Polyamide Polymer Research Articles

Balancing hydrophobicity and surface potential in bio-based bisfuran-containing polyamide coatings for enhanced long-term antibacterial efficacy and endotoxin adsorption

To develop antimicrobial protective materials based on renewable polymers, we synthesized a series of bio-based bisfuran-based polyamide (bFPA) polymers with various functional groups, including allyl quaternary ammonium cations, decyl quaternary ammonium cations, and sulfonate betaine. These bFPA-based coating materials, featuring excellent thermal stability (>230 °C) and biocompatibility, were facilely fabricated on polyurethane (PU) substrates by blending and crosslinking with unsaturated aliphatic PU resin. By altering the combination of different functional groups in bFPA polymers, we controlled the hydrophilicity/hydrophobicity and surface charge properties of the bio-based coating. Compared to pure PU coatings, the bFPA-based coatings with moderate hydrophilicity/hydrophobicity and surface potential significantly reduced the adhesion of model protein and bacteria by approximately 70 % and >99 %, respectively, demonstrating outstanding anti-protein and anti-bacterial adhesion properties. Even after seven cycles of use, the coatings maintained the ability to kill ∼80 % and >99 % of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria, respectively, indicating long-lasting antibacterial activity. Additionally, the optimized bFPA-based coatings effectively adsorbed ∼80 % of endotoxins from damaged Gram-negative bacteria through electrostatic interactions, thereby reducing the risk of inflammation and sepsis. The development of bio-based polyamide coatings with long-term antibacterial and endotoxin adsorption properties significantly advances their safe and reliable application of in the field of biomedical devices.

Unveiling the pore size change in polyamide membrane using aggregation induced emission

Polyamide (PA) membranes play a crucial role in nanofiltration and reverse osmosis separations, while their pore size is primary to determine the separation performance. Current methods for pore size analysis, such as atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and the filtration experiment of neutral molecules are time-consuming and lack real-time capabilities. This limitation hinders in-situ monitoring of pore size dynamics under various operating conditions. Therefore, a rapid and real-time method is highly desirable for pore size analysis. This work presents a novel approach for real-time detection of pore size variations in PA membranes under different solvent conditions. It utilizes aggregation-induced emission (AIE) with tetraphenylethylene (TPE) groups covalently linked to the PA polymer chain during interfacial polymerization using 1-(4-Aminophenyl)-1,2,2-triphenylethene as a co-monomer. Fluorescence intensity of the PA membrane serves as an indicator of the confined state of the TPE molecules within the polymer network, thereby reflecting pore size changes under various conditions. The accuracy of the AIE-based approach is validated through complementary analyses such as small-angle X-ray scattering (SAXS) and rejection of dye molecules. The observed consistency between fluorescence variations in the PA membrane and pore size changes under different solvent conditions confirms the effectiveness of this method. This work provides a valuable visual tool for in-situ monitoring of pore size dynamics in polyamide membranes.

Hyperbranched polymer wrapped UIO-66-NH2 as covalent intermediate layer to enhance polyamide membrane for Li+/Mg2+ separation and acid/alkaline stability

Herein, hyperbranched polyamide covalently wrapped UIO-66-NH2 nanoparticles (PA-UIO-66-NH2) were designed and synthesized via the in-situ self-condensation polymerization of 3,5-diaminobenzoic acid. Mixed matrix intermediate layer thus was prepared by doping it into the diazotization-coupling reaction, to tune the pore size and hydrophilic of the polysulfone (PSF) support. The interfacial polymerized polyamide (PA) nanofilm formed on modified PSF support exhibited optimized improved size exclusion and Donnan effect on separation of Li+/Mg2+. Experimental data showed that the Li+/Mg2+ separation factor (32.24 at Mg2+/Li+ ratio of 15.3) of the PA/m-PSF-2 membrane tuned with such intermediate layer reached 13.27 times that of the controlled PA/PSF-0, and surpassed some commercial PA (NF 270, DL, and DK) and literature reported membranes. Moreover, the related LiCl/water flux enhanced from 1.39 to 1.88 times compared with that of the PA/PSF-0 membrane, up to 244.25 kg m−2 h−1. Such mixed matrix intermediate layer can adsorb and isolate acidic or alkaline cleaning solutions, significantly reducing the impact of cleaning solutions on the rejection rate and water flux of the PA nanofilm during actual application. This work demonstrated that the mixed matrix covalent intermediate layer was an effective approach to construct the fine-tuned structural and robust PA nanofiltration (NF) composite membrane.

Tetraaza macrocyclic complexes of Cu(II), Co(III) and Ni(II) derived from template condensation of 2,6-pyridinedicarbohydrazide and 2,6-diacetylpyridine: Stability investigation and coloring properties on plastics

Completely conjugated 14-membered ring hexaaza ligand complexes of Cu(II), Co(III) and Ni(II) were synthesized by the template cyclo-condensation reaction of 2,6-diacetylpyridine and 2,6-pyridinedicarbohydrazide: [Cu(HL)Cl]·1.35H2O (1), [Cu(HL)Br]·CH3OH (2), [Cu(L)(H2O)]·4H2O (3), [Co(HL)Cl2]·CH3OH (4), (H3O)[Co(H2L)Cl2][Co(HL)Cl2]Cl2·H2O (5), [Co(HL)(SCN)2]·CH3OH (6), [Ni(L)]·3H2O (7) and (H3O)[Ni(L)]Cl·H2O (8). The structure of all complexes derived from this novel diprotic macrocyclic ligand H2L (5,7-dimethyl-3,4,8,9-tetraaza-1,6(2,6)-dipyridinacyclodecaphane-4,7-diene-2,10-dione) were determined by single crystal X-ray diffraction method. The tetraaza 14-membered conjugated macrocycle is N4-tetracoordinated to metal, adopts an essentially planar configuration and forms four fused metallocycles rings, two five-membered and two six-membered chelates. The structures of the studied complexes reveal three isomers out of three possible: with a 5-6-5-6 order of alternation of metallocycles for 1–6, the 5-5-6-6 isomer in 8 and the coexistence of two different isomers with 5-5-6-6 and 6-6-5-5 alternation of metallocycles in 7. Based on the protonation state of the macrocyclic ligand, four forms of the ligand have been registered: bis-deprotonated L2− (compounds 3, 7 and 8), monodeprotonated HL− (1, 2 and 4), neutral H2L (5) and for compound 6 tautomeric (amide → imidic acid) HL− form. The organisation of crystal structures 1–8 depends on the nature of the metal and the composition of the solvents and outer-sphere ions, but shows clear common features for the same type of metal. The hydrolytic study demonstrated a high stability of the Co(III) and Ni(II) complexes in acidic solutions and the most thermally stable are the complexes 3 and 7 with the limit of 350 °C for Ni(II) complex. Testing of the coloring properties of the [Ni(L)] (8) complex on plastics indicates a high coloring efficiency, especially for polyamide polymers.

Macromolecular PEI-modified carbon nanotubes as multifunctional additives in controlling crystallization and enhancing comprehensive performance of polyamide 6 nanocomposites

Despite the promising potential of carbon nanotubes (CNTs) in polymer nanocomposites, their propensity for aggregation and random dispersion within the polymer matrix poses significant challenges. This study introduces a novel approach to enhance the interfacial properties between the CNTs and the polyamide 6 (PA6) matrix by anchoring the polyethyleneimine (PEI) onto the CNT surfaces. The integration of PEI, with abundant amino groups, provides the high density of nucleation sites, facilitating transcrystallization along the surfaces of the macromolecular polyethyleneimine (PEI) modified CNTs (m-CNTs). This transcrystallization process enhances the physical interactions between the m-CNTs and the PA6 matrix, resulting in the substantial improvements in the mechanical properties of the PA6 nanocomposites. Specifically, as compared to the neat PA6, the PA6/m-CNT nanocomposites exhibited the increase of 131.2 % and 54.3 % in tensile strength and Young's modulus, respectively. Additionally, the intimate contact between the embedded CNTs forms the efficient thermally conductive networks. The robust molecular interactions between the m-CNTs and the PA6 polymer chains promote the highly homogeneous dispersion within the PA6/m-CNT nanocomposites, thereby reducing the thermal resistance. This straightforward and effective method presents a viable strategy for improving the interfacial properties of the CNTs reinforced polymer nanocomposites, offering the extensive potential for the future advancements in the interfacial modifications of the polymer matrix nanocomposites.

Analisis Gugus Fungsi dan Sifat Termal Limbah Jaring Ikan Untuk Produk Otomotif

Plastic has been used in daily life due to its durability. Fishing net waste is a type of plastic waste that is dangerous. Fishing net waste can also damage marine biota, such as coral reefs and marine animals. One type of polyamide that is widely used is nylon. Fishing net waste containing nylon has the potential to be recycled. In this research, fishing net waste is used for automotive product applications using a twin-screw extruder. There are five variations: pure polyamide (PA), recycled polyamide (rPA), PA-rPA 50:50, PA-rPA 75:25, and PA-rPA 25:75. To be able to determine the characteristics of the mixed product, several tests were carried out, including testing the thermal properties of the final product with DSC and FTIR testing to identify functional groups. Based on the research results, it was found that all variations contained polyamide polymers, which were characterized by a melting temperature of 218.8–224.4 °C and obtained carbonyl functional groups (C=O) and secondary amine functional groups (N–H) in the FTIR test results, which indicated the presence of amide bonds in the samples.

Molecular Dynamics Simulations of Gas Transport Properties in Cross-Linked Polyamide Membranes: Tracing the Morphology and Addition of Silicate Nanotubes.

This study employs molecular dynamics (MD) simulations to fundamentally provide insight into the role of cross-link density in the CO2 separation properties of interfacially polymerized polyamide (PA) membranes. For this purpose, two atomistic models of pure polyamide membranes with different cross-link densities are constructed by MD simulations to conceptually determine how the fractional free volume of polyamide affects the gas separation performance of the membrane. The PA membrane with a lower cross-link density (LCPA) shows a higher gas diffusion coefficient, a lower gas solubility coefficient, and a higher gas permeability than the PA membrane with a higher cross-link density (HCPA). Moreover, the pristine and modified silicate nanotubes (SNTs) as the fast gas transport channels are incorporated into the polyamide membranes to assess the effect of the SNT/PA interface chemistry on the CO2 separation properties of the membranes. SNTs are systematically modified by three modifying agents with different CO2-philic groups and different interfacial interaction energies with the polyamide matrix. The results of MD simulations demonstrate that the incorporation of silicate nanotubes into the PA matrix increases the gas diffusivity and permeability and decreases the CO2/gas selectivity. Moreover, the membranes containing modified SNTs possessing high CO2-philicity and high SNTs/PA interfacial interactions show a high CO2 separation performance.

Fabrication of flame-retardant PA6/three-dimensional braided glass fiber composites via in situ polymerization

Reaction injection molding method is employed to improve flame retardancy and mechanical properties of three-dimensional braided glass fiber (3D-braided-GF) reinforced in situ polymerized polyamide 6 (PA6) composites. The kernel lies in adding flame retardants, hexaphenoxycyclotriphosphazene (HPCTP), to the reactive monomers to allow it to be in situ filled into composites during preparing PA6 through anionic polymerization, which enables flame retardants to achieve better dispersion. In addition, extremely low-viscosity reactive monomers are easier to immerse in 3D-braided-GF, ameliorating interfacial adhesion between GF and PA6. The preliminary research indicates that samples with 10 wt.% HPCTP concentration can achieve the best mechanical properties and a satisfied flame-retardant grade (UL 94 HB). However, with the incorporation of 15 wt.% HPCTP into samples, the optimum flame-retardant grade (UL 94 V2) and the reduced mechanical performance are obtained. Furthermore, a dual flame retardancy mechanism in both gaseous and condensed phases of samples is further elucidated. This study can provide a reference for scenarios with high requirements for the flame-retardant and mechanical properties, such as high-speed rail and aircraft.

3D composite printing: study of carbon fiber incorporation to different construction thermoplastic matrices in regard to dilatation characteristics

PurposeThe purpose of this paper is to clarify the relationship between the use of different polymer matrices for the preparation of composite materials, namely, polyethylene terephthalate-glycol (PET-G) and polyamide (PA), using Composite Fiber Co-Extrusion technology with the application of two types of carbon fibers, short and continuous. The aim of the study is also to extend the knowledge of the production of composite materials with a defined structure from the point of view of their influence on the microstructure and their physical-mechanical properties.Design/methodology/approachAs part of the experiment, four types of samples were prepared, namely, two types of samples with PA polymer matrix and two types with PET-G polymer matrix. All types contained short carbon fibers and always one set from each polymer matrix in addition to continuous carbon fibers. All types were prepared using the same 3D printing parameters to avoid any further influence. The samples were then tested for microstructure using microCT, mechanical properties using a tensile test and dilatation characteristics from the point of view of aerospace applications. Finally, the raw materials themselves were tested.FindingsThe paper provides insight into the influence of polymer matrix types on the physico-mechanical properties of 3D printed composites. The analysis confirmed that the physico-mechanical results varied with respect to the interface between the polymer matrix and the carbon fiber. The implications of the conclusions can be extended to the development of products in the aerospace and automotive sectors.Originality/valueThis study provides information for composite applications in the aerospace industry, focusing on evaluating dilatation characteristics within very low temperatures (−60 °C) when using carbon fibers (continuous carbon fibers, short carbon fibers and a combination of both) in two types of thermoplastic matrices. This perspective on materials characterisation for aerospace applications is a very important and unpublished approach within the 3D printing of composites. These characteristics are important parameters in the design of prototypes and functional samples with regard to the resulting behaviour in real conditions.

Enhancing proton conduction by regulating proton carrier position in polyamide layer of forward osmosis membrane in osmotic microbial fuel cell

Osmotic microbial fuel cell (OsMFC) encounters the problem of slow transport of proton, which results in a pH imbalance between the anode and cathode, and then a decreased cell performance. Forward osmosis (FO) membrane plays a critical role in proton transport in OsMFC, but the proton transmembrane migration is greatly hindered by the absence of particular proton transfer unit in FO membrane. In this study, high proton conductive carrier sulfo (−SO3H) was imported in the polyamide (PA) layer of FO membrane. The results demonstrated that the position of sulfo on benzene ring in PA polymer chain had a significant effect on proton migration and further the OsMFC property. As sulfo is in the ortho and para of the amino group on benzene ring, the optimal FO-1 membrane was acquired. It indicated that the OsMFC loaded with FO-1 membrane completed 88.31 % increase of water extraction, 50.72 % promotion of maximum power density and 6.02 % enhancement of chemical oxygen demand (COD) removal compared to those of the OsMFC with commercial FO membrane. The molecular dynamics simulation elucidated that the hydrogen bond and electrostatic interaction between atoms both played crucial roles in the proton-transfer process. This method of introducing proton carrier at molecular level aiming to alleviate the rising catholyte pH is economical and convenient for the potential scale-up applications of the OsMFC.

Fabrication of robust polyamide 6 with local cross‐linked structure via dynamic vulcanization

AbstractPolyamide 6 (PA6) is a widely used thermoplastic engineering polymer, and the toughening modification for PA6 is always a main research topic. Meanwhile, the rigidity and heat resistance of PA6 usually deteriorate. To address this conflict, an epoxy compound (EGDE‐GA) was designed and synthesized and used to modify PA6 by dynamic vulcanization in twin‐screw extruder. EGDE‐GA is a linear molecule with a flexible molecular structure, which is favorable to toughening of PA6, and epoxy groups of EGDE‐GA can form local cross‐linked structure to improve the rigidity and retain the heat resistance of PA6. At the loading of 20 wt% of EGDE‐GA, the modified PA6 (PA6/EGDE‐GA 20) exhibited very high elongation at break and notched impact strength, which were increased by 413% and 520%, respectively, compared to those of PA6. The tensile strength was 61.4 MPa, which was higher than that of PA6. The heat deflection temperature remained almost unchanged. The results showed that the modified polymers may possess the high toughness without sacrificing the original rigidity by building the local crosslinked structure using dynamic vulcanization. The findings provide a feasible method for reusing and upcycling PA6 and other polymers with higher value and wider use in the industry.Highlights The polyamide 6 (PA6) is toughened via dynamic vulcanization. The toughness of modified PA6 is increased by 520% compared with pure PA6. The toughened PA6 exhibits higher tensile strength than that of pure PA6. The toughened PA6 maintains its rigidity and heat resistance.

Mechanochemical Encapsulation of Caffeine in UiO-66 and UiO-66-NH2 to Obtain Polymeric Composites by Extrusion with Recycled Polyamide 6 or Polylactic Acid Biopolymer.

The development of capsules with additives that can be added to polymers during extrusion processing can lead to advances in the manufacturing of textile fabrics with improved and durable properties. In this work, caffeine (CAF), which has anti-cellulite properties, has been encapsulated by liquid-assisted milling in zirconium-based metal-organic frameworks (MOFs) with different textural properties and chemical functionalization: commercial UiO-66, UiO-66 synthesized without solvents, and UiO-66-NH2 synthesized in ethanol. The CAF@MOF capsules obtained through the grinding procedure have been added during the extrusion process to recycled polyamide 6 (PA6) and to a biopolymer based on polylactic acid (PLA) to obtain a load of approximately 2.5 wt% of caffeine. The materials have been characterized by various techniques (XRD, NMR, TGA, FTIR, nitrogen sorption, UV-vis, SEM, and TEM) that confirm the caffeine encapsulation, the preservation of caffeine during the extrusion process, and the good contact between the polymer and the MOF. Studies of the capsules and PA6 polymer+capsules composites have shown that release is slower when caffeine is encapsulated than when it is free, and the textural properties of UiO-66 influence the release more prominently than the NH2 group. However, an interaction is established between the biopolymer PLA and caffeine that delays the release of the additive.

Wear and Friction Behaviour of Glass Fiber Reinforced Polyamide 6 Composites and Polyamide-6 Polymer against 30% Glass Fiber Reinforced Polyamide 6 Composite

Bu çalışmada, katkısız poli-amit polimeri ile ağırlık olarak farklı oranlarda (%10-%20-%30) kısa cam elyaf (CE) takviyeli poli-amit kompozitlerin aşınma ve sürtünme davranışları incelenmiştir. Aşınma deneyleri %30 kısa cam elyaf takviyeli poli-amit 6 (PA6+%30CE) kompozit diske karşı kuru ortam şartları altında gerçekleştirilmiştir. Cam elyaf takviyeli PA6 esaslı kompozitler önce ikiz vidalı bir ekstruderde granül formunda üretilmiş ardından enjeksiyon makinasında aşınma test numuneleri basılmıştır. Aşınma testleri 0,5 m/s kayma hızı, 20-30-40 N yükte ve 1500 m kayma mesafesinde yapılmıştır. Deneyler, pim-disk aşınma test cihazı kullanılarak ortam sıcaklığında gerçekleştirilmiştir. Deneyler sonucunda, katkısız PA6 polimerinin sürtünme katsayısı ve aşınma oranı uygulanan yük ile artış göstermiştir. Kısa CE takviyeli PA6 kompozitlerin sürtünme katsayısı da artarken aşınma oranında ise pek artış gözlenmemiştir. En düşük sürtünme katsayısı ve aşınma oranı %30 CE takviyeli PA6 kompozitinde elde edilmiştir. PA6 polimerine %30 oranında CE takviyesi ile kompozitin aşınma direnci katkısız PA6 polimerine göre en az %48 oranında artmıştır.

Evaluation of mechanical properties of 3D printed PETG and Polyamide (6) polymers

The present study endeavors to undertake an exhaustive assessment of the mechanical properties of PETG and Polyamide (6) polymers, fabricated via Material Extrusion (MEX) in 3D printing. The objective of the investigation is to examine the mechanical properties of test samples by varying printing parameters such as nozzle temperature, bed temperature, printing speed, layer height, and infill density. The purpose is to comprehensively evaluate the impact of these printing parameters on mechanical properties. PETG demonstrated superior strength characteristics at a nozzle temperature of 250 °C, bed temperature of 80 °C, infill density of 90%, a printing speed of 40 mm/s, and a layer height of 0.2 mm. Polyamide (6) exhibited greater strength at a nozzle temperature of 260 °C, bed temperature of 90 °C, infill density of 90%, a printing speed of 40 mm/s, and a layer height of 0.2 mm. The outcomes of this study provide significant insights into the mechanical properties of PETG and Polyamide (6) produced via MEX. These insights could be utilized to optimize printing parameters for specific applications. SEM analysis was carried out to study about the layer bonding, build quality, microstructure analysis. Therefore, these results could make a substantial contribution to enhancing the efficiency of 3D printing technology in various industries.

Engineering an Artificial Pathway to Improve the Bioconversion of Lysine into Chiral Amino Alcohol 2-Hydroxycadaverine Using a Semi-Rational Design

Amino alcohols are important compounds that are widely used in the polymer and pharmaceutical industry, particularly when used as chiral scaffolds in organic synthesis. The hydroxylation of polyamide polymers may allow crosslinking between molecular chains through the esterification reactions of hydroxyl and carboxyl groups. Therefore, this may alter the functional properties of polyamide polymers. 2-hydroxycadaverine (2HyC), as a new type of chiral amino alcohol, has potential applications in the pharmaceutical, chemical, and polymer industries. Currently, 2HyC production has only been realized via pure enzyme catalysis or two-stage whole-cell biocatalysis, which faces great challenges for scale-up production. However, the use of a cell factory is very promising for the production of 2HyC in industrial applications. Here, we designed and constructed a promising artificial pathway in Escherichia coli for producing 2HyC from biomass-derived lysine. This biosynthesis route expands the lysine catabolism pathway and employs two enzymes to sequentially convert lysine into 2HyC. However, the catalytic activity of wild-type pyridoxal phosphate-dependent decarboxylase from Chitinophage pinensis (DCCp) toward 3-hydroxylysine is lower, resulting in the lower production of 2HyC. Thus, the higher catalytic activity of DCCp is desired for low-cost and expanded industrial applications of 2HyC. To improve the catalytic activity of DCCp, a mutant library of DCCp was first built using a semi-rational design. The Kcat/Km of mutant DCCp (R53D/V94I) increased by 63%. A titer of 359 mg/L 2HyC was produced in shake flasks, with a 2HyC titer increase of 54% compared to control strain ML101. The results show that the production of 2HyC was effectively increased through a semi-rational design strategy. These findings lay the foundation for the development and utilization of renewable resources to produce 2HyC in microorganisms via an efficient, green, and sustainable biosynthetic strategy for further industrial application.

Friction and Wear Behavior of Polyamide-6 Polymer and Mica and Glass Fiber Reinforced Polyamide-6 Polymer Composites against Poly-phenylene-Sulfide Polymer Composite

Bu çalışmada, katkısız Poliamit (PA6) polimeri ile ağırlık olarak %20 oranında mika katkılı Poliamit 6 (PA6/20M) ve %20 oranında mika/%10 oranında cam elyaf (CE) katkılı Poliamit 6 (PA6/20M/10CE) kompozitlerin tribolojik özellikleri incelenmiştir. Kompozit granül üretimi için önce çift vidalı ekstruder kullanılmış, test numuneleri üretimi için ise enjeksiyon makinası kullanılmıştır. Aşınma ve sürtünme testleri kuru ortam şartları altında %40 kısa cam elyaf takviyeli Poli-fenilen-Sülfit (PPS/40CE) kompozit diskine karşı yapılmıştır. Aşınma deneyleri pim-disk aşınma test cihazı kullanılarak oda sıcaklığında gerçekleştirilmiştir. Triboloji deneylerinde üç farklı yük (10-20-30 N) ve 0.5m/s sabit kayma hızı kullanılmıştır. Çalışma şartları alrındaki malzemelerin sürtünme katsayısı ve aşınma hacmi değişimi belirlenmiştir. Çalışma sonucunda uygulanan yükün artması ile katkısız PA6 polimeri ile PA6/20M ve PA6/20M/10CE kompozitlerinin sürtünme katsayısı sırasıyla %25.2, %29.6 ve %15.2 oranlarında artış göstermiştir. PA6 polimeri ilave edilen %20 oranındaki mika katkısı sürtünme katsayısını %33.0 oranında artırmıştır. PA6/20M kompozitine ilave edilen %10 oranındaki cam elyaf ise sürtünme katsayısını %86.1 oranında azaltmıştır. Uygulanan yükün artırılması ile katkısız PA6 polimerinin aşınma hacmi %200 oranında artarken PA6/20M kompozitinde %291.3 oranında artmıştır. Buna ilaveten PA6/20M/10CE hibrit kompoziti ise %371.4 oranında artmıştır. Deneyler sonucunda en az aşınma hacmi diğer kombinasyonlarla kıyaslandığında minimum %20 oranında PA6/20M-10CE/PPS-40CE kombinasyonunda elde edilmiştir.

CELLULOSE REINFORCED POLYAMIDE COMPOSITES: EFFECT OF PREPARATION METHOD ON COMPOSITE PROPERTIES

Over the years, the preparation method chosen for the preparation of cellulose reinforced nylon or polyamide (PA) composites has proven to be critical in determining the overall properties of the composites. For example, melt processing of cellulose reinforced nylon or PA composites presents challenges, such as (i) irreversible hornification of cellulose material upon drying, before melt processing; (ii) non-uniform dispersion or distribution of cellulose in the polymer matrix; (iii) thermal degradation of cellulose at elevated temperatures and (iv) structural integrity (fibrillation) and shortening of cellulose upon mechanical shearing during melt processing. All these challenges have the potential to compromise the overall properties of the prepared composites. In order to circumvent these challenges, several techniques have been used. For example, hornification, can be overcome by using a technique called wet feeding. Thermal degradation can be overcome by coating cellulose materials via either chemical or physical wrapping with a macromolecule or surfactant. The thermal degradation of cellulose can also be prevented by using in situ polymerization of PA via the ring opening polymerization technique during the manufacture of cellulose reinforced nylon composites, as well as solvent casting in formic acid/water mixtures. The incorporation of up to 50 wt% cellulose nanofibers (CNFs) in PA nanocomposites via solvent casting improved elastic modulus by 64% and tensile strength by 62%. The aim of this manuscript is to review preparation techniques of low cost, high strength composites using cellulose fibers and engineering plastics like polyamides (PAs, nylons).

Support-free interfacial polymerized polyamide membrane on a macroporous substrate to reduce internal concentration polarization and increase water flux in forward osmosis

Macroporous substrates have great potential in the development of high performance thin film composite forward osmosis (TFC FO) membranes. This paper reports on the preparation of TFC FO membrane via support-free interfacial polymerization (SFIP) technology on a macroporous substrate. SFIP technology can effectively break the bottleneck of conventional interfacial polymerization (IP) technology, which makes it difficult to form a complete polyamide (PA) film on the macroporous substrate. Briefly, the complete PA film is formed at the free water-organic phase interface and then attached to the macroporous substrate by vacuum filtration. The monomer concentration and filtration pressure were adjusted to form the optimal SFIP-PA film. Meanwhile, we chose a macroporous polyvinylidene fluoride (PVDF) microfiltration substrate and screened the pore size to reduce the structural parameters and then the internal concentration polarization, which caused the improvement of water flux. The performance of SFIP-PVDF membranes was investigated and discussed. Under the AL-FS mode with DI water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, the SFIP-PVDF membrane, which used a macroporous PVDF substrate with a pore size of 0.45 μm exhibited a water flux (20 L/m2·h) and a reverse salt flux (2.5 g/m2·h). Besides, the membrane showed good stability in the 72 h test. The specific salt flux (Js/Jw) of SFIP-PVDF membranes was much lower than that of IP-PVDF membranes prepared via IP technology, which were incomplete and defective, suggesting that SFIP technology was superior to IP technology. This work effectively exploits the potential of macroporous substrates for the development of high performance TFC FO membranes and provides an insight into the high performance FO membrane design.

Solvent-activated thin-film nanocomposite membranes molecularly tuned with macrocyclic cavities for efficient water desalination and boron removal

Tuning the permeation properties of thin-film nanocomposite (TFN) membranes through the molecular redesign of their underlying nanoarchitecture is a challenging but important task for realizing reverse osmosis (RO) desalination performance above the trade-off limit. Activation by organic solvents, as one of the most facile methods to rearrange the microstructure of RO membranes, can effectively boost the water permeability but is constrained by the significant rejection loss. Here, we innovated an integrative approach whereby soluble organic macrocyclic cavitands (OMCs) with molecular-sieving open cavities were simultaneously dissolved in the activating solvent during membrane post-treatment such that their infiltration into the interfacially polymerized (IP) polyamide (PA) layer enabled the formation of a nanocomposite structure with recovered or even enhanced salt rejections. In this work, prefabricated polysulfone-supported pristine PA membranes were transformed into cavity-bearing nanocomposites after being treated with methanol solutions containing 4-sulfocalix[4]arene (SCA4), an OMC structure with a strongly size-sieving ∼ 3.0 Å cavity opening. This integrative solvent-cavitand treatment allowed their water permeability to increase by up to 129% from 1.98 to 4.53 Lm−2h−1bar−1 with uncompromised or even enhanced NaCl rejection, leading to overall separation performances that well surpassed the permeability-selectivity trade-off line. Meanwhile, these SCA4-infiltrated TFN membranes also demonstrated promising boron removal efficiency with an increase in both the water permeability and boron rejection from 1.95 to 4.17 Lm−2h−1bar−1 and 96.9% to 97.4% at pH = 10, respectively. With the wide array of solvent and soluble nanoarchitecture options, this study could provide a new and versatile direction in designing high-performance TFN membranes for environmentally important separations.

Polymer composites based on aromatic polyamide and fillers of spherical and layered structure for friction units of high-performance equipment

Without the employment of new equipment, with units functioning at high levels of weights, sliding speeds and temperatures, the current growth of the sector is all but impossible. High levels of labour intensity have a detrimental impact on the dependability and durability of the product. Moving joints, which comprise friction units, frequently fail at the same time. It is vital to increase their dependability and durability. This can be accomplished by substituting more recent materials with higher-quality qualities for the friction pair materials. To create such materials, the researchers created an aromatic polyamide polymer that was filled with silicon- (silica gel, bentonite) and carbon-containing (technical carbon, graphite) components. It was determined that depending on their nature, structure and content in the polymer matrix, the addition of these fillers enables the reduction of the coefficient of friction and wear of the produced polymer composites by 1.5–2.5 and 20–40 times, respectively, during frictional interaction with steel. It was found that 10–15% by weight of the examined fillers in aromatic polyamide is the ideal concentration. It has been proven that polymer composites filled with layered materials (bentonite, graphite) perform better in terms of tribological qualities when in contact with steel than those filled with spherical elements (technical carbon, silica gel). The improvement of the tribological properties of the developed polymer composites in comparison to the original polymer was determined based on the microphotographs of steel surfaces and the study of their morphological (roughness) and physical (microhardness) properties. It was determined that the change in the friction nature was due to the creation of an antifriction coating on the metal friction surface from the products of tribochemical reactions occurring during friction.