Influence of surface properties on the dip coating behavior of hollow fiber membranes

Coating processes have become an important fabrication step in membrane production, either to form a separation layer on a porous substrate or to tune specific properties. The coating procedure depends to a large extent on the membrane properties which substantially impedes a prediction of the coating thickness. To give an insight into the coating properties of various hollow fiber membranes, a selection of membranes with different pore sizes was coated with aqueous poly(vinyl alcohol) solutions at various coating velocities. It was found that material properties and pore sizes of the membranes have great influence on coating thicknesses. An intrusion of coating material into the membrane structure was determined with increasing pore size. Pure intrusion without formation of a dense surface layer took place when using a membrane with a mean pore size of ca. 500 nm. Coating results were correlated with the theoretical LLD law and for some membranes the coating thickness can be predicted quite well by the LLD law and its enhancements. When a significant amount of coating material penetrated into the membrane structure the LLD law loses its validity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46163.     

Interfacial evaluation of epoxy/carbon nanofiber nanocomposite reinforced with glycidyl methacrylate treated UHMWPE fiber

Interface interactions of fiber–matrix play a crucial role in final performance of polymer composites. Herein, in situ polymerization of glycidyl methacrylate (GMA) on the ultrahigh molecular weight polyethylene (UHMWPE) fibers surface was proposed for improving the surface activity and adhesion property of UHMWPE fibers towards carbon nanofibers (CNF)‐epoxy nanocomposites. Chemical treatment of UHMWPE fibers was characterized by FTIR, XPS analysis, SEM, and microdroplet tests, confirming that the grafting of poly (GMA) chains on the surface alongside a significant synergy in the interfacial properties. SEM evaluations also exhibited cohesive type of failure for the samples when both GMA‐treated UHMWPE fiber and CNF were used to reinforce epoxy matrix. Compared with unmodified composite, a ～319% increase in interfacial shear strength was observed for the samples reinforced with both 5 wt % GMA‐grafted UHMWPE and 0.5 wt % of CNF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43751.     

Superhydrophobic PES/PDA/ODTS fibrous mat prepared by electrospinning and silanization modification for oil/water separation

With polydopamine (PDA) acting as interlayer, combined with electrospinning technology and a silanization method, here a versatile method for fabricating a superhydrophobic PES/PDA/ODTS fibrous mat is reported. Scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, and contact angle measurements were applied to characterize the morphologies and chemical composition changes of the prepared fibrous mats. Their separation ability for oil/water mixtures was measured by self‐made instruments. The results show that the fabricated PES/PDA/ODTS fibrous mat displays a water contact angle too large to be assessed by the ordinary amount of water applied in a conventional measurement. In other words, a water drop of less than 10 μL adheres to the syringe needle and leaves with it during the measurement. The prepared PES/PDA/ODTS fibrous mat also shows a threshold sliding angle no more than 2.5°. At the same time, this kind of material exhibits superoleophilicity for organic solvents, such as n‐hexane, gasoline, toluene, and chloroform. The experimental contact angles were also analyzed using the Cassie–Baxter model to gain insights into the fundamental microstructure–wetting property relationship. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45923.     

Optimization of biodegradable PEG/PLGA nanofiber mats electrospinning process for anti‐adhesion application

Electrospinning is a direct, continuous, and useful technique to prepare nanofiber by applying electrostatic forces. In this study, poly(lactic‐co‐glycolic acid)/poly(ethylene glycol) (PLGA/PEG) nanofiber mats were prepared, and electrospinning process was optimized to obtain appropriate fiber diameter and hydrophilicity for anti‐adhesion application. Optimization of applied voltage, PEG content, and feeding rate was investigated using response surface methodology. A total of 15 trials were designed to optimize the parameters. Fiber diameter was measured using scanning electron microscopy. Individual and interactive effects of the solution properties were determined. Moreover, the adequacy of the models was verified by validation experiments. For anti‐adhesion test, a nanofiber mat was produced based on the suggested optimum electrospinning conditions. Results showed that optimum fiber diameters were obtained using 7.5% PEG content, applied voltage of 19 kV, and flow rate of 3 mL/h. Experimental results were in good agreement with the predicted fiber diameters. Furthermore, a rat model of sidewall defect‐cecum abrasion was employed to investigate the efficacy of PEG/PLGA in preventing postoperative peritoneal adhesions. Hence, this study provides an overview on the fabrication of PLGA/PEG nanofibers with targeted diameter, which may be used in anti‐adhesion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46282.     

Freestanding fiber mats of zeolitic imidazolate framework 7 via one‐step,scalable electrospinning

We demonstrated the fabrication of freestanding zeolitic imidazolate framework 7 (ZIF‐7) nanofiber (NF) mats by means of one‐step, scalable electrospinning. The formation of ZIF‐7 nanoparticles embedded in polymer fibers was unambiguously pinpointed via X‐ray diffraction, transmission electron microscopy, and adsorption studies. The NF mats exhibited excellent characteristics, with an average diameter of 245 nm, in the adsorption and desorption of carbon dioxide (CO₂); this makes them attractive candidates for gas separation and other selective filtration applications. This excellent property of the ZIF‐7 mats was explained by the gate‐opening phenomenon of ZIF‐7, which yielded a stepwise increase in the overall CO₂ uptake capacity. The mechanical strength of the NF mats was also obtained via large‐strain uniaxial tensile deformation, which enabled preliminary assessment of the mat's suitability for textiles and membranes in targeting separation and filtration applications with large‐area permeability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43788.     

Crosslinked,electrospun chitosan–poly(ethylene oxide) nanofiber mats

Mechanical characterization of nanofiber mats is an underexplored area in biomaterial engineering. In this study, a chitosan–poly(ethylene oxide) copolymer blend was electrospun and crosslinked with glutaraldehyde (GA) for various time periods. The tensile and compressive mechanical integrity of the nanofibers was analyzed with increasing exposure to vapor crosslinking. Solubility, scanning electron microscopy characterization, Fourier transform infrared, uniaxial tensile tests, and nanoindentation analyses were used to identify these trends. The mechanical studies confirmed that the GA vapor crosslinking increased the stiffness and decreased the ductility of the electrospun mats. Increased exposure time to crosslinking led to changes in the mat surface color and resistance to dissolution. Scanning electron microscopy fiber counts verified that exposure to GA vapor crosslinking increased the average fiber diameter. By the use of vapor phase deposition, mechanical properties continued to change throughout the study. The crosslinking exposure time could be chosen to accommodate in vivo mechanical loading. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrospun polyurethane membrane with Ag/ZnO microparticles as an antibacterial surface on polyurethane sheets

A method of antibacterial modification of the polyurethane (PU) surface is presented in this article. An electrospun PU membrane with an incorporated antibacterial agent was applied as a coating of the PU sheets. As an antibacterial agent, a hybrid bimetallic filler was used; it combined the antibacterial effects of silver and zinc oxide. With an electrospun submicrometer‐fiber membrane, the filler was uniformly and thinly applied on the PU surface by compression molding. The antibacterial activities of three filler concentrations were tested, and they demonstrated an effective antibacterial action against Staphylococcus aureus and Escherichia coli. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43020.     

Effect of hybrid polysphosphazene coating treatment on carbon fibers on the interfacial properties of CF/PA6 composites

Carbon fiber (CF) reinforced polyamide 6 (PA6) composite has an extensive application. However, the performances of CF/PA6 composite are constrained by the poor interfacial adhesion between CF and PA6 matrix. In this article, in order to strengthen the interfacial adhesion of CF/PA6 composite, a layer of poly(cyclotriphosphazene-co-4,4′-sulfonyldiphonel) (PZS) hybrid coating with plenty of PZS microspheres (PZSMS) was successfully introduced onto CF surface through facile in situ polymerization. After surface modification, the surface morphologies and the surface chemical structures of fibers changed distinctly. On one hand, the PZSMS provided more contact points and increased mechanical interlocking between CF and PA6 matrix. On the other hand, numerous hydrogen bonds between CF and PA6 were formed due to a great amount of unique polar groups on modified CF surface. Consequently, in comparison with untreated CF, the interfacial shear strength of CF-PZSMS/PA6 composites was improved from 37.68 ± 3.16 to 53.79 ± 3.38 MPa, by 42.75 ± 3.02%. The results indicated that PZS hybrid coating on fiber surface effectively improved the interfacial adhesion of CF/PA6 composites, and the stronger hydrogen bonding and the enhanced mechanical interlocking synergistically played a major role in such significant improvements.     

Enhanced interfacial adhesion of aramid fiber reinforced rubber composites through bio-inspired surface modification and aramid nanofiber coating

In order to improve the interfacial adhesion between aramid fiber (AF) and rubber matrix, a simple and facile method of aramid nanofiber (ANF) coating is demonstrated in this article. Tannic acid (TA) and polyethyleneimine (PEI) are polymerized in an alkaline solution to form a thin TA/PEI (TP) layer that is deposited on the surface of AF to introduce functional groups such as hydroxyl and amino groups. Then, the ANF coating is utilized to construct nanostructures on the surface of AF to improve the interfacial adhesion between the fiber and the rubber. Through hydrogen bonding and/or π-π stacking between the TP layer and the ANF, the ANF coating is firmly attached to the surface of AF. Compared with the untreated fiber, the interfacial adhesion of AF coated with ANF after 1, 3, 5, 7, 9 deposition cycles is increased by 27.8%, 29.1%, 31.5%, 43.1%, and 30.3%, and the mechanical properties of the fibers remain almost unchanged. This method shows its advantages of simple, facile, and time-effective, which is of great significance for industrial applications.     

Experimental study of the effect of zeolite 4A treated with magnesium hydroxide on the characteristics and gas‐permeation properties of polysulfone‐based mixed‐matrix membranes

Nowadays, new methods for gas‐separation processes are being quickly developed. The separation of CH₄/CO₂ and CH₄/H₂ is usually the subject of most related research studies, especially in the membrane gas‐separation process, because of their important role in industry. In this study, we attempted to improve the separation properties of a polysulfone/zeolite 4A mixed‐matrix membrane by modifying the zeolite particle surface. The method included a simple ion‐exchange reaction of magnesium chloride with ammonium hydroxide that yielded the formation and precipitation of magnesium hydroxide whiskers on the surface of the zeolites. The whiskers could omit most of the nonselective voids by interlocking the polymer chains through them and, consequently, improve the permeability, selectivity, and elastic modulus of the membranes. X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and dynamic mechanical analysis proved all the changes recorded after the particle and membrane treatments. SEM images showed the petal‐like morphology of the whiskers that formed on the surface of the particles after the reaction against the smooth surface of the untreated zeolite. At a 30 wt % loading of particles in the polymeric matrix, the selectivities for H₂/CH₄ and CO₂/CH₄ increased by 69 and 56%, respectively; in contrast, the H₂ and CO₂ permeabilities decreased by 2.5 and 10%, respectively. The modulus of elasticity for the treated membrane also increased by 14 and 30% compared to those of the pure and untreated membranes, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44329.     

Study of effect of two sulfonating agents on electrochemical properties of surface-modified polyethersulfone membrane

The work deals with the selection of sulfonating agent and preparation of polymeric coating on membrane step by step. The surface modification of a commercial ultrafiltration polyethersulfone (PES) membrane was covalently attached to the poly(styrene-co-divinylbenzene-co-4-vinylbenzylchloride). The whole process was tracked step by step using analytical methods. Chlorosulfonic acid and trimethylsilyl chlorosulfonate were tested as sulfonating agents. Ion-exchange capacity (IEC), water content, specific resistance, and permselectivity were measured and scanning electron microscope analyzed the surface of the cation exchange membrane. The best results were achieved using 5 wt % chlorosulfonic acid as sulfonating agent. IEC reached values of up to 2.44 meq g⁻¹ of dry matter, permselectivity of 93.6%, area resistances of 10.1 Ω cm², and specific resistance around 299 Ω cm. The prepared cation exchange PES membrane with chlorosulfonic acid can be used in electrochemical processes, for example, in electrodialysis. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48826.     

Study on the preparation and thermal shrinkage properties of nano‐SiO2/UHMWPE/HDPE blend microporous membranes

Nano‐SiO₂/UHMWPE/HDPE blend microporous membranes (NBMs) with different content of nano‐SiO₂ particles were prepared via thermally induced phase separation process. Thermogravimetric analysis was used to investigation of the amount of nano‐SiO₂ particles reserved in NBMs. This approach showed that about 59% of total content of nano‐SiO₂ particles reserved in NBMs. The formation and development of the interface pores were studied by scanning electron microscopy. NBMs performance was characterized by a variety of metrics including thermal shrinkage, melting and crystallization behavior, porosity and pore diameter, and permeability. The results indicated that nano‐SiO₂ particles served as nucleating agent increasing the crystalline of NBMs. The comprehensive properties of NBMs were optimum when the content of nano‐SiO₂ particles was 1%. Compared with pure HDPE separators, NBMs exhibit higher porosity and lower thermal shrinkage due to its high crystalline and the enrichment of UHMWPE chains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41321.     

Effects of polyethyleneimine molecular weight and proportion on the membrane hydrophilization by codepositing with dopamine

Mussel‐inspired chemistry has attracted widespread interest in the surface modification of polymer membranes. We have previously demonstrated a dopamine (DA) assisted codeposition process of polyethyleneimine onto polypropylene microfiltration membranes (PPMMs) for surface hydrophilization. In this work, we further investigate the effects of PEI molecular weight and DA/PEI mass ratio on the codeposition process and membrane performance. The results indicate that only low‐molecular‐weight PEI bring a distinct promotion in both surface wettability and water permeation flux for PPMMs. On the other hand, either excess DA or PEI is detrimental to the surface hydrophilicity of the studied membranes. The optimized PEI molecular weight is 600 Da and the corresponding mass ratio is 1:1 for the surface hydrophilization of PPMMs. These results are beneficial to understand those codeposition processes of dopamine with other polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43792.     

Influence of the coupling agent on the mechanical properties of SiCf/poly(phenylene benzobisoxazole) composites

Poly(phenylene benzobisoxazole) (PBO) was first used as matrix to fabricate the two‐dimensional SiC_f/PBO composites by a lamination method. Different amounts of coupling agent were introduced to improve the bonding between silicon carbide (SiC) fibers and the PBO matrix during the fabrication of the SiC_f/PBO composites. The surface structure and composition of the as‐received PBO and PBO treated with the coupling agent were analyzed, and the morphology and flexural strength of the composites were characterized. The Fourier transform infrared analysis indicated that the hydroxyl groups from the coupling agent were successfully introduced to PBO. The flexural strength of the composites increased at first with increasing content of the coupling agent but decreased with excessive addition of the coupling agent. The flexural strength of the composites was improved from 15 to 89 MPa. The test results suggested that the interaction between the SiC fiber and the treated PBO with the coupling agent was intensified. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39805.     

Structure and adhesive properties of the RFL‐coated continuous basalt fiber cord/rubber interface

The relationships between the structure of the resorcinol‐formaldehyde‐latex (RFL) layer, static adhesion, and interfacial fatigue properties between the RFL‐coated continuous basalt fiber (CBF) cord and a rubber matrix were studied using films prepared from RFL systems with various formulas and H samples prepared with RFL‐coated CBF cord and NR/SBR matrix. Thermomechanical analysis and tensile testing of the RFL films were carried out using a dynamic mechanical analyzer (DMA). The H pull‐out force and fatigue properties were tested using a universal testing machine and an MTS, respectively. The interfacial fatigue life of the RFL‐coated CBF cord/rubber samples exhibited different variation regularity from the variation of the H pull‐out force as F/R and L/RF changed. The static adhesion reflected the connection strength between the cord and the rubber matrix, whereas the characteristics and the properties of the RFL layer played a decisive role in determining the damage rate of the adhesion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44353.     

An oil-contamination-resistant PVP/PAN electrospinning membrane for high-efficient oil–water mixture and emulsion separation

Oil–water separation is an urgent issue due to the frequently occurred oil leakages and increasing discharge of oily wastewater. The pollutional and wastewater can not only damage the environment, but endanger human health. Owing to the small particle size of the oil contamination, it is still a challenge for the separation of oil–water emulsion. In this study, we developed a facile strategy to prepare a hydrophilic polyvinylpyrrolidone/polyacrylonitrile (PVP/PAN) nanofibrous membrane for oil–water mixture and emulsion separation. The lowest water contact angle on the membrane surface can achieve 16.7°, thus the membranes can effectively resist the oil contamination on them. Moreover, the membrane can efficiently separate oil–water mixtures and emulsion by gravity. In addition, it can separate oil–water mixtures in harsh conditions (pH = 1 and 14). Membranes prepared in this work would hold a great potential in the practical use of water treatment and environmental industry.     

Influence of Lignin units on the properties of Lignin/PAN-derived carbon fibers

Lignin was proposed to an attractive precursor for making carbon fibers (CFs) owing to its high carbon yield, low-cost, and renewable sourcing. In this work, Lignin/polyacrylonitrile (PAN)-derived CFs were prepared and characterized to investigate the effects of Lignin units on their porous texture and surface chemistry. The results showed that the LP20-CF prepared from PAN with 20% Lignin had higher surface areas than that of the pristine LP0-CF, and it possessed interconnected multidimensional network with fiber bonding. Moreover, Lignin/PAN-derived CFs contained more oxygen functional groups of CO, COOR, and nitrogen functional groups of N-6, N Q than the pristine CFs. These results indicated that the Lignin could be beneficial to achieve CFs with special structure, developed porosity and rich surface chemistry without activation. Therefore, the utilization of Lignin to produce pores and improve surface chemistry of CFs was a simple and effective strategy for preparing the low-cost and high-performance functional carbon materials.     

Interface enhancement between polytetrafluoroethylene and glass fibers modified with a titanate coupler

The use of glass fibers (GFs), molybdenum disulfide (MoS₂), and talc was evaluated to reinforce polytetrafluoroethylene (PTFE) for potential applications in automobile shock absorber pistons. The orthogonal experiment results show that the optimal GF/MoS₂/talc/PTFE weight ratio was 2:3:3:92 for the PTFE composite; this ratio resulted in better mechanical properties, hardness, low linear expansion, and wear rate. Chemical coupling and high‐temperature activation treatment on the surface of GF greatly enhanced the interfacial adhesion between the PTFE matrix and GF, as revealed by atomic force microscopy analysis. This resulted in reductions in the wear rate and linear expansion coefficient by two orders of magnitude compared with that of PTFE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44668.     

Preparation of aromatic poly(1,3,4‐oxadiazoles) pulps and their paper properties

To improve the paper properties of the poly(1,3,4‐oxadiazoles) (POD), the POD pulps were prepared by prechemical and mechanical methods to increase their polarity, contact area, and interaction. The fibrillated degree of the staple fibers was evaluated by the Canadian Standard Freeness and the specific surface area, while the surface free energy was calculated by the Micro–wilhelmy method. Meanwhile, the functional groups and compositions on the surface of the POD fibers were confirmed by the FTIR–ATR and the X‐ray photoelectron spectroscopy, and the surface morphological structure and the crystalline structure of the POD fibers were observed by the fiber analyzer, scanning electron microscope, and Wide‐angle X‐ray diffraction, respectively. It was found that the pronounced abrasive and distinctive grooves were formed on the surface of the POD fibers after prechemical and mechanical treatment. The surface free energy of POD fibers increased 8.41%, and the polar part increased by 32.10% after treatment. It was confirmed that the polar functional groups and fibril were formed after chemical and mechanical treatment, so the interaction of the POD fibers was highly enhanced, and as a result the apparent density, tensile strength, fold endurance, and tear strength of the paper formed by those treated fibers were all improved apparently. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39818.     

Effect of polyurethane sizing agent on interface properties of carbon fiber reinforced polycarbonate composites

This work is aimed at investigating how molecule structure of polyurethanes (PUs) as sizing agents influence the interface properties of carbon fiber (CF) reinforced polycarbonate (PC) composites. Effects of four PUs as sizing agents for CF on the interlaminar shear strength (ILSS) of CF reinforced PC composites are investigated. It is found that the three PUs except PC–PU as sizing agents on oxidized CF (OCF) made the ILSS of their reinforced PC composites increase up to 62.9 MPa by more than 24.8%. The chemical interaction between PU sizing agents and CF are attributed to high reactivity of isocyanate, but carbonate groups on PC–PU may have a chain unzipping reaction due to active groups on the surface of OCF. The chemical interaction between PU sizing agents and PC are attributed to transesterification. As a result, PUs containing isocyanate or polyester groups are ideal sizing agents for CF reinforced PC composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47982.