Moisture Absorption Characteristics Research Articles

Investigation on the Moisture Absorption Behaviors of Palm Leaves (Corypha umbraculifera) and Their Variation Mechanism.

Palm leaves serve as a traditional recording medium and are widespread in south and southeast Asia, and they have a long history. However, they are sensitive to environmental fluctuations, especially moisture, which may severely affect their conservation status. In this research, the moisture absorption behaviors of palm leaves in different states, including raw, treated, naturally aged, and artificially aged ones, were investigated by intelligent gravimetric analysis (IGA) and water retention value (WRV) to analyze their moisture absorption characteristics. Mathematical model was employed to fit and analyze their water adsorption curves, aiming to explore the content and distribution of the adsorbed water in monolayered and multilayered. Then, the chemical and physical properties of different palm leaves were studied by chemical composition analysis, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM), and low-field nuclear magnetic resonance (low-field NMR), and the relationship between moisture absorption characteristics and their chemical composition and physical structures was analyzed. The results demonstrated that both treatment and aging processes could have a noticeable impact on the moisture absorption of palm leaves, as evidenced by reduced equilibrium moisture content (EMC) at high relative humidity (RH), decreased multilayer water adsorption content, and slightly increased monolayer water adsorption content. Besides, palm leaves exhibit a lower rate of moisture adsorption, at ∼30-50% RH, which facilitates their long-term conservation. The results of chemical and physical analyses revealed that the reduced content of hydrophilic groups was the primary reason for a decrease in palm leaves moisture absorption. Additionally, the fiber structure changes of palm leaves caused by treatment or aging may have different influences on their moisture adsorption, especially the content of monolayer adsorbed water.

Assessing the consequences of water retention on the structural integrity of jute fiber and its composites: A review

AbstractResearchers have compared natural jute fiber to synthetic fibers due to their distinct physical and mechanical properties, which have been recognized for decades. Jute fibers are a very versatile type of vegetable fibers widely used in structural composites and it has also shown potential in various applications such as nanoparticles, building interior, and automotive components. However, designing jute composite parts is a challenging task due to plant origin, growth conditions, age, stem location, extraction method, and non‐uniform fiber cross section. The current review aims to provide a comprehensive analysis of the existing literature on jute fiber and its composites of water and moisture absorption behavior on their performance. The most relevant findings regarding jute fiber water and moisture absorption characteristics have been summarized and analyzed in this review paper. In addition, this article presents an overview of the main characteristics of jute fibers, several parameters influencing the characteristics of jute fibers, jute fiber reinforcement composites, impact of relative humidity, swelling properties on jute fiber composite materials, and potential future research areas are also highlighted.Highlights Higher growing interest of researchers for jute fiber Factors affecting the properties of jute fibers Various way of making jute fiber reinforced composites Influence of moisture on its properties Present and future areas of its upgradation

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

Effect of hygrothermal aging on mechanical properties of continuous flax fiber composites

AbstractThe influence of hygrothermal aging on the mechanical properties of flax fiber‐reinforced polymer (FFRP) composites was studied by examining the mechanical properties and failure mechanism of the composite laminates exposed in distilled water at different temperatures. The resin transfer molding (RTM) process was used to manufacture FFRP laminates, which were then subjected to accelerated aging tests in distilled water at different temperatures. The moisture absorption characteristics of FFRP were analyzed by a water absorption test. Tensile, bending, and low‐velocity impact tests of laminates after different aging conditions were performed. Combined with DSC and FTIR tests, the failure mechanism of FFRP exposure to hygrothermal aging was analyzed. The result indicated that the increase in temperature will accelerate the moisture absorption process of FFRP, and the hygroscopic behaviors at different temperatures conform to Fick's law. In the early stage of hygrothermal aging, the composites undergo post‐curing, and the tensile and bending strengths increase. After that, the tensile and bending strengths are decreased because of the thermo‐oxygen aging of materials and fiber/matrix interface damage. After hygrothermal aging, the impact peak force of FFRP decreases obviously while the absorbed energy increases due to the increase of internal defects and plasticization of composites. The increase of hygrothermal aging temperature aggravates the aging of materials, resulting in a more obvious decline in the tensile, bending, and impact properties of the composites.Highlights The effect of hygrothermal aging on the mechanical properties of FFRP is investigated. With the increase of hygrothermal aging time, the tensile and bending strength of FFRP increased at the early stage of aging and then decreased. After hygrothermal aging, the impact peak force of FFRP decreases and the absorbed energy increases due to the increase of internal defects and plasticization of composites.

Moisture absorption and desorption characteristics and prediction model analysis of building thermal insulation materials

Understanding the isothermal moisture absorption and desorption characteristics of building thermal insulation materials and how they affect thermal conductivity, is curial for accurate building thermal design and energy-saving calculation. In this paper, five types of building thermal insulation materials are selected for investigation. First, the variation trend of the equilibrium mass moisture content of materials in different moisture absorption and desorption stages is studied employing the saturated salt solution method and the constant temperature and humidity box method, and the effect of temperature on the moisture absorption and desorption processes is evaluated. Additionally, the applicable model of the material in the moisture absorption and desorption process is obtained through a fitting analysis of the experimental data. Finally, the influence of the material’s moisture absorption and desorption characteristics on the thermal conductivity is analyzed using the transient thermal conductivity test method. The results highlight that there is a need to consider the moisture absorption and desorption processes to accurately determine the wet material thermal conductivity, and the hysteresis effect of the material in the moisture absorption and desorption processes is directly related to its microstructure and the relative humidity at the initial moisture desorption. At a temperature of 25 oC, the autoclaved aerated concrete exhibits its highest hysteresis rate of thermal conductivity during the moisture desorption process of third stage, reaching 13.2%.

Measurement and modeling of moisture equilibrium and methane adsorption in shales from the southern Sichuan Basin

The adsorption characteristic of methane in water-bearing shale is essential for the accurate estimation of shale gas reserves. The sorption mechanisms of moisture and methane in shale remain poorly understood. In this work, moisture equilibrium measurements in shales were conducted to study moisture absorption characteristics. The governing factors for moisture absorption were determined, and the suitability of moisture absorption models was evaluated. An innovative water saturation apparatus and an improved methane adsorption system were built to measure methane adsorption in high water-bearing shales. The suitability of the Langmuir model in describing methane adsorption in water-bearing shale was studied. A predictive model for methane adsorption in water-bearing shale was developed based on improved BP neural network algorithm, which was further utilized to determine the primary governing factors for methane adsorption. The results revealed that the equilibrated moisture content in shale presents a three-stage and S-type ascending trend with increasing relative humidity. The methane adsorption amount shows a slide-type downward trend with the increase of water content. The Peleg model demonstrates the superior performance in describing the hygroscopic isotherms, and the Langmuir model performs poorly in characterizing methane adsorption in shales with high water contents. The controlling factors for the ultimate moisture content mainly include specific surface area, average pore diameter, carbonate and pyrite content. The methane adsorption in water-bearing shale is mainly governed by water content and specific surface area. The results of this work enrich the understanding of the adsorption mechanisms of shale gas and provide a solid basis for the assessment of shale gas reserves.

Research progress on bamboo fiber reinforced polymeric composites: Processes, properties, and future directions

AbstractCharacterized by rapid maturation, short growth cycles, and high strength and toughness, bamboo can be compounded with polymers to produce bamboofiber reinforced polymeric composites (BFRPCs). These composites exhibit corrosion resistance comparable to traditional materials such as glass fiber and carbon fiber composites. Additionally, they possess features like low density, high strength, degradability, and environmental friendliness, with low production costs and strong industrial applicability. This paper reviews the accomplishments in BFRPCs and provides an overview of the production processes for BFRPCs. Furthermore, it summarizes the research status of mechanical properties, moisture absorption characteristics, interface performance, and flame retardancy of these composites. The current issues with BFRPCs were analyzed. Finally, the paper explores future research directions and potential applications of BFRPCs.Highlights The performance studies on BFRPCs are comprehensively presented. Composite processing of BFPRCs is reviewed. Pros and cons of various types of BFRPCs are analyzed. Overview of the applications of BFRPCs in various domains is presented. Future trends and challenges of BFRPCs are introduced.

Study on moisture absorption characteristics of glass fibre‐reinforced epoxy resin material for composite insulators based on the 3D‐Fick model

AbstractLong‐term exposure to moisture leads to a gradual deterioration of performance and reduced service life of glass fibre‐reinforced epoxy resin (GFRP) material in composite insulators. Therefore, it is necessary to analyse the moisture absorption characteristics of GFRP material and the evolution of damage to their internal interface properties. Moisture absorption tests on GFRP rod material used in composite insulators to obtain their three‐dimensional diffusion coefficients are conducted. Atomic force microscopy was then employed to obtain the composite material system's fibre/matrix interfacial phase parameters. Furthermore, a finite element model incorporating representative volume elements with interfacial phases and a mesoscale transient moisture absorption finite element model for the composite material was established. Finally, the moisture absorption characteristics of GFRP material and the evolution of damage to the interfacial phase under thermal‐humidity cycling conditions were investigated. The results showed that the diffusion coefficient along the fibre direction in GFRP material was higher than that in the perpendicular direction. The moisture diffusion finite element model, incorporating an anisotropic interfacial phase, fitted the anisotropic diffusion coefficients of GFRP material more accurately. As moisture invaded the GFRP material, the mismatch stresses continuously increased during the moisture absorption. Moreover, the non‐uniform arrangement of fibres resulted in uneven distribution of moisture‐induced stresses inside the material, leading to higher mismatch stresses in areas with dense fibre arrangements in the matrix. Prolonged high and low humidity cycles led to the development of micro‐cracks, micro‐porosity, and interface debonding along the fibre direction at the GFRP material interfaces, thereby affecting the anisotropic moisture absorption characteristics of the material. The findings of this study provide valuable insights into the mechanisms underlying the deterioration of GFRP material in composite insulator rods due to moisture degradation.

Performance degradation mechanism of adobe materials under freeze-thaw cycles based on moisture transportation characteristics and microstructural analysis

It is well known that the mechanical properties and appearance of adobe materials degrade significantly during freeze-thaw cycles due to the unique moisture absorption characteristics of soil particles. In order to clarify the performance degradation mechanism of adobe materials under freeze-thaw cycles, the evolution law of the pore structure, attack products, and capillary absorption characteristics were systematically studied when experiencing 10, 20, and 30 freeze-thaw cycles. The results showed that the flocculent hydration product around the Yellow River sediments and aggregate particles gradually reduced during adobe materials subjected to freeze-thaw cycles. Volume expansion caused by the growth of ettringite in macropores and cracks led to the deterioration in pore structure and more water participated in the subsequent freeze-thaw cycles. The porosity and pore volume of adobe materials increased with the increasing of freeze-thaw cycles, and the harmful pores of 50–200 nm rose significantly. After 20 freeze-thaw cycles, harmful pores accounted for 62.3% of the total pore volume of adobe materials, which induced an enlarged moisture transport capacity, and thus the capillary absorption coefficient increased by 18.52 g/(m2·s1/2). As a combined result of above factors, after 30 freeze-thaw cycles, the loss rates in mass and compressive strength of adobe materials were 6.2% and 15.4%, respectively.

Preparation of hygroscopic fabric with a uniform and slow exothermic effect and its thermoregulation evaluation

Hygroscopic-exothermic textiles dissipate heat by absorbing moisture around the skin, which makes humans feel warm in a cold environment. However, the local rapid temperature rising and heat concentration due to uneven sweat distribution can cause a heat sensation that is unfavorable to personal thermal comfort in a relatively short period of time. Herein, hygroscopic fabric with a uniform and slow exothermic effect was prepared to achieve thermal-wet comfort of garments. The hierarchical structure textile consists of an inner layer with moisture diffusion and transport performance, a middle layer with moisture absorption and storage properties and an outer layer with moisture absorption and heat generation characteristics, which achieved the effect of slow and uniform heat dissipation during the moisture absorption by controlling the moisture transmission within the fabric. Based on the study of the uniform and slow exothermic effect of fabrics, five indexes, namely the average temperature value, the maximum temperature value, the temperature distribution uniformity index, the percentage of the heating area distribution at the maximum temperature point on the fabric surface and the initial heating rate, were proposed to evaluate the uniformity and the slowness of moisture absorption and heat dissipation in textiles. The result showed that the initial heating rate of multi-layer fabric could be reduced by 0.11–0.25°C/min compared to the single-layer hygroscopic-exothermic fabric and there was an up to 29.93% increase in the heat dissipation area at the maximum temperature point. The uniformity of temperature distribution after moisture absorption of fabrics increased by 41.6–58%.

Effect of imbibed moisture on monotonic and low‐velocity impact behavior of injection over‐molded short/continuous fiber reinforced polypropylene composites

AbstractDesign of automotive components with over‐molded short/continuous fiber reinforced thermoplastic composites necessitates understanding of their behavior under extreme outdoor conditions. The short, quasi‐isotropic and over‐molded short/continuous glass fiber reinforced polypropylene (PP) composite specimens were prepared as per standard and immersed in water until equilibration to study their relative moisture absorption characteristics and consequent mechanical behavior. As the absorbed moisture mostly occupied the interface between fiber and matrix in laminated composite inserts and moisture absorption of short fiber composite core is insignificant, the moisture absorption of over‐molded composites is just above 50% of that of laminated composites. The flexural, interlaminar shear and impact behavior of equilibrated composites is primarily governed by the quantum of imbibed moisture of composite materials. Optical analysis of failed moisture equilibrated over‐molded specimens showed a marginal delamination between plies of the inserts without any perceptible damage within the short fiber composite similar to dry as molded specimens.

Moisture Absorption Characteristics and Subsequent Mechanical Property Loss of Enset–PLA Composites

One of the drawbacks of natural fibers and their composites is their inherent hydrophilic nature. The effect of moisture on the mechanical properties of composites is irrefutable. This study deals with the hygroscopic characteristics of enset–PLA composites and their effect on the mechanical properties of the composites. To do this, injection-molded composite specimens with different fiber volume fractions, plasticizer ratios, fiber lengths, and fiber ages were considered. The specimens were exposed to distilled water, and the moisture absorption was monitored on a daily basis. Subsequently, the specimens were subjected to mechanical loading to determine the effect of moisture on their strength, stiffness, and strain at break strength. Lastly, the individual and joint effects of the considered factors were scrutinized using an optimal experimental design. The results of the study show that the maximum and minimum moisture uptakes were recorded for 25% and 15% fiber ratios, respectively. Due to the effect of moisture, the tensile and bending strength decreased by 11% and 5%, respectively, for the 15% fiber volume fraction and decreased by 16% and 13%, respectively, for the 25% fiber volume fraction. Increasing the amount of plasticizer increases the moisture resistance. The results indicate that Enset–PLA composites have competitive properties and stability when exposed to moisture.

A comprehensive study on the effect of hybridization and stacking sequence in fabricating cotton-blended jute and pineapple leaf fibre biocomposites

Developing biocomposites by hybridization, which is the combination of two or more materials, can be a potential solution for improving material recyclability and sustainability. This study focuses on creating a hybrid biocomposite reinforced with cotton-blended pineapple leaf fibre (PALF) fabric (174 GSM) and jute fibre fabric (265 GSM) which are thrown away by textile factories. The mechanical, moisture absorption, and vibration characteristics of four stacking sequences of hybrid composites and two unhybridized composites were analyzed. Results indicated that hybridization improved tensile and flexural characteristics compared to pineapple leaf fibre reinforced polymer (PFRP) composites. The jute fibre reinforced polymer (JFRP) composite exhibited the maximum tensile strength of 35.16 MPa, while the hybrid composites achieved a maximum of 32.16 MPa. Among the hybrid composites, jute layers on the outer plies (4P5J-2) demonstrated the maximum tensile modulus of 1.315 GPa. Additionally, the hybrid composite with three layers of jute plies between alternating layers of jute-pineapple plies showed the highest elongation at 15.94%. Among the hybrids, alternate stacking of jute/PALF plies (4P5J-1) gave a maximum flexural strength of 44.36 MPa, which is similar to JFRP (44.91 MPa) and a 78.57% increase in flexural modulus compared to PFRP composite, despite having the lowest tensile strength. Although the JFRP composite exhibited the highest impact strength, the hybrids still outperformed the PFRP composites. With hybridization, moisture absorption decreased, with a maximum of 29.50% compared to the JFRP composite. Furthermore, due to the spiral-like orientation of the yarns, stacking PALF plies on the outside can cause critical damping. Therefore, it is shown in this paper that both hybridization and stacking sequence can significantly influence composite performance. These findings also implies the utilization of textile industry's natural fibres to develop hybrid composites for automotive applications, like brake and accelerator pedals, for a greener future and effective waste material utilization.

Experimental Study on Gaseous Moisture Absorption and Swelling of Red-Bed Mudstone in Central Sichuan, China under Different Relative Humidity Environments

Aiming to resolve the engineering hazards caused by the long-term micro-swelling of red-bed mudstone, gaseous moisture absorption-swelling tests under four ambient humidities were conducted (60%, 70%, 85% and 99%) by developing a set of experimental devices. Based on the moisture absorption characteristics of mudstone, the effects of a vapor pressure gradient on the equilibrium time, moisture absorption rate and swelling rate were discussed. Combined with its mineral composition and pore structure, the correlation mechanism between gaseous moisture absorption and swelling was explained in depth. The experimental results suggested that the whole process was long-term and slow. The swelling rate was lower than the moisture absorption rate by two orders of magnitude. As a result, the duration of a stable swelling strain was two orders of magnitude higher than that of a stable moisture absorption. The characteristic curve of moisture absorption went through three stages: the rapid stage, dominated by crystal layer adsorption; the intermittent expansion stage, dominated by adsorbed water film; and the decelerated stage, dominated by capillary condensation. In the intermittent expansion stage, as the relative humidity declined, the duration of an intermittency increased, and the number of intermittencies decreased. The evolution of the swelling rate obviously lagged the proportion of moisture absorption. This hysteresis effect reached its maximum when the moisture absorption transitioned from the intermittent expansion stage to the decelerated stage. Moreover, the equilibrium time, moisture absorption ratio and swelling strain all had a non-linear proportional relationship with the relative humidity. In this case, the critical value was 85%. Finally, a unified mathematical expression for the gaseous moisture absorption curve was acquired and the relationship between the swelling strain and the increment of moisture content was fitted; this will provide the necessary research basis for a subsequent simulation of its volume change under changing ambient humidity.

Development and mechanical characterization of jute fibre and multi-walled carbon nanotube-reinforced unsaturated polyester resin composite

In recent days, Polymer Matrix Composites (PMCs) have been used in various engineering sectors such as aerospace, automobile and military due to their enhanced mechanical and lightweight properties. Various natural and artificial fibres are used as reinforcement materials to enhance the mechanical characteristics of the PMCs. In addition, the fillers are used to impart the performance characteristics of the composites. This study aims to find the influence of Multi-Walled Carbon Nanotube (MWCNT) fillers on the mechanical and moisture absorption characteristics of the Jute fibre reinforced Unsaturated Polyester Resin (JFUPR) composites. Three layered jute fibre composite samples with varying weight percentages of MWCNT are fabricated through hand layup technique, and their tensile strength, flexural strength, impact strength, hardness and water absorption properties were investigated as per ASTM standards. The outcome revealed that the 8 wt% MWCNT reinforced jute fibre Polyester Resin composite showed enhanced and maximum mechanical properties. After that, the property was decreased due to the accumulation of filler particles in the composite. Also, the water absorption property of the composite was decreased with the increase in the percentage of MWCNT due to the reduced volume percentage of the matrix in the composite.

Rutting and Fatigue Resistance of High-Modulus Asphalt Mixture Considering the Combined Effects of Moisture Content and Temperature

High-modulus asphalt mixtures (HMAM) have been widely used in asphalt pavement in high-temperature areas of China, owing to their advantages in rutting and fatigue resistance. However, moisture and temperature interdependently determine the degradation of pavement performance of the HMAM, owing to the unique climatic conditions in summer in some high-temperature areas of China. There were few studies on the rutting and fatigue properties of the HMAM under the combined action of moisture contents and temperatures. Hence, the moisture absorption characteristics of the HMAM at different temperatures were analyzed. The rutting performance of the HMAM was investigated under different moisture contents and temperatures. The fatigue performance of the HMAM was investigated under different moisture contents, temperatures, and stress levels. Results show that: the rutting and fatigue resistance of the HMAM decrease with the increase in temperature and moisture content. The dynamic stability decreases by 8.9% at 40 °C and by 7.0% at 60 °C on average per 10% increase in moisture content and decreases by 22.7% on average per 10 °C increase in temperature. The fatigue life decreases by 4.1% at 15 °C and by 3.1% at 40 °C on average per 10% increase in moisture content and decreases by 31.3% on average per 10 °C increase in temperature. Finally, a prediction equation was established to predict the fatigue life under different moisture contents and temperatures.

Characterization and compatibility of bio-based PA56/PET

Abstract The properties and compatibility of bio-based PA56 and polyethylene terephthalate (PET) polymers were studied in detail. The experimental results showed that when compared with PET, bio-based PA56 had better moisture absorption, softness, and dyeing characteristics. By calculating and analyzing the macromolecular structures of bio-based PA56 and PET, the difference in solubility was obtained as 4.18 Cal0.5·cm1.5·mol−1. Thermodynamic analysis showed that the measured change in mixing enthalpy far exceeds the range of the compatible system when the proportion of bio-based PA56 exceeded 15%. When the content of bio-based PA56 in PET exceeded 20%, the glass transition temperature of the blends with different proportions all had double peaks and the eutectic phenomenon was not observed. Scanning electron microscopy was used to observe the cross-section morphology of bio-based PA56/PET blends before and after etching. We found that the interface between the two phases was clear and a “sea-island” dispersed structure was formed. The results of the analysis indicated that the compatibility of the bio-based PA56 and PET was not good.

A thermal conductivity model for insulation materials considering the effect of moisture in cold regions

Insulation is an important material for energy conservation and frost heave reduction in cold regions. The thermal conductivity of the insulation materials is usually considered as a constant. However, their thermal performance degenerates due to the absorption of water. To describe the variations of thermal conductivities with water content, a thermal conductivity model for three-phase insulation material was proposed by considering the insulation material's porous and moisture absorption characteristics. A tortuosity correction was introduced to reflect the heat conduction path. Then, the measured results and the existed models were used to evaluate availability of the proposed model. Finally, the quantitative influence of the porosity, water content, and thermal conductivity of solid phase on the thermal conductivity of wet insulation materials was analyzed. The results show that there is close agreement between the predicted results of the new model and the measured ones, with the maximum relative error <15%. The model with tortuosity correction can effectively calculate the thermal conductivities of the insulation materials in a full range of porosity (from 0 to 1). The thermal conductivity decreases with the increase of porosity, but increases with the increase of water content. The solid phase's thermal conductivity has little influence on the thermal conductivity of the insulation materials. The study can provide an effective method to predict the thermal performance variation of the insulation material due to the effect of moisture content in cold regions.

Consequences of Humidity Cycling on the Moisture Absorption Characteristics of Epoxy Resins with Different Network Architectures

Absorbed moisture is a perpetual contributor to the steady loss of performance for in-service epoxy-based polymer materials. On the atomistic scale, the state of individual water molecules in a crosslinked epoxy is dependent on the strength of the secondary bonding interactions they engage in and their local physical environment. However, these chemical and physical variables can be tailored on the macroscopic scale through changes in the experimental curing schedule. In this study, crosslinked epoxy matrices with different network architectures were cured by varying the stoichiometric mixing ratios of the epoxy: hardener combination. The samples were subsequently subjected to fluctuating humidity conditions which comprises repeating cycles of high (∼95% RH) and ambient humidity. Both infrared (IR) spectroscopy and dielectric readings were successful in establishing a strong correlation between moisture absorption, network morphology, and dielectric properties. An anomalous behavior observed during the spectral peak analysis helped us understand how absorption history can redistribute the concentrations of water species at the same moisture concentrations. The results from this study elucidate how the phenomenon of absorption itself can act as a damage initiation event, and they also indicate that the spatial quantification of the different water species across a sample can allow us to map damage sites, nanopores, and areas with an overall higher void content.

Study on static moisture absorption characteristics of porous humidity regulating ceramic building materials

Study on static moisture absorption characteristics of porous humidity regulating ceramic building materials