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Methane reforming is an industrial process for hydrogen production having a high CO2 footprint that can be mitigated either by using renewable methane, or by recycling carbon dioxide from capture. Methane reforming assisted by an oxygen carrier was currently investigated, being an attractive option for production of hydrogen and carbon monoxide mixtures. The distinctive aspect of present research was the development of three dif-ferent granular materials based on CeO2 to be used in fluidized beds, obtained by pelle-tization and calcination at 900 and 1200 degrees C of CeO2 or CeO2/Al2O3 powder. Fluidization and abrasion tests were performed at cold and hot conditions, showing the best attrition re-sistance of materials calcined at the highest temperature, with attrition rate equal to 0.3 %/h. Conversely, thermogravimetric tests at 900 degrees C revealed the best performance of CeO2 granules sintered at lower temperature with respect to the others in terms of oxygen supply capacity, achieving 0.55 of conversion degree. Reforming and regeneration cycles were performed in fluidized bed at 940 degrees C with CeO2/Al2O3 granules, providing in-stantaneous methane conversion up to 37 %, high carrier conversion (0.87) and low carbon deposition (2.9 mg/g) during the reforming step.(c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

The present invention relates to a process, and relevant plant (1), for separating at least one key component (KC) from a multicomponent gas stream (GS) that is caused to flow on a composite membrane (20) comprising dense domains (21) permeable to the key component (KC) and porous domains (22) intended to adsorb preferentially the key component (KC). A permeate stream (PS), separated from the multicomponent gas stream (GS) and containing the key component (KC), is extracted through a discharge line (5) depending on the measured value of the pressure (P) downstream the membrane (20), Upon reaching a predetermined maximum value (pmax) of such pressure (P), the permeate stream (PS) is extracted until reaching a predetermined minimum value (pmin) of such pressure (P) downstream the membrane (20), and upon reaching such predetermined minimum value (pmin), the extraction of the permeate stream (PS) is stopped. Thus by repeating such operations extracting and stopping the extraction downstream the membrane (20), alternated cycles are generated and a pseudo-steady state condition is accomplished, where the plant (1) receives the feed stream (GS) in the continuous mode and releases the permeate stream (PS) in an intermittent manner, while a retentate stream (RS), containing the components of the feed stream (GS) that have not been collected in the permeate stream (PS) is discharged with continuity. By handling the predetermined maximum value (pmax) and minimum value (pmin) of the pressure (P) downstream the membrane (20), that is of the extraction cycle of the permeate stream (PS), it is possible to considerably vary the efficacious permeance value and the separation factor of the process without modifying the membrane (20), the module (10) where it is contained or the feeding conditions.

This article reports on an experimental research dealing with the use of solid sorbents for CO2 uptake from gaseous stream at high temperature. Hydroxyl-apatite and strontium carbonate have been adopted as starting materials for preparing a regenerable sorbent, upon calcination. Both sorbents have been characterized in TG tests with an alternating atmosphere of CO2/Ar and Ar, accomplishing steps of carbonatation and calcination/regeneration at temperature over 900 °C. The apatite based sorbent maintained its capability of CO2 absorption for several cycles, whilst the Sr based sorbent exhibited a quick decay of its capability due to changes of the micro-structure. The CO2 carrying capacity after conditioning reached stable values of around 3% and 5% for apatite and strontium sorbents, respectively. TG curves were worked out in order to obtain kinetic data for both carbonatation and calcination, showing that apatite is slightly more reactive than strontium sorbent. The TG tests were also complemented by a fixed bed experiment aimed at demonstrating the feasibility of apatite regeneration with steam.

The non-equilibrium thermodynamic approach to describing properties of glassy polymers, earlier applied in the so-called NELF model using Lattice Fluid Theory, is generalized to the use of arbitrary equations of state. Application to Statistical Associating Fluid Theory (SAFT) is discussed in detail and use of this approach to predict opr correlate gas solubility in glassy polymers is presented for the case of low-pressure sorption. Prediction procedures rely on volumetric data for the pure polymer and gaseous species, while for data correlation a temperature independent binary interaction coefficient is used as an adjustable parameter. Results from model calculations are compared with literature data for gas solubility in polycarbonate and polysulfone. Analysis of solubility coefficient variations above and below the glass transition temperature indicates thet the non-equilibrium approach is the proper procedure to extend an EoS description of thermodynamic properties to the glassy state.

The diffusion coefficient of ethanol and of n-pentane in PTMSP, at 27°C, was measured as a function of concentration up to a penetrant content of about 12% by weight, for polymer samples obtained through different processes; differential sorptions and desorptions with vapor phases were considered. In the case of ethanol a nonmonotonous behavior was observed for the diffusivity, while in the case of n-pentane the same property was found to monotonously decrease with increasing the penetrant content. The sorption isotherms were also reported, indicating that n-pentane exhibits a typical dual mode behavior, while ethanol follows an unusual s-shape curve. The chemical potential of the dissolved penetrants, calculated directly from the isotherms, shows the very different importance of the energetic interactions of the two penetrants with the polymer units. In spite of the remarkably different concentration dependencies observed for both solubility and diffusivity of the two penetrants, the mobility factors are in both cases monotonously decreasing with the penetrant concentration, and follow very similar trends. The significant differences observed for the concentration dependence of the diffusion coefficients are, thus, associated to the thermodynamic contributions, which are very different for n-pentane and ethanol. Different polymeric films, obtained through different solvent evaporation processes, show quite different solubility, diffusivity and mobility for both ethanol and n-pentane. On the other hand, the ratio between the mobility of the two penetrants as well as the slope of mobility as function of the concentration remains the same for all the different samples inspected. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2245–2258, 1997

Process characterization of 400 nm thick LPCVD-SiO 2 films based on TEOS-Ozone chemistry was performed. Films were deposited on six inch silicon wafers using a single wafer cluster system. The process characterization was carried out starting from a standard process taken as reference, around which the main process parameters, temperature (300-430 o C), pressure (50-80 torr), and gas ratio (3:1-7:1), were varied one at a time whilst keeping the remainder fixed. The effect of process parameters on deposition rate, thickness uniformity within wafer, film stress, etch rate and refractive index was investigated. On the basis of these results the optimum working conditions for the industrial implementation of the process were determined and proven for sidewall spacer formation and 1Mbit EPROM devices. An interpretation of the data of deposition rate is provided in terms of the elementary processes involved

The representation of liquid–liquid equilibria (LLE) in ternary systems composed by water, 1,4-dioxane and different grades of poly(lactic acid) (PDLLA and PLLA), has been addressed through the PC-SAFT equation of state (EoS), in which the scheme of induced association is used to represent the interaction between solvent (dioxane) and non-solvent (water). The model parameters devoted to the description of pure component properties, as well as those pertinent to the representation of thermodynamic behaviour of solvent/non-solvent mixtures, were tuned on the basis of specific pressure–volume–temperature (PVT) data for the corresponding systems. Only the binary parameters for polymer–solvent and polymer/non-solvent pairs were adjusted to obtain a useful representation of experimental LLE data for the ternary systems. A suitable description of the thermodynamic properties of ternary mixtures was obtained using temperature-independent binary interaction parameters in the range 25–80 °C, and the consistency of the approach in the entire composition range was verified against experimental solubility data specifically measured for the polymer/non-solvent pair. The model shows good ability in the description of the thermodynamic properties of the system and it represents a reliable tool for the prediction of LLE also at conditions different from those considered for its set-up. This approach thus represents a useful designing tool for processes, such as thermally induced phase separation (TIPS), used in the preparation of microporous polymeric scaffolds.

The sorption of organic vapors of different chemical nature, molecular weight and polarity in glassy Matrimid 5218 polyimide films is measured and modeled in the entire activity range up to saturated vapor conditions. Experimental isotherms show several different peculiarities according to the nature of the solute component, consistent with the glassy character of the polymeric matrix. These features range from high vapor solubility coefficient at infinite dilution to swelling and plasticization of the polymer matrix depending on temperature and solute affinity. The various behaviors are then discussed by means of a thermodynamic model for properties of glassy polymeric phases. Indeed, the Non-Equilibrium Lattice Fluid (NELF) model is used to interpret the Vapor-Liquid-Equilibrium below Tg, while the corresponding equilibrium Lattice Fluid model was considered to the same purpose for the case of plasticization conditions in the system. This representation is able to describe consistently all different observed features and allows for a predictive procedure to reproduce solubility isotherms over a wide activity range.

The nonequilibrium lattice fluid (NELF) model is here implemented with a simplified relation for bulk rheological behavior of glassy polymers, to obtain a predictive model for pseudoequilibrium solute content and volume dilation induced by swelling agents. The rheological model discussed in this work is ultimately used to derive a relation for the pseudoequilibrium volume of the polymeric system as a function of temperature and solute fugacity. The model makes use of two nonequilibrium parameters which, in turn, can be determined through the analysis of nonequilibrium pVT properties of the polymeric species. The predictive ability of the new model for solubility and volume swelling was tested by means of the comparison of model predictions and correlations with experimental data, available in the literature, for different polymer/penetrant pairs. The results obtained from the comparison allow one to conclude that the model is not just useful to describe the swelling effect of penetrants but also to recognize conditions at which plasticization by solute species induces a glass to rubber transition in the polymeric system.

The present work is focused on the characterization of the sorption properties of gaseous mixtures of CO2 and C2H6 in a crosslinked poly(ethylene oxide) copolymer, XLPEO, in a wide range of temperatures from a modeling point of view, by the use of Sanchez Lacombe EoS

The transport properties of high free volume glassy polymers such as poly(1-trimethylsilyl-1-propyne) (PTMSP) were analyzed by comparing the steady state permeation behavior with the transient diffusion of light hydrocarbons. It has been observed that the apparent diffusivity measured in the two different modes are indeed quite different from one another, even by nearly an order of magnitude. The behavior can be explained by considering the high free volume glassy polymer as a two-phase system formed by a continuous solid phase and a discontinuous nano-void phase, with a suitable degree of interconnections. The influence of pore distribution and pore connectivity on the differences observed between transient sorption and steady permeation behavior has been analyzed by performing various mathematical simulations of transient and steady state diffusion for different morphological structures of the two phase system, used to model the polymer matrix. Qualitative comparison indicates that the difference experimentally observed is associated to a pore interconnectivity effect and to the corresponding anisotropy in pore distribution.

A comprehensive study of the gas barrier properties of hybrid organic–inorganic coatings formed by polyvinyl alcohol (PVOH) and Si-SiO2, obtained via sol–gel technique, was carried out. It has been shown that the oxygen, nitrogen and carbon dioxide transfer rates of barrier polymers such as poly(ethylene terephthalate) and oriented polypropylene can be further reduced, by up to two orders of magnitude, with a thin coating (1–2 μm) of PVOH/Si-SiO2. More notably, it has been observed that the material maintains this feature even after a prolonged contact with water, which is a strong solvent for PVOH. Direct moisture sorption measurements show that silica lowers the water uptake of PVOH and inhibits sorption-induced swelling and plasticization of the polymer. Correlations between the gas transport properties of the hybrid coatings and factors such as the silica content, the type of polymeric substrate, the nature of penetrant and the temperature have been found, providing guidelines for the selection and design of multilayer materials for packaging applications. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

The nonequilibrium thermodynamics of glassy polymers (NET-GP) approach (Macromolecules 2005, 38, 10299.) has been applied to the development of a one-dimensional transport model aimed at describing the kinetics of sorption and dilation of polymeric films in supercritical carbon dioxide. The NET-GP model was combined with a simple rheological constitutive equation to build a sorption-diffusion-relaxation model able to describe mass uptake and swelling kinetics of polymeric films in contact with carbon dioxide over a wide range of pressures and temperatures. The model calculations are compared with data on mass sorption kinetics for CO2 in supported glassy poly(methyl methacrylate) (PMMA) films, measured in a high-pressure quartz crystal microbalance (QCM).

A new experimental apparatus has been set up to analyze the polymer dilation as well as the stress profile induced by vapour sorption in constrained films. The device couples the bending cantilever technique with a new digital micrometer which allows to measure both deflection and polymer swelling at the same time. The apparatus has been applied to study the effects of acetonitrile mass uptake in polycarbonate at 40°C, obtaining the time evolution of swelling and of cantilever deflection during integral sorption tests, in the activity range from zero up to 0.35. A simulation model is also proposed, which couples Fick’s law for diffusion to the study of strain and stress distributions in the cantilever; the mechanical problem has been formulated following the classical laminate theory. The relevant values of the material properties entering the model, as solubility, diffusivity and penetrant induced dilation, have all been determined through separate independent measurements, and the results obtained are in good agreement with the corresponding values reported in the literature. The simulation model is able to predict with good precision both the kinetics of deflection during sorption and its final equilibrium value, as well as the overall swelling kinetics, with no need of any adjustable parameters. The model allows also to calculate the time evolution of the stress profile in the polymer film during sorption/desorption steps.

An analysis of the empirical correlations that relate the solubility coefficient of gases at infinite dilution in glassy polymers to penetrant properties has been performed, by considering gas sorption as a succession of three steps: condensation of the penetrant, dissolution in the equilibrium polymeric phase, and departure of the system from equilibrium. The infinite dilution solubility coefficient is obtained from the contributions of the three steps, the first two of which involve standard equilibrium thermodynamics, while the latter requires nonequilibrium considerations and is described by using the nonequilibrium lattice fluid (NELF) model. The various terms have been evaluated for several gases in polycarbonate, polysulfone, poly(phenylene oxide), and poly(methyl methacrylate). It has been found that the largest term in the expression of solubility is due to condensation, which explains the observed correlation between solubility and critical temperature, while the out of equilibrium contribution to solubility, which generally gives numerical values lower than the condensation term, is in turn more strongly correlated to the penetrant critical volume.

It is observed in general that the solubility of gases and vapors in polymers, both in the rubbery and glassy phase, scales with measures of penetrant condensability, such as the Lennard-Jones parameter, the boiling temperature, or the critical temperature. For rubbery polymers, that behavior was found fully consistent with a simple equilibrium thermodynamic derivation, while no effective theoretical interpretation has been offered so far for the case of glassy polymers. On the other hand, a rigorous expression for the solubility coefficient S 0 in the limit of low pressures can be found based on the NELF model for gas solubility in glassy polymers, which also indicates its dependence on the characteristic parameters of the penetrants, such as cohesive energy density, molar volume and molecular weight. The values of ln( S 0 ) for a series of gaseous penetrants have been calculated with the NELF model for several common glassy polymers as polycarbonate (PC), polysulfone (PSf), poly(phenylene oxide) (PPO) and poly(methyl methacrylate) (PMMA). In all cases, ln( S 0 ) is linear with the penetrant critical temperature, T C , and the dependence on temperature and on the polymer fractional free volume can easily be evaluated by the model. The analysis points out also the specific roles of the energetic and entropic contributions to the trend observed for the solubility coefficient in glassy polymers.

Three models, two of them relying on free volume-the Cohen-Turnbull-Fujita (CTF) model and the Vrentas-Duda (VD) model, and the third being empirical using an exponential concentration dependence of the diffusivity, were applied to desorption data for a series of alkane penetrants (2,2-dimethylbutane, cyclohexane, n-hexane, n-decane, and n-tetradecane) in low-density polyethylene. The CTF model described the desorption data very well and better than the exponential diffusion law. The VD model with the attractive feature of being based on independently determined parameters was unsuccessful in describing the desorption data. Diffusivity data indicated that the three components outside the crystal core were less accessible to n-tetradecane than to the other penetrants. This indication was further substantiated by solubility data.

The solubility of gaseous mixtures of CO2 and C2H6 in cross-linked poly(ethylene oxide) (XLPEO) has been 11 modeled over a wide range of temperatures, pressures, and compositions with the Sanchez−Lacombe lattice fluid equation of 12 state (LF EoS). The model binary gas−polymer parameters have been determined from pure gas solubility data and kept 13 constant with temperature and composition. Multicomponent solubility is then calculated with no additional adjustable 14 parameters, using a fully predictive procedure. The LF EoS model describes well the mixed gas solubility behavior data over wide 15 ranges of temperature (from −20 to 35 °C), pressure (0−20 atm), and composition. The model also allows representation of the 16 solubility selectivity behavior of XLPEO at different conditions, permitting an a priori determination that ethane solubility is 17 significantly enhanced by the presence of CO2, with a consequent reduction in CO2/C2H6 solubility selectivity relative to the 18 pure gas value. In this regard, the behavior of this rubbery polymer is opposite that of many glassy systems, in which competitive 19 sorption is often dominant, and the solubility of the less soluble gas (i.e., C2H6 in this case) is decreased by the presence of CO2, 20 and the CO2 solubility selectivity is enhanced with respect to the pure gas value.

Solubility isotherms for n-pentane and n-hexane were measured in pure poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and in 1-trimethylsilyl-1-propyne/1-trimethylsilyl-1-n-hexyne 70/30 copolymer, using freshly prepared samples as well as aged films, at different temperatures. The experimental values of penetrant diffusivity, mobility and heat of mixing have been reported and discussed, based on direct positron annihilation lifetime spectroscopy information, Dual Mode Sorption Model and Non-Equilibrium Lattice Fluid model. The ageing effect is more pronounced in PTMSP, where it leads to a significant solubility and diffusivity reduction, than in the copolymer where the effect is less important. In the activity range inspected the diffusion coefficient and the heat of mixing are almost concentration independent for PTMSP, while they increase appreciably with concentration in the copolymer, as an effect of the great difference in the free volume present in the two matrices.

The separation performances of polymeric membranes suitable for separation of fluid species in the food and pharmaceutical industry, such as in the Organic Solvent Nanofiltration (OSN) processes, strongly depend on the solubility of the fluids in the polymer membrane. [1-3] The solubility and diffusivity of several pure and mixed liquids of interest for the food and pharmaceutical industry was studied at 35°C into dense films of crosslinked PDMS membrane, that is widely used in membrane separation processes for its good permeation performance and for its resistance to solvents.[4] The effect of the presence of a low molecular weight solvent that swells the matrix on the solubility is analyzed and discussed. The measurement of pure liquid solubility in PDMS was performed gravimetrically, according to the blot and weight method: samples were immersed in vials filled with liquid, placed in a thermostatic bath and weighted at regular intervals with an analytical balance. In this way the mass uptake as a function of time was obtained. In the case of mixed liquids solubility, we considered solutions formed by a volatile component and a second one with negligible vapor pressure. Firstly the measurement of the total mass uptake of the liquid mixture was performed, according to the previously described procedure. Then, the volatile component was allowed to evaporate, until constant weight was obtained. Mass balance calculations provided the separate mass uptake of the volatile and of the non volatile component. In such way we obtained the solubility and diffusivity of a series of pure liquids at 35°C in PDMS: n-alkanes from n-C4 to n-C18, Cyclo-C6, H2O, acetone, linear alcohols from Ethanol to 1-Hexanol, Iso-Butanol and Tert-Butanol, and liquids of interest for the food and pharmaceutical sectors (Ethyl Acetate, PEG 400, Squalene, Limonene, Linalool, Geraniol, Olive oil, Groundnut Oil, Sunflower Oil Oleic acid). The data for homologous classes of penetrants show regular trends which can be explained via entropic and energetic effects. In multicomponent sorption experiments (carried out with mixtures formed by acetone/olive oil, acetone/oleic acid, pentane/olive oil; pentane/oleic acid; pentane/eicosane; tert-butanol/PEG-400; etc.) it was found that the solubility of the less soluble component is deeply enhanced by the presence of the other, more soluble component, that usually is the low molecular weight solvent. For example, the swelling induced by n-pentane promotes the dissolution of eicosane in PDMS, which shows a maximum at an intermediate mass fraction of n-C5 in the mixture. This behavior has been retrieved in many other mixtures and can be properly exploited to tune and design membrane separation processes.

The predictive calculation of the solubility of low molecular weight penetrants in glassy polymers (pure polymers, blends and nano-composites) can be performer based on the knowledge of polymer density, by using the results of the Non-Equilibrium Thermodynamics of Glassy Polymers. Different examples are presented for gases, vapors, liquids and gas mixtures. For swelling penetrants, in the case of bulk rheology relatively slow with respect to the diffusion process, the polymer density varies with time during sorption; consequently the concentration assigned as boundary condition as well as the chemical potential gradient inside the polymer both vary with time. That gives rise to different non-Fickian transport behaviors (anomalous diffusion, two-stage sorption,…) which can be well interpreted by using simple relationships for the polymer bulk rheology. Different examples support the conclusion.

The description of mass transport properties of low molecular weight species in heterogeneous polymeric systems is of great importance. The theoretical analysis of composite materials behaviors is indeed fundamental for the proper material design of such systems for a variety of different applications. Among the others, immiscible polymer blends as well as block copolymers are often of interest for their ability to combine properties of two or more materials. Semicrystalline polymers are also systems of great industrial importance, which require a two phases modeling in order to describe their behavior. In recent years, the development of nanocomposite materials was employed for barrier applications by incorporating impermeable platelets in the polymer phase. This technology is also suitable for the design of membranes for gas separation, and to this aim, particles selective to one or more gases, such as for instance zeolites or metallic organic frameworks, are dispersed in the polymer phase. All these examples are constituted by two, or more, well defined and well distinguished regions (of different length scale) characterized by their value of gas permeability Pi. The resulting permeability of the complete heterogeneous medium is then related to these Pi values but also to the relative weight of the two phases as well as the system morphology, i.e. the shape of the dispersed phase. The aim of this work is to develop a valuable tool for the description of transport properties in composite media, able to evaluate the permeability as function of system morphology. Numerical calculations are thus employed to model the two-phases system in a wide range of relative fraction of the two components and varying their characteristics. Results are then compared with existent model equations in order to investigate their predictive ability and ranges of validity.

Separation processes play a major role in chemical, food and pharmaceutical industry, where they are required for the fractionation of mixtures, the recovery of high valued molecules from complex feedstock and the removal of unwanted substances that could give rise to off specific products, outflavours in food and beverages and shelf-life reduction. The industry of aromas and nutriceuticals requires to deal with feedstock with an initially low concentration of the molecules of interest. Moreover, these molecules should be treated with care, since they are frequently prone to denaturation and degradation, that can be triggered by thermal and chemical stimuli. In several of the above mentioned processes, therefore, membrane-based techniques, such as, for instance, pervaporation and organic solvent nanofiltration (OSN), can offer a viable separation method in alternative to chemical and thermal techniques. In both such processes, the solution-diffusion mechanism of transport inside the membrane plays a relevant role. Therefore, in the design of such processes, the knowledge of the fundamental transport parameters, e.g. diffusivity and solubility, of the interesting liquid components into membrane materials, is required. Indeed, the knowledge of such basic parameters can be the basis for a fundamental understanding and knowledge of the thermodynamic and of the kinetic aspects which control the separation. Unfortunately, a considerable lack of basic transport parameters of liquids in the most interesting polymers is observed in the literature. Such data are useful for the design of membrane modules, but also for the validation of models which can be used to reduce the number of experimental data required. In the present work, the solubility of a series of liquid penetrants (water, n-alkanes, alkyl-alcohols, ethyl acetate, acetone, edible oil components) has been inspected at room temperature, into dense films of both glassy (Matrimid 5218) and rubbery (crosslinked PDMS) polymers.

The evaluation of the mixed gas solubility in glassy polymers is of fundamental importance in several applications such as in the development gas separation membranes. For rubbery polymers the usual equation of state (EoS) models, in their multicomponent version, can be applied to calculate multiple gas solubility in the equilibrium phases; for the case of glassy polymers, a different thermodynamic tool has to be used. The general approach called Non Equilibrium Thermodynamics of Glassy Polymers (NET-GP) [1], coupled to the Lattice Fluid (LF) model for the representation of substances [2], was showed to be able to predict the solubility of gases and vapors in glassy polymers at various pressures based on pure component parameters. The approach is here applied to the modeling of multicomponent gas solubility in a glassy polymeric matrix, to predict the solubility of CH4/CO2 mixtures in Poly(phenyleneoxide) (PPO), C2H4/CO2 and N2O/CO2 in poly(methylmetacrylate) (PMMA), at various pressures, for which experimental data are available. The data show that the solubility of mixed gases differ significantly from the corresponding pure component values: the N2O content in the PMMA is lowered by the increase of CO2 partial pressure; the same effect is observed for the CO2/CH4 pair in PPO. The NELF model is able to predict the experimental behavior observed for mixed gases solubility in both systems; the agreement is indeed remarkable in both cases in the whole pressure range investigated. The present approach allows also to estimate predictively the mixed gas solubility-selectivity of N2/CO2, CO2/CH4 and H2/CO2 mixtures in several glassy polymers including polyimides such as Matrimid, allowing to detect significant deviations from the ideal selectivity behavior and estimate the selectivity of membrane materials.

Cellulose-based nanocomposites are now emerging as promising new materials suitable for a variety of applications. One source for such new nanocomposites is microfibrillated cellulose (MFC), produced by delamination of cellulosic fibers in high-pressure homogenizers. MFC is an organic and biodegradable reinforcement in polymer nanocomposites because of its high aspect ratio, good mechanical properties and ability to form networks: promising properties that may make this material suitable for use in a number of industrial fields and products. The structure and transport properties of a four different films based on two different generations of microfibrillated cellulose (MFC), alone or in combination with glycerol as plasticizer, were investigated through FE-SEM analysis and sorption or permeation experiments. FE-SEM revealed the existence of complex structures in the different samples. A porous, closely packed fiber network, more homogeneous in the samples containing glycerol, was characteristic of the surface of MFC films; while film cross-sections presented a dense layered structure with no evidence of porosity. Water vapor sorption experiments confirmed the hydrophilic character of these cellulosic materials and showed a dual effect of glycerol, which reduced the water uptake at low water activity while enhancing it at high relative humidity, as showed in Figure 1. The observed trends of water sorption can be described considering that both physical adsorption on fiber surfaces and absorption in the cellulose amorphous phase takes place and therefore a dual-model sorption model was employed. The water diffusivity (in the panel in Figure 1) in dry samples was remarkably low for a porous material (10-11-10-12 cm2/s), confirming the existence of complex structures below the film surface; however, when water is present in the system, D rapidly increases with an exponential trend. Diffusivity is also definitely affected by plasticization, being higher for glycerol-containing samples. Similar behavior was observed in permeation experiments. Dry MFC films showed excellent oxygen barrier properties, comparable with those of polymers usually considered suitable for ultra-high barrier applications. Indeed, when dry, the cellulose network presents a particularly compact and stiff structure, causing the observed barrier effect. Furthermore, although MFC films are characterized by a certain porosity, FE-SEM images of sample surfaces suggests that the pores are not substantially interconnected When the water content in the membrane is raised, however, a dramatic decrease in these properties was observed (Figure 2).

Relations between morphological characteristics and effective permeability in nanocomposite systems are here considered in details, both analyzing modeling results for simple systems as obtained in different past attempts and extending the applicability of the latter to more realistic configurations. In this perspective, the same mathematical tool and modeling approach used in a previous paper for the analysis of simple 2-D ordered systems [J. Membr. Sci. 327 (2009) 208–215] are here extended in several different respects. Predictions from numerical simulations for 3-D ordered and random systems, both for the case of low and high concentration of inclusions, are compared with results from previous works and with correlations offered by empirical approaches. A new model is finally proposed for the prediction of permeability in random systems which proves to be reliable in a rather large range of geometrical and morphological configuration.

Polymer blends constitute a valuable way to produce relatively low cost new materials with properties sometimes exhibiting synergistic effects compared to those of the pure components. LLDPE/LDPE blends are widely used industrially to improve the processability of LLDPE or the elongational properties of LDPE, like melt strength. This improvements are beneficial for extrusion and film blowing processes respectively. One of the still debated open questions concerning the structure of polyethylene blends is the miscibility of the two phases, whose investigation is complicated by the identical chemical structure of the two components [1,2]. Deviations from the log-additivity rule of the newtonian viscosity are often taken as a signature of immiscibility. The reason is that theories for miscible blends, like double reptation, predict for the viscosity trends very close to this simple empirical rule. The aim of this work is to characterize the rheological behavior in shear and elongation of five series of LLDPE/LDPE blends whose parent polymers have been chosen with different viscosity and SCB content and length

Based on NonEquilibrium Thermodynamics (NET-GP) approach, a model is here presented and discussed, aimed to the prediction of anomalous characteristics in kinetics for differential sorption of swelling agents in amorphous glassy polymer films. For mentioned conditions, the “two-stage sorption” kinetics is typically observed, in which a first stage of Fickian character is followed by a second stage with kinetic order larger than 0.5 and characteristic time independent of film thickness. NET-GP model, which interprets the out of equilibrium conditions of polymer mixtures below Tg through the use of polymer mass density as order parameter, was successfully used since its introduction [Doghieri and Sarti, Macromolecules 1996, 29, 7885] to describe several non-equilibrium features in solubility isotherms for a number of glassy polymeric systems. By coupling the description of thermodynamic properties from NET-GP with simplified model for the bulk rheology of the system and generalized Fickian law for mass transport, a modeling tool is derived in this work which allows to satisfactorily describe results from experimental analysis of two stage sorption kinetics.

The oxygen barrier properties of composite materials, consisting of a 45 μm thick LDPE substrate coated by a thin layer (0.7–1 μm) of new hybrid organic–inorganic materials based on SiO2 and PE-PEG block copolymers, have been characterized at 35 and 50 °C. A significant decrease (25–40%) of the oxygen transfer rate has been observed for coated samples with respect to bare substrate both at 35 and 50 °C. The effects on the coating permeability of organic–inorganic ratio, molecular weight of the PE-PEG block copolymers and temperature are discussed.

The oxygen transport properties of LDPE films coated with different kinds of hybrid coatings were then obtained in terms of permeability and diffusivity at 35 and 50 °C, and their correlation to various structural and processing parameters is discussed. In this contribution, in particular, we report data obtained at different organic/inorganic (O/I) ratios and for different PE-PEG molecular weights. A second paper of this series re- ports the effects induced in the oxygen permeability by changing the organic phase composition with hydrogen bonding capable organics and by treating with plasma the LDPE surface prior to coating.

The oxygen permeability of composite materials, consisting of a LDPE substrate coated with a thin layer (0.7–1 μm) of new hybrid organic/inorganic materials based on SiO 2 and PE-PEG block copolymers, has been characterized at 35 and 50 °C. The effect of adding a second organic component capable to form hydrogen bonds, namely either poly(4-hydroxystyrene) (PHS) or malic acid, has been studied. While the addition of PHS leads to a further significant decrease (50–70%) of the oxygen permeability both at 35 and 50 °C, on the contrary, the addition of malic acid leads to poorer barrier properties. A slight decrease of the permeability was obtained after plasma treatment of the LDPE surface.

The oxygen barrier properties of composite materials, consisting of a LDPE substrate coated by a thin layer of nanostructured hybrid organic/inorganic materials based on SiO2 and polyethylene-polyethylene glycol (PE-PEG) block copolymers, obtained via a sol-gel technique have been characterized at 35°C and 50°C. A significant decrease (25-40%) of the oxygen transfer rate has been observed for coated samples with respect to bare substrate both at 35°C and 50°C.

L’analisi della dilatazione e della tensione indotte dall’assorbimento di vapori in film polimerici vincolati a un supporto è stata condotta con un nuovo apparato sperimentale che accoppia la tecnica del bending beam con un micrometro ottico. Questo approccio è stato utilizzato per studiare l’assorbimento di acetonitrile in policarbonato depositato su alluminio a 40°C e consente di misurare sia la dilatazione del polimeo che la deflessione della trave composita nel tempo. Si è inoltre sviluppato un modello che accoppia il processo di diffusione con lo studio della tensione in una trave ed è in grado di predire la cinetica della flessione della lastrina e di dilatazione del polimero durante l’assorbimento. Anche i valori di stazionari per tali parametri risultano valutati con precisione ed è inoltre possibile calcolare l’evoluzione del profilo degli sforzi nella membrana polimerica durante l’assorbimento.

The mass transport properties of cyclohexane in different phase separated styrene blockcopolymer, namely polystyrene-block-polybutadiene-block-polystyrene [SBS], polystyrene-blockpolyisoprene- block-polystyrene [SIS] and polystyrene-block-poly(ethylene butylene)-blockpolystyrene [SEBS] were investigated. The solubility and diffusivity in films samples have been measured, as function of concentration, at 60ºC by means of sequences of differential vapor sorption experiments run in a pressure decay apparatus. The effects of both molecular architecture (linear and star-branched for SBS) and microstructure of the elastomer mid-segment (polybutadiene vs poly(ethylene butylene) and polyisoprene) were considered. The sorption results were interpreted and modeled in terms of contributions from rubbery and glassy phases. Comparison between the different data in the binary system as function of solute concentration revealed that friction factor for solute molecules in SEBS and SIS is significantly higher than in SBS. Such results were also confirmed by linear viscoelastic characterization of the different polymers that has been carried out performing small angle oscillatory shear experiments in a wide range of temperatures between the soft block Tg and room temperature. The latter experimental data were analyzed by Time-Temperature Superposition. The relaxation spectrum has been determined and the monomeric friction factor has been extracted. This value has been correlated with results from diffusion experiments leading to a substantial agreement.

In the last years more and more interest has been devoted to the study of nanocomposite materials obtained through the addition of inorganic filler with, at least, one dimension in the scale of nanometer to a polymeric matrix. Continuum-based composite modeling reveals that the enhanced properties are strongly dependent on particular features of the second-phase “particles”; in particular, the particle volume fraction (φ) and the particle aspect ratio (α). A CFD algorithm was used to investigate the transport properties of a system with an impermeable phase dispersed in a polymer matrix; it is a pure diffusion phenomenon of small penetrant molecules in a composite media, simulated from a macroscopic point of view, using a finite volume algorithm. We invoke a simple model developed to describe the permeability in filled polymers; which strives to predict the observed permeability based strictly on tortuosity arguments. The reduction of permeability arises from the longer diffusive path that the pentrants must travel in the presence of the filler. The simulations are performed on these random geometries at different loading fractions and different aspect ratios, in order to have a fairly wide set of data. The results, averaged on the different geometries obtained, show that the permeability decays as function of the filler volume concentration, all the trends appear similar with similar behavior for different lamella characteristic parameters. As one can see analyzing the data set, there is a clear and unique trend considering α times φ as the ruling parameter. The permeability decay shows a power law dependence on α φ scaled with the inverse of the polymeric volume fraction; the exponent seems to have a value in between 1.0, as in Nielsen’s model, and 2.0, which is the one in the most famous Cussler’s formulation.

The correlation between linear viscoelasticity and mass transport properties in styrene block copolymers has been investigated and discussed in terms of segmental dynamics of the soft block. The samples were phase separated polystyrene-block-polybutadiene-block-polystyrene [SBS], polystyrene-block-polyisoprene-block-polystyrene [SIS] and polystyrene-block-poly(ethylene butylene)-block-polystyrene [SEBS]. All samples have a styrene content of approximately 30%. Linear viscoelastic characterization was carried out performing small angle oscillatory shear experiments in a wide range of temperatures between the soft block Tg and room temperature. The latter experimental data were analyzed by Time-Temperature Superposition. The relaxation spectrum has been determined and the monomeric friction factor has been extracted. This value has been correlated with results from diffusion of a small foreign molecule (cyclohexane) in the block copolymers. Solubility and diffusivity of cyclohexane in films samples of the investigated copolymers as function of concentration at 60ºC have been measured by means of sequences of differential vapour sorption experiments run in a pressure decay apparatus. The effects of both molecular architecture (linear and star-branched for SBS) and microstructure of the elastomer mid-segment (polybutadiene vs poly(ethylene butylene) and polyisoprene) were considered. Solubility results were interpreted in terms of contributions from rubbery and glassy phases and pertinent results were used to derive the mobility coefficient from measured data of fickian diffusivity. Comparison between mobility coefficients in the binary system as function of solute concentration revealed that friction factor for solute molecules in SEBS and SIS is significantly higher than in SBS.

The permeability and diffusivity of oxygen in films of PET coated with a thin layer of a hybrid organic/inorganic (ceramer) material have been determined at 65°C. The permeability data are collected using a closed-volume permeation apparatus and the diffusivity has been calculated with the time-lag method. The addition of coating dramatically improves the oxygen barrier properties of the substrate, the apparent permeability of the multilayer film being up to 3 orders of magnitude lower than that of pure PET. The pure coating properties are opportunely calculated by taking into account the effect of the different diffusion resistances in the various layers. The effect of ageing has also been investigated, by comparing the oxygen permeability before and after immersion in water of the films that are suspected to be degraded by water.