Vapor Permeability Research Articles

Design of hydrophobic polymer brush for mitigation of membrane wetting in membrane distillation- computer simulation

Defined as an assembly of polymer chains which are tethered by one end to a surface or an interface, polymer brushes have found many applications. In particular, grafting of hydrophilic polymer brushes to the membrane surface was used to mitigate fouling of filtration membranes. As well, hydrophobic polymer brushes were grafted on top of a solid substrate to be used for organic selective pervaporation. In this work, grafting of hydrophobic brushes to the surface of membranes for membrane distillation (MD) is proposed to prevent MD membranes from wetting. This is not an experimental work but a computer simulation of designing the polymer brush or patterned polymer brush to optimize their effect on wetting prevention. It was found that such an effect increases with an increase in the distance between brushes, the contact angle and the radius of the cylindrical polymer brush. Considering the decrease in the effective area of the membrane used for vapor permeation by grafting of polymer brush, the optimal distance between the brushes was found to be twice as large as the brush diameter for millimeter-sized brush and three times as large as the brush diameter of micro- or nanometer sized brushes.

Cellulose nanocrystals engineered TPS/PBAT granulation through extrusion process and application for compostable carry bags

An economical and scalable process route has been developed for preparation of bio nanofillers, cellulose nanocrystals (CNCs) using acid hydrolysis and ceramic membrane-based continuous neutralization process alternative to conventional dialysis process. Optimized process achieved 42 % yield with crystallinity index of 91.3 % and average size 20–50 nm as confirmed by TEM analysis. Solid-state NMR result shows that the CNCs lateral dimension is comparable to elementary cellulose crystallites. Prior optimized composition of CNCs (Kesari et al., 2022) in TPS was used to prepare bio-nanocomposite with aim to reduced Poly (butylene adipate co-terephthalate) (PBAT) content in packaging films. A strong evolution in the mechanical and rheological properties of the CNCs reinforced blends was observed with increase in PBAT content with optimum blending ratio of 70/30. The composite attained tensile strength and young’s modulus of 11.01 ± 0.15 and 1200.94 ± 16 MPa, respectively with water vapor transmission rate (WVTR) of 63.96 ± 1.02 g/m2/day than neat PBAT (124.56 ± 6.89) which has higher vapor permeation. The thermal analysis confirms with bio nanofillers addition reduced the processing temperature of the polymeric blend. Thus, this work provides an economical and sustainable pathway for high content of biobased carbon (>70 %) for biodegradable packing industry.

Mass transfer fundamentals in pervaporation, perstraction and sorption: A unified approach

The high affinity between an organic solute and a polymeric sorbent or membrane is the basis for separating organic contaminants from water via sorption, pervaporation and perstraction. These processes all share the same features of dissolution and diffusion, and thus their mass transfer characteristics can be correlated. However, they are often dealt with independently, and the research findings from one process are rarely applied to the other. The permeability coefficient in perstraction (for liquid permeation) based on concentration gradient as the driving force for mass transfer and the permeability coefficient for pervaporative transport expressed customarily in analog to vapor permeation can hardly be compared directly, and sometimes seemingly contradictive trends in temperature dependencies of the permeability coefficients for the two process modes may result. Looking into the mass transfer fundamentals pertaining to sorption, pervaporation and perstraction, this work attempted to provide a unified approach to the mass transfer in all these processes. While the permeability coefficient in pervaporation uses equivalent vapor pressure gradient across the membrane as the driving force, this work provided a generalized treatment by taking into account the sorption constants embedded in the permeability coefficients of the different processes so that the performance parameter for one process could be applied to another, which would be especially useful for screening and developing appropriate membrane/sorbent materials. In addition, the relationships among the selectivities of these separation processes were elucidated, which allowed for an intuitive illustration of how the process selectivity changed due to the process mode. Aniline removal from water via pervaporation, perstraction and sorption using a poly(ether-b-amide) membrane/sorbent was used as an example to illustrate and validate the approach.

On the role of defects in modelling approaches for thin film gas barrier coatings on polymer substrates: I. Model development

We present a method to model the gas permeation through silicon-oxide thin film coatings that are afflicted with nanoscale defects. With it, we are able to give an estimation of the diffusion coefficient in bulk by subtracting the influence of the defects. The model is based on data obtained from positron annihilation spectroscopy, which is processed to yield possible defect allocation patterns of the coatings. For a systematic evaluation of these patterns, a path through the coating is calculated and then subjected to in-depth analysis to evaluate the used approach as well as to interpret the results for insights on the permeation mechanisms. The model appears to function as intended and no unexpected behaviour is observed. The defect volume share is overestimated, which can be retraced to the underlying algorithm, and a correction method is applied to the resulting bulk diffusion coefficient. The model gives reasonable results both for oxygen and water vapor permeation. These results can be used in following works that build on the presented model.

Preparation and characterization of poly(vinyl alcohol)/poly(lactic acid) blends containing bio‐based plasticizers

AbstractThe bio‐based plasticizers‐glycerol and lactic acid were used to plasticize and compatibilize PVA/PLA blends during melt blending process. It was confirmed that lactic acid significantly improved the compatibility between glycerol‐plasticized PVA and PLA. Compared with pure PVA, the melting and crystallization temperatures and crystallinities decreased but the crystal form of PVA in the blends was not changed. The thermal stabilities of PVA/glycerol (G)/lactic acid (L)/PLA blends were better than PVA/G/PLA blends. Compared to PVA/G/PLA blends, the tensile and tear strength of PVA/G/L/PLA blends were improved, however, elongation at break decreased. The water absorptions and water vapor permeances of the blends decreased with the addition of hydrophobic PLA, but they increased by incorporation of hygroscopic lactic acid. The surface resistivities of the blends augmented in combination with PLA but declined by adding lactic acid. The melt flow rates of PVA/G/PLA blends were better than PVA/G/L/PLA blends because lactic acid enhanced the interactions among the components. After the addition of lactic acid, the transmittances of the blends increased due to the refined dispersed phases by the compatibilization. The compatibility between the components was predicated by Hansen solubility parameters. These blends showed potential as a novel barrier material for food and medicine packages.Highlights PVA, glycerol, and PLA blends were compatibilized by lactic acid. The melting temperatures decreased with addition of glycerol and lactic acid. The tensile and tear strengths were enhanced with addition of PLA and lactic acid. The hydrophobicity, melt fluidity, and surface resistivity were improved by PLA.

Water Vapor Permeation in Alumina Films on Polymer Substrates

Herein, the water vapor transmission rate (WVTR) of aluminum oxide (Al2O3) films on polyethylene terephthalate (PET) substrates is investigated and is focused on the impact of the film defects on the transmission rate. The aluminum oxide films are prepared on PET substrates by magnetron sputtering, and the effects of the film thickness, sputtering power, temperature, and bias voltage on the WVTR are studied. The surface morphologies of the films are examined using atomic force microscopy (AFM), and a method for obtaining the defect ratio of the film from AFM images is proposed. Subsequently, the influences of the defect ratio on the WVTR are quantitatively evaluated based on a 3D diffusion model. The simulated WVTR values are well in agreement with the experimental ones.

Physicochemical Treatments of Graphene Oxide to Improve Water Vapor/Gas Separation Performance of Supported Laminar Membranes: Sonication and H2O2 Oxidation.

We investigated the previously unexplored domain of water vapor/gas separation using graphene oxide (GO) membranes, expecting future applications, including gas dehumidifiers and superior humidity controllers. While the importance of manipulation of GO nanosheet size and surface chemistry in traditional water purification and gas separation has been acknowledged, their potential impact on water vapor/gas separation remained unexplored until now. We applied sonication and hydrogen peroxide treatments to GO water dispersions and systematically evaluated the size and surface chemistry of each GO nanosheet. Both treatments reduced the GO nanosheet size to shorten the diffusion length, which improved water permeance. In addition, hydrogen peroxide treatment improved the hydrophilicity of the nanosheet. Our novel findings demonstrate that optimization of GO nanosheet size and the increase in their hydrophilicity via hydrogen peroxide treatments for 5 h significantly enhance water permeance, leading to a remarkable water vapor permeance of 4.6 × 10-6 mol/(m2 s Pa) at 80 °C, a 3.1-fold improvement over original GO membranes, while maintaining a water vapor/nitrogen permeance ratio exceeding 10,000. These results not only provide important insights into the nature of water vapor/gas separation but also suggest innovative methods for optimizing the GO membrane structure.

Исследование свойств пищевых пленок на основе агара с добавлением функциональных компонентов

Abstract. In conditions of increasing environmental load from accumulated synthetic packaging materials in environmental objects, there is a need to develop new compositions of biodegradable films that additionally have functional properties to increase the shelf life of products. The scientific novelty of the research lies in the production of new types of biodegradable active films with the addition of protein hydrolyzate as an active component, as well as data on their properties. The purpose of the study is to establish the properties of biodegradable films based on agar with the addition of a suspension of protein hydrolyzate and CMC as active components. Research methods. The control (composed of agar and glycerin) and test samples of films (composed of agar, glycerin and a suspension of MCC and protein hydrolyzate in an amount of 5, 10 and 15 % by weight of the biocomposite) were determined for mechanical properties, microstructure, antioxidant properties, vapor permeability, solubility, and moisture absorption. Results. The introduction of a suspension into the composition of the biocomposite had a negative effect on the mechanical strength of the film – the tensile strength decreased from 9,71 MPa for the control sample to 3,35 MPa for the test sample with 15 % suspension, while the relative elongation was maximum for the sample with 10 % suspension – 54,9 %. The antioxidant properties of the films increased with the addition of the suspension: the antiradical activity of DPPH increased from 57.65 % in the control sample to 63.81 % in the test sample with 15 % suspension, and the phenol content – from 0.253 in the control sample to 0.502 mEq of gallic acid per 1 g for a prototype with 10% suspension. It was noted that the addition of the suspension had a significant effect on vapor permeability and moisture absorption. Thus, the results obtained showed the need for further research into the storage capacity of food products with different humidity levels when packaged in tested films.

Freeze Drying of Organically Modified Layered Silicates as Key Step to Improve the Barrier Properties of Organic Coatings for High Power Electronics Protection

AbstractOrganically modified layered silicates can be used as barrier pigments in organic coating systems to reduce the permeation of water vapor and gases, e.g., oxygen as well as harmful gases that promote corrosion. Unmodified layered silicates are not sufficient to reduce the permeation significantly. However, the arrangement and orientation of the particles have an enormous impact on the later performance in the barrier film. In organic solvents or non‐aqueous polymer matrices the non‐modified layered silicates cannot exfoliate adequately. The organic modification influences the layer spacing and the compatibility to organic solvents. Layered silicates are modified with dodecylamine to enhance the spacing layer. The spacing layer is enhanced by 55% caused by the organic modification as it is commonly known. In contrast to previous work freeze drying of the organically modified layered silicates improved the particle distribution and by this barrier properties significantly. The modified particles reduce the diffusion of water and oxygen by ≈99.6% and 97.2%, respectively. The corrosive gas test of electronic circuit boards shows no growth of dendrites and no failure of the electronics in contrast to protective coating without the layered silicates.

Tannic acid crosslinked chitosan-guar gum composite films for packaging application

Chitosan (CH)-guar gum (GG) composite films crosslinked with tannic acid (TnA) were prepared by solution casting method. The films were then immersed in 5 % aqueous NH3 and dried again. They were characterized by IR spectroscopy, wide angle x-ray diffraction and thermogravimetric analysis. All the films were studied for physicochemical properties such as moisture content, swelling, solubility in water, water contact angle, water vapor permeability, opacity, tensile strength and antioxidant activity. The physicochemical and mechanical properties of films changed significantly when compared to CH as reflected by an increase in the amorphous domains of the films, a decrease in moisture content, swelling and solubility in water. The films turned hydrophobic with concomitant decrease in moisture content, swelling, water-solubility and exhibited improved UV absorption as well as mechanical strength, which in turn was dependent on the tannic acid concentration. These results along with enhanced antioxidant properties, UV absorption with no significant change in water vapor permeation compared to CH suggested that the films could find application in packaging applications.

Effect of membrane morphology on the thermo-physiological comfort of outdoor clothing

This article examines the effect of membrane type and its morphology on the chosen thermo-physiological properties of the middle layer of outdoor clothing. In total four different membranes were selected for the production and analysis of three-layer laminates, which could replace the second and third layers of layered clothing for sports/outdoor purposes. As an outer and lining material a polyester knitted fabric with fleece was chosen, whereas the lamination technology was used to join the individual layers. Chosen properties affecting the thermo-physiological comfort of the laminates were evaluated, to be able to select a membrane that, in combination with the outer and inner layer, enabled the use of laminate as an upper clothing layer – a jacket, thereby replacing the necessity of using a second clothing layer. The following properties were chosen as crucial: thermal resistance, air permeability, vapor permeability (water vapor penetration), and hydrostatic pressure resistance. The utility value methodology was used to evaluate individual fleece-based laminates. For the completeness of this study, two types of commercially available three-layer laminates containing soft-shell fabric as the top layer were incorporated for comparison.

Pioneering the preparation of porous PIM-1 membranes for enhanced water vapor flow.

In this study, porous polymers of intrinsic microporosity (PIM-1) membranes were prepared by non-solvent induced phase inversion (NIPS) and investigated for water vapor transport in view of their application in membrane distillation (MD). Due to the lack of high boiling point solvents for PIM-1 that are also water miscible, the mixture of tetrahydrofuran (THF) and N-methyl-2-pyrrolidone (NMP) was found to be optimal for the formation of a membrane with a developed porous system both on the membrane surface and in the bulk. PIM-1 was synthesized by using low and high temperature methods to observe how molecular weight effects the membrane structure. Low molecular weight PIM-1 was produced at low temperatures, while high molecular weight PIM-1 was obtained at high temperatures. Several membranes were prepared, including PM-6, PM-9, and PM-11 from low molecular weight PIM-1, and PM-13 from high molecular weight PIM-1. Scanning electron microscopy (SEM) was used to image the surface and cross-section of different porous PIM-1 membranes. Among all the PIM-1 membranes (PM) obtained, PM-6, PM-9, PM-11 and PM-13 showed the most developed porous structure, while PM-13 showed large voids in the bulk of the membrane. Contact angle measurements showed that all PIM-1 porous membranes are highly hydrophobic. Liquid water flux measurements showed that PM-6, PM-9 and PM-11 showed minimal water fluxes due to small surface pore size, while PM-13 showed a high water flux due to a large surface pore size. Water vapor transport measurements showed high permeance values for all membranes, demonstrating the applicability of the developed membranes for MD. In addition, a thin film composite (TFC) membrane with PIM-1 selective layer was prepared and investigated for water vapor transport to compare with porous PIM-1 membranes. The TFC membrane showed an approximately 4-fold lower vapor permeance than porous membranes. Based on these results, we postulated that the use of porous PIM-1 membranes could be promising for MD due to their hydrophobic nature and the fact that the porous membranes allow vapor permeability through the membrane but not liquid water. The TFC membrane can be used in cases where the transfer of water-soluble contaminants must be absolutely avoided.

Characterization of lime based insulating mortars for existing buildings in the EU market

There are several lime mortars which have been developed to improve the thermal performance of the facades of existing buildings. They are used as the final coating of a building’s facade thanks to their insulating capacities, weather resistance, vapour permeability, easy application, non-flat substrates adaptability, and/or masonry compatibility. Normally these mortars come into a system to achieve both thermal properties and weathering resistance. The thermally improved mortars, which are lime based, contain an important amount of insulating particles such as cork, diatomaceous earth, expanded clay, expanded perlite or vermiculite, mullite, aerated glass, aerogel, EPS, wood fibres or others. They also may contain pozzolanas and other cementitious particles. They also may contain additives in order to improve its mechanical resistances and/or elasticity. The weathering resistance mortar, the more external one, is suited to complete the mechanical and outdoor resistance properties that the insulated layer lacks. Some of these systems may be obliged to use glass fibre meshes and External Thermal Insulation Composite Systems (ETICS) anchors so they are not as suitable as wanted in historical buildings. In this abstract our main goals are: Acknowledge the reasons to use these mortars, define the multiple layer system that are normally used within these mortars, find which mortars are normally available to be bought in the European Union market, analyse their declared properties and composition, and enlist them according to their potential capacities. Thanks to this paper we will have a better knowledge of the possibilities of lime mortars as insulating material.

Role of water in vapor permeation through graphene oxide membranes

This study demonstrates that GO membranes enable efficient separation of aqueous and alcoholic vapor mixtures and discusses the critical vapor-permeation mechanism.

Study of the temperature and moisture regime of building walls in various construction areas

The article is devoted to the problems of assessing the balance of moisture transfer when calculating protection against waterlogging of building envelopes. For the calculation, several localities have been selected in which the wall of a building with given climatic parameters and internal air parameters for a living space were modeled. In order to model protection against waterlogging, 3 cities were chosen: Smolensk, Izhevsk and Dudinka. A calculation to protect the building envelope from waterlogging has been carried out. The values of resistance to vapor permeation and heat transfer of each layer of a multilayer building envelope have been calculated. The complex of maximum humidification was assessed, on the basis of which the values of the temperature of the greatest humidification were determined. The values of the actual resistance to vapor permeation and the required resistance to vapor permeation were calculated relative to the plane. Three examples of possible moisture transfer balance were obtained. It was also determined that the construction of the building wall under study is permitted in Smolensk and Dudinka. The researched wall cannot be used in Izhevsk.

Food-grade gelatin from camel skin: Extraction, characterisation and potential use for thin film packaging preparation

The present study aims on the extraction of gelatin from camel skin as a tool of agro-food by-products valorization. The extraction was performed through different methods, and the resulting gelatins served as biomaterial for edible films’ preparation. The results showed that Pepsin (P) pre-treatment increased the yield of gelatin extraction to reach 34 and 38%, at 70 and 90 °C, respectively, while it affected the molecular weight and amino acid composition, especially when the P-treatment was coupled with a high temperature (90 °C) in the extraction process. Nevertheless, gelatin extracted without pepsin at 70 °C (G70) showed the highest level of Gly, Pro and Hyp (530 residues/1000), reflecting its high polymerisation, compared to the other gelatins. Then, the extracted gelatins (G70, G90, G70-P and G90-P) were used for the preparation of thin films (∼60 μm), named F-G70, F-G90, F-G70-P and F-G90-P, respectively. Films possessed differences in the structural and techno-functional properties depending on the gelatin used for film formation. For instance, F-G70 was the strongest film and showed the best resistance against water solubility and vapor permeation. The highest mechanical and water resistance correlated with the thermal one, where F-G70 was characterized by the highest glass temperature (Tg = 74 °C) and this value tended to be decreased after increasing the gelatin extraction temperature and Pepsin pre-treatment. Overall, the present results proved that camel skin is a promising matrix of producing gelatin-based packaging intended for food applications.

Investigation of water vapor barrier performances of diamond-like carbon coatings on flexible PET fabricated at room temperature

Polyethylene terephthalate (PET) emerges as the predominant packaging material for food and electronics. To prevent water vapor from penetrating the polymer, an effective method is to deposit a coating on it that does not damage it. Diamond-like carbon (DLC), which can be deposited at low temperatures, offers a promising protective coating. In this research, DLC coatings were chemical vapor deposited (CVD) on PET substrates using an anode layer linear ion source method. The findings indicate that the water vapor transmission rate (WVTR) of PET substrates coated with DLC coating was significantly reduced to as low as 0.12 g/(m2·24 h), which represents a 30 times reduction compared to the uncoated PET substrates. To further understand the mechanism of water vapor barrier capabilities, molecular dynamics (MD) simulation and first-principles density functional theory (DFT) calculation were carried out to verify the capability and active site of the adsorption and dispersion of water molecules on carbon coating and PET. In addition, the DLC coated PET exhibited exceptional flexibility, and even after subjecting it to 2160 bending cycles, it showed no signs of cracking, indicating its mechanical robustness and durability. This research serves as a strong reference for utilizing DLC to address water vapor permeation challenges.

Microfibrillated cellulose (MFC) barrier coating for extending banana shelf life

This study evaluated, for the first time, the feasibility of using 100% microfibrillated cellulose (MFC) for a barrier coating to preserve the shelf life of bananas. MFC was produced from a commercial bleached kraft hardwood pulp through mechanical milling. Barrier coating was accomplished by dipping bananas into aqueous MFC suspensions. Performance of the barrier coating on the banana peel surface was evaluated from visual observations, weight loss, firmness, and dissolved soluble sugars content of the bananas. The results indicated that coating the banana peel surface with MFC delayed the browning and softening of the banana and the conversion of banana carbohydrates into soluble sugars. Furthermore, the extent of mechanical fibrillation in producing MFC affected MFC suspension wettability of banana peel surface, as well as the effectiveness of banana preservation. Casting-made MFC films were used to understand various factors of MFC barrier coating performance. The extent of MFC fibrillation was found to be more effective than increasing the amount of coating in reducing water vapor permeation for better fruit protection.

MORPHOLOGICAL, MECHANICAL, ORGANIC VAPOUR PERMEATION PROPERTIES AND BIODEGRADABILITY OF POLY(ETHYLENE-CO-VINYL ACETATE)/WASTE PISTACHIO SHELL-DERIVED CELLULOSE COMPOSITE MEMBRANES

Cellulose fibers have attracted interest as a suitable candidate for manufacturing composites. In the present work, cellulose derived from waste pistachio shell was used to prepare composite membranes with poly(ethylene-co-vinyl acetate (EVA) via solution casting, and their morphological, mechanical, organic vapour permeation characteristics and biodegradability were evaluated. Scanning electron micrographs showed that the voids in the EVA polymer were filled effectively by cellulose fibers. The mechanical testing of the composites revealed an improvement in Young’s modulus with the increase in cellulose loading. The permeation of polar and non-polar solvents through the membranes was studied and explained by molar size, molecular mass and polarity of the solvents. Nielson’s permeability equation as modified by Baradwaj was used to analyse the relative permeability of the membranes. Soil burial degradation experiments of the composite membranes showed a decrease in weight and tensile strength, revealing the biodegradability of the membranes.

Effect of Hydrophilic Layer in Double Microporous Layer Coated Gas Diffusion Layer on Performance of a Polymer Electrolyte Fuel Cell

Abstract Water flooding under high current and humidity conditions is a main barrier to enhancing the performance of polymer electrolyte fuel cells (PEFCs). This study evaluated a double microporous layer (MPL) coated gas diffusion layer (GDL) consisting of a thin hydrophilic layer coated on a hydrophobic MPL coated GDL. An accurate measurement of the contact angle was introduced to assess the wettability of the MPL. In addition, the water breakthrough pressure and water vapor permeance values were measured to evaluate the water transport ability of the MPL. The oxygen transport resistance was measured using the limiting current density in polarization curves. Appropriate hydrophilic MPL containing 5% Nafion, 25% TiO2, and carbon black in the double MPL enhanced the ability of the GDL to discharge water at the catalyst layer, effectively reducing water flooding. The total oxygen transport resistance obtained with the double MPL was reduced by about 20% compared to that obtained with a hydrophobic MPL. Moreover, the pressure-independent and pressure-dependent resistances were separated from the total oxygen transport resistance measured under various back pressure conditions. The double MPL exhibited a substantially reduced pressure-independent resistance at the interface between the MPL and the catalyst layer.