Moisture Diffusion Coefficient Research Articles

Effect of seawater aging on impact behavior of glass fiber/epoxy laminates with drilled holes

During their service life, composite marine structures made up of glass fiber reinforced polymers are susceptible to be affected by environmental and loading conditions such as seawater and low velocity impacts which can cause them severe structural damage. Based on this fact and concern, the present work investigates the influence of seawater aging on impact behavior of glass fiber/epoxy composite laminates with and without drilled holes. To achieve this goal, glass fiber/epoxy laminates were manufactured by resin transfer molding and then cut into specimens for low velocity impact testing. Before impact tests, specimens were immersed in artificial seawater at 70°C for 1464 h. After that time, dry (before seawater aging) and wet (after seawater aging) specimens were tested at 10 and 15 J impact energies using a drop-weight impact tower. The results of accelerated seawater aging confirmed that the presence of drilled holes in composites does not influence on their moisture absorption content and diffusion coefficient. The impact test results showed that the impact properties of wet specimens are significantly lower respect to dry specimens. It was found that the peak force of wet specimens displays a reduction of approximately 40% with respect to the dry specimens as a consequence of moisture absorption which causes plasticization of the polymeric matrix. Ultrasonic C-scan inspection showed that damage area of wet specimen increased up to 250% compared to that of dry specimen. Fractographic analyses by scanning electron microscopy and X-ray computerized tomography revealed that low velocity impact in composite laminates produced damage mechanisms associated to matrix cracking, fiber/matrix debonding, fiber breakage, and delamination, which were more prominent in laminates with drilled holes and subjected to a previous seawater exposition.

Infrared Drying Characteristics and Quality Variations of Lily Bulbs Under Blanching Pretreatment

Abstract Infrared drying characteristics and quality variations (color change, hardness, contents of polyphenol and flavonoid) of lily bulbs under blanching pretreatment are investigated. Influences of parameters such as pretreatment temperature and time and infrared drying temperature are discussed. Effective moisture diffusivity coefficient, activation energy, and energy consumption were calculated. Results showed that drying time was reduced by 62.5%, 56.3%, and 61.5% at 90 °C compared to 60 °C when blanching time was 4, 5, and 6 min, respectively. A blanching time of 5 min and drying temperature of 70 °C were ideal for pretreatment and drying to maintain good color quality. Hardness value of lily bulb decreased as drying temperature and blanching time increased. Seventy to eighty degree celcius was ideal drying condition to maintain good hardness quality. Blanching time and drying temperature differently affected contents of flavonoids and polyphenols of lily bulbs. Basically, when blanching time was relatively long and drying temperature was relatively high, the content of polyphenols was high.

Atomistic to continuum scale investigations on mechanical properties of epoxy bonded fiber reinforced polymer composite systems under hygro-thermal exposures

Epoxy polymers are widely used as adhesives in bonded composite systems. In this study, multi-scale computational investigations from molecular dynamics (MD) to finite element (FE) simulations are carried out to understand the material behaviour at atomistic level and to evaluate the performance at macro level. MD investigations are carried out to understand the extent of degradation of mechanical (such as strength, modulus) and transport properties (such as moisture diffusion coefficient) due to different environmental conditions like moisture ingress and high temperature. The influence of degree of curing of epoxy (diglycidyl ether of bisphenol-A) and type of hardener (diethyltoluene diamine, diethylene triamine, trimethylene hexadiamine) on the mechanical performance of the cross-linked epoxy polymer systems is also investigated. In-depth investigations are also carried out to identify the factors contributing to the total potential energy of cross-linked epoxy polymers and their role during the process of curing. Diffusion coefficient (key transport property) of epoxy polymer under moisture exposure is also determined using MD simulations. It has been demonstrated that high temperature causes the increase in diffusion in epoxy polymer systems. The observations on the performance of the epoxy system under moisture exposure obtained from MD simulations are translated to the higher length scale. The moisture ingress (in turn, significant reduction in mechanical properties) in epoxy polymer used for bonded composite system is also investigated using FE simulations. It is found that the extent of moisture ingress in the epoxy adhesive increases rapidly when epoxy polymer is environmentally exposed (under high temperature), and thus, the whole system gradually loses its effectiveness due to mechanical degradation. The findings of this study will help in understanding crucial parameters and aid to better use/engineering of epoxy polymers.

Kinetics and variation of volatile components of Atractylodis Macrocephalae Rhizoma during hot-air drying

The present study explored the kinetics and variation of volatile components of Atractylodis Macrocephalae Rhizoma during the hot-air drying process to obtain the optimal process parameters under multiple goals such as drying efficiency and drying quality. The dry basis moisture content and drying rate curves along with the change of drying time of Atractylodis Macrocephalae Rhizoma were investigated at five levels of drying air temperatures(30, 40, 50, 60, and 70 ℃). The relationship between moisture ratio and time in the drying process of Atractylodis Macrocephalae Rhizoma was fitted and verified by Midilli model, Page model, Overhults model, Modified Page model, Logaritmic model, Two terms Exponential model, and Newton model. Meanwhile, the effective diffusion coefficient of moisture(D_(eff)) and activation energy(E_a) in Atractylodis Macrocephalae Rhizoma were calculated under different drying air temperatures. GC-MS was used to determine the volatile components and content changes of the fresh Atractylodis Macrocephalae Rhizoma and dried products at different temperatures. The dry basis moisture content and drying rate of Atractylodis Macrocephalae Rhizoma were closely related to the temperature of the drying medium, and the moisture of the Atractylodis Macrocephalae Rhizoma decreased with the prolonged drying time. As revealed by the drying rate curve, the drying rate increased with the increase in hot air temperature, and the migration of moisture was accelerated. The comparison of the correlation coefficient(R~2), chi-square(χ~2), and root mean standard error(RMSE) of each model indicated that the parameter average of the Midilli model had the highest degree of fit, with R~2=0.999 2, χ~2=8.78×10~(-5), and RMSE=8.20×10~(-3). Besides, the D_(eff) at 30-70 ℃ was in the range of 1.04×10~(-9)-6.28×10~(-9) m~2·s~(-1), and E_a was 37.47 kJ·mol~(-1). The volatile components of fresh Atractylodis Macrocephalae Rhizoma and dried products at different temperatures were determined by GC-MS, and 18, 18, 18, 17, 17, and 18 compounds were identified respectively, which accounted for more than 84.76% of the volatile components. In conclusion, the hot-air drying of Atractylodis Macrocephalae Rhizoma can be model-fitted and verified and the variation law of the moisture and volatile components of Atractylodis Macrocephalae Rhizoma with temperature is obtained. This study is expected to provide new ideas for exploring the drying characteristics and quality of aromatic Chinese medicine.

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

Drying Of Fire Hose With Alternative Methods And Selection Of Optimal Dryer

The aim here is to delay the wearing of hoses and in order to store them and use them in the most efficient way that laying-rallying hoses are dried by decreasing their weight. With this study the objective is decreasing inefficient working hours while saving energy and time. Considering real world conditions, drying hoses are subjected to water absorption for 30, 60 and 90 minutes. Trials are executed in a microwave dryer at 120 W, 350 W and 460 W settings and in a conveyor dryer at temperatures 50 °C, 60 °C and 70 °C. Moisture analysis, strength analysis, drying rate, energy consumption, diffusion coefficient and activation energy calculations were made according to the results obtained. It has been observed that minimum consumption of energy and fastest drying occurred with the power level of 460 W in the microwave dryer. When all of the results are evaluated according to trials, it has been noted that since the mechanisms behind the two dryer systems are not similar and drying times and consumption of energies are different, the microwave dryer is more efficient than the conveyor dryer type.

Drying kinetics and effective moisture diffusivity of pomelo albedo under vacuum‐assisted microwave drying and its semi‐product

AbstractThe five different microwave power levels (800, 640, 480, 320, and 160 W) assisted with the vacuum of 40 kPa were investigated for the drying kinetics, effective moisture diffusivity and rehydration ratio of the dried pomelo albedo. The comparison of some product quality indicators after production and 6 months of storage was also taken place in this study. The higher microwave power levels provided the shorter drying times, the higher moisture diffusion and the drying rates. Drying time at 160 W needed more than 120 min while the rest needed less than 25 min to reach the moisture content below 8% (dry basis). By basing on χ2 and root mean square error and R2, experimental drying data were best performed for the Page equations compared to other eight models (Diffusion approach, Two term exp, Henderson and Pabis, Lewis, Logarithmic, Vermar, Two modified compartment, Wang and Singh). The effective moisture diffusivity coefficient determined by Fick's second law was varied from 1.0 × 10−5 to 6.52 × 10−7 m2/s. The developed models describing the relationship between different drying parameters in this study can be used for optimizing the parameters in the drying process at a larger scale. The microwave power level of 480 or 640 W and the sample weight of 50 g were recommended for the drying of the pomelo albedo. Under these conditions, the dried albedo product possesses high quality. Most of the characteristic quality indicators changed insignificantly as compared after production and stored for 6 months at room temperature (25–28°C).Practical ApplicationsThe albedo layer consists of cellulose, hemicellulose and pectin which can be used as an ingredient in many foods. Microwave vacuum drying in food processing offers several advantages rather than microwave drying and other traditional drying methods. The combination results in a rapid drying rate, which is one of the desired characteristics for rehydrated products. This combined dying technology becomes well‐known nowadays, which can promise in use at the commercial level in product quality.

A Modeling Study for Moisture Diffusivities and Moisture Transfer Coefficients in Drying of “<i>Violet de Galmi</i>” Onion Drying

In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dried in a single layer at different temperatures (40℃, 50℃, 60℃, and 70℃) and for a relative humidity of drying air of 20%. The results showed a reasonably good agreement between the values predicted by the correlation and the experimental observations. This model computed the Biot number, effective moisture diffusivity, and mass transfer coefficient. Effective diffusion coefficient values are obtained between 0.2578 × 10-9 m2·s-1 and 0.5460 × 10-9 m2·s-1. Mass transfer coefficients of “Violet de Galmi” onion drying vary between 3.37 × 10-7 m·s-1 and 13.38 × 10-7 m·s-1. Numbers of mass transfer Biot are found between 0.9797 and 2.9397. The activation energy Ea is 31.73 kJ·mol-1.

Modelling the influence of hot air on the drying kinetics of turmeric slices

The influence of different drying temperatures and slice thicknesses on the drying kinetics of turmeric slices was studied to show how moisture is removed. The best model for predicting the drying kinetics was also determined. Turmeric slices (3 mm, 5 mm, and 7 mm) were dried at 40, 50, and 60 °C in a laboratory oven dryer. Four thin layer drying models (Newton, Henderson and Pabis, Logarithmic, and Page) were fitted to the experimental data and the selection was done based on the model with the highest correlation coefficient (R2), and lowest reduced chi-square (χ2), the sum of square error (SSE), and root mean square error (RMSE). Drying time varied between 420 min and 1140 min as the air temperature increased from 40 °C to 60 °C. The effective moisture diffusivity coefficient increased with increasing drying temperature and was found to be between 1.35×10-10 m2/s, and 5.00×10-10 m2/s, 3.00×10-10 m2/s and 10.91×10-10 m2/s, and 4.56×10-10 m2/s and 13.00×10-10 m2/s at 40 °C, 50 °C, and 60 °C, respectively. The values obtained for the activation energy for moisture diffusion were found to be 56.809, 56.060, and 45.561 kJ/mol for 3, 5, and 7 mm, respectively. The page model was found to best describe the oven drying of turmeric slices.

Evaluation of a Moisture Diffusion Model for Analyzing the Convective Drying Kinetics of Lavandula x allardii Leaves

In the present case study, a moisture diffusion model is developed to simulate the drying kinetics of Lavandula x allardii leaves for non-stationary convective drying regimes. Increasing temperature profiles are applied over the drying duration and the influence of temperature advancing rates on the moisture removal and the drying rate is investigated. The model assumes a one-dimensional moisture transfer under transient conditions, which occurs from the leaf center to the surface by liquid diffusion due to the concentration gradient developed by the surface water evaporation caused by the difference of water vapor partial pressure between the drying medium and the leaf surface. A numerical solution of Fick’s 2nd law is obtained by an in-house code using the finite volume method, including shrinkage and a variable temperature-dependent effective moisture diffusion coefficient. The numerical results have been validated against experimental data for selected cases using statistical indices and the predicted dehydration curves presented a good agreement for the higher temperature advancing rates. The examined modeling approach was found stable and can output, in a computationally efficient way, the temporal changes of moisture and drying rate. Thus, the present model could be used for engineering applications involving the design, optimization and development of drying equipment and drying schedules for the examined type of non-stationary drying patterns.

Energy parameters of corn drying in a hot air dryer powered by exhaust gas waste heat: An optimization case study of the food-energy nexus

This paper presents the energy parameters of corn drying in a convective crop dryer powered by exhaust gas waste heat. The empirical study was applied for drying 1,500 g batch size of an indigenous variety of maize grains (corn kernels). The study considered the impact of the drying air temperature and velocity on the energy indices (total and specific energy consumption, electric and thermal energy demand), drying rate, of the crop dryer, and the moisture diffusion coefficient of the studied samples. Tests were run at varying drying air temperatures (50, 55, and 60 °C) and air velocities (1.0, 1.5, and 2.0 m/s). Results obtained show that the drying parameters had a noticeable influence on the rates of heat transfer and moisture diffusion in the maize samples. The average drying rates varied between 0.83 and 1.4 g/min, whereas drying duration ranged from 305 to 515 min. The thermal efficiency of the drying process ranged from 4.23% to 8.07%. Its values had a direct relationship with the drying air temperature and an inverse relationship with the drying air velocity. The specific energy consumption, which varied between 129.95 and 227.63 kWh/kg increased with increasing air temperature and velocity. Drying air temperature had an inverse effect on the values of the electric energy consumption of the dryer system at constant air velocity. The maximum and minimum thermal energy values were obtained as 97.12 and 55.4 kW-hr, respectively. The activation energy and moisture diffusion coefficient values were in the range of 31.75 to 41.05 kJ/mol and 5.77×10−11 to 1.11×10−10 m2/s, respectively for the studied drying conditions. Prospects for commercial applications as well as recommendations for additional studies were stated.

Evaluation of hydrothermal treatment on physicochemical properties and re-adsorption behaviors of lignite

Lignite is a kind of low-rank coal with abundant reserves and low price in China, but the high moisture content and low calorific value greatly restrict the large-scale utilization of it. Hydrothermal dewatering (HTD) is a promising drying method for dewatering and upgrading lignite. Meanwhile, re-adsorption is an important index to evaluate feasibility of a drying project. In this study, the effects of drying properties of an Inner Mongolia lignite under HTD and moisture re-adsorption of the upgrading lignite after HTD were investigated. The results indicate that HTD upgrading treatment has a significant effect on lignite composition, oxygen-containing functional groups, and pore structure. The effective diffusion coefficient of moisture and activation energy processed with equilibrium moisture decrease with the increasing of temperature. The drying process of equilibrium water can be described by thin-layer dynamics model and the Arrhenius formula. There existed fairly good linearity between the oxygen content, pore structure and moisture re-adsorption rate. The re-adsorption rate of the upgraded lignite was affected by oxygen-containing functional groups with a descending order of Ph-OH, COOH, CO and Ar-OH.

Black soldier fly (Hermetia illucens, L.) larvae for food and feed: modelling drying kinetics

Insects are a new alternative for food and feed and a solution for circular economy. Among the most promising insects, black soldier fly, mainly in the larvae phase, is a solution specially for feed, and in particular in its dried form. The aim of this work was to study the water loss transfer during convective drying of black soldier fly larvae (BSFL). The mass transfer model consisted of mass diffusion with two alternative boundary conditions (no external resistance and convection) and with/without shrinkage, applied with finite elements method, with a triangular mesh of 3,036 elements and a geometry reproducing the shape of the larvae. The moisture diffusion coefficient, estimated from the experimental data assuming an infinite slab, increased from 0.7002×10-10 m2/s at 60 °C to 2.792×10-10 m2/s at 90 °C, with an activation energy of 43.97 kJ/mol. The simulation predicted with detail the water content profile showing a quick water loss on the outer layers of the BSFL at the initial times. The evolution of the overall water content of BSFL during drying was better predicted for long times (when more than 80% of the moisture was removed) and at the highest temperature of 90 °C and showed that diffusion was the dominating mechanism, with small influence of the boundary conditions studied. Although shrinkage between 21 and 29% was considered, depending on the temperature, the inclusion of volume change in the model did not significantly improved the water content prediction.

Assessing the suitability of alkali-activated metakaolin geopolymer for thermochemical heat storage

This study investigates the suitability and potentials of using alkali-activated metakaolin geopolymers as sustainable low-cost thermochemical heat storage materials via water sorption and/or hydration reactions. Four different alkali-activated metakaolin geopolymer formulations were assessed. The cyclic water sorption capacity and moisture diffusion coefficients were assessed via two continuous water vapor sorption/desorption cycles using the dynamic water vapor sorption (DVS), proving the regeneration ability of geopolymers for sorption thermal energy storage. The thermochemical properties of geopolymers, including the dehydration enthalpy and activation energy, were determined. For the amorphous sodium aluminosilicate hydrate gel (N-A-S-H) with bulk Si/Al ratio of 1.5, the mass and volumetric energy storage capacity of 827.9 J/ghydrate sample and 350 kW h/m3 were achieved, with a charging temperature of around 120 °C. The outcomes of this study suggest that alkali-activated metakaolin geopolymers have the potential to be used for both low-temperature water sorption thermal energy storage and medium temperature hydration/dehydration thermochemical energy storage. The energy storage performances of metakaolin geopolymers are closely related to their aluminosilicate framework structures and surface textural properties. The partial crystallisation of the amorphous N(K)-A-S-H gel, resulting in the formation of micropores, which does not seem to affect the maximal water uptake but increases the proportion of the chemically bound water. The presence of the amorphous mesoporous aluminosilicate gel N(K)-A-S-H gel in geopolymers leads to desorption hysteresis at relative humidity higher than 30 %. Further optimisation of the synthesis approach, aluminosilicate framework structures, micro and mesopore structures will be required to optimise their overall thermal energy storage performances.

INFRARED DEHYDRATION OF BLANCHED QUINCE SLICES: STUDY ON PROCESS AND MASS TRANSFER CHARACTERISTICS

In the present work, moisture removal characteristics of quince slices in a convective tray dryer were studied. The blanched slices (with thicknesses of 3, 5 and 7 mm) were dried at drying temperatures of 50, 60 and 70 °C and air flow rates of 1, 1.5 and 2 m/s. The analytical model proposed by Dincer and Dost was used to determine the mass transfer parameters. The obtained Biot numbers (0.108‒0.293) revealed that both the internal and external resistance control the moisture diffusion within the samples. The moisture diffusivity and convective mass transfer coefficient were found to be in the ranges of 1.578×10-7‒7.331×10-7 m2/s and 2.040×10-5‒3.507×10-5 m/s, respectively. The activation energies for moisture diffusion and surface mass evaporation were determined to be in the ranges of 17.607 to 48.019 kJ/mol and 5.270 to 27.430 kJ/mol, respectively.

Analysis of the diffusion characteristics and activation energy of rice drying using low‐field nuclear magnetic resonance

AbstractThis research was conducted to determine the effective moisture diffusion coefficient and activation energy of rice using low‐field nuclear magnetic resonance (LF‐NMR). The results showed that the evaporable water was rapidly removed under high‐temperature drying in the early stages of drying. The diffusion rate of evaporable water at different temperatures in the later stages of drying was not significant. Besides, the activation energy in rice was divided into the activation energy of the conversion of the chemically bound water (15.04–25.69 kJ/mol) to evaporable water and the activation energy of the diffusion of evaporable water from rice (6.42–16.42 kJ/mol), indicating that more energy was needed to dry the chemically bound water from rice. A new method for obtaining the effective moisture diffusion coefficient and the activation energy was proposed based on the relaxation time distribution profiles, revealing the internal relationship between various phase moisture and activation energy. These results will provide a theoretical guidance for the drying process.Practical applicationsThe moisture diffusion characteristics and activation energy of rice were determined using low‐field NMR signal quantities, which were important parameters for optimizing the drying process. In addition, the variable temperature drying method was conducive to the rapid diffusion of moisture in the rice. The chemically bound water within rice required more energy to diffuse than other forms of water components. An internal relationship between moisture content and the activation energy was established to provide a theoretical reference for high‐quality drying techniques.

Improved boundary conditions for models of coupled heat and water vapor transfer between an adsorbent and the ambient

Boundary conditions for coupled heat and water vapor transfer in hygroscopic solids must account for the change in relative humidity by the sorption-induced temperature deviation between the adsorbent and the ambient. Moisture change rates are significantly depressed in adsorbents having a sorption isotherm with a steep slope at an intermediate or high relative humidity. Under such conditions, a poor thermal design of the sorption setup will deteriorate the dynamic response rate. The effect is considered being a general mechanism causing a systematic difference between the steady-state and “effective” transient moisture diffusion coefficients, as shown in an idealized physical model where the developed boundary conditions are applied to a Fickian permeable solid. The signature of this latent heat exchange effect in moisture dynamics is experimentally shown in a series of adsorbents with different sorption isotherms.

Moisture diffusivity, hardness, gelatinization temperature, and thermodynamic properties of ultrasound assisted soaking process of cowpea

AbstractThis study describes the combined effect of ultrasound and temperature on water absorption of cowpea kernel during soaking process. The process was made at 30, 40, 50, 60, 70, 80, and 90°C in water absorption conditions named control (without ultrasound) and ultrasound treatment (40 kHz, 200 W; 50% and 100% amplitude). Fick's second diffusion model for water absorption and asymptotic first order texture model for hardness together with Arrhenius and Eyring–Polanyi approaches were successfully used to evaluate effective moisture diffusivity coefficient (Deff), texture degradation coefficient (kF), gelatinization temperature, and thermodynamic properties of cowpea during soaking process. The models fitted the experimental data satisfactorily with R2 > 0.99, RMSE < 0.09 and X2 < 0.0137. Ultrasound treatment (50% and 100% amplitudes) and temperature increased significantly (p ≤ .05) the Deff and kF of cowpeas during soaking process. Average gelatinization temperature of cowpea from the Fick's and Asymptotic first order texture models together with Arrhenius equations was found as 68.5°C. Negative values of enthalpy, entropy, and increase of Gibbs free energy changes with increasing temperature and ultrasound treatment confirming the effect of temperature and ultrasound on effective moisture diffusivity of cowpea during soaking. Moisture content, harness, Deff, kF and thermodynamic properties of cowpea during soaking process were affected by both the temperature and ultrasound amplitude, which means shortening the soaking and cooking time of cowpea.Practical applicationsThe results of this study could be assisted to industrial producers of cowpea in understanding of heat and mass transfer phenomena during ultrasound‐assisted hydration process of cowpea kernel in soaking, cooking, wet milling, fermentation, formulation of meals, and storage processes.

Determination of the water absorption and water diffusion coefficients by means of infrared thermography measurements

An innovative, relatively simple method of simultaneous determination of two key material parameters describing the sorption properties of capillary-porous materials: the water absorption coefficient and the moisture diffusion coefficient is proposed. The tests were carried out on a gypsum sample, and a thermal imaging (IR) camera was used to record the surface temperature of the sample and thus reconstruct the moisture front. The developed measurement procedure allowed eliminating the influence of temperature drift caused by sample cooling due to evaporation. The main advantage of the proposed method is the ease of its implementation, which results from the growing availability of IR cameras, as well as the many times lower cost of measuring equipment, especially compared to the currently used electromagnetic methods (such as NMR, X-ray) or isotope methods (like γ-ray attenuation). The obtained results were compared with the reference one, confirming the high effectiveness of the proposed method.

Moisture absorption measurement and modelling of a cellulose acetate

With a view toward the application of highly hygroscopic polymers as a humidity responsive self-actuator, the evaluation of the real time moisture concentration in the material becomes a priority. In this paper, the moisture diffusion process in a cellulose acetate (53.3% of acetylation) has been studied. Membranes of cellulose acetate (thickness within the range 66–200 µm) have been prepared, and the moisture absorption at room temperature and at a different relative humidity (RH within the range 21–53%) has been monitored. An analytical model has been used to describe the observed non-Fickian sigmoidal behavior of moisture diffusion. A relaxation factor (β) of about 0.026 s−1 and a moisture diffusion coefficient (D) of 3.35 × 10–6 mm2/s have been determined. At constant room temperature, the moisture concentration at saturation (Csat) has shown a linear relation with relative humidity. The identified values β, D and Csat of the analytical model have been used as input for the finite element simulation of the non-Fickian diffusion. The reliability of the finite element simulations has been confirmed with a second set of experiments.