Moisture Uptake Behavior Research Articles

Macroporous, Highly Hygroscopic, and Leakage-Free Composites for Efficient Atmospheric Water Harvesting.

Hygroscopic composites based on hygroscopic salts and hydrogels are promising for atmospheric water harvesting (AWH), but their relatively low water production and possible salt leakage hinder real applications. Here, we report highly hygroscopic and leakage-free composites from loading LiCl into emulsion-templated sodium alginate and poly(vinyl alcohol) hydrogels with macroporous structures and interpenetrating polymer networks. The resulting composites exhibited an enhanced moisture uptake (up to 3.4 g g-1) and leakage-free behavior even at an extremely high relative humidity (RH) of 90%. Moreover, the composites showed accelerated adsorption, with high adsorption (0.803 g g-1 water at 25 °C and 90% RH within 1 h) and desorption due to the emulsion-templated, highly interconnected macropores. The hygroscopic composites obtained 1.12 g g-1 water per adsorption-desorption collection cycle and showed high reusability, without obvious deterioration in adsorption, desorption, and collection after 10 cycles. With the presence of carbon nanotubes, solar-driven AWH could be realized, without the requirement of additional energy. The highly hygroscopic and leakage-free composites with enhanced and accelerated adsorption and desorption are excellent candidates for efficient AWH.

Impact of water absorption on the creep performance of epoxy/microcrystalline cellulose composites

AbstractRecently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post‐conditioning anomalous effect of moisture uptake on their mechanical and dynamic‐mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog‐bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier‐transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long‐term properties of the composites.

Thermoset-polymer matrix composite materials of jute and glass fibre reinforcements: Radiation effects determination

In this work, woven jute and glass fabrics were used as natural fiber and synthetic fiber reinforcements, respectively, and unsaturated polyester resin was used as a thermoset polymer matrix to fabricate jute/polyester and glass/polyester composites via compression molding. As expected, glass/polyester exhibited superior performance than jute/polyester composites in terms of mechanical properties and moisture uptake behavior. Further, both composite laminates were exposed to gamma (γ) irradiation at a dose of 5 kGy to enhance their performance. After γ-irradiation, it was revealed that tensile strength, bending strength, tensile modulus, bending modulus, and impact strength increased by approximately 14, 28, 20, 21, and 13%, respectively, for the case of jute/polyester composites while glass/polyester composites demonstrated 13, 27, 15, 14, and 22% increase of the values, respectively. Further characterization of the composite samples was performed via moisture uptake in water and salt solutions, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrum (EDS) analysis.

Influence of ultrasonic application on soybean aqueous extract based composite edible film: Characterization and their food application

In this study, a soybean aqueous extract-based composite film was developed by incorporating beeswax, clove essential oil, and span-20 via ultrasonication. The effect of ultrasonication power level (0–600 W) on the rheological properties of the film forming solution (FFS) and important film properties such as water vapor permeability, tensile strength, elongation at break, and opacity was evaluated. It was found that ultrasonication treatment until a power level of 400 W at a constant treatment condition of 15 min and a frequency of 20 kHz improved barrier (water vapor permeability: 2.91 × 10−10 g m/m2·Pa·s) and mechanical properties (tensile strength: 2.53 MPa). Ultrasonication considerably reduced the apparent viscosity of FFS from 1.32 Pa s (control) to 0.188 Pa s (600 W) and improved the flow behavior. The smooth and homogenous surface obtained in SEM analysis validated the enhanced properties obtained for ultrasonication treated films. Model fitting of moisture sorption data of the experiments indicated that the GAB model is best suited to predict the moisture uptake behavior of developed films at all selected temperatures (25, 35, and 45 °C). Sealed samples exhibited a tearing failure during testing with a seal strength value of 59.16 N/m. A qualitative biodegradation test resulted in the degradation of films within 12 days, making them an eco-friendlier packaging option. Application of the developed film as a packaging material for muffins showed that soybean aqueous extract-based film could maintain the moisture content and textural parameters of muffins for up to six days under ambient storage.

Influence of alkaline delignification on moisture uptake behavior and bonding enthalpies of hemp

AbstractRaw hemp fibers are alkaline delignified to evaluate the effect of lignin on the moisture uptake behavior of hemp. Samples are subjected to moisture absorption/desorption isotherms from 5% to 95% relative humidity at three different temperatures (15, 25, and 35°C). The sorption ratio between delignified and untreated hemp is lowered by 25%. Hysteresis makes evident the greater influence of lignin on moisture binding at low relative humidity while at high relative humidity, cellulose plays the most important role. The GAB, Hailwood‐Horrobin and Dent models are fitted to absorption/desorption isotherms. Delignification and temperature decrease the size of the monolayer. The energy constants of the monolayer differ according to the model used. Lignin causes great differences between absorption and desorption. The greater the temperature is, the lower the monolayer energy constant. The energy constants of the multilayer are identical for the three models, showing a greater range of variation in delignified samples than in the untreated samples. Based on primary and secondary energy constants, bonding enthalpies are determined. Estimations in desorption show higher correlation coefficients with the energy constants, which enables to conclude that measures in desorption better explain the effect of delignification on the water uptake behavior of hemp.

Experimental study on the effect of hygrothermal environments combined with the sustained mechanical loads on the strength of composite rings

Despite the high strength-to-weight ratio and corrosion resistance, the performance of composite pipes is strongly affected by the hygrothermal conditions. In this study, the E-glass/Epoxy composite pipes are produced by the filament winding method. The specimens are cut according to ASTM D2290 standard and exposed to three different environmental conditions. The first group of samples is kept intact, the second group is immersed in water, and the third group is subjected to transverse diametrical load and then immersed in water at different temperatures. At the specified time intervals, samples are subjected to the split-disk test method (ASTM D2290) to determine the Hoop Tensile Strength (HTS) of samples. The results show that the moisture uptake behavior at low temperatures followed the Fick's law and at higher temperatures the non-Fickian behavior is seen. The applied preload has no significant effect on the type of moisture absorption behavior. Applying the hygrothermal and strain corrosion conditions to the samples, the HTS of the samples decreases. SEM images shows that the moisture absorption decreases the bonding between the fibers and matrix and also reduction of bonded epoxy on the outer surface of the fiber in saturated specimens is clearly seen.

Influence of Chemical Treatment and Moisture Absorption on Tensile Behavior of Neem/banana Fibers Reinforced Hybrid Composites: An Experimental Investigation

ABSTRACT Hybrid composites composed of neem fiber (N), banana (B) fiber and epoxy resin were fabricated by hand layup method. Three types of composites with blending ratio of B:N (1:4), B:N (1:1) and B:N (4:1) respectively were fabricated and the effects of fiber loading, chemical treatment and moisture absorption on tensile strength of the composites were investigated. The results showed that the fiber loading influenced the tensile strength and the B:N (4:1) composite displayed the superior tensile strength of 52 MPa compared to other composites due to the presence of more amount of banana fiber with high strength. The B:N (1:4) composite exhibited the lowest tensile strength of 47 MPa owing to the presence of more amount of neem fiber with low strength. Chemical treatment of fiber surface improved the tensile strength significantly due to the removal of impurities, lignin and hemicellulose. Silane-treated composite showed the greater tensile strength compared to alkali treated and untreated composites. Silane treated B:N (4:1) composite exhibited 17.5% and 42.3% improvement in tensile strength compared to the tensile strength of alkali treated and untreated composites respectively. Moisture absorption study revealed that the moisture uptake behavior of composite reduced the tensile strength due to the breakage of H-bond. Moisture absorption reduced the tensile strength of B:N (1:4), B:N (1:1) and B:N (4:1) composites by 14.7%, 10% and 5.8% respectively compared to dry samples.

Influence of different viscosity grade Methocel and Ethocel polymers for the development of controlled release dimenhydrinate matrix tablets

Dimenhydrinate is a therapeutic agent used for the treatment of nausea and vomiting. A conventional dose of dimenhydrinate is 50 mg per 8 h. Once-daily controlled release tablets of dimenhydrinate were formulated intended to treat emesis. The tablets were formulated using hydrophilic polymers Methocel® and hydrophobic polymers Ethocel® and subsequently analyzed for pre-compression and post-compression characteristics, % moisture uptake, dissolution profiles and release behavior of the drug. Identification of active ingredient and compatibility of blends were analyzed through FT-IR. Drug release kinetics of dimenhydrinate was assessed at pH 1.2, 4.5 and 6.8. The results of release profiles were evaluated for different kinetic models including model dependent and model independent. The optimized formulation K100M 30% showed ideal pre-compression properties and in vitro characteristics. Tablets exhibited a controlled drug release pattern due to the formation of a viscous gel layer followed by erosion. Furthermore, zero-order best described the release pattern with the value of r2 ˃ 0.99. Once-daily tablets released 98–100% drug in 24 h. Significantly more concentration and higher viscosity grade of hydrophilic polymer ensured the required pattern of drug release.

Designing, Preparation, and Evaluation of Orodispersible Chitosan Anionic Salt Tablets

Oral dispersible tablets (ODTs) are promising pharmaceutical dosage forms and, theoretically, could be used for many active pharmaceutical ingredients. The development of ODTs by direct compression with rapid disintegration and suitable hardness is a formulation challenge. The hypothesis of the present work is to prepare a single super-disintegrant multifunctional excipient for the production of ODTs. A single multifunctional tablet component was prepared by crosslinking of chitosan-hydrochloride (CS-H) using multivalent anionic salts, such as carbonate, phosphate, and sulfate. An optimized tablet characteristic concerning the disintegration time (DT) and the compaction properties is obtained utilizing the response surface methodology (RSM). The DT and elastic ratio (ER) were used as responses, and two other factors were studied, i.e., concentration of anions (Csa) and compression pressure (Pc). The obtained crosslinked chitosan anionic salt powders were also characterized in terms of chemical interaction, flowability, moisture uptake, water sorption, and release behavior of an incorporated chemically reactive model drug (ibuprofen lysinate). Based on RSM, the optimal concentrations of chitosan phosphate and chitosan sulfate (as %) were 61.14, 60.89, and 64.65, respectively. The optimal compression pressures (in Mpa) of chitosan carbonate, phosphate, and sulfate were 107.02, 110.39, and 100, respectively. Moreover, 0.31, 0.15, and 0.47 (predicted elastic ratio) and 8, 17, and 2 (disintegration time, s) were obtained for chitosan carbonate, phosphate, and sulfate, respectively. The infrared spectroscopy and the differential scanning microscopy studies were used as tools to detect the interaction. Mean dissolution time was 20.5 min for chitosan hydrochloride compared with 6.9–8.52 for chitosan anionic salts, while the dissolution efficiency was 0.54 for chitosan compared with > 0.8 for chitosan anionic salts. Drug release was higher from chitosan anionic salt matrix systems compared with that of chitosan hydrochloride tablets. The RSM was successfully utilized to prepare optimized tablets using chitosan anionic salt as a single oral dispersible tablet excipient. These salts exhibited suitable physico-mechanical properties upon compaction with a concomitant super-disintegration ability. The chemical reactivity of chitosan hydrochloride against negatively charged molecules was dependent upon crosslinking with negatively charged anions as indicated by the release behavior of ibuprofen lysinate from the chitosan anionic salt matrix systems.

Moisture Uptake and Thermomechanical Behavior of Epoxy–Amine Networks Derived from Ortho-Substituted Monomers

Ortho-substitution with hydrophobic aliphatic groups has shown reduced moisture uptake in a variety of thermoset networks. In this study, the number and size of ortho-substituents were systematical...

Is Hygrothermal Aging of Construction Polymer Composites a Reversible Process?

This paper presents the effects of wet/dry cycling loading on the moisture uptake behavior of a Fibre Reinforced Polymer (FRP) composite used in the civil engineering sector. FRP samples of various dimensions were cut from an ‘off-the-shelf’ pultruded flat sheet and conditioned in a cyclic hygrothermal environment. A series of 3 consecutive moisture absorption-desorption cycles lasting for 153 days were carried out to investigate the moisture uptake behavior of FRPs. The hygrothermal procedure consisted of immersion in 60°C distilled water until saturation and consecutively drying in a 60°C oven until equilibrium was reached. After the 1st desorption cycle, it was found that FRP samples lose a significant amount of mass due to chemical decomposition, the extent of which increases as wet/dry cyclic loading progresses. The effective mass loss leads to a subsequent significant increase in the rate of moisture uptake. Mechanical behavior of the FRPs aged at 40°C, 60°C and 80°C for 224 days is examined at both ‘wet’ and ‘dry’ states to reveal the reversible and irreversible effects of moisture uptake. It was revealed that the effects of 40°C hygrothermal aging on mechanical performance are reversible when moisture is removed.

Physical and Combustion Properties of Binder-Assisted Hydrochar Pellets from Hydrothermal Carbonization of Tobacco Stem

Hydrothermal carbonization (HTC) combined with pelletization is an efficient upgrading process to convert biomass into energy-dense pellets. Binders usually serve an important role in the quality of biofuel pellets. Here, hydrochar was produced from tobacco stem through HTC, and was pelletized in the presence of various binders. The effect of four kinds of binders (K2CO3, CaCO3, xanthan gum and carboxymethyl cellulose) on the basic fuel properties, mechanical strength, moisture adsorption and combustion characteristics was investigated. The results showed that K2CO3 assisted pellet had decreased compressive strength, increased hygroscopicity and high combustion residues. The compressive strength of pellets increased with increasing amount CaCO3 binder probably due to the hardening effect of enhanced adhesion attraction forces between adjacent particles. Meanwhile, the CaCO3 assisted pellet exhibited the lowest moisture uptake behavior. In addition, the introduction of organic binders led to improved mechanical strength, especially for xanthan binder, which could be ascribed to the formation of solid bridges and enhancement of adhesion forces between particles. TGA results suggested that the binder-assisted pellets exhibited desirable combustion characteristics such as decreased ignition temperature and increased comprehensive combustibility index. Kinetic parameters of the combustion process of binder-assisted pellets were also determined by employing the model free isoconversional Kissinger–Akahira–Sunose method. This study demonstrated that HTC of tobacco stem combined with pelletization in the presence of appropriate binders provide an alternative for solid biofuel pellets production. Hydrothermal carbonization (HTC) of tobacco stem combined with pelletization in the presence of appropriate binders provide an alternative for solid biofuel pellets production.

Experimental and numerical investigations on the effect of alkaline hornification on the hydrothermal ageing of Agave natural fiber composites

Experimental and numerical investigations are performed to evaluate the mass diffusion in Agave Americana natural fiber composites considering several environmental conditions. The effect of fiber pretreatment by alkaline hornification is analyzed on the moisture uptake behavior of the Agave fiber composites. It was observed that water retention value, which is a measure of affinity towards moisture, reduces with each subsequent hornification cycle. The microstructural investigations were performed to analyze the morphological changes in fiber microfibrils. Composite specimens were subjected to accelerated ageing under water and humidity conditions at controlled temperatures between 0 °C and 75 °C. Composites were weighted periodically and mass gain curves were analyzed. A comparison is drawn between the mass gain behavior of composites fabricated using untreated and alkali hornified Agave fibers. The studies have revealed a clear influence of alkaline hornification on the improvement of the hydrothermal durability of the Agave fibers. The effective moisture diffusivity of the composites is determined using edge correction factors for rectanguloid specimens. Finally, the experimental mass gain is compared with the numerical Fick’s law based finite element (FE) approximations.

A further generalized thickness-dependent non-Fickian moisture absorption model using plain woven epoxy composites

Mechanical performance of composite material is widely known to be susceptible to moisture attack. In order to determine the extent of moisture attack, the paper aims to generalize a thickness-dependent moisture absorption model for fiber reinforced composites. For this study, moisture absorption tests were conducted for woven glass/epoxy (2-ply and 6-ply) and woven carbon/epoxy (4-ply and 6-ply) composites, submerged in distilled water at 60 °C up to 94 days. From the measured moisture uptake behavior of the tested materials, a correlation function, linking normalized non-Fickian parameters and normalized laminate thicknesses, was derived to describe moisture absorption behavior of the tested composite materials using fictitious Fickian curve. To characterize non-Fickian moisture absorption behavior of composite materials, the derived correlation function suggested that only two arbitrary materials with different laminate thicknesses would suffice. Such correlation function could prove to ease the characterization of thickness-dependent non-Fickian moisture uptake behavior of fiber reinforced composites.

Effect of moisture absorption on the mechanical performance of natural fiber reinforced woven hybrid bio-composites

ABSTRACTIn the present study, moisture uptake behavior and their effect on mechanical properties of plant fibers were investigated while these fibers were reinforced with epoxy matrix. The developed composites were dipped in tap water for a span of 12 months at room temperature. Hardness (shore-D), tensile, and flexural properties were evaluated after 1 year immersion of samples in water and compared with that of the dry specimens. Water saturated jute/hemp/epoxy composite specimen showed the highest reduction in tensile strength and young’s modulus by 46.9% and 51.8%, respectively. Water saturated hemp/epoxy composite specimen showed the highest reduction in flexural strength by 45.1%. Highest reduction of 39.7% in the flexural modulus was achieved by the jute/hemp/epoxy composite specimen. Hardness had observed no significant decrease in the values due to moisture absorption. scanning electron microscopy images of fractured surfaces of these bio-composites showed quite relevant information regarding weakening of fiber/matrix interface.

Moisture uptake dynamics on desiccant-coated, water-sorbing heat exchanger

Recently a novel concept of water-sorbing heat exchanger has been proposed, which can independently handle latent and sensible loads at the same time and provide a very promising high-efficient solution for temperature and humidity control. Obviously, moisture uptake behavior has great influence on heat exchanger's performance. Here, a series of experiments have been made to clarify whether the linear driving force (LDF) model could be used to describe this behavior and to investigate the water uptake mode at different times. Results show that the LDF model is valid for water-sorbing heat exchanger and the moisture uptake experiences four different modes in general, including non-isothermal adsorption, near-isothermal adsorption, capillary condensation and cooling-based condensation. This study also confirms that salts in porous matrix can accelerate moisture uptake and promote capillary condensation. These results in a great improvement of dehumidification capacity. Besides, an empirical and a semi-empirical framework were developed to evaluate the constant parameters in the LDF model. Meanwhile, a figure of merit of the desiccant, Z, was defined for engineering application, to simplify the LDF model in further.

Reinforcement of Polypropylene Composites Based on Recycled Wool or Cotton Powders

ABSTRACTThis article addresses the preparation and characterization of polymer composites of polypropylene (PP) containing recycled wool or cotton micro-powder. The PP composites were produced in a lab-scale twin-screw extruder. The recycled wool or cotton powder was obtained from wool and cotton waste fibers (from textile industry) by freeze milling technique. The amount of powder (wool or cotton) was varied from 1% to 10 %. Cotton and wool powders were homogenously distributed in the polymer matrix, as observed from scanning electron microscopic (SEM) images. Thermal, physical, and mechanical properties of the obtained composites were investigated by differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), tensile strength, dyeability as well as the moisture uptake behavior is also explored. The overall results clarify that wool or cotton powders could be used as effective reinforcing materials for the production of PP composites with enhanced properties.

Thickness-dependent non-Fickian moisture absorption in epoxy molding compounds

The objective of this research is to characterize the relationship between the moisture uptake behavior and the thickness in epoxy-based molding compounds (EMCs). Experimental results from the literature were adopted for this purpose. A thickness-dependent moisture uptake model was proposed to describe the moisture uptake behavior. In order to apply the model, a methodology to develop the fictitious Fickian curve was suggested. Subsequently, the relationships between the non-Fickian parameters and the thickness were correlated and compared. Results showed that the apparent diffusivity of the fictitious curve was sensitive to the environmental conditions but not the thickness. In addition, when combining all data, it was found that each normalized non-Fickian parameter could be described by a single equation with respect to the normalized thickness. Based on the thickness-dependent model, the moisture concentration across the thickness was further characterized. In conclusion, the model proposed in this study allows the prediction of moisture uptake behavior at various thicknesses of EMCs. This could greatly reduce the time and cost of extensive experimental works.

Method for determination of parameters for moisture simulations in photovoltaic modules and laminated glass

Moisture ingress into photovoltaic modules can be detrimental to the expected lifetime of the photovoltaic device. Hence, better understanding of this process and ways to predict the lifetime of a module are of high importance. Moisture ingress occurs through the polymeric materials used in a PV module, especially through the encapsulant which contacts all the sensitive parts in the module. In this work material parameters of polyvinyl butyral, an encapsulant mostly used for glass–glass modules, are presented and an examination of its lateral moisture transport and uptake behavior was undertaken to attain parameters for use in simulations. The uptake of moisture followed Fickian behavior. The absorption isotherm found was of Type III according to the classification by Brunauer, Emmett and Teller.

Moisture diffusion through (hexadecyltrimethylammonium bromide ‐ Indian bentonite)/(vinylester) nanocomposites in artificial seawater and demineralized water

This paper compares the moisture diffusion properties of organomodified (Indian Bentonite nanoclay)/vinylester containing different amounts of nanoclay on exposure to demineralized water and artificial seawater at room temperature. Moisture uptake behavior of (Indian Bentonite)/vinylester was investigated and compared with that of neat vinylester. Addition of 5 wt% nanoclay decreased the diffusivity and permeability of vinylester in artificial seawater medium, but these diffusion parameters increased in demineralized water medium. Degradation in glass transition temperature and microhardness of the nanocomposites were much greater in specimens aged in demineralized water than in those in artificial seawater medium. Moisture diffusion behavior of the specimens was analyzed by Fick's law and the Langmuir model. The aged specimens were chemically analyzed by using infrared spectroscopy after aging for 146 days. A significant amount of leached organic species was detected in the demineralized water–aged specimens but the same was absent in those aged in artificial seawater. J. VINYL ADDIT. TECHNOL., 22:441–451, 2016. © 2015 Society of Plastics Engineers