfonamide have been successfully fabricated by interfacial polymerization of ethanediamine with the disulfonyl chloride diazoketone on a polysulfone support. The effect of polymerization parameters such as monomer concentration, polymerization time, crosslinking, and surfactant have been systematically investigated in terms of membrane morphology and permeation properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2381–2398, 1997     

Nanofiltration membranes prepared by interfacial polymerization on thin-film nanofibrous composite scaffold

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.     

Transforming covalent organic framework into thin-film composite membranes for hydrocarbon recovery

We, for the first time, employed chemically stable covalent organic framework (COF) (TpPa-1) as a transport-active phase within the polymer (styrene-butadiene rubber; SBR) matrix to make TpPa-1@SBR thin-film composite (TFC) membranes. Three composite membranes, viz., TpPa-1(30)@SBR, TpPa-1(50)@SBR, and TpPa-1(70)@SBR have been prepared with varying COF content. These membranes were characterized for gas permeance and results were compared with the pristine SBR-based TFC membrane. The fully organic nature of chemically stable COF offered good compatibility with the host polymer matrix (SBR) and resulted into flexible TFC membranes even at 70% of COF loading; compared to the other porous material (MOFs or Inorganic fillers), it is appreciable.     

Reinforced thin-film composite nanofiltration membranes: Fabrication,characterization, and performance testing

Hollow-fiber (HF) membranes have the advantage of a higher packing density compared to flat-sheet and spiral-wound configurations. However, the low pressure tolerance of HF membranes limits their applications in nanofiltration (NF). In this study, reinforced thin-film composite (r-TFC) HF NF membranes were fabricated and evaluated in tests with water containing different salts and organic matter. Reinforced polysulfone ultrafiltration membranes were used as a support for a polyamide layer prepared from piperazine and trimesoyl chloride monomers. The interfacial polymerization conditions were optimized via selection of the trimesoyl chloride reaction time that gave the highest membrane performance. A specific permeate flux of 5.1 L m^–2 h^–1 bar^–1, an MgSO₄ rejection of 69%, and an NaCl rejection of 26% at a transmembrane pressure of 6 bars were obtained with the optimized r-TFC membranes. Performance studies with water characterized by synthetic solution demonstrated removals of the total organic carbon, ultraviolet absorbance at 254 nm, and turbidity in excess of 65, 80, and 90%, respectively. The results of this study illustrate the feasibility of manufacturing r-TFC HFs and using them in water-treatment applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48001.     

耐氧化芳香聚酰胺纳滤膜的研究进展

芳香聚酰胺纳滤膜不耐氧化,易被活性氯氧化降解,导致膜性能急剧下降,缩短膜的使用寿命,目前已成为制约芳香聚酰胺纳滤膜应用和发展的关键问题之一。本文综述了芳香聚酰胺纳滤膜的材料和结构,重点概述了芳香聚酰胺氯化和膜性能下降的机制,并进一步介绍了近年来耐氧化芳香聚酰胺纳滤膜的研究进展。     

Air separation characteristics with liquid crystalline alkyl cellulose blend thin-film composite membranes

Composite membranes were made of liquid crystalline triheptyl cellulose (THC)/ethyl cellulose (EC) blends as dense thin films and poly(ether sulfone) (PES) or polysulfone (PSF) as porous support layer. The effects of the composite membrane composition and operating conditions on the air separation characteristics of oxygenenriched air (OEA) permeating through the membranes were studied using a constant pressure-variable volume method. The flux (OEA) through the membranes decreases slightly and the oxygen concentration in the OEA permeated increases with increasing THC content in the thin film from 4 to 15 wt.-%. The OEA flux increases significantly with decreasing thin-film thickness or increasing operating temperature and transmembrane pressure difference. The oxygen concentration in the OEA increases with increasing the thin-film thickness or the pressure difference but decreases slightly with increasing the operating temperature. There is no regular variation in the air separation properties by changing the support from PES to PSF. In long-term tests, the air separation properties remained almost constant for as long as 800 h. An OEA flux of 1.0–1.9·10^-3 cm³ (STP)/s·cm² containing 34.8–39.4 vol.-% oxygen can be attained at 30–55°C and 0.41–0.49 MPa pressure difference in a single pass through the membranes. The OEA flux is much higher for the thin-film composite membranes than for the homogeneous dense membranes made of the same materials.     

Effect of the manufacturing conditions on the structure and performance of thin-film composite membranes

A systematic investigation of the influence of the manufacturing conditions on the structure and performance of thin-film composite (TFC) membranes is presented for polyamide (PA) supported by poly(ether sulfone) (PES). The TFC membranes were composed of an ultrathin PA layer synthesized by interfacial polymerization on top of a porous PES support layer formed by immersion precipitation. For the PES support layer, the role of the wetting pretreatment, initial casting film thickness, and relative air humidity were studied. Assuming a strong correlation between the thermodynamics and the hydrodynamics of the casting process, we derived new insights from scanning electron microscopy images and the experimental data. In view of optimization of the flux through the membranes, a wetting pretreatment should be avoided. Important polymer savings were obtained without a loss of performance through a decrease in the casting thickness in combination with the use of a very smooth support. Last but not least, a high air humidity during casting was found to inhibit the formation of a dense, defect-free skin layer. For the PA layer, the interfacial polymerization method, the drying method, and the curing time were studied. The clamping of the membrane in a frame with one side in contact with the piperazine (PIP) solution and the other side to the air yielded the highest membrane flux and rejection with the lowest use of PIP and trimesoylchloride solution. Because of the absence of a uniform PIP solution layer for some drying methods, nodular PA structures could be observed in the macrovoids of the underlying PES layer because of hexane intrusion; this resulted in a dramatic decrease in the flux. Moreover, the omission of the drying step did not result in a significant loss of performance and enhanced the ease of operation. Finally, a curing time of 8 min was found to be optimal. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

氨基化氧化石墨烯界面聚合制备超薄复合纳滤膜

采用氨基化氧化石墨烯（NGO）为界面聚合水相单体,制备了超薄复合纳滤膜。研究采用傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、原子力显微镜（AFM）表征了NGO以及复合纳滤膜的化学组成和形貌。系统考察了水相单体浓度、有机相单体浓度对于制备的超薄复合纳滤膜性能的影响。该超薄复合膜在低压（0.2 MPa）下纯水通量可达27.8 L·m^-2·h^-1,对小分子染料有较高的截留率（甲基橙截留率74.8%,橙黄钠截留率96.0%,刚果红截留率98.5%,甲基蓝截留率99%）,对于无机盐的截留率较低（Na₂SO₄截留率21.4%,MgSO₄截留率10.7%,NaCl截留率5.3%,MgCl₂截留率1.5%）,展现出优异的染料/盐分离性能。同时制备的复合纳滤膜展现了较好的长周期稳定性以及抗污染特性。     

Layer-by-layer approach to enable polyamide formation on microporous supports for thin-film composite membranes

Polyamide thin-film composite (PA-TFC) membranes make large-scale desalination effective. Interfacial polymerization (IP) is used to make PA-TFC membranes, but it may limit the range of monomers that can be used, which hinders progress toward advanced membranes. Layer-by-layer (LbL) sequential deposition could circumvent kinetic and thermodynamic limitations of the conventional IP process to facilitate incorporation of different co-monomers into the membrane. The selective layer needs to be deposited onto a microporous support, but depositing LbL coatings on microporous supports often results in defective membranes. Using a poly(vinyl alcohol) (PVA) primer between the support and the LbL polyamide layer may prevent defect formation. The water permeance and salt rejection of a three layer, PVA-primed, LbL-based PA-TFC membrane are discussed and compared to a membrane made without the PVA primer and a commercially available membrane. Mass transfer resistances are analyzed using a series resistance model and appear to be small or even negligible compared to that of the polyamide layer. Incorporation of a sulfonated co-monomer into the polyamide via LbL is reported. The combination of a PVA primer layer and LbL sequential deposition may expand the range of co-monomers that could be used relative to polyamide membranes prepared by the conventional IP process.     

Selection of substrate manufacturing techniques of polyamine-based thin-film composite membranes for forward osmosis process

This paper is a comparative study on the preparation techniques used to make the support layer of polyamide-thin-film composite forward osmosis (TFC-FO) membranes. The role played by the support layer preparation technique in membrane performance is thoroughly investigated in this study. Electrospinning is shown to produce membranes of lower structural parameter compared to those obtained by conventional phase inversion techniques. The electrospun polyamide selective layer can also be tailored with the required properties. This makes electrospinning a promising process to design efficient FO membrane substrates. It is shown in this work that the FO water flux is more dependent on the internal structure of the support layer than the preparation materials. The main challenge remaining for substrates to operate in FO is to achieve simultaneously a low structural parameter, a high surface porosity, and the required mechanical properties. As most of today's approaches are not suitable, further materials development is essential in future investigations on TFC-FO membranes.     

Vinyl ester resin modified with silicone‐based additives. I. Mechanical properties

Silicone‐based additives have been used as fire retardants for thermoplastics and present the advantages of improving the processing and impact resistance of the polymers. In this study, we used three different silicone‐based additives as modifiers of a vinyl ester resin. The additives were fine powders made up of about 50 wt % polydimethylsiloxane and 50 wt % silica. The differences among them were the functional groups inserted in the polymer chains and the size and size distribution of the particles. The additives were dispersed in resin containing 35 wt % styrene. To cure the mixture, a conventional catalyst and initiator were used, and the reaction was carried out in three ways, which differed in the curing temperature, postcuring temperature, time, and addition of dimethylaniline (DMA) as a promoter of the polyaddition reaction. Dynamic mechanical analysis showed that the phase behavior of the resulting composites depended strongly on the curing conditions. The flexural modulus of composites containing 5 wt % additive was lower than that for the cured resin. The impact resistance of the composites also depended on the curing conditions but not on the composition or size of the particle of the additive. The fracture morphologies of specimens subjected to impact resistance tests were different for samples cured in the presence or in the absence of DMA, which suggested that it influenced the mechanism of network formation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Cellulose membranes for reverse osmosis Part I. RO cellulose acetate membranes including a composite with polypropylene

With the aim of obtaining RO membranes for brackish water desalination from purified celluloses (cotton linters and bleached bagasse pulp), two reactions (heterogeneous and homogeneous) were applied for the synthesis of cellulose acetate (CA). The efficiency of the membranes was measured and compared with those prepared from purchased CA and prepared CA by acetylation of imported high-grade viscose wood pulp. The effect of blending CA with polypropylene (PP), on the efficiency of the prepared RO membranes was also studied. Results showed that the method of preparation of CA plays a profound effect on the salt rejection and water flux of the RO membranes. The efficiencies of RO membranes formed from heterogeneously acetylated celluloses are higher than those prepared from homogeneous ones. Blending the acetylated cellulose with 9% PP wastes improves the efficiency of membranes prepared from the homogeneously acetylated celluloses.