1,721,185 research outputs found
Test methods for the characterization of gas and vapor permeability in polymers for food packaging application: A review
No full textThe assessment of the transport properties of different substances in polymeric materials is of crucial importance
for the evaluation of packaging performances, aiming to protect packed food products and ensure a prolonged
shelf-life. The most relevant substances for such application can be identified in O2, CO2 and C2H4 (together with
N2 as control) as permanent gases, and water vapor as condensable species. All these penetrants are able to alter
significantly food properties, in term of sensory characteristics, textures, and quality in general. All relevant
techniques for the experimental characterization of mass transport properties in polymeric films or packages are
critically reviewed, focusing in detail on standard methods. Each technique is briefly presented in terms of
apparatus requirements and general procedures, followed by a discussion on its main features
Water sorption in microfibrillated cellulose (MFC): The effect of temperature and pretreatment
Full text linkWater sorption behavior of two different microfibrillated cellulose (MFC) films, produced by delamination of cellulose pulp after different pretreatment methods, is examined at various temperatures (16â65 °C) and up to 70% RH. The effect of drying temperature of MFC films on the water uptake is also investigated. The obtained solubility isotherms showed the typical downward curvature at moderate RH, while no upturn is observed at higher RH; the uptakes are in line with characteristic values for cellulose fibers. Enzymatically pretreated MFC dispersion showed lower solubility than carboxymethylated MFC, likely due to the different material structure, which results from the different preparation methods The experimental results are analyzed by Park and GAB models, which proved suitable to describe the observed behaviors. Interestingly, while no significant thermal effect is detected on water solubility above 35 °C, the uptake at 16 and 25 °C, at a given RH, is substantially lower than that at higher temperature, indicating that, in such range, sorption process is endothermic. Such unusual behavior for a cellulose-based system seems to be related mainly to the structural characteristics of MFC films, and to relaxation phenomena taking place upon water sorption. The diffusion kinetics, indeed, showed a clear Fickian behavior at low temperature and RH, whereas a secondary process seems to occur at high temperature and higher RH, leading to anomalous diffusion behaviors
H2S/CO2/CH4 humid mixed gas permeation in Aquivion® acid ionomer membranes for natural gas sweetening
No full textEffect of relative humidity and temperature on gas transport in Matrimid®: Experimental study and modeling
No full textThe influence of water vapor on the gas permeability of a commercial polyimide, Matrimid® 5218, has
been extensively investigated at three different temperatures (25, 35 and 45 1C), and with four different
penetrant gases (CH 4 , N 2 , CO 2 and He), varying the relative humidity in the range 0–75%.
In all tests performed, the permeability coefficient decreases as the concentration of water vapor in
the membrane increases. In particular, the influence of the presence of water on gas permeability is very
similar for all penetrants, as the same permeability decrease is found, at a given relative humidity,
despite the different thermodynamic and kinetic characteristics of the probe gases considered.
As temperature is raised, the gas permeability is enhanced, as expected. On the other hand, its decrease
with respect to the dry polymer values, as relative humidity increases, is not affected by temperature, and it
remains substantially unaltered from 25 to 45 1C, suggesting that such phenomenon can be directly related
to the amount of water dissolved in the membrane, which is also unaffected by temperature.
Based on the experimental evidence, a simple model is proposed to describe the permeation process
under humid conditions, in the framework of the free volume theory. In particular, it has been considered
that absorbed water molecules influence gas permeability by occupying polymer free volume, reducing its
availability to other penetrants with lower condensability. The model describes accurately the experi-
mental data using only two adjustable parameters for the polymer-water-penetrant system, once the water
solubility is estimated from sorption measurements
"Solubility of Gases and Vapors in Glassy Polymer Blends"
No full textThe solubility of gases and vapors in miscible polymer blends, in the glassy state, has been considered. The sorption isotherms are calculated through the extension to polymer blends of the NELF model, for non swelling as well as for swelling penetrants. The swelling coefficient for the blend is given in terms of the swelling coefficients for the pure polymers. In all cases, the isotherms for the polymer blends can be completely predicted based on the parameters needed for the solubility in the pure polymer. The comparison between the model predictions and experimental data available for PS-TMPC blends are shown in detail and indicate the reliability of the model
CO2 sorption and diffusion in fluorinated polymers for carbon capture and transport application
No full textEffects of random defect distributions in the barrier coating on the gas permeability of multilayer films
No full textThe influence of barrier coating defectiveness on the overall permeating flux through a bilayer film is considered with particular attention to the effect of spatial defect distribution. To that aim, the diffusion equations for the permeating species have been solved in a large number of 3D geometries, built to simulate a bilayer structure with defects randomly distributed on the coating surface. A numerical approach based on finite volume method was used and, for each value of defectiveness considered, ranging from 0.25 to 10%, a minimum number of 200 different geometries were analyzed, in order to obtain statistically meaningful results.The numerical simulations results, which for regular arrays of defects also compares rather well with data available in the open literature, showed that the average flux obtained for each different defectiveness is not a fixed value, but rather shows substantial variations due to the randomness of the defect distribution. In particular, when few defects are present on the surface, differences higher than 10% have been observed in the flux calculated, while deviation lower than 3% with respect to the average value were obtained when the defects fraction on the surface was about 10%.Interestingly, the random distribution of defects on the surface gives average flux which are always smaller than the corresponding ordered geometry and does not result in a Gaussian distribution of the permeate flux. Distributions close to the normal one were indeed observed only for higher defectiveness while, for lower defect fractions, flux distributions with a clear tail towards the lower permeation rates were obtained
Nanocellulose based facilitated transport membranes for CO2 separation
No full textIn the present work the performance of a new membrane material, based on Microfibrillated Cellulose (MFC), was investigated in view of its use in CO2 separation applications. In particular the membranes were obtained by casting, from a solution of carboxymethylated MFC and Lupamin (a Polyvinylamine produced by BASF), followed by a thermal treatment at 105 °C. Permeability of CO2 and CH4 were measured at 35 °C as a function of relative humidity and water sorption experiments were performed as well to relate the previous results to the actual water content in the membrane. As a reference, pure MFC films have been also prepared and their gas permeability tested in the same conditions. The overall results suggest that both MFC and MFC-Lupamin films have really interesting performance for the CO2/CH4 separation showing very high selectivity values (higher than 400) which place both materials well above the trade-off curve of 2008 Robeson's plot. In particular MFC films showed higher maximum selectivity but lower average CO2 permeability with respect to the MFC-lupamin blends probably because of the different level of water absorbed by the two materials. Pure MFC indeed never exceeded 10% water uptake, while the Polyvinylamine blend showed water sorption very similar to the previous material up to 60% RH; it then definitely increased, reaching a mass uptake higher than 50% at the maximum water activity inspected
Effect of relative humidity and temperature on the gas transport properties of 6FDA–6FpDA polyimide: Experimental study and modelling
No full textThe transport of CO2, CH4, N2 and He in films of polyimide 6FDA–6FpDA was studied at different temperatures, from 25 to 45 °C, and Relative Humidity (RH) from 0% to 90%. The permeability of all gases decreases with increasing RH, by factors as high as 44% for CH4 and 35% for the other gases; moreover, the relative decrease of gas permeability with respect to the dry polymer value is constant with temperature and just weakly dependent on the gas type.
Pure water vapour sorption experiments were also conducted on the polymeric films in the same RH and temperature range, showing that water solubility in 6FDA–6FpDA is almost temperature-independent. A strong correlation therefore seems to exist between gas permeability decrease and water content in the membrane, due to the fact that absorbed water molecules occupy a portion of the polymer free volume, that is no longer available for gas permeation. Based on these considerations, the humid permeation results were analysed quantitatively and modelled with a simple approach based on free volume theory
Study on ammonia transport and separation in Aquivion® perfluoro sulfonated acid membranes
Full text linkThe present study reports the results of a series of sorption and permeation tests of pure ammonia as well as
nitrogen and hydrogen carried out on Aquivion C87-05 (short-side chain perfluoro sulfonic acid ionomer). Such
material is indeed of interest for possible applications in sustainable processes for ammonia production, either as
base material for polymer electrolyte membranes in low-temperature electrochemical ammonia synthesis or as a
membrane for effective product separation.
NH3, N2, and H2 permeation tests are performed at different temperatures (20, 35, and 50 ◦C) and both in dry
and humid conditions (R.H. up to 80%), aiming to assess the influence of these parameters on the resulting
permeabilities, while ammonia sorption is inspected at the same temperatures, and pressures up to near saturation conditions.
Pure ammonia permeability reached outstanding values around 7000 Barrer in dry Aquivion membranes,
revealing an increasing trend with upstream pressure, while it decreased with temperature. The same behavior is
recorded for NH3 solubility, indicating that sorption drives the ammonia transport through the membrane.
The obtained separation performances are found to be significantly better than those of other polymeric
membranes proposed for the same separations, as compared to a permeability-selectivity plot.The present study reports the results of a series of sorption and permeation tests of pure ammonia as well as nitrogen and hydrogen carried out on Aquivion C87-05 (short-side chain perfluoro sulfonic acid ionomer). Such material is indeed of interest for possible applications in sustainable processes for ammonia production, either as base material for polymer electrolyte membranes in low-temperature electrochemical ammonia synthesis or as a membrane for effective product separation. NH3, N2, and H2 permeation tests are performed at different temperatures (20, 35, and 50 °C) and both in dry and humid conditions (R.H. up to 80%), aiming to assess the influence of these parameters on the resulting permeabilities, while ammonia sorption is inspected at the same temperatures, and pressures up to near saturation conditions. Pure ammonia permeability reached outstanding values around 7000 Barrer in dry Aquivion membranes, revealing an increasing trend with upstream pressure, while it decreased with temperature. The same behavior is recorded for NH3 solubility, indicating that sorption drives the ammonia transport through the membrane. The obtained separation performances are found to be significantly better than those of other polymeric membranes proposed for the same separations, as compared to a permeability-selectivity plot
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