Influence of triphenylphosphonium pendant groups on the rheological and morphological properties of new quaternized polysulfone

A new quaternized polysulfone with triphenylphosphonium pendant groups was synthesized by reacting chloromethylated polysulfone with triphenylphosphine. The molecular restructurations, generated by hydrogen bonding, electrostatic interactions, and association phenomena in ternary quaternized polysulfone/N,N‐dimethylformamide (solvent)/water (nonsolvent) systems, were evaluated by rheological investigations. The polyelectrolyte effect, induced by enhanced dissociation of the ionizable groups and by mixed solvents' quality, modify the rheological functions, that is, dynamic viscosity, elastic shear modulus, and viscous shear modulus, as well as the thermodynamic parameters obtained from the rheological properties, such as apparent activation energy. These results were correlated with the morphological properties of the films obtained from solutions in solvent/nonsolvent mixtures and compared with other quaternized polysulfones, having different hydrophobic characteristics. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Controllable morphology and wettability of polymer microspheres prepared by nonsolvent assisted electrospraying

Polymethylmethacrylate (PMMA) microspheres with various morphologies are fabricated by nonsolvent assisted electrospraying. The morphology evolution is determined by nonsolvent properties including the solubility parameter, surface tension and viscosity, and nonsolvent induced phase separation is the main reason for the formation of the porous and/or hollow structures. It is found that nonsolvent possessing a high surface tension is beneficial to the formation of a hollow structure, while the large phase separation tendency between nonsolvent and the polymer can promote pore generation on the sphere surface. The nanosized pores, especially hierarchical pores, can enhance the hydrophobicity of the substrate surface coated with these microspheres. On the other hand, nonsolvent with a large viscosity could prevent the growth of the phase separated nuclei, leading to the presence of relatively small and discontinuous pores on the microsphere surface, which can finally cause the decrease of the contact angles. The surface pores of the electrosprayed microspheres are even eliminated if polymer additive, i.e., PVP, is incorporated into the polymer-solvent-nonsolvent solution. The addition of PVP renders the microsphere coated surface hydrophilic, which can be completely wetted by water droplets.     

Fractional turbidimetric analysis of the molar substitution of hydroxyethyl cellulose

High quality packaging films from hydroxyethyl cellulose of low degree of substitution (DS) are being produced commercially in this country and abroad. Increasing demand for this and a variety of other applications requires a rapid and simple production control method for determining hydroxyethyl substitution of cellulose. None of the known analytical methods fulfills these requirements. The present paper describes a method which is based on the relationship between the solubility and the molar hydroxyethyl substitution of hydroxyethyl cellulose. A washed and dried sample of hydroxyethyl cellulose is dissolved in 7% aqueous sodium hydroxide. Methyl alcohol, a nonsolvent, is used to precipitate a fraction of the sample. The turbidity of the equilibrium system is determined and optical density readings are related to molar substitution. The method is most useful in low DS ranges of 2–8% EtO but is susceptile to broader application through adjustment of the composition of the solvent–nonsolvent mixture. Relatively large variations in DP can be tolerated. The molar substitution level of an hydroxyethyl cellulose sample can be obtained in 40 min. by this method, making it a practical production control technique.     

EFFECT OF NONSOLVENT ADDITIVES ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF AROMATIC POLYAMIDE RO MEMBRANES

In this paper discussions are made on the effect of nonsolvent swelling agents on the average pore size and pore size distributions at the surface of polyamide membranes which result from casting solutions involving above nonsolvent swelling agents.

The size of the polymer aggregate in the film casting solution and the size of polymer network pores are correlated to physicochemical data of ions which constitute the electrolytes used as nonsolvent swelling agents. As such ionic properties the charge density and the free energy of transition of ions from polyamide phase to water phase were considered. The validity of the correlation is limited in a range of casting solution composition where the polymer concentration in the casting solution is close to the limiting concentration of polymer at the phase boundary and the molar ratio of the nonsolvent swelling agent to the amide group involved in the polyamide polymer is equal to or slightly more than 0.7.     

Surface properties and antibacterial activity of quaternized polysulfones

Novel quaternized polysulfones (PSFs) with two ionic chlorine contents were investigated, namely, their morphology and antimicrobial activity. Atomic force microscopy (AFM) studies on their membranes showed ordered domains, in which pores and nodules of different sizes and intensities were distributed. The charge density of the quaternized PSFs and the history of the membranes formed from solutions in solvent/nonsolvent mixtures influenced the different aspects of the surface images. The adhesion of Escherichia coli ATCC 10536 and Staphylococcus aureus ATCCC 6538 microorganisms to solutions of the modified PSFs is discussed in correlation with the hydrophobic/hydrophilic properties of the studied polymers and microorganisms. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Solubility and phase separation of poly(L,D‐lactide) copolymers

In this study, the solubility and precipitation properties of medical‐grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D ‐lactide) stereocopolymers was highly dependent on the L /D ratio of the copolymer. The phase‐separation ability was tested by cloud‐point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n‐hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n‐hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L /D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A model study for the recovery of polymides using the dissolution/reprecipitation technique

A model dissolution/reprecipitation process is studied for the recycling of both poly?‐caprolactam (PA 6) and polyhexamethyleneadipamide (PA 6 6). This process comprises dissolution of each of the aforementioned polyamides in an appropriate solvent, reprecipitation by addition of a nonsolvent and finally recovery of the polymers through washing and drying. Dimethylsulfoxide/methyl‐ethyl‐ketone (DMSO/ MEK) proved to be the most suitable solvent/nonsolvent system for the recovery of PA 6, while formic acid/methyl‐ethyl‐ketone was used as a potential pair of solvent/ nonsolvent in the case of recovering PA 6 6. The recycled polyamides were evaluated in terms of the following characteristic properies: molecular weight (based on end‐group analysis and intrinsic viscosity determination), crystallinity and grain size analysis. In all cases, the recycled materials present excellent retention of the properties studied. Finally, the solvent mixtures involved are separated by distillation for reuse.     

Novel surface modifying macromolecules (SMMs) blended polysulfone gas separation membranes by phase inversion technique

In this article an attempt was made to fabricate defect‐free asymmetric polysulfone (PSf) membranes for the separation of oxygen and nitrogen. The approach is based on the enhanced delayed demixing by blending surface modifying macromolecules (SMMs) in the casting solution and by immersing the cast film in isopropanol for a certain period before it is immersed in water. Different SMMs, including hydrophobic and charged SMMs, were synthesized, characterized, and blended to the host PSf. It was found that the charged SMM could indeed contribute to the removal of defective pores from the skin layer and enhancement of oxygen/nitrogen selectivity. The experimental results were further interpreted based on the shift of the phase boundary line on the polymer/solvent/nonsolvent triangular diagram, which occurred when SMMs were blended to PSf, due to the change in the polymer/nonsolvent interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Insulating rigid polyurethane foams from laurel tree pruning based polyol

The present work deals with the production of a natural polyol from laurel tree pruning waste, aiming the preparation of polyurethane foams. The obtained bio-polyol was characterized and applied into foams studying the influence of the isocyanate used and the addition of the physical blowing agent. The incorporation of the polyol allowed 40% polyol substitution for those foams in which TDI was used, and up to 60% using MDI. Apparent density, cell morphology, mechanical, and thermal properties were evaluated. Mechanical and thermal properties of the foams improve to a greater amount of polyol in the matrix. Specifically, the best thermal and mechanical properties (274.99 and 7275.91 kPa for compressive strength and Young Modulus, respectively) were obtained with 50% polyol substitution (0.63 R_NCO/OH). Foams showed small, well-defined cell morphology. Laurel derived polyol can be used for the preparation of foams using MDI, since the mechanical, and thermal properties are promising for obtaining insulation materials in the construction industry.     

High-modulus fibres of nylon-6 prepared by a dry-spinning method

Nylon-6 filaments with tensile strengths at break up to 1 GPa and initial moduli in the range of 16 to 19 GPa have been produced by dry-spinning of solutions of nylon-6 in cosolvent mixtures of formic acid and chloroform followed by hot-drawing at 200°C–240°C. Tensile strengths and elastic moduli of the nylon-6 fibres were strongly dependent on the draw ratio, on the molecular weight of the polymer, on the polymer concentration in the spinning solution and on concentration of nonsolvent in the spinning solution. At high concentrations of nonsolvent in the spinning solution, the as-spun fibres of nylon-6 were composed of ball-like structural units, formed possibly due to the liquid-liquid phase separation in the polymer/solvent/nonsolvent ternary system. Formation of ball-like structures reduced the ultimate mechanical properties of hot-drawn fibres of nylon-6.     

Characterization of the curing process of vinyl plastisols with epoxidized linseed oil as a natural‐based plasticizer

In this work, we have evaluated the curing process of a natural‐based plasticizer, epoxidized linseed oil, as a possible alternative to phthalate substitution for polyvinyl chloride. Several curing times ranging from 6 to 14 min at different isothermal curing temperatures in the 140–220°C range have been selected. The effects of the curing process (in terms of time and temperature) have been determined by mechanical tests, color measurements, and microstructure characterization. The obtained results show that optimum overall properties are obtained for curing times of 10–12 min at 200°C or 8 min at 220°C, which are typical values of industrial processing of vinyl plastisols. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Designing index of void structure and tensile properties in wet‐spun polyacrylonitrile (PAN) fiber. I. Effect of dope polymer or nonsolvent concentration

An index Xη^?1 with numerator calculated solely from solubility parameters and denominator measured by on‐line viscosity of the fiber precursor in coagulation medium was defined as an indicator of the fiber structure and tensile properties. The Xη^?1 values of wet‐spun and wound polyacrylonitrile fibers from their dimethylformamide solutions with different polymer concentrations (series A) or nonsolvent concentrations in 10 vol % polymer solutions (series B) into water with draw ratio of one were determined and compared with the corresponding fiber structure and tensile properties. The Xη^?1 value of about 0.8 × 10⁶ s^?1 led to finger‐like structure with overall fiber porosity of 82 vol %. By reducing Xη^?1 through dope polymer concentration enhancement to 20 vol %, overall fiber porosity decreased to 62 vol % via substitution of some micrometer voids with dense polymer ligament. Accordingly, strong fiber modulus and elongation at break enhancement were observed due to structural defect reduction and cohesive energy density increment. On the other hand, dope nonsolvent concentration increment from 0 to 5 vol % at 10 vol % polymer concentration showed minute overall fiber porosity decrement via Xη^?1 increment through micrometer void substitution with nanometer ones (nuclei). Therefore, mild fiber modulus and elongation at break improvements were detected due to defect size reduction which magnifies mechanical properties improvements. Curve fitting of the Wang's second order modulus‐porosity correlation to the as‐spun fibers modulus‐porosity data verified the solid–liquid phase separation through nuclei growth‐resistance as the main governing morphological evolution mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrogels of starch/carboxymethyl cellulose crosslinked with sodium trimetaphosphate via reactive extrusion

Hydrogels are materials with advantages in specific applications, such as, retention of food active compounds. This work aims to develop starch (S)/carboxymethyl cellulose (CMC) hydrogels with porous structure, using reactive extrusion to promote crosslinking with sodium trimetaphosphate (STMP). The expansion, porosity, degree of substitution, gel fraction, swelling properties, and FTIR are studied, comparing S, S/CMC, S/STMP, and S/CMC/STMP formulations. Samples containing STMP present the same degree of substitution (0.050 ± 0.001). Higher porosity and percentage of open pores are observed in the mixed hydrogel (S/CMC/STMP). Crosslinking increase the swelling capacity at pH 7, and this property, just like the gel fraction, are sensitive to pH variations. The hydrogel S/CMC present the highest swelling rate compared with the other samples, suggesting strong interaction between components. The reactive extrusion process is efficient to produce starch and starch/CMC hydrogels crosslinked with STMP and the overall results demonstrate the advantages of the mixed hydrogel.     

Synthesis of N‐benzyl‐O‐carboxymethylchitosan and application in the solubilization enhancement of a poorly water‐soluble drug (triamcinolone)

N‐Benzyl‐O‐carboxymethyl chitosan (OCChB) was synthesized through a reaction of O‐carboxymethylchitosan (OCCh) and benzaldehyde by the reductive amination method. The chemical structures and physical properties of the derivatives were confirmed by Fourier transform infrared spectroscopy and ¹H‐NMR. The cytotoxicity of the polymers was tested by MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyltetrazolium bromide) assay at concentrations ranging from 0.01 to 1000 μg/mL. The substitution degrees of the derivatives, calculated by ¹H‐NMR, were 12 and 53% for OCChB1 and OCChB2, respectively. The results show that the derivatives were not toxic at 1000 μg/mL and could decrease the surface tension by concentration on the system surface compared with OCCh. Because of this property, OCChB was applied as a solubility enhancer for triamcinolone (TC), a poorly water‐soluble drug. The polymer solutions at 1.0 mg/mL increased the TC solubility up to 3.5 times for OCChB1 and 5.0 times for OCChB2 compared with its solubility in water. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An imidazolium‐functionalized isobutylene polymer having improved mechanical and barrier properties: Synthesis and characterization

Brominated poly(isobutylene‐co‐p‐methylstyrene) (BIMS) is of great use to industries because of its extremely good permeability properties. However, it lacks strength and adhesion necessary to make it amenable to various processing techniques. To overcome the limitations of BIMS, ionic modification via nucleophilic substitution of bromine by 1‐methylimidazole through a facile synthetic route is presented. The modified ionic product was characterized by various techniques such as solubility, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis, and dynamic mechanical analysis. The FTIR spectrum of the obtained samples showed a distinct peak around 1261 cm^?1 corresponding to C? N stretching vibration and reduction in peak intensity around 695 cm^?1 corresponding to C? Br stretching vibration. NMR also clearly showed the occurrence of a singlet peak corresponding to the methyl protons of imidazole in the region of 4.1 ppm and a shift in the methylene protons adjacent to the benzene ring confirming the substitution of bromine atom by imidazole ring. The reaction at reflux temperature of 130°C for 48 h yielded the highest level (3.1 wt %, 1.18 mol %) of modification while optimizing the reaction parameters. The modified ionic polymers displayed greater thermal stability, greater flexibility, improved tensile strength, and higher barrier properties compared to the unmodified BIMS. A 1.8‐fold increase of elongation at break was achieved with 1.18 mol % (3.1 wt %) of modification. The modified polymers also showed remarkable drop in oxygen transmission rate values from 10^?16 to 10^?18 m³ m/m²/s/Pa, which further highlights their improved properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structure Formation of Integral Asymmetric Composite Membranes of Polystyrene‐block‐Poly(2‐vinylpyridine) on a Nonwoven

The formation of an integral asymmetric membrane composed of a cylinder‐forming polystyrene‐block‐poly(2‐vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time. The influence of parameters such as solvent composition, evaporation time of the solution‐cast block copolymer film before phase inversion, and immersion bath temperature is demonstrated. The optimized membranes are characterized in terms of stimuli‐responsive water flux properties. The morphologies of the membranes as well as of the bulk of the block copolymer are imaged by scanning force microscopy, scanning electron microscopy, and transmission electron microscopy.

     

Polylactide. II. Discontinuous dry spinning–hot drawing preparation of fibers

The mechanical properties and morphology of poly(L-lactide) fibers, prepared by the dry spinning–hot drawing process using different nonsolvent/chloroform spinning solutions, were studied in relation to fiber in vitro degradability. Acetone, methanol, ethanol, and cyclohexane were used as nonsolvents in the spinning mixture with as-polymerized PLLA, i.e., PLLA containing 10% of residual L-lactide. The tensile strength, structure, and degradability of obtained fibers were mainly governed by the nonsolvent volatility. Generally, the higher the volatility, the higher the strength, and the faster the degradation. The acetone/chloroform spinning system produced fiber with an increased degradation rate in comparison to the pure chloroform spinning system. © 1994 John Wiley & Sons, Inc.     

Effects of kinetics coefficients on ternary phase separation during the wet spinning process

A new Monte Carlo diffusion model is employed to simulate the phase separation of the ternary system during wet spinning process. Our results illustrate the thermodynamics parameters are the primary factors in morphology determination during the phase separation process. Meanwhile by varying kinetic parameters different fiber structures ranging from dust-like, finger-like to sponge-like morphologies are obtained. The morphological patterns are discussed in relation to the rate of particle exchange and the phase diagram. On the basis of the systematical simulation experiments we propose how the competition between segment–solvent and solvent–nonsolvent exchange determines the ultimate fiber morphologies in spinning solution.© 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of crosslinked membranes with controlled pore size distribution

A technique has been developed to prepare crosslinked, porous/asymmetric membranes from poly(styrene-co-divinylbenzene). Mixtures of styrene monomer, divinylbenzene, benzoin (a photo-initiator), and some dead polystyrene are dissolved in a cosolvent and cast on a flat, transparent substrate. The coating is then irradiated with a UV lamp and subsequently phase separated by exposure to a nonsolvent bath. Pores are generated by phase separation induced by nonsolvent ingression. Crosslinking is achieved via the photo-initiated incorporation of divinylbenzene with styrene, while the membrane morphology evolves. A mechanism for the formation of crosslinked membranes prepared by this technique has been proposed. Experimental results systematically examine the effects of crosslinking and nonsolvent/solvent combinations on pore size and overall membrane structure. Temperature and solvent treatments on the finished membrane structure are also studied.     

Fabrication of an antifouling GO-TiO2/PES ultrafiltration membrane

PES ultrafiltration membrane is widely used in various fields due to its high-filtration efficiency. However, due to its hydrophobicity, PES ultrafiltration membrane has poor antifouling performance, this reduced service life and increased industrial cost. Blending is a common method in ultrafiltration membrane hydrophilic modification. Adding a small amount of inorganic nanoparticles into the polymer membrane can improve the properties of the polymer membrane. However, nanoparticles are not uniformly dispersed in polymer membrane, which hindering the modification ability of nanoparticles to ultrafiltration membrane. In this paper, GO-TiO₂ materials were prepared by hydrothermal method, and GO-TiO₂/PES blended ultrafiltration membranes were fabricated by nonsolvent induced phase separation (NIPs). The experimental results show that GO-TiO₂ disperse uniformly in GO-TiO₂/PES ultrafiltration membrane, which greatly improved the antifouling performance of the membrane. When the addition amount of GO-TiO₂ is 0.6%, the water flux of membrane reaches 194.5 (L m⁻² h⁻¹), and the rejection rate of BSA reaches 89.4%. After three pollutions-cycles, the flux recovery rate of the membrane is 90.2%.