Permeation and sorption of CO2 through amine-contained polyurethane and poly(urea–urethane) membranes

As an absorbent of CO₂, tetraethylenepentamine (TEPA) and/or N-methyldiethanolamine (MDEA) was introduced into the hard segment as chain extenders of the series urethane polymer (PU), urea–urethane polymer (PUU), and segmented urethane/urea–urethane copolymer (SPU) based on 4,4′-diphenylmethane diisocyanate (MDI) and either poly(ethylene glycol (PEG)-400 or -600. The obtained polymers thus contained a nearly equal weight composition of both soft and hard segments and were prepared as polymer membranes for permeation and sorption of CO₂. The properties of the polymer membranes were characterized using a Fourier transform IR spectrophotometer, thermal gravimetric analysis, and rheometric measurement. The permeation and sorption isotherms as a function of temperature and pressure as well as the activation energy of permeability and diffusivity and the enthalpy change of the solution were measured. The test temperatures were carried out above and below the T_gs of soft-segment domains or the T_gh of hard-segment domains. The steady-state permeability (P) and diffusion coefficients (D) obtained ranged from 1.01 to 12.9 barrer and 1.04 to 4.04 cm²/s, respectively, and the solubility coefficients (S), from 0.529 to 3.43 cm³(STP)/cm³ polymer-atm at 10 atm and 35°C. The TEPA-containing polymer membranes showed a smaller P and D but a larger S than did MDEA-containing ones. The membranes comprising PEG-600 exhibit the values of P, D, and S at about 11.5-, 2.5-, and 4.5-fold the PEG-400 ones, respectively. For SPU membranes, above T_gs or T_gs, the pressure dependencies of P followed the modified free-volume model. On the other hand, below T_gs, they exhibited a minimum permeability at a certain pressure caused by the plasticization action of sorbed CO₂. The sorption isotherms of CO₂ indicated that the membranes comprising PEG-400 can be described by a dual-mode sorption model below T_gs. Also, the SPU polymer membranes obied the Henry's law above T_gs as well as T_gh. The characteristic constants of the sorption model were also determined and are discussed. © 1996 John Wiley & Sons, Inc.     

Effect of fractional free volume and Tg on gas separation through membranes made with different glassy polymers

The aim of this work is to study how the characteristics of the polymer used to manufacture gas separation membranes influence its permeability and selectivity. It has been shown that the gas diffusivity decreases with the kinetic diameter of the gas except for CO₂, probably due to its high condensability. While solubility increases with the gas condensation temperature and clearly with the glass transition temperature of the polymer for each gas. The permeabilities of CO₂, CH₄, O₂, N₂ increase for increasing glass transition temperatures. Nevertheless only the selectivity of CO₂ versus the other gases increases significantly when polymers with high glass transition are used. The Robeson limit in a selectivity‐versus‐permeability plot is approached for CO₂/CH₄ when T_g increases. This distance to the Robeson limit, for this pair of gases, results to decrease for increasing T_g. For the case of the O₂/N₂ selectivity remains approximately constant with an appreciable increase in permeability for polymers with increasing T_g. Permeability increases due to the corresponding increase in fractional free volume, FFV, that appears for increasing glass transition temperatures, T_g. This correlation of FFV with T_g has been confirmed by obtaining FFV by different methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Gas transport in poly(vinyl benzoate)

The transport parameters of nine gases (O₂, N₂, CO₂, He, Ne, Ar, Kr, Xe) through poly(vinyl benzoate) (PVB) have been measured by the time lag method above and below the glass transition temperature, T_g The results are compared with the related data of poly(vinyl acetate) (PVAc) by Meares and discussed as the effect of replacement of the methyl group by a phenyl group in the side chain of PVAc. Small molecules, such as H₂, He, and Ne, diffuse more easily through PVAc than PVB, but the tendency is reversed for the larger gases. The activation energy for diffusion is proportional to the squares of the Lennard–Jones diameters of the gases below the T_g. On the other hand, above the T_g, linear relation is obtained to the cubes of the diameters. Solubility behavior is discussed by comparing the heats of solution for PVB and PVAc.     

Structure variation and puncture resistance of stretched crosslinked polyethylene film: Effects of stretching temperature

Crosslinked polyethylene films were prepared and stretched at different temperatures (below and above melting temperature). The stretching temperature exhibited pronounced effects on the structure and puncture resistance of the films. Combining the results of differential scanning calorimetry, 1D X-ray diffraction, 2D X-ray diffraction, and scanning electron microscope, it was demonstrated that the film stretched above T _m has lower crystallinity, thinner lamellar, and larger crystal grain size than that stretched below but near T _m. All the stretched films showed highly oriented lamellae in the bulk and arranged perpendicular to the stretching direction. The crystals of the film stretched below T _m were arranged in highly aligned microfibrils with distinct interlamellar boundary and the crystals of the film stretched above T _m were arranged in a progressively less orderly manner with increased interlamellar entanglement. Due to this structure difference, the puncture resistances of the films stretched above T _m were much larger than that stretched below T _m. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47542.     

Effects of mechanical drawing on gas transport in an emulsion acrylic multipolymer

A study was conducted on the gas sorption and transport properties of a multiphase commercial acrylic polymer trade-named Korad ACV before and after subjecting the polymer to mechanical drawing operations. The Korad system is an emulsion-polymerized amorphous composite comprised of a glassy, predominantly PMMA matrix phase and a ply(butyl acrylate)-dispersed phase surrounded by a PMMA/PBA copolymer shell. Large increases (up to eightfold) in permeability P to several gases were observed upon drawing Korad. The observed changes in the permeability to He, Ar, N₂, and CH₄ on drawing were correlated with the draw ratio, drawing temperature, and molecular diameter of the gas penetrant. Most of the increase in permeability occurred at low draw ratios (1–2). The increases in P were most dramatic for drawing temperatures below or near the T_g of the matrix phase (about 90°C) and were quite small for drawing temperatures 30°C or more above the matrix T_g. The extent of the permeability increase also depended on the gas, being greatest for CH₄ and essentially imperceptible for He. The changes in permeability behavior were interpreted in terms of a morphological transformation in the phase of the drawn Korad, which causes the originally dispersed rubber particles to assume a more continuous character. The behavior of the composite was modeled by the Takayanagi and Nielson treatments of two-phase composite systems. Volumetric, thermal, mechanical, and viscoelastic properties were measured for the as-received and processed Korad films to elucidate physical changes in the drawn polymer.     

Temperature dependency of gas barrier properties of biodegradable PP/PLA/nanoclay films: Experimental analyses with a molecular dynamics simulation approach

Polypropylene (PP)/poly(lactic acid) (PLA)/clay nanocomposite films with various compositions (PP‐rich and PLA‐rich) were prepared. Their structural and barrier properties against CO₂, O₂, and N₂ were investigated. The microstructure of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy, and wide angle X‐ray scattering. The PP‐rich with 75/25 composition revealed the best barrier properties against all the gases which could be justified according to its microstructure. Selectivity of O₂/N₂ and CO₂/N₂ was also measured. It was found that the addition of nanoclay as a gas barrier component reduced the permeability in both systems. The permselectivity was also reduced in the PP‐rich films while it was increased in the PLA‐rich system. Moreover, the temperature dependency of permeability, selectivity, and permselectivity for PP, PLA, and PP/PLA (75/25) samples was examined. The results showed that the temperature dependence of permeability obeyed an Arrhenius equation and order of activation energy of permeability for O₂, CO₂, and N₂ gases was found to be E_P < E_P/PLA < E_PLA. According to solubility measurements, the order of solubility coefficient for gases was as follows: CO₂ > O₂ > N₂. Finally, the molecular dynamics (MD) simulation was performed to estimate the diffusivity coefficients of the gases and showed that solubility increases with increasing temperature, which was in accordance with the experiments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46665.     

Gas transport in poly(alkoxyphosphazenes)

The permeability of four structurally related poly(alkoxyphosphazenes), three isomers of poly(dibutoxyphosphazenes) (PBuP), and poly(di-neopentyloxyphosphazene) (Pneo-PeP), to 13 gases has been determined by the time-lag method. Systematic variations in chemical structure have shown a large effect of side chains on permeabilities and permselectivities. The permeability of poly(di-n-butoxyphosphazene) (Pn-BuP) is of the order of 10^?8 cm³ (STP) cm/(cm² s cmHg) for many gases, and the value for a large gas is higher than that for a smaller one. For small gases such as He and H₂, poly(di-sec-butoxyphosphazene) (Ps-BuP) is as permeable as Pn-BuP, but its diffusivities for larger gases such as Xe and C₃H₈ are about one order lower than those of Pn-BuP. While the permselectivity of Pn-BuP is determined by the solubility, that of Ps-BuP depends on both the diffusivity and solubility factors. The property of poly(diisobutoxyphosphazene) (Pi-BuP) is intermediate between them. These polymers are constitutionally identical, and the only difference is the arrangements of carbons in the side groups. As the side chains become bulky, the permeability decreases, whereas the permselectivity increases. Further decreases of diffusivity and then permeability are observed for Pneo-PeP, whose side groups have one more methyl group than does Pi-BuP. But the solubility data are not much different from other three polymers and the diffusivity factor becomes more significant in permselectivity. The diffusivity depends on the polymer structure much more than does the solubility. The relationships between chemical structure and gas diffusivity and solubility are discussed.     

Synthesis of polymer materials by low energy electron beam. III. Effects of polymerization temperature in EB solid-state polymerization of semicrystalline urethane-acrylate film

In an electron beam (EB) polymerization of a urethane-acrylate prepolymer, the polymerization temperature greatly affected the structure and properties of the resulting gel film. Urethaneacrylate, which was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate, was used as a prepolymer. The prepolymer was semicrystalline and showed a melting point in the region of 50–60°C. The maximum polymerization rate of the prepolymer was obtained when the prepolymer film was irradiated in the temperature range of 25–40°C. EB polymerization below the melting point (T_m) of the prepolymer produced semicrystalline polyurethane-acrylate gel films with a spherulitic texture. On the other hand, EB polymerization above the T_m destroyed the crystalline phase of the prepolymer to give transparent gel films. The gel film cured below the T_m had higher stress at yield, Young's modulus, and tensile strength than those cured above the T_m. Such temperature effects are attributed to whether or not the EB polymerization proceeds with retention of crystalline structure of the prepolymer.     

Syntheses and properties of UV-autocurable prepolymers. Semicrystalline urethane-multiacrylates

A series of UV-autocurable urethane-multiacrylate prepolymers, which were semicrystalline and showed melting points in the region of 40–50°C, was synthesized. Also, the effects of curing temperature and acrylic functionality on the structure and properties of the cured films were investigated. These prepolymers are solids and opaque at room temperature. In general, UV curing reactions of solid prepolymers are less efficient when compared with those of liquid prepolymers. UV curing reactions at curing temperatures below the melting point (T_m) of the prepolymers produced semicrystalline urethane-multiacrylate cured films. On the contrary, UV curing reactions above T_m destroyed the crystalline phase of the prepolymers and improved the transparency of the cured films. The films cured below T_m of the prepolymers had higher both breaking strength and Young's modulus, and a higher glass transition temperature (T_g), but a lower elongation at break than those cured above T_m. Such curing temperature effects were attributed to the retention or disappearance of the crystalline structure of the prepolymers during UV curing reaction. At curing temperatures below T_m, an increase in acrylic functionality of the prepolymer resulted in a fast curing rate and a higher crosslinking density of the cured films. Therefore, an increase in acrylic functionality of the prepolymers gave cured films with higher breaking strength and Young's modulus, but a lower elongation at break.     

Polystyrene/Sn–Pb alloy blends. II. Effect of alloy particle surface treatment on dynamic rheological behavior

The effect of filler surface treatment on the dynamic rheological behaviors of polystyrene filled with Sn–Pb alloy particles was tested below and above the melting temperature (T_m) of the alloy. The mechanical relaxation relevant to the T_m of the alloy in the composite was diminished by the filler surface pretreatment. In the whole temperature range of interest, there existed a secondary plateau of the storage modulus at low frequencies. The effect of alloy particle surface treatment on the plateau was related to the matter‐state change (from solid to liquid) of the alloy. Above the T_m of the alloy, the surface treatment of the alloy affected the secondary plateau, but below the T_m, it did not. The analyses of Cole–Cole diagrams of the systems suggested that untreated and pretreated alloy fillers all retarded the relaxation processes in the molten state of polystyrene below the T_m of the alloy and that the relaxation process was separated into the high‐frequency relaxation of the phases and the low‐frequency relaxation of the droplets above the T_m. The surface treatments of the alloy filler further enhanced this action. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3173–3179, 2002     

Osmotic Dehydration of Apple Cylinders: II. Continuous Medium Flow Heating Conditions

Mass transfer of apple cylinders during osmotic dehydration was quantitatively investigated under continuous medium flow conditions. The influences of the main process variables (solution concentration, operation temperature, contact time, and solution flow rate) were determined. A second-order polynomial regression model was used to relate weight reduction (WR), moisture loss (ML), solids gain (SG), and mass diffusivity (D _m and D _s ) to process variables. The conventional diffusion model using a solution of Fick's unsteady state law involving a finite cylinder was applied for moisture diffusivity and solute diffusivity determination. Diffusion coefficients were in the range of 10^?9–10^?10 m²/s, and moisture diffusivity increased with temperature and flow rate, increased with solution concentration (> 50°Brix), and decreased with increasing solution concentration (< 50°Brix), but solids diffusivity increased with temperature and concentration and decreased with increasing flow rate. A continuous-flow osmotic dehydration (CFOD) contactor was developed to be a more efficient process in terms of osmotic dehydration efficiency: time to reach certain weight reduction (T _w ) and moisture loss (T _m ) were shorter than that of conventional osmotic (COD) dehydration processes. Effectiveness evaluation functions used in this study could be widely applied to osmotic dehydration system evaluation.     

Structure and gas permeability of multi-wall carbon nanotube buckypapers

We report on the filtration behavior, scanning electron microscopy (SEM) and gas permeability of multi-wall carbon mats (buckypapers). The SEM-apparent macropore diameter, image fractal dimension and lacunarity (a measure of translational invariance) of the samples averaged at 38 nm, 1.82 and 0.55, respectively. Their N₂ adsorption analysis revealed an average BET specific surface area of 197 m²/g, BJH pore diameter of 2.67 nm and FHH fractal dimension of 2.492. These parameters were rather insensitive to the preparation conditions. The effective diffusivity of six common laboratory gases (O₂, N₂, H₂, He, CO₂, CH₄) through buckypapers of different thicknesses was also measured. Results fell into the 3-12 × 10⁻⁹ m² s⁻¹ range and correlated with the kinetic diameter of the gases.     

Nonisothermal crystallization of s‐PP fractions

Syndiotactic polypropylene (s‐PP) was prepared by metallocene catalyst and was fractionated with the temperature rising elution fractionation (TREF) technique. The nonisothermal behavior of the obtained fractions was investigated. Fractions was first cooled at different rates and then heated at a constant rate. The parameters such as the peak crystallization temperature (T_c), the onset crystallization temperature (T_on), the difference between T_on and T_c (ΔT₁ = T_on − T_c), the crystallization enthalpy (ΔH), the peak melting temperatures (T_m1, T_m2), and the difference between the T_m1 and T_m2 (ΔT₂ = T_m2 − T_m1) were obtained. The dependence of these parameters on cooling rate, syndiotacticity, and molecular weight was discussed. It is found that T_c, T_on, ΔH, T_m1, and T_m2 systematically increase with increasing syndiotacticity and are depressed on increasing the cooling rate. Cooling rate, syndiotacticity, and molecular weight show different influences on ΔT₁. In the melting process of s‐PP, double peaks were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 897–901, 1999     

Physical aging of thin glassy polymer films monitored by gas permeability

The physical aging at 35 °C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O₂, N₂, and CH₄, for over 200 days. Several techniques were used to accurately determine the thickness of films (∼400 nm-62 μm) in order to obtain absolute permeability coefficients and to study the effects of film thickness on the rate of physical aging. Each film was heated above the polymer T_g to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free volume, was observed at temperatures more than 150 °C below T_g for thin films of each polymer compared to what is observed for the bulk polymers. The films with thicknesses of approximately 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O₂/N₂ selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on physical aging were examined briefly.     

Polystyrene/Sn–Pb alloy blends. I. Dynamic rheological behavior

The dynamic rheological behavior of polystyrene filled with low‐melting‐point (T_m) Sn–Pb was investigated at temperatures below and above the T_m of the alloy, 183°C. In the whole temperature range of interest, there existed a secondary plateau in the plot of the dynamic storage modulus versus frequency (ω) at low ωs, and the influences of alloy content and temperature on the plateau were related to the matter state (liquid or solid) of the alloy. We believe that the secondary plateau observed below the alloy T_m was due to the network‐type structure formed by the agglomeration of solid filler particles, whereas the plateau above T_m was due to the deformability and relaxation of the liquid alloy droplets. By analyzing the Cole–Cole diagrams, we suggest that the alloy fillers retarded the relaxation processes for polystyrene melt when the temperature was lower than the T_m. However, there existed two separated relaxation processes when the temperature was higher than the T_m, that is, the high‐ω relaxation of the phases and low‐ω relaxation of the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3166–3172, 2002     

O2 and N2 gas permselectivity of alternating copoly(vinylidene cyanide–vinyl acetate)

The sorption and permeation of oxygen and nitrogen in and through alternating copoly(vinylidene cyanide–vinyl acetate) [copoly(VDCN–VAc)] (T_g = 176°C) membranes annealed for different periods just below T_g, 160°C, were investigated over the pressure range from 100 to 1000 cmHg. The dual-mode sorption and mobility models were used to analyze the results. A sub-T_g annealing of copoly(VDCN–VAc) caused a slight decrease in the amount of sorption in the membranes. This decrease in the amount of oxygen and nitrogen sorption can be attributed to a decrease in the Langmuir sorption capacity term, C′_H, with increasing sub-T_g annealing period. The densification of copoly(VDCN–VAc) membranes caused simultaneously by the annealing remarkably reduced diffusion coefficients for both gases. The reduction in diffusion coefficients of Langmuir mode, D_H, for both gases was found to be larger than that of Henry's law mode, D_D. Furthermore, permselectivity of oxygen to nitrogen, the ratio of permeability coefficient of oxygen to nitrogen (P O₂/P N₂), reached to 11.8 for the copoly(VDCN–VAc) annealed for 30 h. Evidently the reduction of D_H and D_D for nitrogen with increasing annealing period was much larger than that for oxygen.     

Anionic copolymers of octanelactam with laurolactam (nylon 8/12 copolymers). VII. Study of diffusion and permeation of gases in undrawn and uniaxially drawn (conditioned at different relative humidities) polyamide films

The permeability coefficient of a wide range (0/100–100/0 octanelactam/laurolactam [OL/LL] mol/mol) of novel copolyamides (nylon 8/nylon 12) was determined and related to the diffusion rate over a range of temperatures: T_g–30 to T_g + 40°C. An inflection in the plot of permeability vs. 1/T (K) provided an indirect indication of glass transition value and agreed satisfactory with DSC and DMTA measurements. Both uniaxially drawn and undrawn membranes were evaluated and the permeability values were correlated with the % crystallinity. The reduction in solubility, diffusivity, and permeability with increasing draw ratio was attributed to a substantial increase in % crystallinity. Finally, the effect of absorbed water on gas permeability of polyamide films was examined. In most homopolyamides and copolyamides, the higher the water absorption of films the higher the permeability values. © 1993 John Wiley & Sons, Inc.     

Improvement of the processability of poly(ether ketone ketone) by the addition of a thermotropic liquid crystalline polymer

The addition of a thermotropic liquid crystalline, wholly aromatic copolyester, TLCP, improved the melt processability of poly(ether ketone ketone), PEKK. The tensile strength and modulus of the blends also improved with increasing TLCP, but the elongation at break decreased significantly. The blends were phase‐separated, but the polymers were partially miscible as evident from shifts of the glass transition temperature (T_g) of each component towards that of the other component in the blend. Similarly, the melting points (T_m) of both components were depressed by blending. When the crystallization temperature was above T_m of the TLCP, the PEKK crystallization rate in the blend was slower than for the pure material, while crystallization was faster when the temperature was below T_m of the TLCP. Polym. Eng. Sci. 44:541–547, 2004. © 2004 Society of Plastics Engineers.     

Effect of sub-Tg relaxations on the gas transport properties of polyesters

The relationship was determined between sub-T_g molecular motions and the transport of O₂ and CO₂ in amorphous polyesters and copolyesters based on poly(ethylene terephthalate) [PET] and poly(1,4-cyclohexylenedimethylene terephthalate) [PCDT], Modifications of the polyester with certain acid co-monomers restricted the molecular motions that occurred in the β-relaxation region and in turn decreased the O₂ diffusion coefficient. The solubility coefficient was unchanged by those modifications. Modification of PET with 1,4-cyclohex-anedimethanol increased the magnitude of the β-relaxation and both the diffusion and solubility coefficients of O₂. Similar relationships between the β-relaxation magnitude and CO₂ permeability were also found. The temperature dependence of O₂ permeability followed an Arrhenius relationship, with different activation energies (E_p) above and below the β-relaxation. The activation energy was smaller below the β-relaxation. Values of E_p above and below the β-relaxation did not depend on the chemical structure of the polymer.     

Relation between liquid-liquid phase separation and crystallization in isotactic and syndiotactic polypropylene solutions

The effects of the stereospecificity of a polymer chain and of the interaction in polypropylene (PP) solutions on the relation between liquid-liquid phase separation and crystallization were investigated by using an isotactic PP (i-PP) and a syndiotactic PP (s-PP) of high stereoregularity and of similar molar mass. Dialkyl phthalate was used as a solvent. A series of dialkyl phthalates with a different number of carbon atoms in the alkyl chain was employed to control the interaction between polymer and solvent. Phase transition temperatures were measured by optical microscopy with a hot stage. Liquid-liquid phase separation temperature (T_L-L) in the system of i-PP and dihexyl phthalate was located below its melting temperature (T_m). However, T_L-L for the s-PP system in the same solvent was elevated much above its T_m due to a decreased T_m and increased T_L-L. The reduced solubility of s-PP is primarily attributed to enhanced hydrophobicity arising from alternate positioning of the methyl groups along the polymer chain. As the length of the alkyl chain in the phthalate increases, T_L-L decreases significantly and T_m decreases slightly, resulting in the value of T_L-L shifting below that of T_m for the solution of s-PP and dinonyl phthalate. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 159–163, 1998