Glass‐transition temperature of poly(vinylidene fluoride)‐poly(methyl acrylate) blends: Influence of aging and chain structure

The glass‐transition temperature (T_g) of the poly(vinylidene fluoride) (PVF₂)‐poly(methyl acrylate) (PMA) blends increase with aging time. The T_g versus log(time) plots are straight lines whose slope values depend on the head to head (H–H) defect content of PVF₂ samples and on the composition of the blends. The values of polymer–polymer interaction parameters (χ) increase with an increase in the H–H defect of PVF₂ for a fixed composition of the blend. Consequently, the T_g of the blend decreases with an increase in the H–H defect of the PVF₂ sample. However, after aging for longer times this decrease of the T_g with H–H defects is lower than those of the unaged blends. The possible reasons are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1541–1548, 2001     

Application of poly(phthalazinone ether sulfone ketone)s to gas membrane separation

A series of poly(phthalazinone ether sulfone ketone) (PPESK) copolymers containing different component ratios of bis(4‐fluorodiphenyl) ketone and bis(4‐chlorodiphenyl)sulfone with respect to a certain amount of 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one were synthesized by polycondensation. Glass transition temperatures of these polymers were adjusted from 263°C to 305°C by changing the ratios of reactants. Gas permeability and selectivity of the dense membranes of the polymers for three kinds of gases (CO₂, O₂, and N₂) were determined at different temperatures. The result indicated that the membrane of PPESK (S/K = 1/1, mol ratio) had an excellent gas separation property. Permeability of the polymer membranes for CO₂, O₂, and N₂ was P = 4.121 barrier, P = 0.674 barrier, and P = 0.0891 barrier, respectively. Separation factors of α and α were 7.6 and 46, respectively. New material was made into a composite membrane with silicone rubber for blocking up leaks and defects on the surface of its nonsymmetrical membrane. As a result of the test, permeability of the composite membrane was J = 7.2 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg and J = 0.99 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg, whereas the α was still higher than 7. These showed that PPESKs had a bright prospect as the potential membrane material for high‐temperature gas separation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2385–2390, 1999     

Hydrolysis reaction of poly(ethylene terephthalate) using ionic liquids as solvent and catalyst

The hydrolysis of poly(ethylene terephthalate) (PET) was studied using ionic liquid 1‐n‐butyl‐3‐methylimidazolium chloride ([Bmim][Cl]) as solvent and acid‐functionalized ionic liquid 1‐methyl‐3‐(3‐sulfopropyl)‐imidazolium hydrogen sulfate ([HSOpmim][HSO₄]) as catalyst. The effects of temperature, time, and dosages of solvent and catalyst on hydrolysis results were examined. Under the optimum conditions of m(PET) : m(H₂O) : m([Bmim][Cl]) : m([HSOpmim][HSO₄]) = 3 : 4 : 6 : 0.6, reaction temperature 170°C and time 4.5 h, the conversion of PET and the yield of terephthalic acid (TPA) were almost 100% and ≥88%, respectively. After easily separated from the product, the ionic liquids could be reused eight times without obvious decrease in the conversion of PET and yield of TPA. Hence, an environmental friendly strategy for chemical recycling of PET was developed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Gas permeabilities of poly(trimethylsilylpropyne) membranes surface modified with CF4 plasma

Surface fluorination of poly(trimethylsilylpropyne) (PTMSP) membranes by CF₄ plasma was studied. The surface fluorination of the membranes was carried out in an atmosphere of CF₄ in a capacitively coupled discharge apparatus with external electrodes. Dramatic increase in selectivity (P/P) was observed. The effect of fluorination conditions such as duration of treatment and discharge power on the permeabilities of the membranes was studied. X-ray photoelectron spectrometric data of modified PTMSP membranes showed a drastic alternation in the surface layer. The P and P/P of the membranes were observed to be dependent on the F/C atomic ratio. At F/C > 1, the P/P value of the membranes could be more than four. © 1993 John Wiley & Sons, Inc.     

Solvent effect on structural change of poly(vinyl alcohol) physical gels

In this study, the relationship between the polymer–solvent interaction and the network structure of poly(vinyl alcohol) (PVA) gels prepared with organic solvents such as N-methylpyrrolidone (NMP) and ethylene glycol (EG) are investigated. The values of the intrinsic viscosity [η] and Huggins constant k′ of dilute PVA solutions indicate that the attractive interaction between PVA and NMP is higher than that between PVA and EG. The X-ray result shows that PVA–EG gels have a (101) diffraction peak of PVA crystal that appeared at about 2θ = 19°, while PVA–NMP gels only show a broad amorphous scattering peak. On the other hand, Fourier transform infrared results of PVA/EG gels also clearly show an intense peak at 1141 cm⁻¹ due to the crystalline absorption. The results of H¹ pulsed nuclear magnetic resonance show that the spin–spin relaxation time, and respectively, related to the polymer-rich and polymer-poor components decrease, and the fractional amount of the polymer-rich component, f^s, increases, while that of the polymer-poor component, f^l, decreases with an increase in the concentration of polymer. At a given concentration, the value of f^s in the PVA–EG gel is larger than that in the PVA–NMP one. These facts indicate that the crystallinity in the PVA–EG gel is higher than that in the PVA–NMP gel, implying that the aggregation of PVA chains is much easier in the poor solvent, EG, than in the good solvent, NMP. The structural change with aging time in the PVA–EG gel is very remarkable because of the significant syneresis, indicating that the opaque PVA–EG gel with higher crystallinity has a comparatively heterogeneous and unstable network structure than the PVA–NMP gel does. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2477–2486, 1998     

Polymer miscibility in mixed organic liquids. An extension of the two-dimensional approach

Previous work on the two-dimensional approach to polymer miscibility in organic liquids is extended to polymer–mixed liquid system. From thermodynamic considerations methods for calculating δ_h of the mixed liquid and χ_H of the polymer–mixed liquid system from properties of pure components are proposed, where δ_h is the hydrogen-bonding solubility parameter of the liquid, and χ_H is a term which takes account of the dispersion and polar interactions between the liquid and the polymer and of effects due to temperature and molecular size of the liquid. Using these two calculated parameters, the solvent power of the mixed liquid can be determined from its location on the χ plane.     

Viscoelastic properties and transitions during thermal and UV cure of a methacrylate resin

The solidification behavior of a dimethacrylate system during UV and thermal cure at temperatures from the T_g of the monomer (T) to above the ultimate T_g of the polymer (T) is investigated using torsional dynamic mechanical analysis. Gelation and vitrification times are quantified using several criteria for the transitions, and the data are presented as a function of cure temperature in TTT diagrams. The influence of cure method and temperature on the mechanical properties, degree of conversion, and gel content of the cured samples is discussed. The results show that gelation occurs before or at the same time as vitrification at all temperatures, including T. With UV cure, gelation generally occurred within seconds, whereas the properties continued to develop for minutes or hours afterwards. The method of cure was found to influence the properties of the cured material. When prepared above T, the UV cured material had a higher T_g, a higher crosslink density, and a higher degree of conversion than the thermally cured material.     

Sorption and transport properties of the semi‐interpenetrating network based on crosslinked poly(vinyl alcohol) and poly(styrene sulfonic acid‐co‐maleic anhydride) as proton‐conducting membranes

This study investigates the sorption and transport properties of hydrocarbon membranes based on poly(vinyl alcohol) network and poly(styrene sulfonic acid‐co‐maleic acid) (PSSA‐MA). The water and methanol self‐diffusion coefficients through an 80 wt % PSSA‐MA interpenetrating SIPN‐80 membrane measured 3.75 × 10^?6 and 5.47 × 10^?7 cm²/s, respectively. These results are lower than the corresponding values of Nafion® 115 (8.89 × 10^?6 cm²/s for water and 8.63 × 10^?6 cm²/s for methanol). The methanol permeability of SIPN‐80 membrane is 4.1 × 10^?7 cm²/s, or about one‐fourth that of Nafion® 115. The difference in self‐diffusion behaviors of Nafion® 115 and SIPN‐80 membranes is well correlated with their sorption characteristics. The solvent uptake of Nafion® 115 increased as the methanol concentration increased up to a methanol mole fraction of 0.63, and then decreased. However, the solvent uptake of the SIPN‐80 membranes decreased sluggishly as the methanol concentration increased. The λ values of water and methanol (i.e., λ and λ) in Nafion® 115 are quite close, indicating no sorption preference between water and methanol. In contrast, the λ value is only one‐third λ for a SIPN‐80 membrane. Accordingly, the SIPN membranes are regarded as candidates for direct methanol fuel cell applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Miscibility of linear low density polyethylene (LLDPE)-graft-poly(methyl methacrylate) with poly(vinylidene fluoride) (PVF2) and its application as compatibilizer LLDPE/PVF2 blends

Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to study the miscibility of blends of a graft copolymer of poly(methyl methacrylate) on linear low density polyethylene (LLDPE-g-PMMA, G-3) with poly(vinylidene fluoride)

1 Systematic name: poly(1,1-difluoroethylene).

(PVF₂) and the compatibilization of blends of LLDPE/PVF₂. The specific interaction between PMMA side chains and PVF₂ in G-3/PVF₂ binary blends is weaker than that between the homopolymers PMMA and PVF₂. There are two states of PVF₂ in the melt of a G-3/PVF₂ (60/40, w/w) blend, one as pure PVF₂ and the other interacting with PMMA side chains. The miscibility between PMMA side chains and PVF₂ affects the crystallization of PVF₂. LLDPE-g-PMMA was demonstrated to be a good compatibilizer in LLDPE/PVF₂ blends, improving the interfacial adhesion and dispersion in the latter. Diffusion of PMMA side chains into PVF₂ in the interfacial region reduces the crystallization rate and lowers the melting point (T_m) and the crystallization temperature (T_c) of PVF₂ in the blends.     

The phase diagram and morphology of blends of poly(vinylidene fluoride) and poly(ethyl acrylate)

The phase diagram and crystallization behaviour of the polymer blend system consisting of poly(vinylidene fluoride) (PVF₂) and poly(ethyl acrylate) (PEA) have been examined. The melt exhibits phase separation upon heating to 10°C–50°C above the melting point of the PVF₂, depending on the composition. The cloud point and equilibrium melting point curve (for α-PVF₂) intersect at about 180°C and a composition of 50% (by weight) PVF₂. The polymer-polymer interaction parameter, χ, was calculated from the equilibrium melting point depression data and found to be −0.16 (at 170°C). Spherulite growth rate data have been measured as a function of composition and temperature. Assuming regime II crystallization a value of the product of the surface free energies of the α-PVF₂ crystals was calculated to be 4.4 × 10⁻⁴J²m⁻⁴. In blends crystallized from the one phase melt the texture of spherulites becomes more open and the spherulite extinction ring spacing (due to lamaller twist) becomes larger with increasing crystallization temperature. In addition the ring spacing increases with PEA content at constant crystallization temperature.     

Chlorinated poly(vinylidene fluoride)

Chlorinated poly(vinylidene fluoride) (PVF₂) was prepared by introducing chlorine gas into a CCI₄ suspension of PVF₂ at reflux temperature. Polymer crystallinity and softening point decrease, while solubility and adhesion increase with the degree of chlorination. In contrast to PVF₂, the chlorinated polymer is soluble in low-boiling common organic solvents, such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane. Chlorinated PVF₂ is resistant to dehydrochlorination and is thermally more stable than PVF, chlorinated PVF, PVC, or chlorinated PVC. Chlorinated PVF₂ coatings on wood, prepared by solution casting at room temperature, show outstanding weathering resistance.     

Permeability of dense (homogeneous) cellulose acetate membranes to methane,carbon dioxide,and their mixtures at elevated pressures

Mean permeability coefficients for CH₄ and CO₂ (P̄ and P̄) in cellulose acetate (CA, DS = 2.45) were determined at 35°C (95°F) and at pressures up to about 54 atm (800 psia). The measurements were made with pure CH₄ and CO₂ as well as with CH₄/CO₂ mixtures containing 9.7, 24.0, and 46.1 mol % CO₂. In the measurements with the pure gases, P̄ was found to decrease with increasing pressure, as expected from the “dual-mode” sorption model. By contrast, P̄ passes through a minimum and then increases with increasing pressure, probably due to the plasticization (swelling) of CA by CO₂. The values of P̄ and P̄ determined with the mixtures containing 9.7 and 24.0 mol % CO₂ decrease with increasing total pressure; this behavior is adequately described by the extended “dual-mode” sorption model for mixtures. By contrast, the values of P̄ and P̄ obtained with the mixture containing 46.1 mol % CO₂ pass through a minimum and then increase as the total pressure is raised, probably also due to the plasticization of CA by CO₂. The CO₂/CH₄ selectivity (≡P̄/P̄) of the CA membrances decreases with increasing total pressure and, at constant pressure, decreases with increasing CO₂ concentration in the feed mixture. The effects of exposing the CA membranes to high-pressure CO₂ prior to the permeability measurements (“conditioning” effects) on P̄ and P̄ have also been studied. © 1996 John Wiley & Sons, Inc.     

Influence of tacticity of poly(methyl methacrylate) on the compatibility with poly(vinylidene fluoride)

A calorimetric study was carried out on blends of poly(vinylidene fluoride) (PVF₂), and isotactic, atactic and syndiotactic poly(methyl methacrylate) (i-, a-, and s-PMMA). The occurrence of single glass transitions over a broad composition range, as well as the lowering of the crystallization and melting temperatures of PVF₂, indicated a complete compatibility of PVF₂ with i-, a-, and s-PMMA. The measured T_g values followed Gordon-Taylor's rule with k values of 2.38, 1.72, and 1.39 for the systems of PVF₂ with i-, a-, and s-PMMA, respectively, leading to new values of the jump Δe of the thermal specific expansivity at the glass transition: 1.9 × 10^?4 cm³/g K for PVF₂ and 2.6 × 10^?4 for s-PMMA. From the melting point depressions of PVF₂ crystals, it appeared that the interaction of PVF₂ segments with i-PMMA segments is stronger than with s-PMMA segments. A thermodynamic analysis of the melting point depressions after crystallization of PVF₂ at a constant relative undercooling of 0.07 resulted in values of the binary interaction parameter of about ?0.1 and 0 for PVF₂ with i- and s-PMMA, respectively.     

Blends of the alternating ethylene–tetrafluoroethylene copolymer with poly(vinylidene fluoride)

Blends of the alternating ethylene–tetrafluoroethylene copolymer (ETFE) with poly(vinylidene fluoride) (PVF₂) were prepared by melt-mixing. Compatibility, morphology, thermal behavior, and mechanical properties of the ETFE/PVF₂ blends with various compositions were studied by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), tensile tests, and scanning electron microscopy (SEM). DMA studies showed that the blends have separate glass transition temperatures (T_g) close to those of the pure polymers. ETFE and PVF₂ are incompatible. Marked negative deviations from simple additivity were observed for both the ultimate strength and the elongation at break over the entire composition range. The interfaces between ETFE and PVF₂ are weakly bonded with rather poor interaction. SEM observations revealed that the blends have a two-phase structure and the adhesion between the phases is poor. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:295–304, 1997     

Preparation and characterization of positively charged composite nanofiltration membranes by coating poly(ether ether ketone) containing quaternary ammonium groups on polysulfone ultrafiltration membranes

The novel positively charged poly(ether ether ketone)s (PEEKs) with pendant quaternary ammonium groups were synthesized by copolymerization of 3, 3′‐dimethylaminemethylene‐4,4′‐biphenol (DABP), 3,3′,4,4′‐tetramethylbiphenol, and 4,4′‐bisfluorobenzophenone followed by reaction with iodomethane. The resulting copolymers were used to prepare thin film composite (TFC) nanofiltration (NF) membranes via the dip‐coating method. The effects of different parameters such as copolymer concentration and curing time on the membrane performance (flux and rejection of inorganic salts) were investigated. The optimum parameters were that 1.5 wt % quaternary ammonium PEEK containing 1.8 quaternary ammonium groups per unit with 0.5 wt % DMSO coated on the polysulfone (PSf) support membrane and cured at 100°C. The results of the performance testing showed that the trend for rejection was R > R > R_NaCl > R (R = rejection), which was a typical positively charged membrane. The best performance of these composite nanofiltration membranes was 91.3% rejection for 500 ppm MgCl₂ and 62.5 L/m² h water permeability at 0.4 MPa. The MWCO of the membrane was 800 Da. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermoreversible gelation of nitrocellulose solutions

Thermoreversible gelation of concentrated solutions of nitrocellulose was examined. The sol–gel transition diagrams were established using the ball‐drop method. The critical gel concentrations (C_gel), defined as the lowest concentration for gelation to occur, are approximately proportional to the reciprocal of the molecular weight of nitrocellulose. In addition, the values of C_gel[η] lie in the concentrated regime where entanglement effects are present. These facts suggest that the entanglement of polymer chains is a necessary condition for the formation of nitrocellulose gels. Moreover, the association of polymer segments is identified as another factor affecting the gel stability. This is evidenced by both the enhancement of the gel stability in poor solvents and the large enthalpy of mixing at low temperatures. Because of the presence of the association, the number of polymer chains in a junction point is larger than two, which is the value predicted by assuming entanglements as the only factor responsible for gelation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4000–4008, 2003     

Polymer blends containing poly(vinylidene fluoride). Part II: Poly(vinyl esters)

Blends of poly(vinylidene fluoride) PVF₂, with poly(vinyl acetate), PVAc; with poly(vinyl propionate), PVPr; and with poly(vinyl butyrate), PVBu, were prepared by solution blending. Solutions containing PVF₂ with either PVPr or PVBu exhibited phase separation, and it was concluded that neither of these polymers are miscible with PVF₂. Phase separation did not occur with solutions containing PVF₂ and PVAc. Dried samples of this blend system were subjected to differential thermal analysis, dynamical mechanical testing, and visual observations of their melts. From these results, it was concluded that PVF₂ and PVAc are miscible. The detailed results and the structural implications of these observations are discussed.     

Oxidative coupling of methane over a La2O3/CaO catalyst. Optimization of reaction conditions in a bubbling fluidized-bed reactor

Oxidative coupling of methane over a La₂O₃/CaO catalyst was investigated in laboratory-scale fluidized-bed reactors (ID = 5 and 7 cm) in the following range of reaction conditions: T = 700 – 880°C, P = 41 – 72 kPa and P = 6 – 29 kPa. The maximum C₂₊ selectivity and yield amounted to 73.8% (T = 800°C, X = 13.1%, Y = 9.7%) and 16.0% (T = 840°C, X = 34.0%, S = 47.2%), respectively. Axial gas concentration profiles revealed that C₂₊ selectivity was not only influenced by oxidative consecutive reactions, but also by steam reforming of ethylene. When diluting the catalytic bed (m_cat = 145 g) with quartz (m = 200 and 400 g), a slight decrease of the selectivity (1–2%) was observed. The dilution of the feed gas with nitrogen only led to only a small increase (< 2%) of the C₂₊ selectivity.     

Conversion of SO2 into elemental sulfur by using the RF plasma technique

This study demonstrates a new approach for converting SO₂ into elemental sulfur by adding CH₄ in a radio-frequency (RF) plasma reactor. With the applied power (P) of the RF reactor specified at 90 W and operating pressure set at 4000 N/m², it was found that as the CH₄/SO₂ ratio (R) was increased from 0.3 to 1.0, most sulfur-containing products were in the form of elemental sulfur. While R was increased from 1 to 2, the content of elemental sulfur was decreased significantly, but CS₂ was increased dramatically. While R was increased from 2 to 3, both elemental sulfur and CS₂ contents became quite comparable. Nevertheless, it was found that both H₂ and CO (that is, syngas) were the main nonsulfur-containing products under all testing conditions. These results indicate that the use of the RF plasma technique was not only beneficial to convert SO₂, but also was able to convert CH₄ into useful materials. For R = 0 (that is, no CH₄ was introduced), it was found that the SO₂ conversion (i.e., η) = 0.084, indicating that the RF plasma process was inadequate to convert pure SO₂ without adding CH₄ as a reducing agent. While R was increased to 2, it was found that η was improved significantly to 0.968 accompanied with η = 0.999. But as R was increased from 2 to 3, both η and η were slightly decreased. Both η and η also were sensitive to the applied power (P). As P was increased from 15 W to 90 W at R = 2, it was found that both η and η were increased dramatically from 0.247 and 0.320 to 0.968 and 0.999, respectively. But as P was increased from 90 W to 120 W, the increase on both η and η became very limited. Based on these, this study suggests that the operating condition of R = 2 and P = 90 W would be the most appropriate combination for SO₂ conversion. © 2004 American Institute of Chemical Engineers AIChE J, 50: 524–529, 2004     

Effect of dodeca‐tungstophosphric acid on morphology and performance of polyvinyl alcohol membrane for gas separation

In this article, organic/inorganic membrane was prepared for gas separation by incorporating dodeca‐tungstophosphric acid (PWA) into the base polymer. Flat‐sheet composite membranes were produced via dry‐phase inversion method. In the first stage, the effects of PWA concentration on morphology and performance of polyvinyl alcohol (PVA) membranes were elucidated. For this stage, the preparation of membranes was carried out at constant temperature of 40°C. The porosity of the prepared membrane was slightly increased with addition of PWA. By increasing the PWA concentration up to 6 wt % in the membrane recipe, the permeability of N₂, O and air was improved from 50,000 (for no addition of PWA) to around 160,000, 140,000, and 80,000 L m^?2 h^?1, respectively. For H this was enhanced from 110,000 to 230,000 L m^?2 h^?1. The ideal selectivity of the membrane was slightly improved for N₂/air (from 1 to 1.2). For N₂/O₂ pair, the initial drop (from 2.5 to 1.5) was followed by a slight increase (1.5–1.9). Moreover, the selectivity was decreased for H₂/air (from 2.8 to 1.8) and H₂/N₂ (from 2.2 to 1.7) by increasing the PWA concentration. The 10 wt % PVA membrane with 6 wt % PWA demonstrated superior performance compared with the other compositions. In summary, the presence of PWA in the casting solution results in lower flux for O₂ and higher selectivity for H₂/O₂ pair. In the second stage, the effects of solvent evaporation temperature (10, 27, 40, and 80°C) on morphology and performance of the membranes were studied. By increasing the temperature, the number and size of voids were increased. The permeation of gases was improved from 100,000 L m^?2 h^?1 (at 10°C) to 150,000 (O₂), 250,000 (air), 380,000 (N₂), and 600,000 L m^?2 h^?1 (H₂) by increasing the temperature up to 80°C. This increment resulted in selectivity alteration either increment or diminishment. The selectivity was changed from 1.3 to 3.2 (H₂/O₂), 0.8–2.5 (N₂/O₂), 1.2–2.4 (H₂/air), 0.6–1.5 (N₂/air) and 2.0–1.5 (H₂/N₂). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009