Fabrication of Polyamide-6 Membranes—The Effect of Gelation Time towards Their Morphological, Physical and Transport Properties (original) (raw)
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Materials Research, 2011
The membranes properties prepared from water/formic acid (FA)/ polyamide 66 (PA66) and water/hydrochloric acid (HCl)/polyamide 66 (PA 66) systems has been studied. The different solvents interact distinctly with the polymer, affecting the membrane morphology. The asymmetric structure of the membranes showed a dense top layer and a porous sublayer. The membranes M-HCl prepared from HCl/PA 66 system showed a larger dense layer (around 23 μm) in compared to those prepared from FA/PA 66 system (M-FA) (around 10 μm). The membrane morphology was a determinant factor in results of water absorption, porosity and pure water flux. The lower thickness of dense layer in M-FA membranes resulted in a higher water absorption and, consequently, porosity, approximately 50%, compared with M-HCl membranes, approximately 15%. The same trend was observed to permeate flux, the lower thickness of dense layer higher pure water flux.
Influence of thermal treatment on the pervaporation separation properties of polyamide-6 membranes
Separation and Purification Technology, 2000
Integrally-skinned asymmetric polyamide-6 membranes were prepared by casting 15 wt.% solution of polymer in 85 wt.% formic acid onto a glass plate and precipitation in water at 4°C. The obtained membranes were dried for 1 h at different temperatures ranging from 25 to 140°C in air and from 25 to 200°C in vacuum, respectively. The pervaporation separation properties of such treated membranes were studied with binary water-2-propanol mixtures consisting of 5 to 95 wt.% water. The membranes showed water permselectivity over a wide range of the feed composition. Thereby the water permselectivity reached a maximum at low water contents in the feed mixture. The selectivity was improved by thermal treatment of the membranes at temperatures above the glass transition temperature T g of polyamide-6 ( :60°C). However, the permeate flux decreased with increasing drying temperature due to the removal of entrapped water from amorphous domains, the formation of new crystalline domains and the decrease of the pore size and of the specific surface area during the thermal treatment. These effects were confirmed by dsc measurements, X-ray scattering experiments and BET measurements.
Polyamide-based composite membranes: Part 2. Interaction, crystallization and morphology
Desalination, 2008
In this work, the interaction, crystallization and morphology of membranes derived from polyamides/poly (vinylalcohol) (PA/PVA, PA: PA66, PA69, PA610 and PA612) blend materials are studied at various weight fractions and various crystallization temperatures. The experimental work includes differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM) and scanning clectron microscopy (SEM). The equilibrium melting temperatures of polyamides in the blends are obtained using Hoffman-Weeks plots, and the interaction parameters are calculated using the Nishi-Wang equation, which is based on the Flory-Huggins theory. The values of the Flory-Huggins interaction parameters χ 12 are negative. Significant upward shifts of ν NH are observed with increasing volume fraction of PVA. The morphology of membranes is impressively complex, diverse, and irregular. All compositions that show nodular morphology are in the µm-scale and the size of the nodules increases with increasing PA6 content. Large void cavities are observed in the substructure for the lower polymer concentrations.
Polyamide 66 membranes with PVP addition prepared by phase inversion
Desalination and Water Treatment, 2011
The membranes prepared from synthetic polymer are used worldwide in separation processes. Polymeric membranes from polyamide 66 (PA 66) in hydrochloric acid (HCl) at the concentrations of 10 and 15 wt.% were prepared by phase inversion method. Poly(vinyl pyrrolidone) (PVP) was used as the polymeric additive in the casting solution to improve the morphology and properties of the PA 66 membranes prepared. The membranes analyzed by Fourier transform infrared (FTIR), maintaining the same chemical structure of pure PA 66 membranes, indicating that the PVP was eliminated in nonsolvent bath. The determination of cloud point showed that PVP addition promotes a thermodynamic instability in the casting solution, reducing the time precipitation and infl uencing in the dense layer formation of the membrane. The scanning electron microscopy (SEM) showed that the PVP addition promoted a decrease in the thickness of dense layer and an increase in the percentage of the porous sublayer, greater uniformity of pores membrane. The pure water fl ux membranes with PVP addition was higher than in membranes of pure PA 66. The pure water fl ux increases from 1365 to 2590 l m -2 h -1 and from 66 to 362 l m -2 h -1 at the concentration of 10 and 15 wt.% of PA 66, respectively.
Chemical Industry and Chemical Engineering Quarterly, 2021
High-performance polymeric membrane technology is rapidly developing worldwide with the introduction of new materials and processes. Considerable research efforts are being made to establish a polymer membrane that can be used for ultrafiltration (UF) or nanofiltration (NF) applications. The development of modified polyamide-66 polymer and its compatibility in wastewater are essential elements in the quest for advances and improvements in membrane technology. The optimized conditions for membrane synthesis are critical in making it commercially viable. Response Surface Methodology (RSM) was used to find the optimum dissolution of polyamide-66 in formic acid. A model was developed and validated with experimental data, and it showed good agreement with R2 0.9984. The optimized condition for minimizing viscosity was determined. For minimum viscosity (3.64 cp), the optimum temperature and wt.% were 20 ?C and 0.6, respectively.
Effect of substituents on the permeation properties of polyamide membranes
Journal of Membrane Science, 2006
Aromatic polyamides, designed for evaluation as gas separation membranes, were processed into dense films, whose properties were measured with special emphasis on their mechanical and thermal properties. The polymers had been synthesized from monomers bearing side substituents, such as methyl, iso-propyl or tert-butyl, and various hinge-like connecting linkages of p-phenylene moieties, which yielded amorphous aromatic polyamides, with improved solubility, high glass transition temperatures (over 250 • C) and excellent mechanical properties (tensile strength about 100 MPa, and moduli about 2.0 GPa). The permeability of the polymer films were investigated using helium, oxygen, nitrogen, carbon dioxide and methane. Gas permeability typically increased with increasing free volume, and, in general, free volume could be related to the chemical structure. The analysis of the transport parameters (permeability, diffusivity and solubility coefficients) as a function of the chemical structure, confirmed the predominant role of the side substituents and of the linking groups connecting phenylene units on the permeation properties. Besides, a molecular modelling study carried out via computational chemistry, made it clear that an acceptable theoretical explanation can be given of how the nature of hinge groups between aromatic rings can affect torsional mobility and gas diffusion of aromatic polyamides.
Phase behavior and mechanism of membrane formation for polyimide/DMSO/water system
Journal of Membrane Science, 2001
A macrovoid-free, sponge-like porous membrane was prepared from polyimide/DMSO/water system, whereas a finger-like membrane was obtained from a polyimide/NMP/water system by phase inversion. The sponge-like membrane structure was investigated by the thermodynamics and kinetics of the phase separation process. The rates of phase separation for both systems were similar, but their phase diagrams were significantly different. The distinct features of the phase diagram for the polyimide/DMSO/water system are: (1) extremely narrow miscibility gap, (2) close gelation point to the binodal curve, and (3) almost parallel tie-line passing through the gelation point to the polymer-solvent axis. These properties hinder the phase separation process to proceed further, i.e. the growth of the polymer-lean phase is, thus frozen or stopped in the early stages. Therefore, the membrane morphology will be determined at an earlier stage in the polyimide/DMSO/water system than polyimide/NMP/water, resulting in a macrovoid-free, sponge-like membrane.
Desalination
The formation of polyamide thin film composite (TFC) membranes via interfacial polymerization (IP) of mphenylenediamine (MPD) in water with trimesoyl chloride (TMC) in hexane was studied. Parametric studies were conducted by varying reaction time, curing time and curing temperature. It is evident from the results that increasing the polymerization time results in decreasing the membrane surface roughness and increasing solid-liquid interfacial energy. Also with increasing the polymerization time, surface morphology changes from "nodular" and "leaf like" morphology to "hill and valley". The other involving parameters were the thin film thickness, which the results indicated that PA thin film thickness increased with polymerization time and moreover the acidic feature of PA film varied during polymerization process. Increasing polymerization time led to decreasing membrane water flux and increasing salt rejection since the PA layer became thicker and the extent of cross-linking increased. Also, it was shown that the curing conditions affect on membrane performance and with increasing curing time and temperature, salt rejection was increased and flux was decreased.
Structural Characterization of Thin-Film Polyamide Reverse Osmosis Membranes
Industrial & Engineering Chemistry Research, 2014
This study aims to explore the structural characteristics of the inhomogeneous top layer of thin-film composite membranes when pretreated by different methods: room temperature−oven, ethanol−hexane in a solvent exchange process, and freeze-drying. An evaluation of the nano-order free-volume pore size of the polyamide samples was carried out by nanopermporometry (NPP) and was quantitatively compared with the free-volume pore estimated from normalized Knudsenbased permeance (NKP) and with positron annihilation characterization (PALS). NPP results denoted a bimodal polyamide membrane structure described by a dense matrix and highly permeable regions. The application of different condensable vapors (water, hexane, and isopropanol) resulted in a free-volume pore size smaller than d p = 0.6 nm for dense regions, which was confirmed after NKP and PALS. In addition, the influence of highly permeable regions on permeance decreased in the following order: ethanol−hexane > freeze-drying > room temperature−oven samples, demonstrating an effective membrane structure alteration after different pretreatments.