Effect of sub-Tg annealing on CO2 sorption in polycarbonate

High pressure CO₂ sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.     

Diffusion and sorption for carbon dioxide in Kapton at extremely low pressure

Pressure-dependent solubility and diffusion coefficients for carbon dioxide in glassy polymers have been well described using the “dual sorption and transport model.” However, the plastisization effect by high-pressure carbon dioxide seems to promote the pressure dependence of the sorption and transport coefficients. To avoid the relaxation process by the plastization which is superimposed on the diffusion process, the diffusion and sorption of carbon dioxide were measured at extremely low pressure (below 1 cmHg). Linear isotherms observed for CO₂ sorption into Kapton were interpreted in terms of the dual model equation at extremely low pressure. From the permeation curve of the Kapton/CO₂ system, the diffusion and permeation coefficients were obtained according to the usual manner, and both coefficients were independent of pressure. Sorption and transport parameters were obtained from sorption isotherms and average values of the permeation coefficients. The parameters thus obtained were substituted in an approximated dual sorption and transport equations at extremely low pressure and the pressure independence of the diffusion and permeation coefficients were sufficiently reproduced. It is a good technique to experiment at such extremely low pressure when the validity of the dual model is evaluated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1013–1017, 1998     

Mass transport process for the adsorption of Cr(VI) onto water‐insoluble cationic starch synthetic polymers in aqueous systems

Dynamic adsorption behaviors between Cr(VI) ion and water‐insoluble amphoteric starches was investigated. It was found that the HCrO ion predominates over the initial pH ∼ 2–4, the CrO ion predominates over the initial pH ∼ 10–12, and both ions coexist over the initial pH ∼ 6–8. The sorption process occurs in two stages: the external mass transport process occurs in the early stage and the intraparticle diffusion process occurs in the long‐term stage. The diffusion coefficient of the early stage (D₁) is larger than that of the long‐term stage (D₂) for the initial pH 4 and pH 10. The diffusion rate of HCrO ion is faster than that of CrO ion for both processes. The D₁ and D₂ values are ∼ 1.38 × 10⁻⁷–10.1 × 10⁻⁷ and ∼ 0.41 × 10⁻⁷–1.60 × 10⁻⁷ cm² s⁻¹, respectively. The ion diffusion rate in both processes is concentration dependent and decreases with increasing initial concentration. The diffusion rate of HCrO ion is more concentration dependent than that of CrO ion for the external mass transport process. In the intraparticle diffusion process, the concentration dependence of the diffusion rate of HCrO and CrO ions is about the same. The external mass transport and intraparticle diffusion processes are endothermic and exothermic, respectively, for the initial pH 4 and pH 10. The k_d values of the external mass transport and intraparticle diffusion processes are ∼ 15.20–30.45 and ∼ −3.53 to −12.67 kJ mol⁻¹, respectively. The diffusion rate of HCrO ion is more temperature dependent than that of CrO ion for both processes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2409–2418, 1999     

Sorption phenomena in nafion membranes

Sorption phenomena of water and aqueous salt solutions by a perfluorinated polymer containing sulfonic acid groups (Nafion) were investigated. The temperature and concentration dependencies of the sorption by the membranes in the acid and salt forms were studied. The apparent activation energies for the diffusion of water in the H-form membrane and in the K-salt form were obtained as 4.9 and ca. 13.0 kcal/mole, respectively. The sorption kinetics during the neutralization of the membranes were observed in several aqueous solutions. A maximum in the sorption curve during the neutralization process was found and explained as resulting from the differences in the diffusion coefficients of water and of the cations and from the different number of water molecules absorbed by a SOH⁺ (acid) site and a neutralized site. The diffusion coefficients D of several cations (K⁺, Cs⁺, Ba²⁺, and Ca²⁺) were determined and found to be considerably smaller than that of water. For the various cations, log D was related linearly to q/a, where q is the cation charge and a is the separation between centers of charge of the cation and anion. The dependence of water sorption upon the degree of neutralization of the membrane was also studied at room temperature. It was observed that for membranes of a low degree of neutralization a secondary sorption process existed, while no such secondary sorption could be found for the pure acid or the highly neutralized membranes. This secondary sorption was attributed to a structural rearrangement in the polymer. The apparent diffusion coefficient of water and the number of water molecules absorbed at equilibrium by an ionic site, n_s, were obtained as a function of the degree of neutralization. The diffusion coefficient of water was dependent strongly on both the degree of neutralization and type of the salt, but no quantitative relation could be established. For all the salts studied in this paper, n_s was linearly related to the degree of neutralization, x, supporting the assumption that the value of n_s could be divided into those water molecules absorbed by an SOH⁺ (acid) site, n_h, and those absorbed by a neutralized site, n_m. It was found that the value of q × n_m had a strong correlation with a characteristic constant of the cations since a plot of q × n_s versus log (q/r) yielded a straight line (r being the radius of the cation).     

Synthesis,characterization, and thermodynamic properties of poly(3‐mesityl‐2‐hydroxypropyl methacrylate)

Poly(3‐mesityl‐2‐hydroxypropyl methacrylate) (PMHPMA) was synthesized in a 1,4‐dioxane solution with 2,2′‐azobisisobutyronitrile as the initiator at 60°C. The homopolymer and its monomer were characterized with ¹H‐ and ¹³C‐NMR, Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, size exclusion chromatography, and elemental analysis techniques. According to size exclusion chromatography analysis, the number‐average molecular weight, weight‐average molecular weight, and polydispersity index of PMHPMA were 65,864 g/mol, 215,375 g/mol, and 3.275, respectively. According to thermogravimetric analysis, the carbonaceous residue value of PMHPMA was 14% at 500°C. The values of the specific retention volume, adsorption enthalpy, sorption enthalpy, sorption free energy, sorption entropy, partial molar free energy, partial molar heat of mixing, weight fraction activity coefficient of solute probes at infinite dilution (Ω), and Flory–Huggins interaction parameter (χ) were calculated for the interactions of PMHPMA with selected alcohols and alkanes by the inverse gas chromatography method at various temperatures. According to Ω and χ, selected alcohols and alkanes were nonsolvents for PMHPMA at 423–453 K. Also, the solubility parameter of PMHPMA (δ₂) was found to be 24.24 and 26.33 (J/cm³)^0.5 from the slope and intercept of (δ/RT) ? χ/V₁ = (2δ₂/RT)δ₁ ? δ/RT at 443 K, respectively [where δ₁ is the solubility parameter of the probe, V₁ is the molar volume of the solute, T is the column temperature (K), and R is the universal gas constant]. The glass‐transition temperature of PMHPMA was found to be 386 and 385 K by inverse gas chromatography and differential scanning calorimetry techniques, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 101–109, 2006     

Inverse gas chromatography of poly(vinylisobutyl ethers) and polymer-solute thermodynamic interactions

Gas chromatography (GC) retention behavior of atactic and isotactic poly(vinylisobutyl ether) stationary phases has been studied in the temperature range 30–90°C using 16 solutes which include various alkanes, alkylbenzenes, and chlorinated aliphatic hydrocarbons. The bulk sorption equilibrium retention data have been employed to derive various thermodynamic quantities at infinite dilution of solutes in the polymers, viz., χ, χ^*, χ_H, χ_S, X₁₂, δH_S, h . Their dependence on temperature, polymer structure, and chemical nature of solutes has been discussed.     

Solution and diffusion properties of cyclohexane,cyclohexanol, and cyclohexanone in poly(ethylene glycol) by inverse gas chromatography

The solution and diffusion properties of cyclohexane, cyclohexanol, and cyclohexanone in poly(ethylene glycol) (PEG) and crosslinked PEG have been studied in the temperature range of 368.15 to 403.15 K using inverse gas chromatography (IGC) technique. The infinite dilute activity coefficient (Ω) and diffusion coefficient (D) have been determined for the above solvent/polymer systems. Accordingly, several thermodynamic functions, the diffusion pre‐exponential factor, and activation energy have been attained. The results showed a decrease in Ω and an increase in D with rising temperature. The order of the relative magnitude of Ω and D of the solvents were explained by comparing their interactions with the polymer and their collision diameters, respectively. Moreover, Ω and D in crosslinked PEG were smaller than those in PEG at various temperatures. The analysis of Ω, the infinite dilute selectivity and capacity showed the possibility of using crosslinked PEG as an appropriate membrane material for the separation of cyclohexane, cyclohexanol, and cyclohexanone mixture. A thermodynamic study also implied that the solvent sorptions in the polymers were all enthalpically driven in the experimental range. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Syntheses and properties of carboxymethyl chitosan/urea–formaldehyde snake‐cage resins

A series of novel snake‐cage resins were synthesized using carboxymethyl chitosan (CM‐CTS) as the snake resin and urea–formaldehyde resin (UF) as the cage resin. Such factors as the optimal synthesis conditions, content of the crosslinking agent, and sorption capacities for metal ions of the above‐mentioned resins were investigated. The experimental results show that these resins have appropriate swelling properties and good mechanical stability. They do not run off in water, HCl, and NaOH aqueous solutions. To form a stable network system, NH₄Cl was used as a crosslinking agent to crosslink urea and formaldehyde in synthesis. The sorption experiment showed that the sorption properties of the resins in the presence of the crosslinking agent NH₄Cl are better than those without a crosslinking agent. The investigation of the FTIR spectra indicated that the chelate groups, such as —OH, —CO and NHCH₂CO, in snake‐resin molecules participated in the coordination with the metal ions, but the —C?O bonds in the cage resin UF did not. The snake resin CM‐CTS in the snake‐cage resins was the major contributor of sorption. The sorption dynamics showed that the sorption was controlled by liquid film diffusion. The isotherms can be described by Freundlich and Langmuir equations. The saturated sorption capacities of the resins for Cu²⁺, Ni²⁺, Zn²⁺, and Pb²⁺ were 1.48, 0.78, 0.13, and 0.02 mmol g^?1, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 310–317, 2002; DOI 10.1002/app.10331     

Phenoxy resin: Characterization,solution properties,and inverse gas chromatography investigation of its potential miscibility with other polymers

A commercial sample of a copolymer of bisphenol-A and epichlorohydrin (Phenoxy) has been carefully fractionated in a dioxane/methanol mixture. Mark-Houwink constants in THF and the molecular weight distribution of the raw material have been obtained on the basis of the universal calibration procedure. Conformational magnitudes such as the characteristic ratio C_∞ or the steric factor σ have been determined from viscometric data at 63°C in a good (dioxane) and a θ-solvent (1,2-dichloroethane). Inverse gas chromatography was used to study phenoxy miscibility with a variety of polymers. Using different probes as model compounds, the partial molar enthalpy of mixing ΔH at infinite dilution has been determined. Results were correlated with the reported miscibility of phenoxy with polyesters, polyethers, and polyoxides. A linear multiparametric correlation of ΔH with polarizabilities, dipole moments, and hydrogen bond accepting powers provides for a comprehensive analysis of other miscible systems.     

Gas chromatographic measurements of infinite dilution diffusion coefficients of volatile liquids in amorphous polymers at elevated temperatures

Measurements were made of infinite dilution diffusion coefficients of volatile liquids in amorphous polymers at elevated temperatures, using inverse gas chromatography. The liquids used were benzene, toluene, ethylbenzene, and n-decane. The polymers used were polystyrene and poly(vinyl acetate), and temperatures ranged from 30°C to 120°C above the glass transition temperatures of the polymers. Packed chromatographic columns were used to obtain data of the variation of the plate height with the average gas velocity, which was then used to determine diffusion coefficients with the aid of the van Deemter equation. In the present investigation, we have used different sizes of glass beads (0.3, 0.5, 0.6, and 1.0 mm in diameter), depending on the system temperature and the polymer/solute pair chosen. An attempt was made to correlate on the diffusion coefficient D measured at various temperatures T, using in Dζ as ordinate and 1/[(K₂₂ + T ? T_g2)/T_c] (hereafter referred to as the reciprocal of reduced free volume temperature, 1/T_RF) as abscissa, in which ζ = M^1/2/TV, M being the molecular weight, T_c the critical temperature, and V_c the critical volume of the solute, K₂₂ is a free volume parameter of the polymer, and T_g2 is the glass transition temperature of the polymer. It has been found that such plots give rise to two linear regions having different slopes, separated by a critical value of 1/T_RF. The critical value of 1/T_RF is found to be insensitive to the type of solute and the type of polymer used. We have concluded that the infinite dilution diffusion coefficient of volatile liquids in amorphous polymers is controlled predominatly by the free volume of polymer above a critical value of 1/T_RF, but energy effects are significant below the critical value of this parameter. In order to apply the generalized relationships in conjunction with gas chromatographic measurements, the results of this study indicate that, for values of 1/T_RF larger than a critical value, which is approximately 4.8, the following expression, In Dζ = α + b/T_RF, may be used to predict infinite dilution diffusion coefficients of volatile liquids in amorpous polymers at elevated temperatures, in which α is a constant, independent of the type of solute, and b is approximately a constant for a given polymer in the free volume region, independent of the type of solute. More experimental studies are needed, particularly for temperatures higher than those reported in this study, to corroborate and/or extend the correlations presented here.     

Inverse gas chromatography of poly(n-butyl methacrylate): Effect of flow rate on specific retention volume and detection of glass transition temperature

Flow-rate effect on specific retention volume (V) was studied by eluting aliphatic, aromatic, and chlorinated aliphatic probes at infinite dilution on poly(n-butyl methacrylate) stationary phase at different temperatures from ?10 to 150°C, encompassing both the glass transition (T_g) and the softening temperatures of the polymer. The effect became pronounced as the temperature was reduced below 100°C. V decreased with an increase in the flow rate: first linearly at temperatures between 70 and 100°C, and then nonlinearly at all temperatures below 70°C. The retention diagrams of n-pentane, isooctane, and cyclohexane alone enabled the detection of glass transition. Dichloromethane gave a linear retention diagram through T_g without showing the flow-rate effect.     

The solubility of gases and volatile liquids in polyethylene and polyisobutylene at elevated temperatures

The solubility of gases and volatile liquids in low-density polyethylene (LDPE) and polyisobutylene (PIB) at elevated temperatures has been correlated, using the experimental data available in the literature. In the present study, a Henry's constant K_p at a total pressure of approximately 1 atm defined as P₁ = K_PV, where P₁ is the partial pressure of the solute in the vapor phase and V is the solubility (cm³ solute/g polymer at 273.2 K and 1 atm), is correlated for nonpolar solutes with the following expressions: (1) For LDPE, ln(1/K_P) = ?1.561 + (2.057 + 1.438ω) (T_c/T)²; (2) For PIB, ln(1/K_p) = ?1.347 + (1.790 + 1.568ω) (T_c/T)², in which ω is the acentric factor and T_c the critical temperature of the solute. In obtaining the above correlations we have used 27 solutes covering 115 data points for LDPE, and 18 solutes covering 148 data points for PIB. We have calculated values of 1/K_p from the literature data reported in terms of the retention volume (V), weight-fraction Henry's constant (H₁), activity coefficient at infinite dilution (Ω), Flory–Huggins interaction parameter (χ), or V/P obtained from high pressure sorption experiments. The correlations obtained in this study permit one to estimate with reasonable accuracy the solubility of gases and volatile liquids in either LDPE or PIB, with information on the acentric factor (ω) and critical temperature (T_c) only. The relationship for LDPE is also applicable for solubilities in high-density polyethylene. Relationships for the heat of vaporization of solutes from infinitely dilute LDPE or PIB solutions are also derived from the temperature variation of 1/K_p.     

The effect of gel composition on the uranyl ions adsorption capacity of poly(N‐vinyl 2‐pyrrolidone‐g‐citric acid) hydrogels prepared by gamma rays

Poly(N‐vinyl 2‐pyrrolidone‐g‐citric acid) (PVP‐g‐CA) hydrogels with varying compositions were prepared from ternary mixtures of N‐vinyl 2‐pyrrolidone–citric acid–water by using ⁶⁰Co γ‐rays. The effect of gel composition on the uranyl ions adsorption capacity of PVP‐g‐CA hydrogels was investigated. Uranyl adsorption capacity of these hydrogels were found to be in the range of 18–144 mg [UO]/g dry gel from the aqueous solution of uranyl nitrate and 22–156 mg [UO]/g dry gel from the aqueous solution of uranyl acetate, depending on the content of citric acid in the hydrogel, while poly(N‐vinyl 2‐pyrrolidone) hydrogel did not sorb any uranyl ion. The swelling of PVP‐g‐CA hydrogel containing 2.7 mol % CA was observed in water (1620%), in uranyl acetate solution (1450%) and in uranyl nitrate solution (1360%), as compared to 700% swelling of pure PVP hydrogels. The diffusion coefficients were varied from 12.57 up to 4.04 • 10⁻⁸ m² s⁻¹. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1037–1043, 2000     

Numerical and experimental investigation of three-dimensional flow in extrusion dies

The univariant element, Q₁ P₀, and the multivariant elements, QP₀ and R P₀, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q₁ P₀ element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q P₀ and R P₀, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.     

Morphological studies of the modified materials: Low-density polyethylene/poly(acrylic acid)/europium(III) and low-density polyethylene/poly(acrylic acid)/uranyl ion

The morphology of low-density polyethylene (LDPE) modified by in situ sorption and thermal polymerization of acrylic acid (AA) in the matrix was examined. The microstructure of the LDPE/poly(acrylic acid) (PAA) materials after Eu³⁺ and UO ion exchange was investigated. The phase behavior of these materials was analyzed using X-ray diffraction, scanning electron microscopy (SEM), and thermal measurements (DSC). The X-ray dif-fraction studies showed that PAA is located at amorphous region of the matrix. The LDPE/PAA surface, as investigate by SEM, was apparently homogeneous before and after Eu³⁺ and UO ion exchange, respectively. Two T_g values were found for the LDPE/PAA material before and after Eu³⁺ ion exchange. Also, three and four T_g values were found for LDPE/PAA after UO ion exchange depending on the amount of UO in the modified matrix. This indicates microphase domains in the LPDE/PAA-, LPDE/PAA/Eu³⁺-, and LPDE/PAA/UO -modified materials, although a lack of visible phase separation in the micrographs was observed. © 1996 John Wiley & Sons, Inc.     

Estimation of the energetic parameters associated with the aerobic degradation of quinoline by Comamonas acidovorans in continuous culture

An estimation of the true growth yields and maintenance coefficients for Comamonas acidovorans DSM 6426 under continuous cultivation on quinoline has been performed. The data were checked for consistency using available electron, carbon and nitrogen balances. The true biomass energetic yields, η_max, and energetic maintenance coefficients, m_e, were estimated using two models based on control of growth rate and control of substrate uptake rate, respectively. The estimations were converted to the various familiar true growth yield and maintenance units such as substrate-based (Y, m_S/X), oxygen-based (Y, m) and carbon dioxide-based (Y, m) units. For the complete mineralization of quinoline by C. acidovorans, values of η_max = 0.371 and m_e = 0·0426 h^?1 were obtained.     

Intrinsic birefringence of nylon 6

Different values are reported in the literature for the intrinsic birefringence of the crystalline (Δn) and the amorphous (Δn) phases in nylon 6. Mostly, these values have either been determined by extrapolation (and then it is assumed that Δn = Δn) or calculated theoretically. In this study, intrinsic birefringence values Δn and Δn for nylon 6 were determined using the Samuels two-phase model which correlates sonic modulus with structural parameters. Three series of fiber samples were used: (1) isotropic samples of different degrees of crystallinity for estimation of E and E moduli at two temperatures. The following modulus values were obtained: 1.62 × 10⁹ and 6.66 × 10⁹ N/m² for 28.5°C, and 1.81 × 10⁹ and 6.71 × 10⁹ N/m² for ?20°C; (2) anisotropic, amorphous fiber samples for estimation of Δn = 0.076 and E = 1.63 × 10⁹ N/m² at 28.5°C; (3) semicrystalline samples of various draw ratios for estimations of Δn = 0.089 and Δn = 0.078. All measurements were carried out with carefully dried samples to avoid erroneous results caused by moisture.     

Study on the thermal stability of heterogeneous nucleation effect of polypropylene nucleated by different nucleating agents

The thermal stability of the heterogeneous nucleation effect of polypropylene (PP) nucleated with an organic phosphate (A) and two kinds of sorbitol derivatives (B and D) was investigated by DSC multiscanning. For pure PP, the peak temperature of crystallization (T) was little changed with an increasing number of DSC scans, indicating that nucleation of PP is thermally stable. For the PP nucleated with an organic phosphate (PPA), the temperatures at the onset of crystallization (T) and at the completion of crystallization (T); the peak temperature of crystallization (T) and melting (T); and the heat of crystallization (ΔH_c) and fusion (ΔH_m) of PP are higher than those of pure PP and were little influenced with an increasing number of DSC scans. For PP nucleated with the sorbitol derivatives (PPB and PPD), the T, T, T, and T decreased with an increasing the number of scans. These results indicated that the thermal stability of heterogeneous nucleation effect of the nucleating agent A is higher than that of nucleating agents B and D. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1643–1650, 2002     

Surface free energy analysis of polymers and its relation to surface composition

The dispersion force component of surface free energy, γ, and the nondispersive interaction free energy between solid and water, I, were determined by the two-liquid contact-angle method, i.e., by the measurement of contact angles of water drops on plain solids in hydrocarbon, for commercialy available organic polymers such as nylons, halogenated vinyl polymers, polyesters, etc. A method to estimate the I values from the knowledge of the polymer composition is also proposed, on the basis of the assumption of the spherical monomer unit and the sum of interactions between functional groups and water molecules at the surface.