Thick Polyamide Research Articles

Highly permeable polyamide nanofiltration membranes fabricated via the construction of anionic covalent organic frameworks /polydopamine composite interlayer

Thin-film composite nanofiltration (TFC NF) membranes can separate neutral/charged solutes and play an essential role in water purification. However, the permeability of traditional NF membranes is severely limited by excessive mass transfer resistance due to the thick polyamide (PA) layer. Introducing porous nanomaterials as an interlayer into PA NF membranes has been recognized as an effective approach to improve permeability. Herein, a novel composite interlayer consisting of anionic covalent organic frameworks with abundant sulfonic acid groups (COF-SO3H) and polydopamine was designed to regulate interfacial polymerization to construct the highly permeable TFC NF membranes. The surface negative charge and hydrophilicity of the TFC NF membranes can be controlled by the abundant polar groups in the composite interlayer. Moreover, mass transfer resistance can be reduced by introducing COF-SO3H to create additional water transport channels. The results showed that the optimal membrane manifested attractive permeability (44.2 L⋅m−2⋅h−1⋅bar−1) and a high Na2SO4 rejection (98.7 %), almost 3-fold higher than that of the original TFC membrane. Furthermore, the optimal membrane exhibited favorable anti-fouling performance and stability. This work provides insight into strategies for fabricating highly permeable TFC NF membranes through the introduction of an interlayer.

Structure Analysis and Its Correlation with Mechanical Properties of Microcellular Polyamide Composites Reinforced with Glass Fibers

Thin-walled and thick-walled microcellular moldings were obtained by MuCell® technology with nitrogen as a supercritical fluid. 2 mm thick polyamide 6 (PA6) with 30% wt. glass fiber (GF) samples were cut from automotive industrial elements, while 4 mm, 6 mm, and 8.4 mm thick moldings of PA6.6 with 30% wt. GF were molded into a dumbbell shape. The internal structure was investigated by scanning electron microscopy (SEM) and X-ray computed microtomography (micro-CT) and compared by numerical simulations for microcellular moldings using Moldex3D® 2022 software. Young’s modulus, and tensile and impact strength were investigated. Weak mechanical properties of 2 mm thick samples and excellent results for thick-walled moldings were explained. SEM pictures, micro-CT, and simulation graphs revealed the tendency to decrease the cell size diameter together with increasing sample thickness from 2 mm up to 8.4 mm.

Design and Analysis of Novel Microstrip-Based Dual-Band Compact Terahertz Antenna for Bioinformatics and Healthcare Applications

This paper presents a compact microstrip-based dual-band antenna for terahertz (THz) technology, catering to the increasing demand for high-frequency, high-gain, and wideband THz antennas. THz technology has numerous applications, including its demands in bioinformatics and healthcare. To address this need, the proposed antenna operates in two frequency bands: 3.6 THz to 4.3 THz and 5 THz to 5.7 THz, enabling its use in THz band communication. The antenna design features a microstrip patch with two transverse slots and one longitudinal slot as a radiator, fed with a microstrip line. The transverse slots enable dual-band resonance, while the longitudinal slots enhance bandwidth and efficiency. Using a 10µm thick polyamide material with a dielectric constant of 3.55, the antenna achieves a compact size of 40 × 40 µm2, lightweight construction, high radiation efficiency, and a wide impedance bandwidth. Simulation results confirm good impedance matching characteristics, with minimal voltage standing wave ratio and return loss of -10dB or less. The antenna exhibits an impedance bandwidth of -10dB at 700 GHz, a peak radiation efficiency of 85%, a peak gain of 7.86 dB, and an omnidirectional radiation pattern. These favorable attributes position the proposed antenna as an excellent choice for various THz applications, particularly in bioinformatics and healthcare applications.

One-Step Construction of the Positively/Negatively Charged Ultrathin Janus Nanofiltration Membrane for the Separation of Li+ and Mg2+

To coordinate the trade-off between the separation and permeation of the nanofiltration membrane for the separation of Mg2+/Li+, we regulated poly(ethyleneimine)/piperazine interface polymerization parameters to construct a positively/negatively charged ultrathin Janus nanofiltration membrane at a free aqueous-organic interface. At the optimized interfacial polymerization parameters, 0.03 wt % of piperazine reacted with trimethylbenzene chloride prior to poly(ethyleneimine), forming a primary polyamide layer with fewer defects or limiting large-scale defects of the polyamide layer. The controlled subsequent reaction of poly(ethyleneimine) and trimethylbenzene chloride results in a Janus nanofiltration membrane, with one side enriched with the carboxyl groups, the other side enriched with the amine groups, and a dense polyamide structure in the middle. Under the optimum conditions, the positive potential of the rear surface of the prepared membrane was 14.57 mV, and the water contact angle reached 71.31°, while the negative potential of the front surface was -25.48 mV, and the water contact angle was 12.93°, confirming a Janus membrane with opposite charges and large hydrophilicity differences in the front and rear surfaces. With a high cross-linking degree, a 40 nm thick polyamide layer is 29.09% more thinner than the traditional polyamide membrane. The ultrathin Janus nanofiltration membrane showed an excellent separation factor (SLi,Mg of 18.26), stability, and water permeability flux (10.6 L·m-2·h-1·bar-1). The rejections to MgCl2, CaCl2, MgSO4, and Na2SO4 are measured above 90% at a nearly constant permeability of 10.6 L·m-2·h-1·bar-1, particularly stable rejections to MgCl2 and Na2SO4.

Nanorod-interlayered thin film composite membranes for ultrafast nanofiltration

Customizing high-performance nanofiltration membranes that can break the trade-off effect is critical to the development of membrane separation. Building an intermediate layer between the support and the selective layer to accelerate water transport is considered to be an effective solution to this issue. However, the synthesis of interlayered thin-film composite membranes (i-TFCs) on non-polar substrates with large pores and high porosity remains challenging. Here, we report a high-performance i-TFC membrane with FeOOH nanorods as interlayers. The porous and robust nanorods greatly increased the water transport paths and the mechanical strength of the membrane. Under the high pressure of 20 bar, the i-TFC membrane still remained a high salt rejection above 96 % while showing a high pure water permeance up to 48.9 L·m−2·h−1·bar−1. Furthermore, the presence of nanorods enhanced the hydrophilicity and compactness of the substrate, leading to the formation of a 23-nm thick polyamide layer without nanorod structures. The versatility of the strategy was also demonstrated with three different hydrophobic substrates. This work will thus provide further insights into the development of high-performance membranes for molecular separations.

A Micro 4-port THz MIMO antenna for nano communication networks

This paper proposes a micro nature inspired UWB 4-port MIMO antenna design with dimensions of 45μm × 45μmăoperating from (2.38–11.18) THz and 130% impedance bandwidth realised on a 2μm thick polyamide substrate. Each radiator is made by superimposing self-similar elliptic structures to create a palmate leaf-like pattern that ensures wideband response. The ground topology is made up of semi-elliptic orthogonal reflectors connected to a center-fed annular circle with rotationally symmetrical parasitic stubs that operate as an isolator, resonator, and neutralizer. The antenna elements are ordered orthogonally with an inter-element distance of d0 = 0.05λ0 (λ0 is the lowest working wavelength at 2.38 THz) and an inter-element port isolation distance of d0 = 0.05λ0. The parasitic stub inclusion increases the lower/higher band 10-dB impedance matching response, and the proposed ground structure has good isolation coefficients (18−22)dB. An equivalent circuit model with R-L-C lumped elements was modelled and simulated to validate. In both indoor and outdoor propagation environments, the MIMO diversity parameters (Envelope channel coefficient (ECC), Total active reflection coefficient (TARC), Diversity gain (DG), Channel capacity loss (CCL), Mean effective gain (MEG), and Multiplexing efficiency) show good characteristics to leverage. The suggested MIMO antenna can be employed for THz band and molecular/nano communication networks owing to its radiation performances (realised gain of > 8 dBi with > 60% radiation efficiency).

Concentrations of Beetroot (Beta vulgaris L.) Peel and Flesh Extracts by Reverse Osmosis Membrane

The objective of this investigation was to concentrate betalains, phenolics, and antioxidants from the extract of peel and flesh of beetroot (Beta vulgaris L.). Thin-film composite reverse osmosis (RO) membrane composed of the thick polyamide barrier layer, microporous polysulfone interlayer, and polyester support web was used in membrane module. In a later exercise, thermo-instability of betalain color compounds was investigated with different temperatures. After the filtration of the aqueous extract of flesh, betacyanins, betaxanthins, and total betalains were increased by 5.2, 6.1, and 5.5 times, respectively. Likewise, the mentioned bioactive compounds were increased by 3.7, 4.9, and 4.2 times after filtration of the aqueous extract of peel. The amounts of total betalains measured in the final flesh extract were two times lower (14.33 ± 0.15 mg·g−1 dm) compared to the peel concentrate (30.02 ± 0.28 mg·g−1 dm). The superior amount of phenolic was shown in the final flesh extract (34.47 ± 0.19 mg GAE·g−1 dm) compared to peel extract (12.74 ± 0.42 mg GAE·g−1 dm). The antioxidant activity in final beetroot peel extract and flesh extract were 24.65 ± 1.42 mg ASE·g−1 dm and 11.6 ± 0.1 mg ASE·g−1 dm, respectively. The recovery of thermo-sensitive bio-colorants was achieved by membrane filtration with the least thermal degradation.

Effect of sealing on the feed out face of trench silos on the performance of confined calves

ABSTRACT This study aimed to evaluate the productive performance, dry matter intake, apparent digestibility and ingestive behavior of feedlot calves fed corn silage from the feed out face of trench silos with different types of sealing. The animals were divided into three treatments with four repetitions: Conventional seal - double-sided polyethylene of 110µm thickness; Double-sided seal - double-sided polyethylene of 200µm thickness; and Double seal - composed of double face polyethylene with a thickness of 80µm superimposed on a polyamide translucent vacuum film with a thickness of 20µm. The use of double face sealing provided 12.63% increase in average daily gain and improved food conversion by 0.62 percentage points. The apparent digestibility of the diet with double-face sealing system silage was 4.30% higher than the diet with double-face sealing silage and 11.00% higher than the diet with conventional sealing silage. It is recommended to use the double face sealing with 200µm polyethylene and double face sealing with 80µm thick polyethylene on top of a 20µm thick polyamide translucent vacuum film.

MXene Nanosheet Templated Nanofiltration Membranes toward Ultrahigh Water Transport.

The demand for thin-film composite (TFC) nanofiltration membranes with superior permeance and high rejection is gradually increasing for seawater desalination and brackish water softening. However, improving the membrane permeance remains a great challenge due to the formation of excrescent polyamide in the substrate pores and thick polyamide film. Herein, we fabricated a high-performance TFC nanofiltration membrane via a classical interfacial polymerization reaction on a two-dimensional lamellar layer of transition-metal carbides (MXene). The MXene layer promoted the absorption of the reactive monomer, and higher amine monomer concentration facilitated the self-sealing and self-termination of interfacial polymerization to generate a thinner outer polyamide film from 68 to 20 nm. The almost nonporous lamellar interface inhibited the formation of inner polyamide in the substrate pores. In addition, the MXene lamellar layer could be eliminated by mild oxidation after interfacial polymerization to avoid imparted additional hydraulic resistance. The resulting TFC membrane conferred a high rejection above 96% for Na2SO4 and excellent permeance of 45.7 L·m-2·h-1·bar-1, which was almost 4.5 times higher than that of the control membrane (10.2 L·m-2·h-1·bar-1). This research provides a feasible strategy for fabricating a high-performance nanofiltration membrane using two-dimensional nanosheets as a templated interface.

Microdosimetry with a 3D silicon on insulator (SOI) detector in a low energy proton beamline

IntroductionAn accurate description of the radiation quality of proton beams is a precondition to increase our understanding of radiobiological mechanisms and to develop accurate biological response models for radiotherapy. However, there are few detectors capable of measuring microdosimetric quantities with high spatial resolution along the entire Bragg curve due to the rapid increase in stopping power at the Bragg peak (BP) and distal dose fall-off (DDF). The aim of this work was to measure the microdosimetric spectra along the Bragg curve in a low energy proton beamline used for radiobiological experiments with a novel 3D silicon-on-insulator (SOI) “mushroom” microdosimeter. MethodA silicon microdosimeter with an array of 3D structured diodes, creating well-defined sensitive volumes (SV) with excellent spatial resolution was used for microdosimetry. The microdosimeter was used to measure microdosimetric spectra and the relative dose throughout the Bragg curve of a 15 MeV proton beam by sequential insertion of 16 μm thick polyamide absorption films in front of the microdosimeter. The results were tissue corrected with a novel correction function and compared to Monte Carlo (MC) simulations performed in GATE. ResultsThe measured dose-mean lineal energy (yD‾) increased from 8 keV/μm at the entrance to 24 keV/μm at the BP, rising to a maximum of 35 keV/μm at the DDF. The measured yD‾ showed an overall good agreement with the MC simulated values, with deviation of less than 2% at the BP and DDF, while the largest deviation (12%) was found at the entrance. Clear changes in microdosimetric spectra were seen for each 16 μm step at the BP and DDF. ConclusionThe SOI microdosimeter with its well-defined 3D sensitive volumes is an excellent tool for characterizing low energy beamlines that demands very high spatial resolution. The good overall agreement between experimental and simulated results indicated that the detector is capable of accurate microdosimetric measurements.

Sub-10 nm Polyamide Nanofiltration Membrane for Molecular Separation.

To separate small molecules from the solvent with high permeability and selectivity, the membrane process is thought to be highly effective with much lower energy consumption when compared to the traditional thermal-based separation process. To achieve high solvent permeance, a sub-10 nm thick polyamide nanofiltration membrane was synthesized through interfacial polymerization of ethidium bromide (EtBr) and trimesoyl chloride (TMC). Thanks to the extremely low solubility of the EtBr monomer in the organic phase, the polymerization process was strictly limited at the interface of the water and hexane, leading to an ultrathin polyamide membrane with a thickness down to sub-10 nm. When used in nanofiltration, these ultrathin membranes display ultrafast water permeation of 40 liter per square meter per hour per bar (L m-2 h-1 bar-1 ), and a high Congo red rejection rate of 93 %. This work demonstrates a new route to synthesize ultrathin polyamide membranes by the traditional interfacial polymerization.

Ultrapermeable Thin Film ZIF‐8/Polyamide Membrane for H2/CO2 Separation at High Temperature without Using Sweep Gas

AbstractThe use of thin film composites containing metal–organic frameworks (MOFs) as filler is of widespread interest for nanofiltration issues, since their thin selective layer allows a high permeation flow. The application of this kind of membranes for gas separation should provide a better permeance in comparison with other polymeric membranes and a reduction in the amount of MOF required for their fabrication. Here, the preparation of 50–100 nm thick polyamide flat membranes containing zeolitic imidazolate framework‐8 (ZIF‐8) nanoparticles is shown via interfacial polymerization, containing a lower amount of MOF (0.013 g m−2 membrane) as compared to other membranes used for gas separation. The membranes are applied for H2/CO2 separation at high temperatures and pressures, showing a stable performance at 180 °C for at least seven days. Outstanding separation values are 328 GPU of H2 and a H2/CO2 selectivity of 18.1 at 180 °C and 6 bar feed without transmembrane pressure. These membranes, also measurable without sweep gas, are highly suitable for industrial application.

An Experimental Study on the Tensile Behaviors of Ultrasonic Welded T-joints for Polyamide Composite

In this paper, an experimental investigation on ultrasonic welding of polyamide composites reinforced with glass fiber has been carried out. The effect of ultrasonic welding parameters, such as welding time, air pressure, hold time and the amount of glass fiber in the composite on tensile strength of weld joints were determined using response surface methodology. This methodology was applied for developing a mathematical model which can predict the main effects of the above parameters and their impacts on tensile strength of T-welded ultrasonic joints in 4-mm thick polyamide composite sheets. The analysis of variance was performed to check the adequacy of the developed model. A comparison was also made between the predicted and actual results. The results showed that a maximum failure force of about 4759 N is obtained when vibration amplitude, air pressure welding time, holding time and amount of glass fiber are 35 microns, 3.6 bar, 1.84 seconds, 0.9 seconds and 41 percent, respectively .The joint strength of welded parts increased with the fiber content in the composites.

Single-Walled Carbon Nanotube Film Supported Nanofiltration Membrane with a Nearly 10 nm Thick Polyamide Selective Layer for High-Flux and High-Rejection Desalination.

Fabricating nanofiltration (NF) membranes with high permeating flux and simultaneous high rejection rate for desalination is rather significant and highly desired. A new avenue is reported in this work to design NF membrane by using polydopamine wrapped single-walled carbon nanotube (PD/SWCNTs) ultrathin film as support layer instead of the use of traditional polymer-based underlying layers. Thanks to the high porosity, smooth surface, and more importantly optimal hydrophilic surface of PD/SWCNTs film, a defect-free polyamide selective layer for NF membrane with thickness of as thin as 12 nm is achieved. The obtained NF membrane exhibits an extremely high performance with a permeating flux of 32 L m-2 h-1 bar-1 and a rejection rate of 95.9% to divalent ions. This value is two to five times higher than the traditional NF membranes with similar rejection rate.

Chemical bond strain in molecules of polyamide 6 coatings on the steel surface

The structure and stresses of chemical bonds in a 20 μm thick polyamide 6 (PA 6) coating on the steel surface are studied by IR spectroscopy. It is found that PA 6 molecules in the coating are oriented parallel to the metal surface and the content of metastable crystalline (γ) and mesomorphic (β) phases in it is twice as low as in PA 6 films. In the crystalline α phase, the molecular skeleton is compressed and “lateral” (respective to the skeleton) chemical bonds are extended. In the mesomorphic β phase, the concentration of overstressed (extended to a prerupture state) parts in the molecular skeleton is higher than in the film. These effects are explained by a change in the PA 6 low-frequency vibration spectrum at the PA 6-metal interface.

Li3+ ion irradiation effects on polyamide nylon6,6 studied by positron annihilation lifetime and Doppler broadening spectroscopy

AbstractSwift Heavy ion (SHI) irradiation of polymeric materials changes their free volume properties which are strongly correlated to their macroscopic structure. 250 μm thick Polyamide Nylon‐6,6(PN‐6,6) polymer films were irradiated with 50 MeV Li3+ ions from Pelletron accelerator to the fluences of 5 x 1010, 1011, 5 x 1011, 1 x 1012, 5 x 1012, 1013 and 3.5 x 1013 ions/cm2. The effect of heavy ion irradiation on the free volume was studied by Positron Annihilation Lifetime (PAL) and Doppler Broadening Spectroscopy (DBS). Mean free volume hole radius, free volume and fractional free volume of micro‐voids, obtained from o‐Ps lifetime decrease with fluence and is attributed to cross linking. S parameter which is supposed to change due to vacancies type defects created due to SHI irradiation also decreases. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Interfacial polymerization of thin film nanocomposites: A new concept for reverse osmosis membranes

Here, we report on a new concept for formation of mixed matrix reverse osmosis membranes by interfacial polymerization of nanocomposite thin films in situ on porous polysulfone supports. Nanocomposite films created for this study comprise NaA zeolite nanoparticles dispersed within 50–200 nm thick polyamide films. Hand-cast pure polyamide membranes exhibit surface morphologies characteristic of commercial polyamide RO membranes, whereas nanocomposite membranes have measurably smoother and more hydrophilic, negatively charged surfaces. At the highest nanoparticle loadings tested, hand-cast nanocomposite film morphology is visibly different and pure water permeability is nearly double that of hand-cast polyamide membranes with equivalent solute rejections. Comparison of membranes formed using pore-filled and pore-opened zeolites suggest nanoparticle pores play an active role in water permeation and solute rejection. The best performing nanocomposite membranes exhibit permeability and rejection characteristics comparable to commercial RO membranes. As a concept, thin film nanocomposite membrane technology may offer new degrees of freedom in tailoring RO membrane separation performance and material properties.

Near infrared (NIR) spectroscopy compared with thermogravimetric analysis as a tool for on‐line prediction of water diffusion in polyamide 6,6

AbstractNIR spectroscopy in the transmission mode and thermogravimetric analysis were used to predict diffusion of water into polyamide 6,6 samples immersed in water at 40, 60, 75 and 90 °C for different periods of time. The sorption curves between 40 and 75 were sigmoidal indicating that the surface concentration was time dependent. The sorption curves were readily fitted by the use of a time‐dependent surface concentration and a water‐concentration‐dependent diffusivity. The zero‐concentration water diffusivity decreased non‐linearly and the activation energy of diffusion increased from 24 to 58 kJ mol−1, with decreasing temperature. The surface concentration relaxation time decreased rapidly. The sorption of water in thick polyamide samples was readily characterized by FT‐NIR spectroscopy. The accuracy and feasibility of this method was similar to conventional thermogravimetric methods. The greatest advantage of FT‐NIR, however, is the possibility of detecting and monitoring the moisture concentration on‐line and in a non‐destructive way.© 2002 Society of Chemical Industry

X-ray photoemission studies on vapour-phase-deposited polyamide films

In this article we describe the preparation of thick polyamide (PA) films of poly(4,4′-oxy-bis( p-phenylene)terephthalamide) by co-deposition of terephthalolyldichloride (TDC) and 4,4′-oxydianiline (ODA) under high vacuum conditions. The molecules react in the condensed phase with elimination of hydrochloric acid to form polyamide. Chlorine-containing molecules are entrapped in the polymer matrix and are released only by annealing to temperatures of 523K. X-ray photoelectron spectroscopy (XPS) and infrared absorption (FTIR) measurements show that the reaction between TDC and ODA is essentially complete at room temperature, and that only small changes in the overall stoichiometry take place by annealing to higher temperatures. Attempts to produce PA by co-condensation of dimethylterephthalate (DMT) and ODA were not successful, presumably due to the high activation barrier for the reaction between the ester and the diamine in the absence of a catalyst. The experiments and XPS results will be compared to those of polyimide formed by the reaction of pyromellitic dianhydride (PMDA) and ODA. The apparent deficit in O1s and C1s carbonyl intensity for polyamide and polyimide cannot be accounted for by deviations from stoichiometry and are explained by final state effects in the photoemission process.

A new partition thin-layer chromatographic method for steroid separations.

TLC plates with a 25 mu thick polyamide stationary phase were modified for the separation of neutral steroids by impregnation with propylene glycol. A mixture of tritiated 5 alpha-androstan-3 alpha,17 beta-diol, testosterone, 17 beta-hydroxy-5 alpha-androstan-3-one and 4-androstene-3,17-dione was applied to the plate and developed in a toluene mobile phase to a height of 13.6 cm. This resulted in complete resolution of the 4 compounds as detected by a gas flow scanner or imaging analyzer. Cutting and elution of peak areas with methanol resulted in quantitative recovery of all four steroids. The thinness of the layer also permitted a 3-5% counting efficiency on scanning, resulting in good quantitation of recovery without liquid scintillation counting. The high sorptive capacity of the polyamide layer also enabled extracts of normal human serum to be defatted on the TLC plate by development with pure hexane prior to the toluene step. The new method thus offers several advantages over existing methods for steroid separations and should be adaptable to separations of other relatively non-polar compounds.