Structure Of Polyamide Research Articles

Characteristics and competitive mechanisms of polycondensation and cyclization induced by end‐groups in polyamide 6 melt

AbstractPolycondensation and ring‐formation reactions are the main factors that cause instability in the molecular structure of commercial polyamide 6 (PA6) during melting. In this study, the mechanisms and interactions of the ring‐formation and polycondensation reactions induced by various factors were thoroughly investigated. The findings suggest that the average molecular weight of PA6 increased by 20.4% during melting. The total monomer and oligomer content increased by 79.2%, and the ring‐forming reaction was promoted with an increase in temperature. Moreover, a high concentration of the end‐amino in PA6 promoted the ring‐forming reaction, whereas similar concentrations of the end‐amino and end‐carboxyl groups were more conducive to the polycondensation reaction. In short, the nitrogen atoms in the end‐amino group on the PA6 molecular chain attack the carbonyl carbon at different sites, including the carbonyl carbon in the amide bond and the carbonyl carbon in the end‐carboxyl group, which is the key to the strength of the ring‐formation and polycondensation reactions.

Impact of cationic surfactants molecular structure on physicochemical structure and properties of polyamide reverse osmosis membrane via tailoring interfacial polymerization

Surfactants assisted interfacial polymerization (IP) has been demonstrated as an effective method to finely tailor the structure and performance of polyamide (PA) reverse osmosis (RO) membranes. However, little is done to illustrate how molecular structure of cationic surfactants affects IP and the amounts of surfactants incorporated into PA. In this study, three types of quaternary ammonium cationic surfactants were employed to assist the IP process and to fabricate RO membranes. Results show that these three cationic surfactants can not only significantly accelerate m-phenylenediamine (MPD) diffusion from aqueous phase into oil phase and promote the PA crosslinking, but also can be incorporated into PA to affect the surface properties (hydrophilicity, charge properties). Benzyl dimethyl phenyl ammonium chloride (BDMPAC) having two benzene rings had been found to be incorporated into PA with the highest amount because of its similar benzene structure as PA. Moreover, benzalkonium chloride (BAC) with the longest aliphatic tail induced a pronounced Marangoni convection during IP, resulting in an enlarged surface area of PA with large leaves and abundant internal/backside voids, and thus the highest water permeance. This study demonstrates a facile and simple way of using cationic surfactants to engineer the high-performance polyamide RO membrane.

Structure and mechanical properties of biobased polyamide 11 specimens subjected to different heat treatments

Structure and mechanical properties of biobased polyamide 11 specimens subjected to different heat treatments

New strategy for structure rearrangement of thin-film composite (TFC) polyamide (PA) membranes and offering potential use in both aqueous and organic solvents

The purity of sodium hexafluorophosphate (NaPF6) is crucial for the preparation of electrolytes in manufacturing. We propose a simple process in order to induce membrane structure rearrangement process (SRP) by activating thin-film composite (TFC) membranes with polyamide (PA) structure and explore their potential green recycling application in concentrating sodium-ion batteries (SIBs) electrolyte. The method utilizes a solution containing polar aprotic solvent as the soaking and activating solution to swell and disintegrate the loosely cross-linked PA layer, and a non-solvent solidification solution complete the SRP, enhancing the permeability of the PA layer while maintaining high rejection rates for divalent ions. Subsequently, during the further treatment of the membrane surface in structure rearrangement, tert-butanol (TBA) is introduced into the aqueous solution to reconstruct the surface PA layer, further improving the permeability. The optimal D8010T10 achieved a permeation flux of 24.2 L m−2 h−1·bar−1, with rejection rates for sodium sulfate (Na2SO4), magnesium chloride (MgCl2), and magnesium sulfate (MgSO4) reaching 94.7 %, 98.4 %, and 99.1 % respectively. And the mechanism of SRP with different solvent is analyzed and explained through dissipative particle dynamics (DPD) simulations. This study provides a commercially viable approach for manufacturing high-performance membranes. The D8010T10 membrane achieves more than 90 % separation efficiency for sodium hexafluorophosphate (NaPF6) dissolved in different solvents, providing a potential solution for the concentration and recovery of NaPF6 in lab-scale, verified its potential use in the organic solvent nanofiltration (OSN) and a path way for waste membrane recycling and degrading use in the industry.

Analyzing Impact Strength Improvement in Polymer Laminates: A Comparative Study of Machine Direction Oriented (MDO)-PE/LLDPE and Polyamide (PA)/LLDPE Structures

The mechanical strength of 2 film structures, machine-direction-oriented polyethylene (MDO-PE) laminated with linear low-density polyethylene (LLDPE) and polyamide (PA) laminated with LLDPE was evaluated. PA/LLDPE films demonstrated superior impact strength (0.834 J/mm²) compared to MDO-PE/LLDPE films (0.445 J/mm²). Tensile strength for modified LLDPE (C₆) was 40 N/mm², higher than standard LLDPE (C₈) at 33 N/mm². The elongation at break for LLDPE reference C₈ was 689 %, compared to 682 % for LLDPE sample C₆. Film stiffness was measured at 162 MPa for the LLDPE reference C₈ and 122 MPa for the LLDPE sample C₆. PA films exhibited increased mechanical strength due to their intrinsic polyamide structure, while MDO-PE films benefited from molecular orientation during production. The modified LLDPE or C₆ displayed improved impact resistance and tensile strength with reduced stiffness. MDO-PE/LLDPE films are promising for sustainable and robust food packaging. HIGHLIGHTS Comparative Mechanical Strength of Films: Polyamide (PA) films, owing to their chemical structure rich in amide groups, exhibit superior mechanical strength compared to machine direction-oriented polyethylene (MDO-PE) films. Peeling Strength Dynamics: PA/LLDPE laminates display greater initial peeling strength; however, MDO-PE/LLDPE laminates show a gradual increase in peeling strength, indicating potential for improved long-term adhesion. Impact of LLDPE Density on Mechanical Properties: A comparison between LLDPE C₈ and LLDPE C₆ highlights the influence of polymer density on mechanical characteristics, with LLDPE C₆ demonstrating enhanced impact and tensile strengths at the expense of modulus and elongation. Strength Variability Among Laminates: The mechanical properties of laminated films are significantly influenced by the nature of their constituent layers, revealing the complexity of integrating polymers with differing characteristics. Potential of MDO-PE/LLDPE Laminates: Despite the superior properties of PA/LLDPE laminates, MDO-PE/LLDPE emerges as a viable alternative for sustainable and cost-effective packaging solutions, necessitating further validation to fully harness its advantages. GRAPHICAL ABSTRACT

Synthesis of Cycloaliphatic Polyamides via Palladium-Catalyzed Hydroaminocarbonylative Polymerization.

Polyamides represent one class of materials that is important in modern society. Because of the numerous potential applications of polyamides in various fields, there is a high demand for new polyamide structures, which necessitates the development of new polymerization methods. Herein, we report a novel and efficient palladium-catalyzed hydroaminocarbonylative polymerization of dienes and diamines for the synthesis of cycloaliphatic polyamides. The method employs readily available starting materials, proceeds in an atom-economic manner, and creates a series of new functional polyamides in high yields and high molecular weights. In contrast with the traditional polyamides based on adipic acid, the cycloaliphatic polyamides have superior thermal resistance, higher glass-transition temperature, and better solubility in common organic solvents, thus probably featuring the merits of high-performance and good processability.

Prompted by surface-engineered honeycomb Turing nanostructures: Reflections on polyamide structure, growth and performance

The robust correlation between the performance of thin-film composite (TFC) reverse osmosis membranes and the polyamide (PA) active layer determines the necessity of precise design of the PA layer, and this regulation primarily involves the surface morphology and internal characteristics of the PA layer. In this study, we fabricated honeycomb Turing structure or nanovoid-rich TFC series membranes using polar/nonpolar organic phase additives. Characterization and simulation results confirmed that the enhancement of membrane performance relied more on the abundant nanovoids within the PA layer rather than the ordered honeycomb lattice surface. Notably, the TFC-nDCE membrane with multilayer nanovoids exhibited an approximately 89 % improvement in water permeability while maintaining satisfactory salt rejection (98.29 %). We emphasized the significant role of nanovoids in the diffusion process of amine monomers and investigated the potential relationship between nanovoids and the degree of surface cross-linking. Building upon this, a new insight into the formation of nanovoids induced by PA anisotropic growth was presented through a careful analysis of the amine monomer diffusion rate and the morphological evolution of nanovoids. The structure-property relationship between internal structures, surface morphologies, and performances was systematically and thoroughly investigated, pointing out the direction for the rational design of TFC membranes.

Nanomorphogenesis of polyamide membranes by regulating activator-inhibitor diffusivity difference

The use of nanofiltration (NF) membranes featuring crumpled polyamide layers with excellent permeance and selectivity is promising for efficient water reclamation. Although diffusion-driven instability has been regarded as the key mechanism for forming crumpled polyamide structures, in-depth analyses of the morphological and structural features of these membranes are still lacking. We used ammonium carboxymethylcellulose (CMC) and glutaraldehyde (GA) to crosslink and form a pH-responsive interlayer to manipulate the interfacial polymerization (IP) process and the microstructures of interlayered thin-film composite (TFNi) membranes. Experimental observations and molecular dynamics simulations indicate a transition point in the spatial patterns from irregular to regular polyamide nanostructures by tuning the diffusivity difference between the reactant monomers in the two immiscible phases during the IP process. Compared with irregularly crumpled TFNi membranes, regularly crumpled TFNi membranes exhibited polyamide layers with higher aspect ratios (i.e., height/lateral dimension), potentially offering an increased filtration area and sufficient nanovoids. TFNi membranes exhibited a 2.5-fold increase in permeance compared to pristine polyamide membranes, along with twice the selectivity (up to 87.2) for Cl−/SO42−. Our work provides molecular insights into the tuning of morphological features and membrane performance of crumpled polyamide membranes.

Selective ion permeation enables reduced combined gypsum-organic fouling of loose nanofiltration membranes

During the long-term operation of NF membranes, the occurrence of combined gypsum-organic fouling is a significant challenge. While numerous studies have focused on enhancing the fouling resistance of NF through various methods (e.g., antiscalants, pretreatment), there has been limited exploration into the correlation between its structural looseness and fouling resistance. Herein, we conducted an experimental study to evaluate the correlation by employing three NF membranes with different looseness degrees: a custom-developed loosely structured NF membrane (CLNF), the moderately loose NF270, and the tightly structured NF90. Our findings indicated that NF membranes with loose polyamide structure exhibited superior fouling resistance to gypsum scaling and combined gypsum-organic fouling, induced by model organic matters like bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA). After applying SA-coating to calibrate the surface properties of the membranes to exclude the influence of surface roughness, hydrophilicity, and functional groups, our study attributed the difference in fouling resistance to variations in ionic selectivity stemming from membrane looseness. Specifically, the primary advantage of looser polyamide NF membranes lies in enhanced Ca2+ permeation, which not only reduces the “egg-box” effect and surface foulant accumulation but also diminishes cake-enhanced concentration polarization, effectively mitigating gypsum-organic fouling. In real water testing scenarios, the enhanced fouling resistance of loose NF membranes was further affirmed. This research underscored the unexpected benefit of loose NF membranes in terms of fouling resistance, providing a novel insight for future application.

Machine learning – Driven surface grafting of thin-film composite reverse osmosis (TFC-RO) membrane

Modifying reverse-osmosis (RO) membrane performance is challenging and time-consuming due to the complex interplay of various factors that influence the membrane's performance. To address this challenge, we have explored the potential of using machine-learning (ML) to graft the polyamide (PA) surface of an RO membrane to increase water permeability and overcome the limitations of the permeability/selectivity tradeoff. We identified moieties with positive and negative contributions toward water permeability by applying Shapley-Additive-exPlanations (SHAP) analysis to our model as an explainable artificial intelligence (XAI) method. We attempted to improve the subunits of the PA's structure with positive Shapley values and graft the polyamide RO membrane layer of a commercial membrane, Dupont XLE, resulting in a substantial increase in water permeability. The membranes were characterized using FTIR, EDS, and SEM analysis, and their performance was evaluated for water permeance and NaCl rejection using a dead-end stirred cell. The modified membrane exhibited a significant improvement in the commercial membrane's water flux, increasing from 2.45 LMH to 4.9 LMH. Our results demonstrate the potential of using ML to replace traditional trial-and-error methods for modifying PA-RO membrane polyamide layers and advancing the development of higher efficient and sustainable RO membranes for water treatment and purification applications.

Harmonic amide bond density as a game-changer for deciphering the crosslinking puzzle of polyamide

It is particularly essential to analyze the complex crosslinked networks within polyamide membranes and their correlation with separation efficiency for the insightful tailoring of desalination membranes. However, using the degree of network crosslinking as a descriptor yields abnormal analytical outcomes and limited correlation with desalination performance due to imperfections in segmentation and calculation methods. Herein, we introduce a more rational parameter, denoted as harmonic amide bond density (HABD), to unravel the relationship between the crosslinked networks of polyamide membranes and their desalination performance. HABD quantifies the number of distinct amide bonds per unit mass of polyamide, based on a comprehensive segmentation of polyamide structure and consistent computational protocols derived from X-ray photoelectron spectroscopy data. Compared to its counterpart, HABD overcomes the limitations and offers a more accurate depiction of the crosslinked networks. Empirical data validate that HABD exhibits the expected correlation with the salt rejection and water permeance of reverse osmosis and nanofiltration polyamide membranes. Notably, HABD is applicable for analyzing complex crosslinked polyamide networks formed by highly functional monomers. By offering a powerful toolbox for systematic analysis of crosslinked polyamide networks, HABD facilitates the development of permselective membranes with enhanced performance in desalination applications.

Compatibility Study of Polyamide (PA6) with Lubricant Bases for Electric Vehicle Applications

This study explored the crucial relationship between base fluids and polyamide, a prevalent polymer in electric vehicle (EV) components, with the aim of enhancing the longevity and performance of EVs in the context of thermal management by immersion cooling. Focusing on polyalphaolefin and polyol ester as base fluids, an immersion test was conducted to assess their interaction with polyamide 6 using adapted ASTM standards. The results revealed the significant influences of both fluids on the physical properties and chemical structure of polyamide. Polyol ester demonstrated a lesser impact on the chemical and mechanical properties of polyamide 6.

Stable nanoscale sea-island structure of biobased polyamide 56/poly (butylene adipate-co-terephthalate) blends compatibilized by interfacial hyperbranched structure: Toward biobased polymer blends with ultrahigh toughness

Developing biobased materials is a considerably effective approach to save fossil resources and reduce emissions. Biobased polyamide 56 (PA56) is an excellent engineering material, but it has low toughness. Herein, to enhance the toughness of PA56, an ultra-tough biodegradable material, i.e., poly (butylene adipate-co-terephthalate) (PBAT) was introduced into PA56. Moreover, a self-synthesized epoxy-terminated hyperbranched polyester (EHBP) was used to improve the compatibility of the blended materials. The results of differential scanning calorimetry and Fourier-transform infrared spectroscopy indicated that the epoxide group of EHBP could react with PA56 and PBAT to form a block-like polymer structure and limit the crystallization behavior of the blends. The scanning electron microscopy results show that the addition of EHBP considerably reduced the dispersed-phase size in the blends, forming a nanoscale island structure. Moreover, the hydrogen bonds formed between EHBP and PA56/PBAT enhanced the intermolecular interaction between the two materials. Thus, PA56 blends with ultrahigh toughness were successfully prepared. The prepared PA56/PBAT/EHBP blend exhibited a notch impact strength of 20.71 kJ/m2 and a breaking elongation of 38.3 %, which represent increases of 427.3 % and 252.8 %, respectively, compared with those of pure PA56. Thus, the proposed method is suitable for toughening PA56 and broadening its applications.

Comparative analysis of polyamide nanofiltration membranes resistance to different acids: Insights from experiments and density functional theory simulations

Recent research has focused on the acid resistance of polyamide nanofiltration (NF) membranes, a critical aspect for their stability during practical applications. However, the impact of different acids, particularly the role of various anions, on NF membrane acid resistance remains unexplored. Our research systematically evaluates NF membrane performance and property alterations under various acids at identical pH levels, supplemented by density functional theory (DFT) simulations. Results reveal that membranes treated with H₃PO₄ retain desirable NF performance, in stark contrast to those treated with H₂SO₄ and HCl, which undergo significant degradation. Specifically, H₃PO₄-treated membranes showed only a 4.2 % decline in Na₂SO₄ rejection, compared to a dramatic 83.3 % decline for HCl-treated membranes under identical pH. This degradation is linked to the acids infiltrating the polyamide structure. The membrane's enhanced resistance to H₃PO₄ is primarily due to the strong negative charge of phosphate ions, influenced by the Donnan effect, which prevents deep penetration into the membrane. This is further supported by DFT simulations, which reveal that the interaction energy between the membrane surface and phosphate ions is over twice as high as with chlorine ions, highlighting the importance of ion-specific interactions. This research highlights the crucial role of anions in acidic environments for the maintenance and operation of NF membranes in industrial applications. It provides key insights for enhancing membrane efficiency and longevity under acidic conditions.

Phytic acid and ferric chloride compound additives-regulated interfacial polymerization for high-performance nanofiltration membrane

To balance the permeability-selectivity trade-off effect of the polyamide nanofiltration membrane, interfacial polymerization regulation strategy is widely used to optimize the physicochemical structure of the polyamide film. In the present work, the compound additives of phytic acid and ferric chloride were added into the aqueous phase to regulate the interfacial polymerization process. On the one hand, a lot of piperazine monomers will be adsorbed around the phytic acid molecules due to the electrostatic interaction between phosphoric acid groups and amino groups. Meanwhile, the phytic acid molecules and ferric ions can form a complex in the piperazine solution, which results in a low diffusion rate of the other piperazine monomers without adsorbed on the phytic acid and ferric chloride complex due to steric hindrance. The synergistic effect of electrostatic interaction and steric hindrance leads to the optimized nanofiltration membrane with a thinner and looser polyamide structure. The best-performing nanofiltration membrane exhibits an approximately four-fold water permeance (28.4 L m−2 h−1 bar−1) compared with the controlled M0 nanofiltration membrane (6.5 L m−2 h−1 bar−1) without obviously sacrificing the Na2SO4 rejection (96.9 %). This simple interfacial polymerization regulation strategy provides a novel insight for the preparation of high-performance NF membrane.

Molecular Structure Characterization of Micro/Nanoplastics by 193 nm Ultraviolet Photodissociation Mass Spectrometry.

The degradation of macroplastics results in micro/nanoplastics (MNPs) in the natural environment, inducing high health risks worldwide. It remains challenging to characterize the accurate molecular structures of MNPs. Herein, we integrate 193 nm ultraviolet photodissociation (UVPD) with mass spectrometry to interrogate the molecular structures of poly(ethylene glycol) terephthalate and polyamide (PA) MNPs. The backbones of the MNP polymer can be efficiently dissociated by UVPD, producing rich types of fragment ions. Compared to high-energy collision dissociation (HCD), the structural informative fragment ions and corresponding sequence coverages obtained by UVPD were all improved 2.3 times on average, resulting in almost complete sequence coverage and precise structural interrogation of MNPs. We successfully determine the backbone connectivity differences of MNP analogues PA6, PA66, and PA610 by improving the average sequence coverage from 26.8% by HCD to 89.4% by UVPD. Our results highlight the potential of UVPD in characterizing and discriminating backbone connectivity and chain end structures of different types of MNPs.

Development of polyamide 6‐graphene oxide nanocomposite and direct‐joining with aluminum alloy for lightweight engineering applications

AbstractLightweight polyamide composites and structures have been widely studied and employed in several industrial sectors. In this study, the development of a nanocomposite of polyamide 6 and graphene oxide (PA6‐GO) by melt‐compounding and the joining with aluminum alloy AA6061 through direct‐adhesion injection overmolding are addressed. PA6‐GO nanocomposite exhibited well‐dispersed thin (300 nm) GO platelets distributed within the PA6 matrix, which resulted in an increase of 21% in the tensile modulus and 16% in the yield stress for a filler loading of 0.5 wt%. PA6‐GO/AA6061 hybrid joints showed good mechanical anchorage through the complete filling of the polymer into micro‐scale grooves designed onto the metal surface, which ensured outstanding shear strength of 7.1 ± 1.0 MPa, comparable to other polyamide‐metal hybrid joints reported in the literature. This indicates that the processing routes and materials developed are promising for lightweight engineering applications.Highlights A PA6‐GO nanocomposite with enhanced tensile properties was developed. A joint of PA6‐GO and AA6061 with outstanding shear strength was obtained. Fast and efficient melt‐processing routes were employed. These materials are promising for lightweight engineering applications.

In‐situ generated ZnO nanoparticles for enhanced performance of thin film nanocomposite membrane in forward osmosis process

AbstractThis work developed a novel approach to the in‐situ synthesis of ZnO nanoparticles to modify the polysulfone (PSf) porous membrane substrate. The zinc acetate was added to the casting solution, and ZnO nanoparticles were synthesized during phase inversion. The non‐solvent pH and zinc acetate concentration controlled the ZnO synthesis and loading. Their effect on the substrates properties in terms of morphology, hydrophilicity and porosity was studied thoroughly. The result shows that the ZnO nanoparticles was not formed in acidic pH, while ZnO nanoparticles with size of 20 nm could be easily formed in basic pH. The successful synthesis of ZnO nanoparticles was investigated using FTIR and EDX analysis. The EDX images verify that in‐situ synthesis led to a more uniform dispersion than conventional incorporation method. Then the effect of ZnO loading on the interfacial reaction and polyamide (PA) structure was investigated. SEM images verify the successful synthesis of a uniform and defect‐free PA thin film on ZnO modified substrates. FO performance results show an enhancement in water flux and salt rejection as a result of ZnO incorporation in thin film nanocomposite (TFN) membranes, where TFN 1 wt.% in‐situ membrane showed 40% higher water flux than the control TFC membrane. The porous and hydrophile substrate in TFN 1 wt.% in‐situ membrane is responsible for improved separation performance. These modified membranes displayed uniform dispersion of ZnO nanoparticles within substrates, confirming that this method could effectively restrain the aggregation of the nanoparticles.

Synthesis, Characterization, and Proton Conductivity of Muconic Acid-Based Polyamides Bearing Sulfonated Moieties.

Most commercially available polymers are synthesized from compounds derived from petroleum, a finite resource. Because of this, there is a growing interest in the synthesis of new polymeric materials using renewable monomers. Following this concept, this work reports on the use of muconic acid as a renewable source for the development of new polyamides that can be used as proton-exchange membranes. Muconic acid was used as a comonomer in polycondensation reactions with 4,4'-(hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline, 2,5-diaminobencensulfonic acid, and 4,4'-diamino-2,2'-stilbenedisulfonic acid as comonomers in the synthesis of two new series of partially renewable aromatic-aliphatic polyamides, in which the degree of sulfonation was varied. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H, 13C, and 19F-NMR) techniques were used to confirm the chemical structures of the new polyamides. It was also observed that the degree of sulfonation was proportional to the molar ratio of the diamines in the feed. Subsequently, membranes were prepared by casting, and a complete characterization was conducted to determine their decomposition temperature (Td), glass transition temperature (Tg), density (ρ), and other physical properties. In addition, water uptake (Wu), ion-exchange capacity (IEC), and proton conductivity (σp) were determined for these membranes. Electrochemical impedance spectroscopy (EIS) was used to determine the conductivity of the membranes. MUFASA34 exhibited a σp value equal to 9.89 mS·cm-1, being the highest conductivity of all the membranes synthesized in this study.

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.