Series Of Polyamides Research Articles

Long-term investigation on the daily variability of microplastic concentration and composition - Monitoring in the effluent of a wastewater treatment plant

The discharge of treated wastewater into receiving waters by wastewater treatment plants (WWTPs) is considered as one of the main pathways for microplastics (MPs) to enter the environment. To gain a better understanding of the temporal variability of MPs in WWTP effluents, this study investigated the concentration and composition (size, shape and polymer type) of MPs in the effluent of a German WWTP over the course of one month. 24-hour mixed samples were collected daily by a custom built automated sampling unit for MPs. Particles and fibers ≥11 μm were analyzed using Fourier transform infrared microspectroscopy. The MP concentration showed large daily fluctuations and ranged between 9.64 103 m−3 and 8.44 104 m−3 MPs over the study period. However, there was no significant correlation between the MP concentration and the precipitation or discharge from the WWTP. In contrast to the MP concentration, the MP composition in terms of size and shape was consistent over the study period. There were strong correlations between the time series of the polymer types polypropylene, polyethylene, polystyrene, polyester, ethylene-vinyl-acetate, cellulose artificially modified as well as the polymer cluster acrylates/polyurethanes/varnish. The time series of polyamide showed no significant correlation with the time series of any other polymer type. This study established a one month long high-resolution time series of MP concentration and composition, and thus provides a valuable basis for future research on the temporal variability of MP inputs into the environment from WWTP effluents.

Preparation of SiO2@EVA core–shell particles via post-emulsification method with polydisperse SiO2 particle sizes and the critical thickness-to-diameter ratio in PA6/SiO2@EVA system

Core-shell particles with rigid core and soft rubber shell have been proven to be effective in strengthening and toughening polymers simultaneously when the rubber shell thickness is controlled within a critical range. However, the critical value of the so-called thickness-to-diameter ratio τ (the ratio of the rubber shell thickness to the rigid core diameter) obtained in the previous work are all from polymer blends containing core–shell particles with monodispersed particle size. Does the critical τ value still exist in the core–shell toughening system with polydisperse particle sizes? Is it possible to produce core–shell particles with polydisperse particle sizes but the same τ value? In this paper, the post-emulsification method is first reported to prepare core–shell particles with polydisperse SiO2 particles as the rigid core and ethylene–vinyl acetate copolymer grafted maleic anhydride (EVA-g-MAH) as the rubber shell, in which the thickness of the rubber shell can be well controlled and tuned via varying the feeding weight ratio of SiO2 and EVA-g-MAH. The τ value is only determined by the weight ratio of SiO2 and rubber, and has nothing to do with the SiO2 particle size. A series of polyamide 6 (PA6)/SiO2@EVA core–shell toughening systems are prepared via melt blending process. It is proved the existence of the critical τ value (τcbd) above which brittle-ductile transition happens in the core–shell toughening system with polydisperse core–shell particle sizes. The value of τcbd is 0.069 in PA6/SiO2@EVA core–shell toughening system.

Improvement of mechanical and wear resistance property by varying glass fiber contents and amino-silicate coupling agents on polyamide 612 composites

Among the polyamide series polymer materials, PA612 has excellent mechanical properties and low moisture absorption characteristics. This work studied the effect of coupling agent addition on the crystallization behavior, adhesive wear, mechanical, thermal, and morphological attributes of glass fiber (GF) reinforced PA612 composites. Amino-silane was applied as a coupling agent to enhance the interfacial adhesion between glass fiber and the PA612 matrix. The loading level of the coupling agent was changed to 0.5, 1.0, and 2.0wt%, while the GF loading level in the composite material was 10, 15, 20, and 30wt%. The composite materials were analyzed via X-ray diffraction, tribological characterization, and adhesion wear test. The mechanical, rheological, and thermal properties were also investigated. In addition, scanning electron microscopy (SEM) analysis was used to study the analytical samples’ wear and fracture surfaces. Test results unveiled that adding 1.0wt% amino-silane coupling agent upgraded the fiber-matrix adhesion, mechanical properties (tensile strength:136 MPa), and corresponding wear resistance of GF reinforced PA612-based composites. Furthermore, it is compatible with pure PA612 substrates and has similar processing rheological behavior. These results reveal that the compiled PA612 matrix is highly viable for tribological applications comprising automotive parts, bearings, and bearing materials for space applications.

Antibacterial and desalting behavior of forward osmosis membranes engineered with metal ions

The current Covid-19 aggravates membrane biofouling issue caused by bacteria and viruses which are widely present in water. Herein we synthesized a series of polyamide (PA)-based membranes engineered with distinct metal ions (Cu2+, Fe3+) via one-step metal-ligand ligation for forward osmosis (FO) separation. The antibacterial and desalting behavior of membrane were investigated by systematically varying the influential factors including the charge status, complexation ability and antibacterial mechanism of metal ions as well as testing conditions. All the newly synthesized membranes exhibit better performance with markedly increased water permeability and selectivity. Therein the Fe3+ − membrane increases water fluxes by 93% (FO mode) and 112% (PRO mode) relative to the nascent PA membrane with 0.5 M NaCl as the draw solution. Both Cu2+ and Fe3+ on membrane surface dramatically improve the membrane bactericidal efficacy against Escherichia coli via destroying the bacterial phospholipid layer. Remarkably, the metal ions on membrane surface are easily regenerated after being consumed by bacteria by simply immersing the membranes into the corresponding nitrate solutions. The separation performance and antibacterial properties of the regenerated membranes are comparable to those of the fresh membranes. When using brine from reverse osmosis process as the draw solution, the Fe3+ membrane recovers water from brackish water up to 70% higher than the nascent PA membrane. This study provides a practical strategy to develop FO membrane with sustainable antibacterial activity and desalination performance.

Synthesis and characterization of trace aromatic copolyamide 6 with tunable mechanical and viscoelastic behavior

AbstractBis(6‐aminohexyl) terephthalamide/adipic acid (BAHT‐AA) was chosen to be used as a comonomer to develop a novel polyamide 6 (PA6) with the trace‐content aromatic structure. A series of polyamide 6 copolymers (coPA6) with trace BAHT‐AA loading were synthesized to yield the modified copolyamides with multiple interactions of hydrogen bonding and π‐π stacking on the PA6 backbone. It was proved that the thermal stability and mechanical properties of coPA6 were significantly enhanced because of the introduction of the trace BAHT‐AA segment. More importantly, adding a trace (1, 2, and 4 mole%) of BAHT‐AA could effectively increase the network structure and highly decrease the free volume fraction in the polymer system that is proved by the relaxation behavior and melt viscoelastic behavior. The results showed that the integrated performances of coPA6 were better than that of pure PA6, which was highly correlated with the aforementioned multiple interactions. For example, outstanding tensile strength (73.0 vs. 56.8 MPa), and modulus (1167 vs. 929 MPa), and so on. This work provided the traditional PA6 with the modification of outstanding mechanical and thermal performances, thus expanding its application for the plastics and textile industries.

Improved separation performance of polyamide based reverse osmosis membrane incorporated with poly(dopamine) coated carbon nanotubes

AbstractA series of polyamide thin‐film nanocomposite (PA TFN) membranes have been fabricated by incorporating hydrophilic poly(dopamine) (PDA) coated carbon nanotubes (CNTs@PDA) into the PA selective layer via interfacial polymerization. The effects of PDA coating thickness on surface characteristics and separation performances of membranes are studied in detail. The PDA coating makes the surface of PA TFN membrane more hydrophilic, smoother and less electronegative. The desalination performance is obviously influenced by the coating thickness of PDA and the loading concentration of PDA@CNTs. The water fluxes of PDA@CNTs incorporated PA TFN membranes have been improved without sacrificing NaCl rejections. When the loading concentration is 0.0010%, the maximum water flux is 48.1 L m−2 h increasing by 45% compared with that of pristine PA membrane. Meanwhile, the NaCl rejection is up to 99.8%. The CNTs@PDA incorporated PA TFN membranes exhibit better anti‐fouling property and separation performance durability. This work proves that CNTs@PDA has great potential application in PA TFN membranes.

Synthesis and Characterization of New Organosoluble and Thermally Stable Aromatic Polyamides Containing Flexible Ether, Ketone, and Methylene Linkages

AbstractA new aromatic diacid monomer, namely, 1,4‐phenylene‐bis‐[[4′‐(4″‐carboxy methylene) phenoxy phenyl] methanone] (PBCPPM) is successfully synthesized and characterized by physical constant, FT‐IR, NMR (1H and 13C) spectroscopy, and mass spectrometry. Synthesis of new series of polyamides with high thermal stability and improved solubility are performed by Yamazaki's direct phosphorylative polycondensation method from new PBCPPM with different aromatic diamines. The inherent viscosity of these polyamides is in the range 0.47–0.81 dL g−1. All these polyamides are amorphous or partly crystalline and reveal good solubility in polar aprotic solvents and exhibit glass transition temperatures between 201 and 232 °C. Initial decomposition temperatures are in the range 300–367 °C and T10 is in the range of 376–414 °C indicating good thermal stability of these polyamides. The present observations suggest that these polyamides can find potential applications as high performance polymers.

Triphenylamine based redox-active, fluorescent polyamides: synthesis and photophysics

An electroactive series of polyamides was synthesized from 4,4′-diamino-4′′-phenoxy triphenylamine (1), 4,4′-diamino-4′′-benzyloxy triphenylamine (2) and terephthaloyl or isophthaloyl chloride. The FTIR (Fourier Transform Infrared) spectral characterization and solubility test of the subsequent polyamides (PA I-IV), UV-vis, photoluminescence spectral analysis (PL) and cyclic voltammetry were utilized to assess photophysical and electrochemical properties of the materials. The oxidative-thermal stability of the polyamides as judged by thermogravimetric analysis was found to be in the range 438-532 °C with the char yield more than 53% at 800 °C. Introduction of aryloxy triphenylamine units along with polymer backbone flexibility improved the organosolubility of the synthesized polyamides (PA I-IV). The appreciable organosolubility of the (PA I-IV) is enough to be used in coating applications such as inkjet printing. Bluish green light emission from our synthesized materials upon excitation at 375 nm is credited to the triphenylamine linked amide-based polymer chain. Both pendent phenoxy and benzyloxy groups at para position in (PA I-IV) have also elevated the HOMO energy levels and hence lowered the onset oxidation potential. Additionally, the computational analysis was also conducted to get optimized ground-state geometry by DFT method (B3LYP) with 6-31G basis set. The 3-dimensional distributions of both HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of the polymers were obtained. The computational data of the polymers also augmented the experimental data suggesting their future use as redox-active materials.

Novel triphenylamine-based polyamides: Efficient preparation via benzoxazine-isocyanide-chemistry at room temperature and electrochromic properties investigation

A type of novel triphenylamine (TPA)-based diisocyanide derivative, 4-isocyano-N-(4-isocyanophenyl)-N-(4-methoxyphenyl)aniline (M1), was successfully synthesized via Hofmann treatment of its primary amine precursor (2). A series of polyamides (P1–P3), which containing TPA units in backbones, were successfully synthesized via efficient benzoxazine-isocyanide-chemistry (BIC) at room temperature by using M1 and bifunctional benzoxazines as starting monomers. Chemical structures of P1–P3 were verified by FT-IR, 1H NMR and gel permeation chromatography (GPC) analyses. Polymers’ films were prepared by solution coating (using DMSO as solvent), and electrochemical properties of P1–P3 were investigated by cyclic voltammetry (CV). P1–P3 exhibited single-step highly reversible oxidation process, reflecting their good electrochemical activity. Electrochromic properties of polymers were further analyzed by spectroelectrochemical techniques. New absorption bands at ~750 nm appeared in UV–vis spectra of P1–P3 when the applied voltage reached ~0.65 V, accompanied by the obvious visual color change (from colorless to blue-green). Response time and coloration efficiency of P1–P3 were also investigated here. The work carried out in this study proved that BIC can act as powerful tool to construct novel functional polyamides.

Polyamide 66 and amino-functionalized multi-walled carbon nanotube composites and their melt-spun fibers

A series of polyamide 66 (PA66) and multi-walled carbon nanotube (MWNT) composites were condensed using amino-functionalized MWNTs (AMWNTs), hexanediamine adipate salts, and adipic acid as raw materials. The covalent grafting of maleic acid diamine onto the surfaces of the MWNTs by a Diels–Alder reaction prevented the AMWNTs from suffering entanglement, and facilitated excellent dispersion of AMWNTs in the PA66 matrix. Analyses revealed not only that the AMWNTs are uniformly dispersed in the PA66 matrix, but also that a strong interfacial interaction exists between the AMWNTs and the matrix. An AMWNT loading of only 0.5 wt% ensured a maximum dispersibility of AMWNTs in the PA66 matrix, which was far better than that of MWNTs. Additionally, the crystallization and melting behavior of PA66/AMWNT (PACNT) composite fibers were characterized. Finally, mechanical testing results demonstrated that the Young’s modulus and tensile strength of the composite fiber with 0.5 wt% AMWNT loading were increased by about 384% and 140%, respectively, compared with those of the pure PA66 fiber. Therefore, the proposed PACNT composite fibers are promising for high-performance applications.

Structural and Kinetic Profiling of Allosteric Modulation of Duplex DNA Induced by DNA-Binding Polyamide Analogues.

A combined structural and quantitative biophysical profile of the DNA binding affinity, kinetics and sequence‐selectivity of hairpin polyamide analogues is described. DNA duplexes containing either target polyamide binding sites or mismatch sequences are immobilized on a microelectrode surface. Quantitation of the DNA binding profile of polyamides containing N‐terminal 1‐alkylimidazole (Im) units exhibit picomolar binding affinities for their target sequences, whereas 5‐alkylthiazole (Nt) units are an order of magnitude lower (low nanomolar). Comparative NMR structural analyses of the polyamide series shows that the steric bulk distal to the DNA‐binding face of the hairpin iPr‐Nt polyamide plays an influential role in the allosteric modulation of the overall DNA duplex structure. This combined kinetic and structural study provides a foundation to develop next‐generation hairpin designs where the DNA‐binding profile of polyamides is reconciled with their physicochemical properties.

Synthesis and properties of polyamides from 2,5‐furandicarboxylic acid

ABSTRACTThe aim of this study is to investigate the synthesis of 2,5‐furandicarboxylic acid (FDCA)‐based copolyamides. Indeed, FDCA monomer may be a potential bio‐based alternative to phthalic acids. A series of polyamides and copolyamides, PA 6‐I(x)/6‐F(y), are synthesized in a pilot scale reactor by melt polycondensation of salts based on FDCA, isophthalic acid (IPA), and 1,6‐hexamethylenediamine. The chemical structure and composition of the resulting copolymers are extensively characterized by NMR (1H, 13C, and 2D), MALDI‐TOF as well as size exclusion chromatography and solution viscosimetry. Their thermal properties are studied by differential scanning calorimetry and TGA and also by a molecular modeling technique. It is pointed out that, during the synthesis, FDCA‐rich polymers overcome a massive decarboxylation of FDCA, preventing the production of high molar mass polymers. It is also found that all polymers are amorphous and that the glass transition temperatures decrease as the amount of FDCA in the polymer increases. This is confirmed by the results from molecular dynamics. In addition, it is observed that the copolymers become more hygroscopic when the amount of FDCA in the copolyamides increases. However, the water uptake of PA 6‐I(x)/6‐F(y) with 90 > x > 50 is lower than those of PA6 and PA 66 polyamides. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45901.

Synthesis and Electrochromism of Highly Organosoluble Polyamides and Polyimides with Bulky Trityl-Substituted Triphenylamine Units.

Two series of polyamides and polyimides containing bulky trityl-substituted triphenylamine units were synthesized from condensation reactions of 4,4′-diamino-4′′-trityltriphenylamine with various dicarboxylic acids and tetracarboxylic dianhydrides, respectively. The polymers showed good solubility and film-forming ability. Flexible or robust films could be readily obtained via solution-casting. The use of aliphatic diacid or dianhydride reduces interchain charge transfer complexing and leads to colorless polyamide and polyimide films. These polymers showed glass-transition temperatures in the range of 206–336 °C. Cyclic voltammograms of the polyamide and polyimide films displayed reversible electrochemical oxidation processes in the range of 0–1.0 or 0–1.3 V. Upon oxidation, the color of polymer films changes from colorless to blue-green or blue. As compared to the polyimide counterparts, the polyamides showed lower oxidation potentials and thus a higher electrochromic stability and coloration efficiency. Simple electrochromic devices were also fabricated as a preliminary investigation for electrochromic applications of the prepared polymers.

Electrical, morphological and thermal properties of microinjection molded polyamide 6/multi-walled carbon nanotubes nanocomposites

A series of polyamide 6/multi-walled carbon nanotubes (PA6/CNT) nanocomposites were prepared using a masterbatch dilution process, followed by microinjection molding of a part with a three-step decrease in thickness along the flow direction. Morphology observations revealed that there was a preferential orientation of CNT in the flow direction, which is attributed to the prevailing high shear rates in µIM. The distribution of CNT after melt processing was evaluated by dissolving experiments. Additionally, the correlation between electrical resistivity and development of microstructure for each section of the microparts was considered. The thermal behavior of PA6/CNT nanocomposites and corresponding microparts was evaluated using differential scanning calorimetry. Results indicated that the addition of CNT had little effect on the melting behavior of PA6/CNT nanocomposites and corresponding microparts. However, the crystallization behavior was changed significantly and a double crystallization peak was observed for samples incorporating CNT.

Polyamides based on a partially bio-based spirodiamine

In this study novel, fully and partially bio-based polyamides containing spiroacetal moieties in the backbone derived from bio-glycerol and bio-ethanol were prepared and characterized. The renewable diamine employed to obtain a series of polyamides was synthesized by means of thiol-ene click chemistry and therefore contains flexible thioether as well as rigid spiroacetal moieties. Two different chemical pathways for the polymerization were investigated and evaluated. The polymerization of polyamide salts proved to be the most promising method and therefore salt polymerization was applied in the synthesis of polyamides with aliphatic and aromatic dicarboxylic acids. Subsequently, the structure of the polymers was confirmed by Maldi-ToF analysis and additionally thermal and mechanical properties were investigated revealing Tg’s between 24 and 80°C and ductile materials with moduli between 1.0 and 1.5GPa. Both semicrystalline and amorphous polyamides were thermally stable and therefore suitable for thermal processing. In the end, degradation studies were performed on the acetal containing polyamides which showed that the polymers were stable at pH 3 and higher.

New Polymer Syntheses Part 59. Synthesis and Characterization of New Polyamides and Copolyamides Containing Thianthrene Moiety and Based on Methyl- and/or Tertiarybutyl-Cyclohexanone in the Main Chain

Two new series of polyamides and copolyamides based on methyl-cyclohexanone and tertiary-butyl-cyclohexanone in the main chain were synthesized via the solution polymerization of 2,6-bis(m-aminobenzylidene)-methylcyclohex-anone VI, 2,6-bis(m-aminobenzylidene)tertiary-butyl-cyclohexanone VIII, and its copolyamides with p-phenylene diamines and m-phenylene diamines with diacid chlorides of thianthrene (2,7-Dichloroformylthianthrene-5,5`,10,10`-tetraoxide IV. These polyamides and copolymides ranged from yellow to orange color and had inherent viscosity up to 0.35-0.89 dL/g. All the polyamides and copolymides were insoluble in common organic solvents but dissolved completely in concentrated H2SO4. The thermal stabilities of the prepared polyamides were evaluated by TGA and DTG analyses. X– ray analysis showed these polymers having low degree of crystallinity in the region 2q = 5 – 60°. The morphological properties of some selected polyamides were detected by SEM.

About the use of IDENTIFY—a thermoanalytical database—for characterization and classification of recycled polyamides

For some spectroscopic measurement techniques such as mass spectrometry or Fourier transform infrared spectroscopy, online libraries have long been established. Those software-based libraries allow for comparisons of the measurement data with spectra collections archived in databases. Comparing own measurement values with literature or textbook data is an established procedure for the correct interpretation and final evaluation of the results obtained. In the field of thermal analysis, however, such library comparisons have been sorely lacking so far. This work presents the use of IDENTIFY for identification of polymers and also for classification of samples within a quality control procedure. A series of polyamides are therefore investigated using differential scanning calorimetry.

Synthesis and Characterization of New Polyamides Containing Thianthrene Moiety and Based on Dibenzylidene Derivatives

A new series of polyamides based on diarylidene derivatives were synthesized from 2,5bis(m-aminobenzylidene)cyclopentanone VIII, 2,6-bis(maminobenzylidene)cyclohexanone IX, 2,7-bis(m-aminobenzylidene) cyclheptanone X and bis(m-aminobenzylidene) acetone XI by reaction with diacid chlorides of thianthrene (2,7Dichloroformylthianthrene -5,5`,10,10`-tetraoxide IV. using solution polycondensation technique. These polymers ranged from yellow to orange color and had inherent viscosity up to 1.08-0.65 dL/g. All the polyamides were insoluble in common organic solvents but dissolved completely in concentrated H2SO4. The thermal stabilities of the prepared polyamides were evaluated by TGA and DSC analyses. The morphological properties of some selected polyamides were detected by SEM.

Synthesis, characterization, and biological activities of organosoluble and thermally stable xanthone-based polyamides

A series of polyamides, poly (xanthone-amide)s (PXAs) were prepared by direct polycondensation of 2,7-diaminoxanthone with various available aliphatic and aromatic dicarboxylic acids. The monomer and all the PXAs were characterized by FT-IR, 1H NMR and 13C NMR. The prepared polyamides showed inherent viscosities in the range of 0.41–0.68 dL g−1 in NMP at 25 °C. The PXAs with low crystallinity were soluble in aprotic polar solvents such as DMF, NMP, DMSO, and DMAc at room temperature. These PXAs showed low glass transition temperatures (T g) (200–310 °C) and high thermal stability, the 10 % weight loss temperature was up to 432 °C under nitrogen. These polymers exhibited strong UV–Vis absorption maxima at 301–316 nm in NMP solutions. Their photoluminescence showed fluorescence emission maxima around 433–444 and 503–521 nm for aliphatic and aromatic polyamides, respectively. The resulting polymers were analyzed for their antioxidant activities using DPPH assay and the antibacterial activities against some bacterial strains (S. aureus, B. subtilis, E. coli and P. aeruginosa). The results revealed that the antioxidant and antibacterial activities of PXAs were more than xanthone nucleus and used standard, respectively. It showed that these polymers can be used in pharmaceutical and food industries (food packaging).

Synthesis and Investigation of Transition Metal Removing of Novel Thermally Stable Polyamides bearing Calix[4]arene in their Backbones

A series of polyamides having calix[4]arene units in the backbone which are called polycalixamides were prepared by direct polycondensation of dicarboxylic acid derivative of calix[4]arene with commercial diamines. The polycalixamides were obtained in high yields and possessed inherent viscosities of 0.42–0.55 dl/g and glass transition temperatures between 145 and 172°C. These polycalixamides were amorphous and therefore readily soluble in polar aprotic solvents such as NMP, DMSO, DMAc and THF. According to thermogravimetric analysis, these polymer series displayed high thermal stability ranged from 330 to 353°C at the point of 10% weight loss and char yields between 40.7–58% at 700°C in nitrogen. The temperature of maximum decomposition applied in DTG curves of polymers were among 326 to 369°C. The photophysical study was performed by UV-absorption spectroscopy and maximum wavelength for each polymer specified in details. It is found that these polyamides were highly efficient for sorption of Cu2+, Cr2+, Co2+ and Cd2+ in solid-liquid extraction.