Water Vapor Transport Properties Research Articles

Water vapor transport properties of bio-based multilayer materials determined by original and complementary methods

To enhance PLA gas barrier properties, multilayer designs with highly polar barrier layers, such as nanocelluloses, have shown promising results. However, the properties of these polar layers change with humidity. As a result, we investigated water transport phenomena in PLA films coated with nanometric layers of chitosan and nanocelluloses, utilizing a combination of techniques including dynamic vapor sorption (DVS) and long-term water vapor adsorption–diffusion experiments (back-face measurements) to understand the influence of each layer on the behavior of multilayer films. Surprisingly, nanometric coatings impacted PLA water vapor transport. Chitosan/nanocelluloses layers, representing less than 1 wt.% of the multilayer film, increased the water vapor uptake of the film by 14.6%. The nanometric chitosan coating appeared to have localized effects on PLA structure. Moreover, nanocelluloses coatings displayed varying impacts on sample properties depending on their interactions (hydrogen, ionic bonds) with chitosan. The negatively charged CNF TEMPO coating formed a dense network that demonstrated higher resistance to water sorption and diffusion compared to CNF and CNC coatings. This work also highlights the limitations of conventional water vapor permeability measurements, especially when dealing with materials containing ultrathin nanocelluloses layers. It shows the necessity of considering the synergistic effects between layers to accurately evaluate the transport properties.

Moisture-driven CO2 pump for direct air capture

Direct Air Capture, the chemical separation of carbon dioxide (CO2) from air, is considered a necessary approach to generate negative carbon emissions and in turn limit global warming, though energetic and monetary costs must continue to decline to meet the needed gigaton scale. The promise of energy-efficient and continuous carbon dioxide membrane separation has only recently been investigated with the development of facilitated chemical transport and novel electrochemically driven methods. This work demonstrates the potential for continuous pumping of CO2 from air using commercial anion exchange membranes driven solely by a water vapor gradient. A reactive transport model that couples ionic transport with moisture sensitive bicarbonate chemistry in charged polymers, also termed moisture swing sorption, was developed alongside experimentally measured equilibrium and transport properties of CO2 and water vapor in Fumasep FAA-3 to determine the mass transport limits of such a system. The results show that the commercial membrane is kinetically limited by the moisture sensitive chemistry, enabling a CO2 current of 1.1 μmol/m2∙ s. In diffusion limited materials, a CO2 pumping flux can reach 11 μmol/m2∙ s in and peak performance is expected with a dry air relative humidity around 50% pumping into a saturated water vapor permeate. In all configurations, water loss becomes the major cost in such a separation and must be managed through optimal polymer design or water recovery mechanisms. The work demonstrates the applicability of a new driving force, the evaporation of water, to meet the energetic demand of CO2 separation from air.

Investigation of the Side Chain Effect on Gas and Water Vapor Transport Properties of Anthracene-Maleimide Based Polymers of Intrinsic Microporosity.

In the present work, a set of anthracene maleimide monomers with different aliphatic side groups obtained by Diels Alder reactions were used as precursors for a series of polymers of intrinsic microporosity (PIM) based homo- and copolymers that were successfully synthesized and characterized. Polymers with different sizes and shapes of aliphatic side groups were characterized by size-exclusion chromatography (SEC), (nuclear magnetic resonance) 1H-NMR, thermogravimetric (TG) analysis coupled with Fourier-Transform-Infrared (FTIR) spectroscopy (TG-FTIR) and density measurements. The TG-FTIR measurement of the monomer-containing methyl side group revealed that the maleimide group decomposes prior to the anthracene backbone. Thermal treatment of homopolymer methyl-100 thick film was conducted to establish retro-Diels Alder rearrangement of the homopolymer. Gas and water vapor transport properties of homopolymers and copolymers were investigated by time-lag measurements. Homopolymers with bulky side groups (i-propyl-100 and t-butyl-100) experienced a strong impact of these side groups in fractional free volume (FFV) and penetrant permeability, compared to the homopolymers with linear alkyl side chains. The effect of anthracene maleimide derivatives with a variety of aliphatic side groups on water vapor transport is discussed. The maleimide moiety increased the water affinity of the homopolymers. Phenyl-100 exhibited a high water solubility, which is related to a higher amount of aromatic rings in the polymer. Copolymers (methyl-50 and t-butyl-50) showed higher CO2 and CH4 permeability compared to PIM-1. In summary, the introduction of bulky substituents increased free volume and permeability whilst the maleimide moiety enhanced the water vapor affinity of the polymers.

Lightweight Concretes with Improved Water and Water Vapor Transport for Remediation of Damp Induced Buildings

Most of the historical and old building stock in Europe are constructed from masonry, when brick, stones, or their combination are bound with traditional mortars. Rising damp, due to accompanying effects, is the main factor influencing the quality of indoor climate as well as having an important impact on the durability of masonry structures. In this study, new types of lightweight concrete with waste aggregate content as a suitable material for remediation of damp damaged masonries were designed and tested. Alternative aggregate served as silica sand substitution in the range of 0–100 vol.%. Basic structural properties, mechanical resistance, water, and water vapor transport properties were measured after 28 days of water curing and were compared with dense reference concrete and with traditional masonry materials as well. Moreover, the porous structure of produced concretes and changes caused by usage of alternative aggregate usage were evaluated with the mercury intrusion porosimetry (MIP) technique. Obtained experimental data showed the suitability of modified concretes with 25–50 vol.% of waste aggregate content to ensure acceptable strength and hydric properties, and these properties were found to be comparable with masonry structures and materials used in the past.

Air-to-air enthalpy exchangers: Membrane modification using metal-organic frameworks, characterisation and performance assessment

Air-to-air membrane enthalpy exchanger is one of the environmentally friendly technologies that has been increasingly used in the building sector to recover the waste energy due to ventilation. In this study, we report the development of a facile approach for the deposition of a thin layer of the metal-organic frameworks (MOFs) ZIF-8 and HKUST-1 on polyvinylidene fluoride (PVDF) membranes in order to improve their water vapour transport properties. Material characterisation and properties determination were carried out for the tested membranes. It was shown that the surface hydrophilicity of the coated membranes was improved as compared to the pristine membrane. In general, the water vapour diffused through the coated membranes was higher than the pristine membrane at all the test conditions, while insignificant differences in the mechanical properties between the pristine membrane and the coated membranes were observed. The performance of the coated membranes in an air-to-air membrane enthalpy exchanger was then experimentally assessed. It was found that the effectiveness improved from 44.4% for pristine PVDF45 to 45.9% and 47.7% for the ZIF-8@PVDF45 and HKUST-1@PVDF45 membranes, respectively, at the flow rate of 0.24 L/s. This study provides a useful and facile method to enhance the performance of polymeric membranes used in air-to-air membrane enthalpy exchangers, which could potentially reduce both building energy consumption and greenhouse gas emissions.

Transport properties of water vapor through hemp fibers modified with a sustainable process: Effect of surface morphology on the thermodynamic and kinetic phenomena

The paper is focused on a deep analysis of transport properties of natural hemp fibers (HF) functionalized through a mechano-chemical treatment assisted by high energy ball milling. The effect of milling time on fibers’ morphology was investigated by means of the scanning electron microscopy and FTIR spectroscopy. The results show that the mechanical effect induced a reduction of the mean diameter of hemp fibers and, simultaneously, the achievement of a close packing of cellulose chains. The barrier properties appeared to be dependent either on the packing of cellulose or the water cluster formation. Fick’s law solution in cylindrical coordinates was used to simulate experimental sorption kinetics and to extrapolate the diffusion parameters. The change of diffusion with equilibrium moisture content was described through an empirical relationship. Sorption isotherms were explained on the basis of Park model which accounts for a dual mode sorption at low activities as well as the water clustering phenomenon occurring at high activities. The mean cluster size (MCS) of water molecules was estimated through the application of Zimm Lundberg theory. Finally, the spreading pressure calculation allowed to estimate the driving force of diffusion inside the systems.

WATER VAPOR TRANSPORT IN PLASTERS CONTAINING SUPERABSORBENT POLYMERS

A proper characterization of material properties represents an important step towards an efficient building design. Considering the present issues in the construction sector, moisture loads pose a risk not only to increased material deterioration but also to the health of building inhabitants. In this paper, modified plaster mixtures with superabsorbent admixture are designed in order to improve passive moderation of finishing layers against varying humidity conditions. The relationship between the amount of applied superabsorbent admixture and resulting water vapor transport properties is identified and the influence of temperature on water vapor transport is analyzed. The steady-state cup method is used for the determination of water vapor transport properties, namely the water vapor diffusion permeability, water vapor diffusion coefficient and water vapor diffusion resistance factor. The obtained data show temperature as a very significant factor affecting water vapor transport in the analyzed plasters. Considering the dry-cup method arrangement, relative humidity probes should be used for monitoring relative humidity under the sealed sample for a sufficiently precise determination of water vapor pressure gradient.

A multi-scale model for fluid transport through a bio-inspired passive valve.

Tillandsia landbeckii is a rootless plant thriving in the hyper-arid Atacama Desert of Chile. These plants use unique cellulose-based microscopic structures called trichomes to collect fresh water from coastal fog. The trichomes rely on a passive mechanism to maintain an asymmetrical transport of water: they allow for the fast absorption of liquid water deposited by sporadic fog events while preventing evaporation during extended drought periods. Inspired by the trichome's design, we study fluid transport through a micrometric valve. Combining Grand Canonical Monte Carlo with Non-Equilibrium Molecular Dynamics simulations, we first analyze the adsorption and transport of a fluid through a single nanopore at different chemical potentials. We then scale up the atomic results using a lattice approach, and simulate the transport at the micrometric scale. Results obtained for a model Lennard-Jones fluid and TIP4P/2005 water were compared, allowing us to identify the key physical parameters for achieving a passive hydraulic valve. Our results show that the difference in transport properties of water vapor and liquid water within the cellulose layer is the basis for the ability of the Tillandsia trichome to function as a water valve. Finally, we predict a critical pore dimension above which the cellulose layer can form an efficient valve.

Water vapor permeation and morphology of polysulfone membranes prepared by phase inversion

The aim of this work was to study the effect of different variables in the morphology and water vapor permeation of asymmetric membranes. Different from other works on vapor induced phase inversion this work focus on the formation of a dense skin capable of separating small molecules like gases and on the transport properties of water vapor instead of liquid water. It also correlates the morphologies with the permeability. The results show that higher polymer concentrations lead to denser skin and lower permeability. Water vapor transmission rates varied from 30 to 48 g/m2.h depending on membrane morphology. They also show that for membranes with the same type of skin layer the permeability depends on the sub-layer. Finally, the results suggest that different mechanisms were responsible for the formation of the membranes.

Influence of Waste Plastic Aggregate and Water-Repellent Additive on the Properties of Lightweight Magnesium Oxychloride Cement Composite

The aim of the present study is to improve the thermal and hygric performance of magnesium oxychloride (MOC) cement composites by the incorporation of waste plastic-based aggregate and the use of the inner and surface hydrophobic agents. The crushed waste expanded polypropylene particles were used as a full replacement of natural silica sand. The aggregate properties were evaluated in terms of their physical and thermal parameters. The caustic calcined magnesite was studied by SEM, XRF, and XRD spectroscopy. The MOC cement composites were characterized by SEM/EDS, XRD, and FT-IR spectroscopy and measurement of their structural properties, strength parameters, thermal conductivity, and volumetric heat capacity. Assessment of water- and water vapor transport properties was also conducted. The results show significantly improved thermal parameters of MOC cement composite containing expanded polypropylene (EPP) as aggregate and indicate high efficiency of surface hydrophobic agent (impregnation) as a barrier against the transport of liquid and gaseous moisture. The resulting lightweight EPP-MOC cement composite with improved thermal insulation function and suitable mechanical properties can be used to produce thermal insulation floors, ceilings, or wall panels reducing the operational energy demand of buildings.

Water Vapor Transport Properties of Polyurethane Films for Packaging of Respiring Foods

Thermoplastic polyurethane (PU) polymers with different chemical compositions were synthesized and casted to films, and their water vapor barrier properties at different range of relative humidity (RH) were characterized. The water vapor permeability (WVP) of packaging films is one of their most important properties to identify their suitability for use as packaging materials and is rather a complicated phenomena if the polymer has polar nature. The WVPs of PU films are determined both by permeation measurements which are a steady-state method and water vapor sorption measurements which are a non-steady-state method. Effective permeability (Peff), solubility (Seff), and diffusion (Deff) coefficients of PU films were determined at 23 °C within the RH range of 0–97%. It was found that Peff, Seff, and Deff increased with increasing RH gradient due to water vapor and polymer interactions. Microscopic images showed that 1,4-butanediol (BDO) helped to improve porous structure. Castor oil (CO) caused a decrease in the intensity of active absorption sites, namely, the C=O···H-N hydrogen bonds between chains. Results of two methods were yielded in the same magnitude of order. In most cases, the non-steady-state (sorption) method yields higher WVP values than steady state. At 0➔85% RH, the difference was up to 8-fold. Conditioning and equilibrating of films at 50% RH helped to reach sorption data approximate to permeation data. It was suitable to use sorption measurements to estimate the WVP which is a considerable simplification for polar polymers, e.g., developed PU film.

Eco-friendly concrete with scrap-tyre-rubber-based aggregate – Properties and thermal stability

Increasing amount of waste tyres represents a global problem as tyres can pose a risk to the environment if not treated properly. Recycling of waste tyre rubbers in civil engineering as aggregate in cement concrete can be an effective environmental and economic approach. As problems associated with the use of waste tyre rubber in concrete production are not completely understood, a detailed analysis of rubber concrete prepared from used tyre rubber-based aggregate involving testing of its mechanical, basic physical, microstructural, hygric and thermal properties, and behaviour after exposure to elevated temperatures is presented in this paper. Testing of mechanical performance included measurement of compressive strength, flexural strength, secant and dynamic modulus of elasticity. Thermal conductivity was determined in the dependence on moisture content, from the dry to fully water saturated state. Dry volumetric heat capacity was also tested. Specific attention was paid to the hygric performance of rubberized concrete that was characterised by the water and water vapour transport parameters. Investigation of concrete properties after its thermal exposure included testing of mass loss, mechanical resistance, bulk density, and thermal conductivity that was tested as property having direct relation to concrete structural parameters. The use of scrap-tyre-rubber aggregate resulted in a decrease of the unit weight, worsening in mechanical parameters and a significant reduction in thermal conductivity of prepared rubberized concrete. Rubber-based aggregate almost did not affect water transport properties, while water vapour transport properties increased with rubber amount in the mix. No significant changes on concrete characteristics related to rubber incorporation occurred at temperatures up to 300 °C. However, after exposure to 400 °C, significant changes in measured concrete properties were observed, which was in line with the thermogravimetric analysis of the used tyre-based rubber. Nevertheless, based on rubberized concrete functional properties at common ambient conditions it can be considered as an alternative lightweight material, bringing benefits to the environment and economy as it is produced from crap available in a large amount and at a negligible cost.

Water vapor transport properties of interfacially polymerized thin film nanocomposite membranes modified with graphene oxide and GO-TiO2 nanofillers

Graphene oxide (GO) and its composite with TiO2 (GT) were utilized as nano-filler materials to prepare highly permeable and water vapor selective nanocomposite membranes. The nano-fillers were characterized using different analytical tools to determine their physicochemical properties. Nanocomposite membranes were prepared by dispersing the nano-fillers in aqueous phase monomer solution for interfacial polymerization reaction on the inner surface of Polysulfone hollow fiber membrane. Surface morphology and bonding chemistry of the nanocomposite membrane was analyzed using various analytical tools. The two types of nano-fillers were compared for their compatibility with the polyamide matrix, and consequently, the water vapor separation performance of the resulting membrane. Results revealed that both the nano-fillers are firmly attached to the polyamide layer via hydrogen and covalent bonds. GT based membranes have higher surface roughness and better hydrophilicity as compared to GO. In addition, GT membranes have more carboxyl groups and lesser degree of cross-linking due to the interference with interfacial polymerization reaction. This leads to a higher permeance (2820 GPU) and a water vapor/nitrogen selectivity when compared to other TFN membranes reported in literature. The nano-fillers act as active sites for preferential transport of water vapor molecules through the membrane thereby, significantly improving water vapor permeance.

Improved abrasion resistance of textile fabrics due to polymer coatings

Textile fabrics are often subject to abrasion, starting from exposed parts of garments to a variety of technical textiles. Abrasion protection by usual coatings, however, can significantly decrease the water vapor transport through a fabric which is often not desired, especially in the case of garments. In our paper, we report on an approach to combine increased abrasion resistance with sufficient water vapor transport properties. For this, different polymers (poly(methyl methacrylate), acrylonitrile butadiene styrene, or amorphous polyamides) were coated on cotton and polyester woven fabrics. The results of abrasion tests against sandpaper show significantly increased abrasion resistance. The absolute evaporation resistance, measured by a Permetest testing device, was only slightly increased up to values still acceptable for typical garments. Images of all coatings by helium ion microscopy deliver an explanation for the measuring results. Polymer coatings on the polyester fabric resulted in a slight reduction of the hydrophobicity, while coating the cotton fabric severely increased the contact angles of the originally superhydrophilic material.

High‐strength concrete based on ternary binder with high pozzolan content

Several high‐strength concrete mixes containing ternary binders composed of Portland cement, silica fume, and waste brick powder are designed. Taking into account the functional properties of hardened mixes, together with their supposed environmental qualities and economic benefits, the practical limits of pozzolan content in the binder are analyzed. Based on a wide set of material characterization experiments including mercury intrusion porosimetry, scanning electron microscopy, and X‐ray diffraction analysis, complemented with a series of measurements of basic physical properties, mechanical parameters, and water and water vapor transport properties, the binder consisting of 57% Portland cement, 18.5% silica fume, and 24.5% brick powder is identified as the optimum in the studied system. The excellent functional properties of the mix with such a high pozzolan content are achieved due to the synergetic effects of the combination of silica fume and waste brick powder on concrete properties. The fineness of brick particles, together with the dual character of the applied brick powder acting as active pozzolan and microfiller at the same time, is found to magnify the ability of silica fume to fill the intergranular space through the improvement of the granulometry curve.

Hydration and water vapour transport properties in yeast biomass based films: A study of plasticizer content and thickness effects

Research on biodegradable films is a topic of strategical interest in the field of food science and technology. These films are membranes conformed by biopolymers that interact strongly with water and they generally require the addition of plasticizer in order to improve its integrity and mechanical properties. The study of the hydration and water transfer properties through these films, as well as understanding in what way the thickness and the addition of the plasticizer affect these properties, is essential for a better knowledge and optimization of the required protective function of these membranes. In this work the hydration kinetics and water transport through biodegradable films obtained from yeast biomass were studied, in order to know the performance against changes in thickness and glycerol content. Hydration kinetics experiments allowed obtaining solubility of water in the matrix film, and the diffusion coefficient. Results demonstrated that when glycerol content was increased, the solubility of water increased while diffusion remained constant. Moreover, when the film thickness was grown, the solubility of water decreased but the diffusion increased. Experimental water vapour permeability obtained through traditional cup method was compared to the theoretical permeability calculated by multiplying diffusion coefficient and water solubility. The good agreement observed between both values allowed the analysis of how solubility and diffusion contributed to permeability. As a result this study revealed that the increment of permeability with the plasticizer content was due to the increase in solubility, while the effect of the thickness increasing permeability was dominated by diffusion.

The Comparison of Water, Water Vapour Transport Properties and Mechanical Characterization of Two Commercial Plasters on Market in the Czech Republic

This article deals with the comparison of two different renovation plasters produced by different companies in the Czech Republic. The selected stuccos were Feinputz 212 supplied by HASIT Šumavské vápenice a omítkárny s.r.o and Kbelosan F from Knauf Praha spol. s.r.o. They were studied in the means of basic physical properties, mechanical properties, water transport properties and water vapour transport properties. Results revealed only slight variations in bulk density, matrix density and open porosity, but in the means of transport properties, the plaster Feinputz 212 showed much higher openness to water and water vapour transport.

Gas and water vapor transport properties of mixed matrix membranes containing 13X zeolite

Mixed matrix membranes (MMM) containing 13X zeolite particles were prepared to study the impact of hydrophilic inorganic component on membrane gas and water vapor transport properties. Rubbery ethylene-vinyl acetate copolymer (EVA), hydrogenated nitrile rubber (HNBR), and glassy polysulfone (PSF) varying in permeability were selected as membrane matrices. The incorporation of 13X decreased gas permeability of all MMMs and had only a marginal effect on ideal selectivity (e.g. 20wt% loading reduced N2 permeability by 21%, 19%, and 4% for PSF, EVA, and HNBR, respectively). The observed trend was in agreement with the diminished free volume size obtained from the positron annihilation lifetime spectroscopy (PALS) measurements suggesting pore blockage. In contrary, water vapor permeability through all MMMs was significantly enhanced by zeolite filling (e.g. 30wt% loading increased H2O permeability by 153%, 34%, and 22% for PSF, EVA, and HNBR, respectively). This was explained as due to the increased water solubility documented by the sorption results, that compensates for the effect of the reduced water diffusivity in MMMs. The variations in MMMs permeabilities were also found to depend on zeolite particle size and its porosity. Two opposite effects were noticed of increased water vapor permeability and decreased gas permeability for MMMs filled with smaller but more porous particles. The water permeation through PSF based membranes may cause debonding at the particle/matrix interface and deterioration of the MMMs properties as indicated by their enhanced gas permeability and reduced selectivity.

Preparation of poly(glycolide-co-lactide)s through a green process: Analysis of structural, thermal, and barrier properties

We have successfully synthesized poly(lactide), poly(glycolide), and poly(lactide-co-glycolide) copolymers in bulk by ring-opening homo- and copolymerization of glycolide and l-lactide, using sodium hydride as the environmentally friendly and nontoxic initiator. Random copolymers were obtained, and the microstructure was characterized by nuclear magnetic resonance (1H and 13C NMR) and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). The mechanism of reaction was elucidated by analysis of the polymer end groups. Homopolymer and copolymers films and their blends were obtained, and structure and physical properties analyzed. Thermal degradation analysis showed superior characteristics of copolymers with respect to the blends. Transport properties of water vapor were also evaluated and correlated to the copolymer composition.

Impact of seam types on thermal properties of athletic bodywear

This study investigated the differences in thermal properties of primary seam types used in athletic apparel construction. Traditional seam types, such as overlock and flatlock, as well as adhesive films, were studied. Laboratory experiments in a controlled environment showed that adhesives created a considerably thinner seam than the other methods, while flatlock seaming showed the greatest increase in the garment weight because of dense stitching. A series of thermal manikin tests and statistical analysis showed a significantly higher thermal insulation rating in a bodysuit constructed with flatlock seams, which was found to have lower air permeability than the overlock and adhesive physical property testing samples. There was no significant difference in water vapor transport properties among the three test seams. The findings of this study provide the impacts of seams on thermal properties of active bodywear, which may have practical applications in the sports apparel industry’s decision-making in activewear design and production.