Structure Of Polyamide Research Articles

Structure and Potential Applications of Polyamide 6/Protein Electro-spun Nano-fibrous Mats in Sorption of Metal Ions and Dyes from Industrial Effluents

The main objective of this work is the preparation of nano-fibrous mats (NFM) from polyamide 6 (PA6) reinforced and functionalized by renewable proteinic waste and examining their potential use for the sorption of heavy metal ions and dyes from wastewater from textile plants. Two renewable waste biopolymers; namely keratin (from waste of wool combing) and sericin (from degumming of natural silk) were extracted and regenerated. NFM were prepared by electro-spinning of PA6/ biopolymer composites in formic acid using nozzle-less electro-spinneret. The potential of the prepared mats for sorption of Cr+6, Cr+3, Cu+2, and Pb+2 cations as well as anionic and cationic dyes from wastewater was assessed. The prepared composites were characterized by measuring their viscosity, nano-fibre diameter, pore size, thickness, and air permeability. The morphological structure of the electro-spun NFM was investigated by scanning electron Microscopy. Chemical and physical properties of the obtained mat were studied FTIR, TGA, DSC, and XRD. The capacity of the prepared NFM for sorption of cations and dyes depended on the mat composition and the nature of the adsorbed cation or dye.
 This work meets some environmental and economic demand by extraction of keratin and sericin from waste materials and their utilization in reinforcement of PA6 NFM for sorption of selected cations as well as dyes from textile effluents.

Probing and relating the morphology, structure and performance evolution of low pressure RO membranes under chlorine exposure

The polyamide layer of reverse osmosis (RO) membrane is susceptible to chlorination degradation. Guidelines for validation and integrity monitoring of the low pressure RO (LERO) membrane morphology and performance upon chlorination is still rarely reported. In this study, we selected three commercial LERO membranes (i.e., LP, ULP and LCLE) to study their structure and separation performance change for exposing to chlorine under both pressurized and static chlorination conditions, with different active chlorine concentrations and pH. At the pressurized testing, the membrane water flux increased at the initial stage due to the decrease of water passage restriction by the destroy of the hydrogen bond in the polyamide, and then the water flux sharply decreased and gradually leveled off, which should be resulted from the destroy of chemical structure of polyamide and membrane compaction under high pressure. The salt rejection slightly changed, presumably due to the combination of tightening effect, compactness and defect plugging by foulants. As for the static chlorination test, active chlorine concentration and chlorination time were not unequivocalness at the same chlorination intensity. Higher active chlorine concentration could cause more serious chlorination degradation. Based on the water flux change at neutral pH and under static chlorination conditions, a flux reduction equation with active chlorine concentration was fitted by y = axb (1＜x＜1000), which could help us to predict the water flux under a specific chlorine concentration and time.

Pareto distribution in the system of polyamide particle clusters on the water surface

The present article considers a theoretical model of the formation of the Pareto distribution in a system of two-dimensional polyamide structures on the water surface. Complexes of polyamide granules collide with each other on the surface, moving in background liquid flows caused by random thermal gradients in the liquid bulk. Small complexes with a size of fractions of mm become organized into clusters with a complex structure and a size of a few cm under the action of surface tension forces. Numerical calculation taking into account the decomposition of large clusters provides power-law distribution of the density of complexes over their area. The results of the theoretical calculation are confirmed by the experimental data.

STUDY ON THE INFLUENCE OF ELECTRON BEAM ON THE PHYSICOCHEMICAL PROPERTIES OF POLYAMIDE 6

In this research work has been studied the effect of electron irradiation on the properties and structure of PA6 polyamide. The treatment was carried out with an industrial pulse accelerator in air with an irradiation dose in the range of 100-400 kGy. The processed polymer was also studied by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray phase analysis and differential scanning calorimetry. According to the results of the study was known that electron beam treatment affects the crystal structure of polyamide-PA6, reducing its size. Also, it was found that the radiation dose of 200 kGy is optimal for preserving the crystal structure in comparison with 100, 300 and 400 kGy.

In situ engineering of an ultrathin polyamphoteric layer on polyketone-based thin film composite forward osmosis membrane for comprehensive anti-fouling performance

Thin film composite (TFC) membranes easily suffer from fouling induced by oil and other pollutants during forward osmosis (FO) due to the relatively hydrophobic chemistry and rough structure of polyamide (PA). To achieve comprehensive anti-fouling properties, poly(2-methacryloyloxyethyl phosphorylcholine-co-2-aminoethyl methacrylate hydrochloride) (MPC-co-AEMA) was immobilized on top of a polyketone (PK)-based TFC membrane following a single-step simultaneous deposition with dopamine. The adhesive properties of polydopamine (PDA), as well as the covalent interactions between PDA and MPC-co-AEMA, ensured the firm immobilization of the MPC-co-AEMA on PA layer. As a result of the simultaneous deposition of PDA and MPC-co-AEMA, a high-performance and superhydrophilic and underwater superoleophobic TFC membrane was engineered. In addition, the outstanding water adsorption capacity of the polyamphoteric layer resulted in better protein adhesion mitigation. FO operation using various foulants also demonstrated a high fouling resistance of the PK-TFC-PDA/MPC membrane, especially during the treatment of wastewater emulsion containing high concentration of oil and bovine serum albumin (BSA). In summary, the findings in this study could provide insights into the preparation of anti-fouling membranes for wastewater purification using FO.

High permeability composite nanofiltration membrane assisted by introducing TpPa covalent organic frameworks interlayer with nanorods for desalination and NaCl/dye separation

• A TpPa layer with nanorods was prepared as an auxiliary interlayer. • TpPa interlayer played a decisive role for the formation of PA skin layer. • The PA/TpPa-12/PAN membrane showed excellent nanofiltration performance and NaCl/dyes selectivity. Nanofiltration (NF) membrane with high permeability and selectivity is extremely crucial for water purification. Herein, we prepared a high permeability thin-film nanofibrous composite (TFNC) membrane via interfacial polymerization (IP) technique assisted by introducing TpPa covalent organic frameworks (COFs) interlayer with nanorods on the polyacrylonitrile (PAN) nanofibrous substrate for NF. TpPa COFs interlayer with nanorods played a decisive role in adjusting the structure and performance of polyamide (PA) skin layer. On the one hand, TpPa COFs interlayer could regulate the diffusion and transfer rate of piperazine in the aqueous phase solution during IP process, which would modulate the mophology and reduce the thickness of the PA skin layer. Meanwhile, the TpPa COFs nanorods could create massive voids under PA layer to enhance the flux of TFNC membrane. Additionally, the TpPa COFs with nanoporous structure themselves also provided additional nanochannels for water transport. The structure of COFs interlayer could be tuned by altering the Pa contents of aqueous phase solution, which further optimized the overall performance. The permeation water flux of optimal TFNC membrane could reach to 104.8 L m −2 h −1 with a relatively high rejection of 98.4% for Na 2 SO 4 under 0.5 MPa, which was about 2.3 times than that of the unmodified PA membrane prepared without TpPa COFs interlayer. Besides, the optimal membrane exhibited good selectivity to NaCl/dye solution (NaCl/Acid Fuchsin was 402.5 and NaCl/Congo Red was 398.0) and long-term test stability. This work showed a new avenue to prepare high-performance NF membrane for the potential applications in water desalination and dye wastewater recovery.

The adsorption of aromatic macromolecules on graphene with entropy-tailored behavior and its utilization in exfoliating graphite

Aromatic macromolecules tend to form a compact conformation after physically adsorbed on graphene and it brings about great entropy loss for physisorption, due to the strong interaction between aromatic macromolecules and graphene. However, previous researches have validated the availability of aromatic macromolecules to stabilize graphene based on physisorption. In order to clarify the underlying mechanism of this physisorption process on graphene, a series of aromatic polyamide copolymers are used as models in this research. Apart from their adsorbed conformations on graphene, the conformations of these copolymers as the free states in diluted solutions are taken into consideration. Although these copolymers present the fully extended conformation on graphene, their conformations in diluted solutions vary largely with the copolymer composition. It is verified that the copolymer with smaller conformational change could have the better stabilization effectiveness for graphene, rather than the one having stronger interaction with graphene. Therefore, the entropy-tailored behavior for the adsorption of aromatic macromolecules on graphene is put forward. Based on this mechanism, the chemical structure of aromatic polyamide is optimized and furthermore it is utilized to directly exfoliate natural graphite flakes. Eventually, high-quality graphene nanosheets with a large dimension and low defects are obtained. Moreover, its exfoliating effectiveness is superior to those of the commonly used exfoliating agents nowadays.

Finely tuned polyamide structure with green plasticizers to construct ultrafast water channels for effective desalination

Highly permeable reverse osmosis (RO) membranes are desirable for alleviating the energy burden and ensuring future water sustainability. Herein, the effectiveness of green plasticizer-assisted interfacial polymerization (GPAIP) for preparing polyamide thin-film composite (TFC) RO membranes with significantly enhanced water permeability was demonstrated. The presence of green citrate plasticizers, namely tributyl citrate (TBC) or acetyl tributyl citrate (ATBC), led to the formation of new hydrogen bonds and inhibited the formation of the initial interchain amide-amide bonding, thus markedly reducing chain rigidity as demonstrated by the decreased elasticity modulus. More flexible polyamide chains resulted in the creation of more ultrafast water channels during filtration. Furthermore, TBC-modified membranes exhibited more elastic polyamide layers and higher water flux than that of ATBC-modified membranes on account of the presence of both hydrogen bond acceptors (OH) and hydrogen bond donors (C=O) in TBC molecules. Specifically, water flux of 0.6 wt% TBC-modified and 0.6 wt% ATBC-modified membranes was 83.6 L m−2 h−1 and 49.7 L m−2 h−1 respectively, more than 5 times and 3 times that of the pristine membrane. The excellent performance of TFC RO membranes fabricated via GPAIP together with the facile membrane manufacturing process offered the possibility of breaking the predicament in desalination field, which could eventually help ease the current freshwater crisis.

Relationship between crystalline structure of polyamide 6 within carbon fibers and their mechanical properties studied using Micro-Raman spectroscopy

We aim to determine the relationship between the local crystalline structure of polyamide 6 (PA6) within carbon fibers (CFs) and the mechanical properties of unidirectional CF-reinforced PA6 composites. Two types of CFs with different surface profiles (one smooth and one rough), used as reinforcements, were employed for the transverse Charpy impact test of unidirectional PA6/CF composites. The surface profile of CF influenced the impact strength and debonding appearance. The crystalline structure of PA6 within CFs was investigated using micro-Raman spectroscopy with a spatial resolution of 1 μm. Based on the Raman study, it was suggested that the impact strength and debonding appearance were attributed to the varying polymorphism (α-phase, mesomorphic β-phase, and γ-phase crystal) of the PA6 matrix between the interface and locations away from the interface (i.e., the bulk region), depending on the surface profiles of CF.

Strain-Induced Form Transition and Crystallization Behavior of the Transparent Polyamide.

A transparent polyamide, poly(4,4′-aminocyclohexyl methylene dodecanedicarboxylamide) (PAPACM12), was studied and characterized by in situ wide-angle X-ray diffraction (WAXD) to establish the relationship between its crystallization behavior, crystalline form transition under external fields, and macroscopic properties. During the heating process, cold crystallization occurred and increased, and there was no form transition below the melting point. During the isothermal process, PAPACM12 exhibited the same crystalline structure as that during the heating process. The crystalline structure of PAPACM12 was attributed to α-form crystal, which is the stable form, according to the WAXD diffraction peaks of the conventional AABB-type polyamides. During stretching deformation, the crystal transition from α-form to γ-form and strain-induced crystallization were observed to contribute to the PAPACM12 with higher breaking strength and elongation. This study firstly determine the crystalline structure of transparent polyamides, and then the controlled strain-induced crystallization and transformation are demonstrated to be effective preparation methods for polyamides with high properties.

Enhanced Water Permeability and Antifouling Property of Coffee-Ring-Textured Polyamide Membranes by In Situ Incorporation of a Zwitterionic Metal-Organic Framework.

Modulation of the polyamide structure is critically important for the reverse-osmosis performance of thin-film composite (TFC) membranes in the field of water reuse and desalination. Herein, zwitterionic nanoparticles of zeolitic imidazolate framework-8 (PZ@ZIF-8) were fabricated and incorporated into the polyamide active layer through the interfacial polymerization method. A hydrophilic, zwitterionic coffee-ring structure was formed on the surface of polyamide thin-film nanocomposite (TFN) membranes due to the adjusted diffusion rate of m-phenylenediamine (MPD) from the aqueous phase into the organic phase during the interfacial polymerization process. Surface characterization demonstrated that the coffee-ring structure increased the amounts of water transport channels on the membrane surface and the intrinsic pores of PZ@ZIF-8 maintained the salt rejection. Antifouling and bactericidal activities of TFN membranes were enhanced remarkably owing to the bacterial-"defending" and bacterial-"attacking" behaviors of hydrophilic and zwitterionic groups from PZ@ZIF-8 nanoparticles. This work would provide a promising method for the application of MOFs to enhance the bio-/organic-fouling resistance of TFN membranes with high water permeation and salt rejection.

The role of phase transfer catalysts on properties of polyamide thin-film composite forward osmosis membranes

In this article, 1,3,5-benzenetricarbonyl trichloride (TMC), m-phenylenediamine (MPD) and phase transfer catalysts (PTCs) were used to produce polyamide thin-film composite (TFC) forward osmosis (FO) membranes through interfacial polymerization (IP) reaction. The effects of dodecyl trimethyl ammonium chloride (DTAC), sodium dodecyl sulphate (SDS) and dodecyl dimethyl betaine (BS12) on the polyamide molecular aggregation structures, surface morphology and FO separation performance of the membranes were systematically investigated. In the FO process, concentrated 1.0 M NaCl aqueous solution was chosen as the draw solution and 0.1 M NaCl aqueous solution was used as the feed solution (at room temperature). Separation performance included the water flux (Jw) and reverse salt rejection (reverse solute flux, RS). The experiment proved that PTCs can regulate the molecular chain aggregation state and surface morphology of polyamide, which can lead to a relatively definite improvement in water flux (11.5 L m−2 h−1) (DTAC-polyamide). Simultaneously, the polyamide surface morphology was found to play a major role in the water permeability of the FO membrane rather than the density of the skin layer (i.e., degree of cross-linking), and we found that a relatively smooth surface is more conducive to weakening the external concentration polarization (ECP) phenomenon that occurs in the FO process. We attribute this mechanism on polyamide to the size effect and charge interaction of PTCs. In the current study, the balanced effect of the synergistic interaction of the molecular structure and rough surface of polyamide on FO separation performance should be comprehensively considered.

Experimental Characterization of Commercial and Synthesized Aromatic Polyamide Films for Reverse Osmosis Membranes

The complex structure of the active aromatic polyamide (APA) layer of reverse osmosis membranes needs to be precisely described for understanding and predicting solute rejection. A commercial rever...

Thermomechanical and sequential stress performance of photovoltaic backsheets

Photovoltaic backsheet technology is utilized to protect the interior components of solar modules from environmental stress as well as provide electrical insulation to the module. The growing demand for solar energy and longer module service life requirements have brought backsheet performance into focus. Despite being a protective packaging material, many backsheets have exhibited failure in the field, limiting the performance and service life of entire modules. Most backsheets consist of multiple polymeric layers laminated together using adhesives. A new backsheet, with a high performance polyamide structure, has been developed as the solution to module failure. Primarily, it contains a unique polyamide-ionomer alloy targeted at improved weather resistance. In this research, several photovoltaic industry standard backsheets, and the novel polyamide compositions of multilayered backsheets fabricated from the coextrusion process, were examined using thermomechanical analysis (TMA). The coefficient of thermal expansion (CTE) for entire backsheets and their constituent layers was used to model the thermomechanical behavior of various backsheet constructions. Subsequently, thermal cycling was performed in the TMA to examine the intrinsic thermal behavior of the backsheets. Thermal cycling in the TMA indicates the resilience and dimensional stability in the coextruded structures as opposed to the laminated structures. Lastly, results from a Module Accelerated Sequential Testing (MAST), are included to show the mechanical integrity of these backsheets after sequential exposure to stressors including damp heat, ultra-violet (UV) light radiation, and thermal cycling. The laminate backsheets deteriorated extensively after sequential exposure to these stressors, while the novel coextruded structures retained their physical properties.

Synthesis of a hyperbranched polyamide charring agent and its flame-retarding and toughening behavior in epoxy resin

A hyperbranched polyamide charring agent (HPCA) was synthesized by amidation of 1,2,3,4-butanetetracarboxylic acid and melamine, and its chemical structure was characterized. Such a charring agent, combined with ammonium polyphosphate (APP), was applied in epoxy resin. V-0 rating in the UL-94 vertical burning test and 32.3% of Limiting Oxygen Index were achieved with only 10% total flame retardant loading. A HPCA/APP ratio of 1/1 showed better flame retardant properties than the system with only HPCA or APP involved, indicating an apparent synergistic effect. The residual char at high temperature was analyzed by using FTIR and X-ray Photoelectron spectroscopy (XPS) to further explore the above synergistic mechanisms. Additionally, HPCA, as a co-curing agent, was grafted into the crosslinking net of epoxy resin due to the reactivity of carboxylic acids with epoxy group and hydroxyl group. The introduced hyperbranched polyamide structure effectively improved the toughness of original rigid crosslinking net of epoxy resin.

Influence of Polymer-Silicate Nucleator on the Structure and Properties of Polyamide 6

Physico-chemical properties of developed nickel-containing modified silicate materials as the nucleators for composites based on polyamide 6 are presented. As it was established, additive of the nucleator modified by polyvinylpyrrolidone promotes the increase of crystallinity degree of polyamide 6 and the decrease of crystallite size. It was found that changes in the structure of the material cause the increase of its tensile strength, surface hardness and Vicat softening point.

Study on crystal structure and phase transitions of polyamide 12 via wide-angle X-ray diffraction with variable temperature

Polyamide 12 (PA12) is a long carbon chain polyamide with plenty of excellent properties. In this work, PA12 samples were prepared in three ways: solution casting (α-crystal form at 30 °C and α + γ-crystal form at 40, 50, 60, and 80 °C, respectively), melt slow cooling (γ-crystal form), and melt quenching (γ-crystal form), which undergoes isothermal crystallization in the range from room temperature to the temperature close to the melting point. The crystallization behaviors, including the crystal transition, d-spacing, and crystallinity, upon heating and cooling were measured by the wide-angle X-ray diffraction (WAXD) from 30 to 235 °C. The results show that the α-crystal form gradually transforms into γ-crystal form during heating, indicating the occurrence of Brill transition. The γ-crystal form is stable below Tm, whereas the γ-crystal form can transform into γ-crystal form above 110 °C. Only γ-crystal form appears when cooling, and most of the crystallization has been completed before cooling to 170 °C. The investigation provides more theoretical supports of phase transitions in PA12 for deep understanding of the modification, optimization, and application.

New insights into tailoring polyamide structure for fabricating highly permeable reverse osmosis membranes

Herein, plasticizer-assisted interfacial polymerization was developed to fabricate thin-film composite (TFC) reverse osmosis (RO) membranes with improved water permeability and comparable salt selectivity. Three representative phthalate acid esters, including dimethyl phthalate (DMP), dibutyl phthalate (DBP), and dioctyl phthalate (DOP), served as the plasticizer. FTIR results revealed that the introduction of plasticizers disrupted original amide-amide bonding between polyamide chains, converting polyamide structure from stiff to flexible, thus significantly promoting water diffusion efficiency through the polyamide matrix. Besides, the presence of plasticizers led to the creation of more voids in the polyamide layer, where water transport resistance was relatively low. Specifically, with the addition of 0.6 wt% DMP, water flux enhanced from 19.1 L m−2 h−1 of the virgin membrane to 72.5 L m−2 h−1, with NaCl rejection declining from 99.3% to 98.3%. And 0.6 wt% DBP-modified membrane showed water flux of 44.0 L m−2 h−1 and NaCl rejection of 98.9%. It was interesting to discover that DOP possessed the poorest plasticizing capacity, which contradicted the traditional cognition that DOP is one of the most resultful plasticizers for polymers. We believed it was the sizable alkyl moieties in DOP that suppressed the interaction between DOP molecules and polyamide chains.

Mechanical Properties of Thermoplastic-Based Hybrid Laminates with Regard to Layer Structure and Metal Volume Content

Multi layered lightweight material compounds such as hybrid laminates are composed of different layers of materials like metals and unidirectional fibre-reinforced plastics and offer high specific strength. They can be individually tailored for applications like outer cover panels for aircraft and vehicles. Many characteristics especially layer structure, volume contents of the embedded materials as well as layer surface adhesion determine the performance of a hybrid laminate. In this study, the influence of layer structure and metal volume content are evaluated with regard to the mechanical properties of the recyclable hybrid laminate CAPAAL (carbon fibre-reinforced plastics/aluminium foil laminate), which consists of the aluminium alloy AA6082 and a graded structure of glass and carbon fibre-reinforced polyamide 6. Hybrid laminates with different ratios of the fibre-reinforced plastic and numbers of aluminium layers were manufactured by thermal pressing. The consolidation quality of in total four laminate structure variations, including 2/1 and 3/2 metal-to-fibre-reinforced plastic layer structures with fibre orientation variation, were investigated by light microscopy through cross-sections and further on computed tomography. For determination and evaluation of the mechanical properties metrologically instrumented quasi-static tensile and three-point bending tests, as well as tension-tension fatigue tests for the establishment of S-N curves were performed. The results were correlated to the microstructural observations, revealing significant influence by the consolidation quality. The layer structure proved to have a proportional impact on the increase of quasi-static tensile and flexure strength with a decrease in metal volume content. Orienting some of the fibre-reinforced plastic layers in ±45° leads to a more evenly distributed fibre alignment, which results in a higher consolidation quality and less anisotropic bending properties. Fatigue results showed a more complex behaviour where not only the metal volume content seems to determine the fatigue loading capability, but also the number of metal-fibre-reinforced plastic interfaces, hinting at the importance of stress distribution between layers and its longevity over fatigue life.

A Cellular Automata Approach for the Modeling of a Polyamide and Carbon Aerogel Structure and Its Properties.

In this work, a cellular automata (CA) approach was used to generate 3D structures of polyamide and carbon aerogels. Experimental results are used as initial data for materials’ digital representations and to verify the developed CA models. Based on the generated digital structures, a computer study of aerogels’ mechanical properties was conducted. The offered CA models can be applied for the development of new nanoporous materials such as aerogels of different nature and allow for a reduction in the amount of required full-scale experiments, consequently decreasing development time and costs of new material formulations.