Polyamide Matrix Research Articles

Enhancing ion separation efficiency: Janus charged nanofiltration membrane fabricated via polyethyleneimine-manipulated interfacial polymerization

This research introduces highly efficient nanofiltration (NF) membranes designed for the effective rejection of both divalent cations and anions, a critical feature for advanced water treatment technologies. We have devised a simple yet adaptable approach for fabricating Janus polyamide (PA) thin-films characterized by dual charges, which exhibit pronounced selectivity towards both mono-/divalent anions and cations. Leveraging a straightforward interfacial polymerization (IP) process, we integrated high molecular weight polyethyleneimine (PEI) within the PA matrix. This strategy ensured the preferential formation of a dense, negatively charged upper layer dominated by piperazine (PIP), while cationic macromolecular PEI facilitated the emergence of a loose and positively charged lower layer, thus giving rise to a distinctively charged and structurally heterogeneous PA thin-film. Furthermore, the strategic inclusion of PEI inhibits the diffusion of the PIP, thereby promoting the development of nano-wrinkled structures. This structural innovation not only enhances pure water permeance (16.0 L m−2 h−1 bar−1) but also optimizes ion selectivity through the coordination of steric hindrance and Donnan effects. Consequently, the Janus charged NF membranes we developed exhibit exceptional selectivity for mono-/divalent ions, particularly demonstrating remarkable ion selectivity for Cl−/SO42− and Li+/Mg2+ of 102 and 24, respectively. Our findings introduce a pioneering avenue for fabricating NF membranes that proficiently separate mono-/divalent ions, promising significant advancements in water treatment and purification endeavors.

Polyamide 6/carbon fibre composite: An investigation of carbon fibre modifying pathways for improving mechanical properties

Carbon fibre-reinforced polyamide 6 (PA6) composites exhibit exceptional mechanical properties, making them a highly attractive material option for various industries. Their ability to combine the advantages of carbon fibres with the versatility of PA6 provides opportunities for lightweight, high-performance applications. This work presented the fabrication of a PA6/carbon fibre composition with carbon fibre was modified by two different chemicals: nitric acid and diglycidil ether bisphenol A (DGEBA). The tensile strength at break, flexural strength, Rockwell hardness and Izod impact were measured to compare the mechanical properties of composites based on the PA6 matrix with two different modified carbon fibres. The morphology of PA6-based composite with different modified carbon fibres was observed by scanning electron microscopy. The results showed that PA6 is more compatible with acid-modified carbon fibre than DGEBA-modified carbon fibre and unmodified carbon fibre. In comparison to composite materials containing unmodified carbon fibre and DGEBA-modified carbon fibre, composite containing acid-modified carbon fibre increase tensile strength (16–38% and 7–15%, respectively), flexural strength (18–66% and 51–70%, respectively), Izod impact (23–65% and 32–78%, respectively) and Rockwell hardness (50–400% and equivalence, respectively).

A Novel Strategy for Fabrication of Polyamide 66/Nanohydroxyapatite Composite Bone Repair Scaffolds by Low-Temperature Three-Dimensional Printing.

Due to the decomposition temperature of Polyamide 66 (PA66) in the environment is close to its thermoforming temperature, it is difficult to construct porous scaffolds of PA66/nanohydroxyapatite (PA66/HAp) by fused deposition modeling (FDM) three-dimensional (3D) printing. In this study, we demonstrated for the first time a method for 3D printing PA66/HAp composites at room temperature, prepared PA66/HAp printing ink using a mixed solvent of formic acid/dichloromethane (FA/DCM), and constructed a series of composite scaffolds with varying HAp content. This printing system can print composite materials with a high HAp content of 60 wt %, which is close to the mineral content in natural bone. The physicochemical evaluation presented that the hydroxyapatite was uniformly distributed within the PA66 matrix, and the PA66/HAp composite scaffold with 30 wt % HAp content exhibited optimal mechanical properties and printability. The results of in vitro cell culture experiments indicated that the incorporation of HAp into the PA66 matrix significantly improved the cell adhesion, proliferation, and osteogenic differentiation of bone marrow stromal cells (BMSCs) cultured on the scaffold. In vivo animal experiments suggested that the PA66/HAp composite material with 30 wt % HAp content had the best structural maintenance and osteogenic performance. The three-dimensional PA66/HAp composite scaffold prepared by low temperature printing in the current study holds great potential for the repair of large-area bone defects.

Fabrication and property characterization of biocomposite based on polyamide 11 and AP1 green ramie fiber modified with epoxy

AbstractIn this article, Vietnam ramie fiber from Moc Chau, Son La province was chosen as a reinforcement for polyamide 11 (PA11) to prepare full–biocomposites. To enhance the compatibility and adhesion with the matrix, the original ramie fiber (oRF) was treated with Ca(OH)2 solution (tRF) and then modified by epoxy (mRF). Properties and structure of these fibers were characterized by tensile test, chemical composition, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The obtained results showed the removal of hemicellulose and lignin after treatment improved the morphology and mechanical properties of the fiber. Rheology in melting state indicated the increase in the torque of PA11 matrix by adding tRF and mRF. The improvement in mechanical properties was observed for both PA11/tRF and PA11/mRF composites. After modification, epoxy on the fiber surface enhanced the adhesion and compatibility with the matrix. This led to a strong increase in Young's modulus, tensile strength and flexural strength of about 37%, 57%, and 33%, respectively. tRF and mRF also improved thermal stability of the composite as shown in TGA and DSC analysis. Finally, mRF showed a better compatibility with PA11 than tRF by observation of SEM images.

Amphiphilic Interlayer Regulated Interfacial Polymerization for Constructing Polyamide Nanofiltration Membranes with High Perm-Selectivity of Mono-/Divalent Salts.

High-quality thin-film composite (TFC) membranes with high selectivity and permeability have great significance owing to their practical applications, specifically for the accurate differentiation of monovalent and divalent ions. However, the trade-off effect between selectivity and permeability is still a big challenge due to the difficult structure adjustment of the selective layer. Herein, polydopamine (PDA) functionalized with a hydrophobic long alkane chain was first explored as a functional amphiphilic interlayer to synthesize high-quality TFC membranes via a confined interfacial polymerization (IP) reaction. The amphiphilic interlayer not only restricted the formation of the polyamide (PA) matrix in the pores of the substrate but also accelerated spatially more homogeneous polymerization and formed a PA active layer with a more uniform pore size distribution. The method may provide an effective principle for the construction of versatile polyamide-based membranes with high perm-selectivity on various supports. The NaCl/Na2SO4 separation factor of the D-8/PA membrane reached as high as 204.07, while the flux increased up to 25.71 L m-2 h-1 bar-1. This progress provides a more feasible way for the construction of high-quality TFC membranes with a devisable and creative amphiphilic interlayer for industrial application.

Preparation of nano-CuO@BaSO4 under room temperatures and its application in PA6 composites

In this work, by simply using barium hydroxide (Ba(OH)2·8H2O) to react with cupric(II) sulfate pentahydrate (CuSO4.5H2O) in methanol under room temperatures, cupric oxide and barium sulfate co-precipitates (CuO@BaSO4) were one-step prepared, and the methanol can be recycled after separating the co-precipitates. The CuO@BaSO4 co-precipitates were then blended with polyamide 6 (PA6) to prepare PA6-CuO@BaSO4 composites and composites fiber via melt extrusion and melt spinning methods to improve the mechanic and antibacterial properties synchronously. The as-prepared CuO@BaSO4 co-precipitates have a regular size of 30–50 nm and are highly compatible with the PA6 matrix. Further investigations disclosed that the CuO@BaSO4 co-precipitates had a good dispersion in the PA6 matrix and synchronously improved the mechanical properties and thermal stability. What’s more, the PA6-CuO@BaSO4 composites showed excellent antibacterial performance and high spinnability. The bactericidal rate reached 100% when adding tiny content (0.24 wt%) of Cu2+ into PA6 fibers.

Tailoring morphology for improved dispersibility of hydrophilic silica nanoparticles to fabricate thin-film nanocomposite membranes

Improving the dispersibility of nanomaterials is a promising approach to enhance the performance of thin-film nanocomposite (TFN) membranes. In this study, hydrophilic nonporous, mesoporous, and dendritic mesoporous silica nanoparticles (NSNs, MSNs, and DMSNs) with a uniform particle size were utilized as aqueous phase additives to prepare TFN membranes through in-situ polymerization. The electrostatic adsorption of nanoparticles increased the concentration of amine monomers on the surface of the polysulfone (PSF) substrate. In collaboration with the steric hindrance effect, nanoparticles restricted the diffusion of piperazine (PIP) into the organic phase to polymerize with the acyl chloride monomers. Compared to TFC-0, the TFN membranes exhibited a rougher surface with increased negative charge and had more channels that facilitated the transportation of water molecules. Among the nanoparticles, DMSNs exhibited excellent dispersibility, ensuring their uniform distribution within the polyamide (PA) matrix. Furthermore, DMSNs possessed an open central-radial pore structure, offering more efficient channels for water molecules to cross the membrane. Therefore, a highly crosslinked, defect-free, and hydrophilic PA layer of TFN-DMSNs was achieved. In the performance characterization, TFN-DMSNs demonstrated a high water/salt permselectivity (A/B) of up to 32.25 bar−1, and exhibited good resistance to acidic/alkaline environments as well as foulants during the operation. This study proposes a novel approach to prepare advanced TFN membranes by optimizing the morphological structure of nanoparticles.

Ionic Hyperbranched Poly(amido-amine)-Incorporated Nanofiltration Membranes for High-Efficiency Dye Desalination.

High-efficiency dye desalination is crucial in the textile industry, considering its importance for human health, safe aquatic ecological systems, and resource recovery. In order to solve the problem of effective separation of univalent salt and ionic dye under the condition of high salt, ionic hyperbranched poly(amido-amine) (HBPs) were synthesized based on a simple and scalable one-step polycondensation method and then incorporated into the polyamide (PA) selective layers to construct charged nanochannels through interfacial polymerization (IP) on the surface of a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane. Both the internal nanopores of HBPs (internal nanochannels) and the interfacial voids between HBPs and the PA matrix (external nanochannels) can be regarded as a fast water molecule transport pathway, while the terminal ionic groups of ionic HBPs endow the nanochannels with charge characteristics for improving ionic dye/salt selectivities. The permeate fluxes and dye/salt selectivities of HBP-TAC/PIP (57.3 L m-2 h-1 and rhodamine B (RB)/NaCl selectivity of 224.0) and HBP-PS/PIP (63.7 L m-2 h-1 and lemon yellow (LY)/NaCl selectivity of 664.0) membranes under 0.4 MPa operation pressure are much higher than PIP-only and HBP-NH2/PIP membranes. At the same time, this project also studied the membrane desalination process in a simulated high-salinity dye/salt mixture system to provide a theoretical basis and technical support for the actual dye desalination process.

Investigating the effect of recycled irregular metallic particles embedment on the interlaminar strength of polyamide-based composites

ABSTRACT In this research, for the first time, the effect of embedding irregular and jagged steel particles of recycled milling dendritic chips on the improvement of compressive and interlayer strength of thermoplastic polyamide6 (PA6)-based, 200 g/m2 plain weave E-glass-fabric-reinforced composite laminates was investigated. The goal here is to examine whether the sharp spikes on the particles can penetrate adjoining laminate layers to provide superior interface toughness compared to spherical toughening particles. In-plane compression tests, according to ASTM D695-15 standard, show that through thickness expansion leads to delamination and subsequent failure. Consequently, theoretical considerations suggest that enhancements in interface toughness should lead to an increase in compression strength. For this purpose, steel particles with three size ranges, 300–600 µm, 150–300 µm, and 75–150 µm, were prepared and embedded into the composite laminates using film-stacking and hot-pressing process, in four different volume fractions. The particle distribution, impregnation, and bonding with the PA6 matrix were analyzed using optical and scanning electron microscopy imaging. Overall, results demonstrate a very good mechanical bonding between the particles and the thermoplastic matrix. Some interlocks between the particles and composite laminates were observed which has led to an improvement in the compressive strength of the composite laminate.

Thin film nanocomposite nanofiltration with tannic acid-Fe(III) complexes functionalized Ti3C2Tx for enhanced divalent-salinity-water separation with a superior durability

Incorporating nanomaterials for a thin film nanocomposite (TFN) layer has been verified effective to improve the separation performance of nanofiltration (NF) membranes, whereas the poor compatibility between nanomaterials and polyamide (PA) matrix leads to a decrease in the salt rejection and pollution resistance. In this study, inspired by a new interface-bridging idea, Ti3C2Tx was bonded with tannic acid-Fe(III) (TA-Fe(III)) complexes, and then incorporated into a PA matrix for the first time to obtain a novel TFN NF membrane. The introduction of TA-Ti3C2Tx was found to effectively reduce the diffusion of piperazine, and thus result in the induction of a thinner, lower roughness, more hydrophilic, and defect-free PA layer. With the addition of 0.015 wt% TA-Ti3C2Tx, the TFN membrane obtained the highest water permeability of 12.17 L m−2 h−1 bar−1, almost twice that of the pristine membrane, with a high Na2SO4 rejection above 97 %. In addition, the TA-Ti3C2Tx-filled TFN membranes were verified to exhibit excellent antifouling performance and pressure resistance with a high durability, which is crucial for the practical application in salinity water treatment. This study provides an effective strategy to tailor the interfacial microstructural of nanoparticle-filled NF membranes for superior divalent-salinity-water separation.

Mechanical and tribological properties of basalt fiber fabric reinforced polyamide 6 composite laminates with interfacial enhancement by electrostatic self-assembly of graphene oxide

Exploring simple, efficient and applicable interfacial optimisation methods is important to enhance the overall performance of basalt fibre (BF) fabric-reinforced thermoplastic composite laminates. Graphene oxide (GO) was introduced on the surface of BF fabric through electrostatic self-assembly to improve the interfacial bonding of BF fabric-reinforced polyamide 6 (PA6) composites laminates (BF/PA6) for enhancing the mechanical and frictional wear properties of the composites. It was concluded that surface electrostatic assembly of GO resulted in a significant increase in surface roughness, wettability, surface energy and surface chemical activity of BF fabrics without damaging the fibre backbone structure. With the GO concentration of 0.8 g/L, the interlaminar shear strength, impact strength, flexural strength and flexural modulus of the BF/PA6 composites were increased by 85.1 %, 43.2 %, 53.2 % and 63.4 %, and the average friction coefficient and wear rate was reduced by 15.2 % and 40.5 %, respectively. The introduced homogeneous GO strengthens the interfacial bonding of such fibre-fabric reinforced thermoplastic composites by creating mechanical engagement, similar compatibility and chemical cross-linking between the BF fabrics and the PA6 matrix. With enhanced interfacial bonding, the BF fabric reinforced thermoplastic composites possess enhanced stress damage resistance. Under frictional reciprocating stress, the introduced GO inhibited the generation and expansion of microcracks, formed frictional transfer film to play solid lubrication and anti-wear role, and enhanced the thermal stability of the composites to mitigate the frictional thermal damage. The interfacial enhancement method of BF fabric-reinforced thermoplastic composites provided in this study is simple, green, efficient and has good potential for application.

Enhancement of flexural properties of carbon fiber-reinforced polyamide 6 via oriented crystallization of polyamide 6 among carbon fibers

The effect of the crystalline structure of polyamide 6 (PA6) among carbon fiber (CF) on the mechanical properties of PA6/CF composites was explored using two types of PA6 with different spherulite sizes. Infrared (IR) spectroscopy showed that intra/intermolecular interactions were nearly equivalent for the two types of PA6. The viscoelasticities in the molten state were almost identical; that is, the molecular weights of the PA6s were comparable. The mechanical properties of the PA6 matrix with smaller spherulites (PA6a) in PA6/CF were superior to those of the PA6 matrix with larger spherulites (PA6b). Polarized light microscopy, wide-angle X-ray scattering, and polarized Raman spectroscopy revealed oriented crystals of PA6a in the PA6a/CF composite and random crystals of PA6b in the PA6b/CF composite. Therefore, the superior mechanical properties of PA6/CF are due to the oriented crystal chains of PA6, which support the overall stress transfer in composites.

Fatigue and durability assessment of PA6-based carbon fiber composites for lightweight applications

The use of lightweight structural elements across various industries has seen significant progress due to the adoption of carbon fiber-reinforced polymers (CFRPs). Among these, polyamide 6 (PA6) stands out as a prevalent thermoplastic polymer, renowned for its exceptional processability, favorable mechanical attributes, and cost-effectiveness. These qualities position it as a compelling candidate for serving as a matrix material in CFRPs. Nevertheless, as these composites find application in the development of lightweight automotive components, there arises a need for a more comprehensive comprehension of their mechanical characteristics and responses under diverse loading scenarios, encompassing fatigue behavior. So, this study investigated the mechanical behavior of CFRP based on the PA6 matrix under tensile and fatigue loading. The volumetric fractions of CF, PA6 matrix, and voids of the CF/PA6 composites were determined by acid digestion analysis, and the values of 48%, 51.6%, and 0.4%, respectively, indicated the good quality of the studied laminate. Tensile tests showed good repeatability, and the results were used to establish fatigue limits at a ratio (R) of 0.1. Fatigue tests showed that the CFRP had an infinite life of 1 million cycles at a stress level of 75%. Fractographic analysis revealed that specimens tested at lower levels of fatigue had better fracture aspects compared to those tested at higher levels. These findings contribute to the understanding of the fatigue behavior of CFRP with PA6 matrix and provide insights for their potential use in applications for lightweight structures.

Novel approach to the 3D printing of biphasic calcium phosphate/molybdenum disulfide composite reinforced with polyamide12

In practical terms, the successful treatment of critical-sized bone defects remains a formidable obstacle. Among various options for bone regeneration, a customized 3D composite scaffold is widely acknowledged as the optimal choice. In the present study, we have developed a specialized composite scaffold utilizing biphasic calcium phosphate/molybdenum disulfide (BCp/MoS2) reinforced with polyamide12 (PA12) through the selective laser sintering (SLS) technique, employing different laser powers: 16W, 18W, 20W, and 22W. Notably, the BCp/MoS2/PA12 scaffold described in this research has not been explored in previous investigations. Analysis using a 3D profilometer reveals that the surface properties of the scaffold exhibit a robust mechanical interconnection between the 3-wt percent (Wt%) BCp/MoS2 composite within the PA12 matrix, particularly at a laser power of 22W. Remarkably, the mechanical properties of BCp/MoS2/PA12, including tensile strength (47.64 ± 0.42 MPa) and Young's modulus (2.31 ± 0.15 MPa), surpass those of pure PA12. These enhanced mechanical characteristics hold promising implications for the future advancement of bone tissue engineering. To comprehensively evaluate the composite scaffolds, we thoroughly investigated their thermal behavior and conducted morphological analysis. Moreover, after 21 days, in vitro live/dead results exhibited living cells along with their distinctive filopodia morphology, providing compelling evidence of the composite's non-toxicity. Further cell adhesion results showed enhanced growth, multiplication, and more reliable attachment and spreading across the composite surface. Encouragingly, the observed biological activity of the BCp/MoS2/PA12 scaffold with a 3 wt% concentration at a laser power of 22W suggests its significant potential for application in implant-related scenarios.

Study of thermal and mechanical behavior by analyzing reinforcement effect of graphene nanoplatelets on polyamide-66 composite system developed via melt-mixing technique

In the present study, graphene nanoplatelets (GNP) reinforced polyamide 6,6 (PA-66) composite was studied to investigate the thermal and mechanical properties of PA-66/GNP composite. The composites were developed by varying wt% (1, 3, 5, and 10 wt%) of GNP loading using a co-rotating, intermeshing, twin-screw extruder via melt-mixing and injection molding process. In order to understand the thermal and mechanical behavior of PA-66/GNP composite, various thermal (TGA and DSC) and mechanical (tensile, impact, and flexural) tests were carried out. The FTIR spectral analysis was done to identify the presence of different functional groups in the PA-66/GNP composite, indicating the strong enough Vander-Waals interaction between the PA-66 matrix and GNP filler contents. The TGA result shows a significant enhancement in the thermal stability of the composite by increasing wt% of GNP. The DSC analysis exhibits a significant reduction in enthalpy of fusion (∆Hm) and a decrease in the degree of crystallinity with increasing wt% of GNP, reflecting a depressed form of α-crystalline structure. Further, the significant growth in tensile modulus and tensile strength were identified under the mechanical performance of the PA-66/GNP composite. An increasing trend in tensile modulus and tensile strength characteristics was observed, and tensile modulus exhibited an enhancement of ∼96% than pure PA-66 at 10 wt% of GNP. Also, the tensile strength is found to be ∼16% higher than that of pure PA-66 matrix. Similarly, the impact test result shows a decreasing trend in impact strength on increasing wt% of GNP reinforcements, indicating the restriction to the molecular mobility due to improved brittle behavior. Further, the flexural modulus is found to be increased by ∼28% at 10 wt%, and the flexural strength is found to have an enhancement of ∼9% at 3 wt% than pure PA-66 polymer matrix of GNP loadings, respectively. The influence of GNP filler content reinforced PA-66 composite on the thermal and mechanical properties is found to be noteworthy.

Synergistic effect of Mn2+ with unzipped carbon nanotubes on enhancement of mechanical properties of polyamide 66

Multi-walled carbon nanotubes (MWCNTs) are widely recognized for their exceptional mechanical properties and potential to reinforce composite materials. However, the requirement for high MWCNT concentration remains a challenge in achieving effective reinforcement. In this study, using unzipped multi-walled carbon nanotubes (uMWCNTs) and transition metal filler as a means to significantly enhance the mechanical properties of polyamide 66 (PA66) and incorporating 0.2% w/w of uMWCNTs-Mn as filler allowed us to increase PA66's tensile strength by over 74% and its Young's modulus by over 100%. The structural and functional integrity of uMWCNTs-Mn and PA66 matrix were investigated in detail. This work reveals that the enhancement of mechanical properties is mainly due to the interfacial interaction between uMWCNTs-Mn sheets and the PA66 matrix, the coupling effect of manganese ions, and increases the crystallinity and reduces the size of microcrystals. This work's findings provide a novel approach to the preparation of high-performance composites with low concentrations of carbon nanostructures, which holds significant implications for the development of advanced materials.

Innovative integration of pyrolyzed biomass into polyamide 11: Sustainable advancements through in situ polymerization for enhanced mechanical, thermal, and additive manufacturing properties

The incorporation of pyrolyzed biomass, i.e., biochar, in polymers can be viewed as a sustainable approach that reduces bio-waste in a smart way. Herein, various biochar concentrations were integrated into the biobased polyamide 11 (PA11) matrix via in situ polymerization. Scanning electron microscopy (SEM) micrographs demonstrated the homogeneous dispersion of up to 50 wt% biochar within the PA11 matrix, free from any phase separation, particle agglomeration, or crack formation. Consequently, there was a remarkable enhancement in mechanical and thermal properties. Notably, tensile strength and modulus increased by 35% and 72%, respectively, while the thermal decomposition process was significantly delayed with the incorporation of biochar particles. Furthermore, the viscoelastic performance of the PA11 matrix exhibited substantial improvement upon the addition of the filler particles. These impressive results verified the excellent interfacial compatibility achieved between the PA11 matrix and biochar, owing to the utilization of in situ polymerization. To demonstrate the potential application of these composites in additive manufacturing, a filament with a uniform diameter was fabricated from a composite comprising 50 wt% biochar. It was successfully employed in material extrusion to print a complex object. The resulting structure exhibited high shape fidelity, precise dimensions, and no noticeable defects. This groundbreaking strategy not only highlights the utilization of biochar as a sustainable filler but also underscores the efficacy of in situ polymerization in fabricating high-performance PA11/biochar composites for various demanding applications, including filament production for additive manufacturing.

Bifunctional polyhedral oligomeric silsesquioxane engineered polyamide membrane for efficient Li+/Mg2+ separation

Nanofiltration membrane technology holds great promise in extracting lithium (Li) from salt-lake brines. However, designing nanofiltration membranes with both high water permeance and ion selectivity remains a grand challenge. Here, amino-functionalized polyhedral oligomeric silsesquioxane (8NH2-POSS) nanocage is designed as a bifunctional molecular filler into polyamide (PA) layer during the interfacial polymerization of polyethyleneimine (PEI) and trimesoyl chloride (TMC). The 8NH2-POSS not only provides abundant amino groups to increase the membrane electropositivity from +4.5 mV to +33.2 mV (pH = 6.0), but also enlarges the pore size of PA matrix and constructs additional water channels to facilitate water transport. The optimal POSS-PA membrane has a rejection rate of 98.1 % to 1 g/L MgCl2, a pure water permeance of 12.0 L m-2h−1 bar−1 and an exceptional separation factor (SLi,Mg) of 13.9 at an ultralow Li+/Mg2+ mass ratio of 1:150, surpassing the benchmark PA membranes.

Stoichiometric effect on the structural transformation and spatial variation of polyamide reverse osmosis membranes: A molecular dynamics study

Reverse osmosis based on polyamide membranes is currently the leading technology for desalination and water purification. However, the spatial variation of polyamide architecture, especially regarding stoichiometric criteria at the real reaction interface during membrane fabrication, is poorly understood. Here we conducted equilibrium molecular dynamic simulations, mimicking the practical construction of polyamide matrices using a variety of monomer component stoichiometries, to investigate resulting differences in both the morphological transformation and mass transport through the polymer network. Our simulations indicated that an equal stoichiometry of the reactive functional groups predominantly resulted in favorable polyamide matrix qualities such as a high crosslinking density, uniform pore size distribution, and adequate layer compactness. Despite the thickness-dependent water diffusion across the active layer, an analysis of polyamide membrane density revealed depth heterogeneity, particularly for membranes constructed under unequal concentrations. Consequently, uncontrollable defects are likely to be created, as evidenced by the partial penetration of Na+ across such membranes. In addition, the residual functional groups in the polyamide matrices (–COOH and –NH2) influenced the transport behavior of ions near the membrane surface. Overall, our simulations provide a visual platform for understanding the stoichiometry-induced relationship between membrane structure and performance, which may guide the future design of defect-free and scaling-resistant reverse osmosis membranes.

Reinforcement effect of glass fiber modified by tannic acid and polyethyleneimine on polyamide 6 composites with no volatile organic compounds emission

AbstractAs an important surface modifier, conventional silane coupling agents generally emit volatile organic compounds (VOCs) like methanol or ethanol during the modification of glass fiber. To avoid VOCs emission, a phenol/amine co‐deposition of tannic acid (TA) with polyethyleneimine (PEI) was used to modify glass fiber (TP‐GF) based on mussel‐inspired surface chemistry. The reinforcement effect of TP‐GF on polyamide 6 (PA6) matrix was investigated, and the corresponding results were compared with those of γ‐aminopropyltriethoxysilane (KH550) modified glass fiber (KH550‐GF)/PA6 composites. The results showed that the interfacial adhesion between TP‐GF and PA6 matrix was superior to that between KH550‐GF and PA6 matrix, and thus TP‐GF/PA6 composites manifested more excellent mechanical properties than KH550‐GF/PA6 composites. Among these composites, TP‐GF (1.05 wt% of coating amount)/PA6 composites exhibited the optimal mechanical properties (tensile strength: 151.3 MPa, notched impact strength: 13.8 kJ m−2) compared with KH550‐GF (1.33 wt% of coating amount)/PA6 composites (tensile strength: 144.8 MPa, notched impact strength: 9.5 kJ m−2). In particular, the notched impact strength was significantly increased by 45%. Notably, there was no VOCs generation during the preparation of TP‐GF, indicating that TP‐GF could be used as an environmentally friendly glass fiber for the fabrication of high‐performance PA6 composites.