Moisture Absorption Kinetics Research Articles

Chemical extraction and its effect on the properties of cordleaf burbark (Triumfetta cordifolia A. rich) fibres for the manufacture of textile yarns

Tropical Triumfetta cordifolia (TC) fibre extracted from the equatorial region of Cameroon has been characterized as a potential fibre for textiles. An investigation of extraction parameters to soften this fibre is crucial to use it as a biobased material in the spinning process. To obtain textile quality fibres, 34 sodium hydroxide extraction tests were carried out to study the effect of extraction conditions on its characteristics. Thus, three levels of concentrations (0.5, 1.0 and 1.5 wt%), temperatures (80, 100 and 120 °C) and durations (120, 180 and 240min) were used for extraction by cooking, and at room temperature, durations of 120, 150 or 180 min with three concentrations (2.5, 3.0 and 3.5 wt%) were considered. Only 6 combinations produced fibres that were clear and soft to the touch, without defects (corrugations, stuck fibres) and without residual bark epidermis at the macroscopic scale. For these fibres, the dissolution of non-cellulosic substances, morphological, physical, thermal and mechanical properties depended on the austerity of the alkaline retting. Under mild conditions, the SEM surfaces of the fibres showed large residues of the middle lamella, which made the lignin content (10 wt%) and hydrophilic function higher. Under medium conditions, the fibre surfaces were clean and slightly wrinkled (at 80 °C; 120min). Under severe conditions, heterogeneous transverse shrinkage and wrinkling were observed and accompanied by cellulose degradation (39 wt%) with a significant reduction in tenacity at 16cN/tex. The medium extraction conditions were considered more effective, and their fibres showed cellulose content up to 49 wt%, density up to 1.39 g cm−3, “Fickian” moisture absorption kinetics with saturation up to 11 wt%, thermal stability up to 237 °C, Young's modulus up to 3.7 GPa, tensile strength up to 113 MPa and tenacity up to 40cN/tex. These new results were compared with lignocellulosic textile fibres in the literature, showing similarity with banana, sisal and jute fibres.

Effect of graphene on the mechanical properties and moisture absorption kinetics of nano filler reinforced glass fiber composites

Recently, Graphene nanofillers have been used as a means of enhancing mechanical properties to a great extent. It has outstanding barrier properties, including stiffness at low loads and flame retardancy. It’s wonderful reinforcing properties make Graphene one of the most promising nano-fillers for orthopaedic leg braces. The composites were made by adding Graphene as a nano-filler to epoxy resins at suitable weight percentages (2 %, 4 %, 6 %, 8 %, and 10 %). An experiment on moisture absorption was conducted using a five-layer laminate, which was hand-fabricated and uniformly thick. In accordance with ASTM standards, experiments were conducted to evaluate the effect of Graphene on the mechanical properties and the moisture absorption kinetics of these materials. After absorbing moisture at different temperatures with varying Graphene loading, the nano-filler reinforced GFRP materials were submitted to tensile, flexural, and impact tests. Results of tensile and flexural tests showed Graphene incorporation of up to 4 % weight provided a maximum tensile strength of 92 MPa as well as a maximum flexural strength of 176 MPa. With the addition of 6 % Graphene nano-filler, the impact strength of GFRP composite was enhanced to 5.8 J. In direct result of these experiments, composites have been applied in a diverse range of industries.

Neurofuzzy modelling of moisture absorption kinetics and its effect on the mechanical properties of pineapple fibre-reinforced polypropylene composite

Natural fibres possess low density, less abrasiveness, good strength and sound absorption capacity and its significance lies in being renewable and biodegradable. The mechanical characteristics and moisture absorption of pineapple fibres reinforced with polypropylene resin are focused in this study. Chopped fibres and unidirectional fibre mats of pineapple were reinforced with polypropylene resin to make pineapple fibre/polypropylene composites. The length of the pineapple fibres and the orientation of the layup of the fibre mats are varied to make composite specimens and the mechanical properties are tested. Moisture absorption studies were carried out and it was confirmed to follow Fickian diffusion. A total of 384 samples were tested and it was observed that all the samples reached its saturation in moisture absorption before 720 h and the strength was inversely proportional to the moisture absorbed. Specimens reinforced with unidirectional fibre mats of alternate orientation possessed high strength irrespective of the moisture absorbed when compared to the specimens reinforced with chopped fibres of random orientation. Neuro fuzzy modelling using ANFIS tool box in MATLAB was used to correlate the static mechanical properties of pineapple fibre-reinforced polymer under different moisture conditions, fibre orientations, fibre volume percentage, fibre size, etc.

Effect of Dry-Wet Circulation on Moisture Absorption of Autoclaved Aerated Concrete

Moisture absorbability is the characteristic of autoclaved aerated concrete that differs from other wall materials. For autoclaved aerated concrete, dry-wet circulation is the main actual service environment and can directly affect moisture absorbability, which influences cracking performance of structure. In this study, autoclaved aerated concrete with dry-wet circulation times of 0, 30, 60, 150, and 270 is selected. The experiment is performed under the condition of temperatures 20°C, 30°C, 40°C, and 50°C and relative humidities (RH) of 40%, 60%, and 80%. The temperature and humidity have significant effects on moisture absorption. When the dry-wet circulation times are increased, the moisture absorption performance improves; when comparing the specimen at the dry-wet circulation of 0 times with the specimen of dry-wet circulation of 270 times, the amount of moisture absorption content increased by 85.7%, at the temperature of 50°C and RH of 80%. Origin software is chosen to fit the moisture absorption kinetics model. SPSS software is used to analyse the linear regression and variance. The results of hygroscopic kinetics showed that the fitting effect of the double exponential function was optimal, and the temperature and humidity were closely correlated with the specimens under dry-wet circulation, for R2 greater than 0.941.

Mathematical modeling and thermodynamic properties of rice parboiling

AbstractDue to the importance of hydration stage for parboiling, related studies are insufficiently addressed in the literature. The objective of this study was to model the moisture absorption kinetics of paddy rice, as well as estimate the thermodynamic properties involved in the hydration. The observed mass transfer in the process was directly influenced by the temperature of the system, showing changes in absorption capacity over time. The models addressed allowed satisfactorily describing the moisture gain under various thermal conditions. Particularly, the model based on Fick's second law best represented the experimental data. The effective diffusion coefficient was adjusted to an Arrhenius equation and a new model was generated, capable of describing hydration. The coefficient presented positive dependence with the temperature increase and allowed the determination of different forms of process energy. It was concluded that the hydration of the rice in the parboiling process is nonspontaneous and exothermic.Practical applicationsThis study allowed characterizing the moisture transfer in the hydration stage of the parboiling process, exploring the time and temperature relationship. From these data, mathematical modeling was used as a quality tool, guaranteeing for the parboiling industries control and optimization of the process in a cheap and easy way. In addition, this study presented relevant information on the thermodynamic properties, which made it possible to understand the different forms of energies and phenomena involved. This information can help, in a practical way, in the elaboration of industrial projects aimed at the parboiling of rice.

Moisture absorption kinetics of FruitPad for packaging of fresh strawberry

This study analysed the moisture absorption kinetics of FruitPad embedded with different concentrations of fructose with further application of such pads in packaging of fresh strawberries. The FruitPad was exposed to different storage conditions (temperature and RH) and moisture absorption kinetics was gravimetrically determined over 5 days of storage. FruitPad with 30% fructose showed highest amount of moisture absorption (0.94 g of water/g of pad) at 20 °C and 100% RH. The Weibull model combined with the Flory-Huggins model adequately described changes in moisture content of the FruitPad with respect to storage time and humidity (R2 = 93–96%). The FruitPad containing fructose minimized in-package condensation compared to the pad without fructose. Weight loss of packaged strawberry was less than 0.9% which was much below the acceptable limit of 6% for strawberry.

Modeling rice and corn hydration kinetic by Nicolin–Jorge model

AbstractThis article presents the application of Nicolin–Jorge model in describing the hydration kinetics of rice and corn grains. The model was validated by hydration data of both grains for different hydration temperatures. The results show a satisfactory adequacy of the model to the data, even applying the data to the cylindrical and planar geometries, since the original model was proposed to describe the soybean hydration kinetics, considered spherical. Even as the parameters fitted for both cases have behaved differently depending on the temperature, the model predicted properly the reach of equilibrium moisture for very long hydration times.Practical applicationsThe approach presented in this article is useful in describing the moisture absorption kinetics by rice and corn grains. The model applied fits satisfactorily the experimental data and is applicable when the hypothesis of constant mass transfer coefficient in moisture absorption is not enough to correctly describe the behavior of the kinetic curve of moisture as a function of time for such grains. The proposed approach is applicable to any project that requires prior knowledge of the moisture profile of the grains. The advantage of the model used is the simplicity of the analytical solution obtained and that the model possesses physical grounds, although the grains are considered to be a lumped parameter system, which is an adequate consideration for practical applications.

Water absorption, residual mechanical and thermal properties of hydrothermally conditioned nano-Al2O3 enhanced glass fiber reinforced polymer composites

The durability of the nano-Al2O3 enhanced glass fiber reinforced polymer (GFRP) composites in hydrothermal environment is necessary for hydro/hygro thermal applications. The present investigation emphasizes the effect of nano-Al2O3 filler concentration on moisture absorption kinetics, residual mechanical and thermal properties of hydrothermally treated GFRP nano-composites. Nano-Al2O3 particles were mixed with epoxy matrix through temperature assisted magnetic stirrer and followed by ultrasonic treatment. It has been observed that, the addition of 0.1 wt% of nano-Al2O3 into the GFRP nano-composites reduces the moisture diffusion coefficient by 10%, as well as improves the flexural residual strength by 16% and interlaminar residual shear strength by 17% as compared to the neat epoxy GFRP composites. However, the glass transition temperature has not been improved by the addition of nano-Al2O3 filler. Weibull design parameters have been determined for dry and hydrothermally conditioned nano-composites. A good agreement between the experimental and the simulated stress–strain results has been observed. The interface failure mechanism has been evaluated by field emission scanning electron microscope to support the new findings.

Chemical properties and water absorption kinetics of transgenic corn grain (2B587 Hx) and its conventional isoline (2B587)

In the hydration process, besides influencing processing conditions, the cultivar may also influence water absorption by the grains and, consequently, yield and quality of the milled products. Therefore, the moisture absorption kinetics of the transgenic corn grain 2B587 Hx and its conventional isoline 2B587 were studied, as well as the chemical characterization of the samples in natural conditions. The water absorption kinetics of the grains was modeled using Peleg's equation at hydration temperatures of 40, 50, 60, and 67 °C. The 2B587 Hx transgenic corn, compared with the 2B587 conventional corn, had higher carbohydrate and ash contents and lower crude fiber content. The water absorption by the grains, which was satisfactorily represented by Peleg's model, occurred more quickly as the temperature increased. Peleg's constant, k1, which is inversely related to the initial hydration rate, varied from 405.2 to 141.5 min g/g for conventional corn and from 429.5 to 149.5 min g/g for transgenic corn at temperatures from 40 to 67 °C. The choice of the cultivar may depend on the specifications required by the industry for the main final products.

Humidity-Regulating Trays: Moisture Absorption Kinetics and Applications for Fresh Produce Packaging

For packaged fresh produce, inappropriate high relative humidity (RH) levels and condensation of water vapour cause premature spoilage. Humidity-regulating trays were developed to solve this issue. They were made from a thermoformed multilayer structure: polyethylene (outside)/foamed hygroscopic ionomer (active layer) with 0 or 12 wt% NaCl/hygroscopic ionomer (sealing layer, inside). Moisture absorption kinetics of the humidity-regulating trays with 0 and 12 wt% NaCl (T-0 and T-12, respectively) was investigated under different RH conditions (76, 86, 96 and 100 %) at 13 °C for 16 days. Additional trays containing 7 g of distilled water were closed with a high barrier lidding film, and the headspace RH was continuously monitored as a function of time. As control, a polypropylene (control-PP) tray was used. Strawberries and tomatoes were used to test capability of the trays to regulate in-package RH. The amount of water absorbed by the T-0 and T-12 trays was 7.6 and 13.2 g, respectively. Active hygroscopic ionomer layer was effective in water vapour absorption, and the integration of NaCl into this active layer increased the water vapour absorption capacity of the tray. The Weibull model adequately described the moisture sorption kinetics of the individual packaging trays as a function of time. The headspace RH of trays covered with a lidding film was found to be 89.8, 99.6 and 100 % in the T-12, T-0 and control-PP trays, respectively. The T-12 trays containing fresh produce best regulated the in-package RH below 97 % and maintained overall quality, but at the expense of slightly higher product weight loss (2–3 wt% for strawberry, 1 wt% for tomatoes) compared to the control-PP trays (0.3–0.6 wt%).

Preparation and Characterization of Diatomite/Ground Calcium Carbonate Composite Humidity Control Material

Humidity control material is a kind of healthy environmental friendly material. The diatomite/ground calcium carbonate composite humidity control material (DE/GCC) was prepared by calcinations using diatomite (DE) and ground calcium carbonate (GCC) as raw materials. The obtained samples were characterized by X-ray diffraction, field emission scanning electron microscope, Fourier transform infrared spectroscope and low-temperature nitrogen adsorption method to determine the mineral compositions, functional groups, microstruc- ture, surface element compositions and pore structure, respectively. The moisture absorption performance of sam- ples were tested under high relative humidity conditions (RH=70%, 80%, 90%) and the constant temperature of 30 . The moisture absorption dynamics and humidity control mechanism were analyzed. It is indicated that the ℃ calcium silicate and calcium hydroxide are formed in the DE/GCC during the calcinations process. Compared with the raw materials, the content of mesopore increases in the DE/GCC sample, which is in favor of the capillary con- densation. After 36 h test in the environment with relative humidity of 70%, 80% and 90%, the moisture contents of DE/GCC reach 7.213%, 11.159% and 14.701%, which are about 2.1, 2.9 and 3.0 fold as those of DE, respectively. The moisture absorption kinetics follows the pseudo-second-order model.

Effect of aging on the mechanical performance of GF/pCBT composites

In this paper, we studied the mechanical performance of the thermoplastic composites serviced in aging environment. A serious of specimens was exposed in various conditions for up to 28 days, and then the hygroscopicity and mechanisation of the material were investigated. It is found that water absorb rate first increases and then decreases with increasing of the duration in corrosion tests. Chloride ion concentration and corrosion time have influence on the moisture absorption kinetics of the materials. Results also show that mechanical properties such as modulus and strength of poly cyclic butylene terephthalate and its glass fibre-reinforced composites various with moisture absorption curves.

Effect of Aging on the Performance of Glass Fiber Reinforced pCBT Resin

In the present paper, pCBT casts and pCBT/E-glass fiber composites were prepared. In order to study the mechanical performance of the thermoplastic material in the aging environment, the specimens were exposed to salt spray, hygrothermal as well as immersion conditions. The hygroscopicity and mechanisation of the material were studied. From this research work, it is found that, in corrosion tests, the water absorb rate increases at the beginning of the test and decreases with the increase of time. Chloride ion concentrationb and a higher corrosion time have some influence on the moisture absorption kinetics. The results also show that the mechanical properties such as modulus and strength of pCBT and its glass fiber composites change with the trendency of moisture absorption curves.

Isotherm moisture absorption kinetics in natural-fiber-reinforced polymer under immersion conditions

In natural-fiber-reinforced polymer, absorption of water or moisture is a significant issue in maintaining strength and stiffness. To enhance the understanding of water and moisture sorption behavior, the kinetics of moisture sorption in natural-fiber-reinforced polymers are investigated under immersion conditions. Samples of hemp-bast-fiber-reinforced polyethylene are prepared using an injection molding technique at different hemp fiber volume fractions (vf). The samples are then immersed in water for 274 days. Moisture content and uptake rate are analyzed at different fiber volume factions and matrix crystallinity percentages. A simplified two-dimensional contraction model is developed to investigate the contraction effect on the moisture uptake; it shows that a matrix with high crystallinity has more stiffness contraction on the reinforcing natural fibers, which limits the maximum amount of the absorbed moisture. The Fickian diffusion is found to be the dominant mechanism, shifting toward pseudo-Fickian or anomalous diffusion depending on the natural fiber volume fraction and the crystallinity percentages of the matrix. The natural-fiber-reinforced polymers diffusivity is evaluated and modeled to characterize the ability of liquid molecules to diffuse into these composites at different hemp fiber volume fractions. Both the crystallinity percentage of the matrix material and the volume fraction of the reinforcing fibers were found to interactively affect the sorption kinetics of the tested natural-fiber-reinforced polymers.

Moisture Absorption of Laminated Bamboo Composite and its Influence on Mechanical Properties

Laminated bamboo composite (LBC) has received a great attention due to its environmental friendly characteristics and excellent physical and mechanical properties, therefore it is necessary to investigate the durability of the LBC material in ambient environment (temperature and relative humidity). In this paper, firstly, LBC materials were manufactured in laboratory. Moisture absorption and thickness swelling kinetics of the materials at different temperatures and relative humidity were investigated. Then effects of ambient environment on mechanical properties were evaluated at three different ambient temperatures (21 °C, 36 °C, and 60 °C) and different moisture contents. It is found that the moisture absorption and the thickness swelling increase with temperature, relative humidity and ageing time before an equilibrium condition is satisfied. Parameters of the diffusion coefficient and the swelling rate increase with the temperature. In addition, there is a significant decrease in mechanical properties of the moisture-saturated specimens compared to the dry ones. And the degradation of the bending property and the compressive strength is found to be a function of the moisture absorption during the initial period and becomes stable as the absorption process approaches equilibrium. Finally, surface erosions are shown by scanning electron microscopy (SEM) after the hydrothermal aging at 60 °C.

Comparative 3D simulation on water absorption and hygroscopic swelling in japonica rice grains under various isothermal soaking conditions

Cracking in rice grains caused by moisture absorption is a major concern among food processors because it has a detrimental effect on the texture. This paper aimed to simulate moisture diffusion three dimensionally (3D) using Fick's diffusion equation, compare the results with an empirical model (Peleg's equation), and simulate in 3D the hygroscopic swelling in rice during soaking at 25, 35, 45 and 55 °C. This study intends to provide preparatory information in understanding the cracking mechanism during soaking. The concept was based on finite element analysis to evaluate both the moisture diffusion and hygroscopic expansion coefficients of milled rice using the reconstructed 3D model of rice geometry. The proposed model was satisfactory for describing the moisture absorption kinetics with root mean square error (RMSE), that ranged from 0.66 to 2.52% dry basis. The results of the 3D simulation of hygroscopic swelling were found to be adequate in representing the swelling characteristics of rice. Analysis of 3D simulation enabled both quantitative and qualitative assessment of the changes in the amount, distribution of moisture, and expansion in the geometry of rice grains.

Aging-impact coupling based analysis upon glass/polyester composite material in hygrothermal environment

The objective of this present paper is an investigation of aging-impact coupling upon the polyester matrix E-glass fibers composite materials in hygrothermal environment. In the first part of the study, laminate composite plates were aged in an artificial hygrothermal environment using a climatic chamber at 50 °C temperature and 95% of relative humidity. The gravimetric readings showed discrepancy with respect to Fick’s law which indicates the non-Fickian character of the moisture absorption kinetics. The application of the Carter–Kibler’s model confirmed the Langmuir’s behaviour governing the absorption up to a lap time. In the second part of the study, low energy impacts test were carried out on both aged and non-aged composite plates in a bending configuration on two metallic supports. The impact loads were applied using drop-mass tower. The mechanical responses of aged and non-aged plates such as impact force, bending, contact duration, energy dissipation and damage are highlighted and analyzed.

Thermal stability and moisture uptake of 1-alkyl-3-methylimidazolium bromide

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, (BMIM)Br, and 1-n-octyl-3-methylimidazolium bromide, (OMIM)Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition tempera- ture, previously determined from fast scan TG experi- ments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 C interval in the range 533-573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of (BMIM)Br and (OMIM)Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol -1 , respectively. The moisture absorption kinetics of these ILs at 25 C and 30% relative humidity (RH) and at 85 C and 85% RH were also stud- ied. Water uptake of ILs exposed at 25 C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 C/85%RH fortuitously fit into the Henderson-Pabis model.

Durability studies of montmorillonite clay filled epoxy composites under different environmental conditions

Even though fiber reinforced polymer (FRP) composites are used in many applications, their integrity overtime is still unknown and remains a major concern. Due to inherent viscoelastic nature of polymers and their composites, exposure to elevated temperature and moist conditions results in matrix cracking, plasticization, and interfacial debonding and so on resulting in premature failure of composite structures. Researcher have found that failure in environmentally exposed composites is mainly dominated by matrix whereas the effect on fiber is minimal. Recent advancement in polymeric nanocomposites has shown significant enhancement in mechanical and thermal properties with small weight % addition of nanoclay particles. Most of studies on modified polymeric composite have been carried out at room temperature and to the best of our knowledge no studies are performed under extreme/long-term conditions. Hence, an attempt is made in this work to study nanophased epoxy composites under accelerated ageing conditions. Epoxy resin was modified by incorporating nanoclay at different weight percentages using magnetic mixing method and then samples were prepared for various tests. The samples were subjected to hot (elevated temperature: dry, wet at 60 and 80 °C) and cold (subzero: dry, wet, −18 °C) conditions for 15, 45 and 90 days, respectively. Moisture absorption kinetics, quasi-static flexure and micrographic studies were performed of these composites and compared with the samples aged at control conditions. Percentage weight increase was observed in all the wet conditioned samples with a maximum of 3.1% in neat and 2.1% in 2 wt% nanophased epoxy samples. Quasi-static characterization showed degradation in strength and modulus for all conditioned neat samples with a maximum decrease of 37% and 22% in strength and modulus of hot–wet (80 °C) samples conditioned for 90 days in comparison to room temperature samples. 2 wt% nanophased samples showed increase in strength and modulus (7% and 38% under room temperature, 20% and 29% under hot–wet (80 °C) ∼90 days conditions) over neat samples when similarly conditioned. Scanning electron micrographs (SEM) showed significant decrease in number of cracks in 2 wt% nanophased samples in comparison to neat samples.

A Linear Driving Force (LDF) Approximation of Moisture Diffusion Kinetics in White Rice

Soaking characteristics of white rice grain in water are studied at 25, 40, 60, 70 and 80 °C. The kinetics of mass transfer are modeled using a linear driving force (LDF) approximation with constant diffusivity, which is capable of predicting the moisture ratio profile with time. This approximation is a relatively new approach in food engineering applications for systems in which the rate of mass transfer is controlled by intra-particle diffusion and nonlinear adsorption through porous adsorbent. The mass transfer is also modeled through Fick's law for unsteady-state diffusion using finite difference (FD) method, and compared with the LDF model. In general, the moisture uptake curves calculated with this new approximation compare favorably with the finite difference solution obtained in spherical coordinates, producing results of similar accuracy. Both the methods give a good agreement with the experimental data. The values of the effective diffusion coefficients are between 7.33×10-11 m2/s and 1.43×10-10 m2/s for a temperature of 25 and 80 °C respectively. Although gelatinization of starch is observed at a higher temperature which influences the increase in moisture content, the moisture uptake curves calculated with this new approximation compare favorably with the numerical solution of the non-linear diffusion equation. As such, it can be safely used to predict the unsteady-state moisture absorption kinetics of a rice grain, for the temperature range investigated.