Water Absorption Kinetics Research Articles

Water absorption and enzymatic degradation of poly(lactic acid)/rice starch composites

Poly(lactic acid) (PLA) composites consisting of PLA, rice starch (RS) (0–50 wt%) and epoxidised natural rubber (ENR50) were compounded by a twin-screw extruder and compression moulded into dumbbell specimens. Tensile tests were performed to characterize the mechanical properties of the PLA/RS composites. Morphological studies were done on the tensile fractured surface of the specimens by using scanning electron microscopy (SEM). Twenty weight percent of RS achieved a good balance of strength and stiffness. Beyond 20 wt% loading of RS, the tensile strength and elongation at break of PLA decreased drastically. This may be attributed to the agglomeration of RS, which could then act as stress concentrator. The incorporation of ENR50 increased the tensile strength and elongation at break of the PLA/RS composites remarkably, owing to the elastomeric behaviour and compatibilisation effects of ENR50. Interestingly, the morphology of PLA/RS composites transformed to a more ductile one with the addition of ENR. The kinetics of water absorption of the PLA/RS composites conforms to Fick's law. The M m and D values are dependent on the RS and ENR concentrations. The tensile properties of the PLA/RS composites deteriorated after water absorption. The retention-ability and recoverability of the PLA/RS composites are relatively low, attributed to the hydrolysis of PLA, degradation of the PLA–RS interface and leaching of the RS particles. In addition, the tensile properties of PLA/RS composites decreased drastically upon exposure to enzymatic degradation. Extensive pinhole and surface erosion on the PLA/RS composites indicate high degree of hydrolysis. Whilst the addition of ENR leads to some improvements in tensile properties, nevertheless, it enhanced the biodegradability of the PLA/RS composites when exposed to water and α-amylase enzymatic treatments.

Accelerated Aging of Hybrid Ramie-Cotton Resin Matrix Composites in Boiling Water

The effect of accelerated aging by immersion in boiling water on the tensile behavior of a hybrid ramie-cotton fabric polyester composite was evaluated. Under these conditions, fast water absorption by the lignocellulosic fibers took place, causing a sharp reduction in the tensile strength of the composite during the first 5 h of immersion. A decrease in Young's modulus and an increase in the deformation at break were observed at longer immersion times. It was shown that resin embrittlement occurred under the aging conditions used in this work, which was attributed to the leaching out of low molecular weight substances. Therefore, the plasticizing effect observed with the composites was attributed to the presence of the lignocellulosic fibers. The water absorption kinetics were satisfactorily modeled using the Fickian model.

Cinética de la ascensión del agua por capilaridad en la “Arenisca de La Marina” (Jurásico superior de Asturias)

The water movement by capillarity inside La Marina Sandstone (yellow variety) of the Jurassic of Asturias, used as dimension stone, is studied. The rock texture has been characterized under different techniques: elastic wave velocity, Hg porosimetry and X-ray computed tomography. Using the obtained results the modelling and interpretation of the water absorption kinetics due to capillarity have been done. The X-ray tomograhy allows to image the absorption process and to calculate the size of the radius of capillary access. All the results and observations confirm the anisotropic behaviour of the capillarity due to the presence of Liesegang rings perpendicular to the bedding surfaces.

Influence of the morphogranulometry and hydrophobicity of talc on its antisticking power in the production of tablets

Antisticking power varies according to the talc considered. It is difficult to define the physical properties of talc implicated in its antisticking power. In this work, different talcs were characterized and an evaluation made of their performance in reducing sticking in tablet manufacturing. Determination of the specific surface area was made by permeametry, morphogranulometric analysis by laser diffractometry using a method, which made it possible to assess the mean thickness of talc particles, and measurement of water absorption kinetics was taken to assess hydrophobicity. The relationship between the characteristics of talcs and their antisticking power was then considered. There is a correlation between the particle size of talc and surface hydrophobicity. The detaching force of tablets appears to be dependent on the basal dimension of talc.

Effects of hydrothermal ageing on the thermal behaviour of poly(vinyl chloride) filled with wood flour

AbstractThe hydrothermal ageing of wood‐flour‐filled PVC produced by dry‐blending in a high‐speed mixer in the presence of a plasticizer and other processing additives was carried out to investigate its thermal behaviour, and the results obtained were compared with those for the unfilled material. The dry‐blended compounds were prepared as films by a calendering process. The accelerated hydrothermal ageing was carried out by immersing the samples in boiling water at 100 °C for 110 h. The thermal behaviour of the reference and the aged samples in water was characterized by differential scanning calorimetry (DSC) and determination of the weight changes. The study has shown that during hydrothermal ageing, the samples from the whole formulations absorbed water, for instance, for 30 wt% filled PVC (F30), 16 wt% of water absorption was obtained, while this was only 2.2 wt% for unfilled PVC (F0). It was also noticed that the formulations filled with wood flour up to 10 wt% exhibited similar water absorption kinetics, i.e. the water was mostly absorbed during the first 50 h and the amount absorbed was less than 5 wt%. On the other hand, the 30 wt% filled samples regularly absorbed water up to almost 16 wt% after 100 h of immersion. The DSC data showed that hydrothermal ageing significantly affected the onset temperature of decomposition (Td) of the unfilled samples by decreasing this temperature from 228 to 215 °C. For the 30 wt% filled samples, only additive migration was observed, while the Td remained almost unchanged. Furthermore, from the DSC data, processability of the 30 wt% filled PVC samples at elevated temperatures, i.e. 180 to 200 °C was shown. Copyright © 2004 Society of Chemical Industry

Absorption of Water by Thin, Ionic Films of Gelatin

This paper discusses absorption of water by thin, dry films of gelatin. Experiments using a wet-stamping technique were performed to characterize water uptake in terms of (i) equilibrium profiles of the water density inside the gel and (ii) the kinetics of water absorption. It was found that, in contrast to pure gelatin films, which absorb water approximately uniformly, films of gelatin doped with ionic additives have exponentially decaying equilibrium water profiles. The process of water absorption by both doped and undoped gels was described by a theoretical model based on the minimization of grand potential functional. The results of this model are in agreement with the experiment.

Kinetics of water absorption and hygrothermal aging rubber toughened poly(butylene terephthalate) with and without short glass fiber reinforcement

The objectives of this paper were to investigate the water absorption and hygrothermal aging behavior of rubber-toughened poly(butylenes terephthalate) (RT-PBT) with and without short glass fiber (SGF) reinforcement. The rubbers used in the study were AX8900 and EXL2314, both of which are acrylate-based terpolymer. The effect of the hygrothermal aging on its fracture properties was also studied. The kinetics of the water absorption study were carried out on the injection-molded samples of the RT-PBTs and the SGF-reinforced rubber-toughened PBT (SGF-RT-PBT) at three immersion temperatures, 30, 60 and 90°C, for a total of 450 h. The study of the deterioration caused by the hygrothermal aging was conducted by investigating the fracture parameters and flexural properties of all the materials as both hygrothermally aged (HA) and redried state (RD). The modes of the failure of HA and RD samples were studied using the scanning electron microscopy (SEM) technique. It was found that all the samples conformed to Fickian behavior and the kinetics of absorption exhibited a strong dependency on the rubber types, presence of SGF, as well as the immersion temperature. Generally, SGF-RT-PBT showed a better resistance to hygrothermal aging than that of RT-PBT and PBT, though a declining trend was observed in the fracture parameters, Kc and Gc. However, an opposite observation was exhibited in the flexural properties in some, but not all cases. Finally, the results obtained from SEM micrographs showed that permanent damage occurred in the materials and the hygrothermal aging had suppressed the plastic deformation ability of the PBT matrix and both types of impact modifiers where brittle failure was observed. Fiber pull-out was apparently the failure mode of the SGF-reinforced materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 506–516, 2004

Study of some factors affecting water absorption by amaranth grain during soaking

Water absorption by amaranth grain in plain water was determined at 30, 40, 50 and 60 °C by recording the weight increase in grain with respect to time. Water absorption kinetics at these temperatures was described by the Fick’s second law solution for diffusion out of sphere. Effective diffusion coefficients varied between 2.63 and 8.25 × 10 −12 m 2/s for the range investigated. The activation energy for diffusion obtained was 32.1 kJ mol −1. The rates of absorption in SO 2 aqueous solution (0.01%, 0.02% and 0.03%, v/v) were slightly higher than in plain water at 40 and 60 °C. However, the increase in SO 2 concentration did not seem to increase significantly water absorption. Amaranth grain soaked in 0.02% (v/v) SO 2 aqueous solution and variable lactic acid concentrations (0.0025% and 0.0050%, v/v) was performed at 40 °C. Absorption rates for lactic acid concentrations were ≈9.1% higher than those steeped only in SO 2 aqueous solution; lactic acid concentration had no effect on the absorption rate. The amount of total solids leached in sulfur dioxide solution with lactic acid (200 ppm SO 2 + 0.005% lactic acid) was the highest when compared with the other steeping media investigated.

Effect of processing on hydration kinetics of three wheat products of the same variety

The kinetics of water absorption of firik, dövme and wheat was studied at 20°C, 30°C, 50°C and 70°C using Peleg's equation. The equation was capable of predicting water uptake of the three cereals. The Peleg's constants K 1 and K 2 were affected by temperature. The temperature dependence of 1/ K 1 followed an Arrhenius-type relationship. The activation energy was in the range of 9696–24 288 kJ/kg mol.

New Colloid Silicate Solutions for Restoration and Conservation of Stone Facades

The kinetics of water absorption by samples taken from facades of buildings (marbled footinglimestone, bricks, plaster), both in initial state, those treated with solutions of classical water repellentsand new hydrophilic and hydrophobic colloid silicates, was studied, and the state of the initial materialwas assessed. Recommendations on how to stabilize stone and protect it from the destructive influence of the humid atmosphere are given.

Water sorption and diffusion studies in an epoxy resin system

The kinetics of water absorption in epoxide materials was studied by the aid of a diglycidyl ether of bisphenol-A–triethylenetetramine (DGEBA–TETA) epoxy–resin system containing various amounts of the plasticizer THIOCOL (0–40 phr). The presence of plasticizer permits the formation of products with different crosslinking densities and hydrophilic characters. Dynamic water absorption experiments were carried out at 15, 40, and 70°C. For the fitting of the experimental results, a new model was used, based on a model proposed earlier by Jacobs and Jones. This model considers epoxide product as a two-phase system consisting of a master phase (where the major part of the water is absorbed), which is homogeneous and nonpolar (phase 1), and of a second phase with different density and/or hydrophilic character (phase 2). By making the assumption that water diffusion can take place independently in the different phases of the material in accordance with Fick's second law, we can calculate the diffusion coefficient D and the water content at saturation M∞ for each phase separately. Equilibrium water sorption measurements were performed at 40°C, and the data were analyzed and discussed based on the Guggenheim–Anderson–de Boer (GAB) equation, the results being in support of the two-phase model used in the analysis of absorption kinetics. The linear expansion coefficient and the glass transition temperature of the materials, employed in the discussion of the results, were measured by thermomechanical analysis. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1165–1182, 1999

Polymerization of vinyl acetate in homogeneous systems obtained in presence of acrylic acid

The composition ranges over which microemulsions are formed in systems containing vinyl acetate, acrylic acid, water with nonylphenol ethoxylated with 25 mol ethylene oxide monomaleate as surfactant were studied. Conductometric and refractometric investigations have shown the existence of some aqueous/organic, bicontinuous and organic/aqueous microemulsions. The types of precursor microemulsions influence the conversion of monomers. In the presence of a crosslinking agent, diethylene glycol bis maleate, hydrogels are formed whose water absorption depends on the composition of the initial microemulsions. The kinetics of water absorption suggests the modification of polymer network structures as a function of the crosslinked monomer content and the ratio of organic to aqueous phases.

Influence of water absorption on poly–ethylene oxide-based polymer electrolytes complexed with ammonium, sodium and magnesium perchlorates

The influence of water absorption on polyethylene oxide and its complexes with NH4ClO4, NaClO4 and Mg(ClO4)2 (for O/M=10 and 3) has been studied. A quantitative estimation of water absorption kinetics has been carried out. The changes in microstructure and thermal behaviour due to water absorption have been studied using X-ray diffraction and thermogravimetric/differential thermal analyses. The electrical conductivity of different films has been measured as a function of relative humidity and explained in terms of the generation of free mobile ions due to water absorption. © 1998 Chapman & Hall

Thermal and diffusion processes in laser-induced stress relaxation and reshaping of cartilage

The thermodynamic characteristics of the ‘bound-to-free’ phase transformation of water are studied by means of differential microcalorimetry and FTIR spectroscopy. This phase transition controls the stress relaxation and reshaping of cartilage which we have observed previously under moderate laser heating. It is shown that the FTIR spectrum of bound water in cartilage differs from that of free water in cartilage, and that both show differences to the FTIR spectrum of pure water. The proportion of bound water in cartilage is found to be of the order 4%. We have examined water liberation and absorption kinetics and found them to be controlled by diffusion through the tissue and also by the bound-to-free water transformation. The theoretical modelling and experimental data allowed calculation of diffusion coefficients and the activation energy for water transfer. The latter was found to be close to the heat of phase transformation of water. We have established that the drying and wetting processes in cartilage are reversible (fully or in a part, depending on the temperature of preliminary drying) and can be described by identical solutions of the diffusion problem, with coefficients of water diffusion being the same. The mechanism of water diffusion in cartilaginous tissue is also discussed.

Water and nitrate absorption kinetics in the nychthemeral cycle of rose grown in the greenhouse using a recirculating solution

Abstract An experimental hydroponic system (nutrient film technique N.F.T. system) was used to measure the water and nitrate uptake rates of rose (Rosa hybrida) on a short term basis: hourly fluctuations over a nychthemera. Nitrate and water uptake are subject to large diurnal variations as is well known for most species. Water absorption closely follows the climatic demand with a large peak occurring during the day, whereas nitrate absorption seems to peak slightly before. Relating absorption to agroclimatic factors, we are able to formulate a model in order to evaluate the nitrate needs of the plant. This approach is a first step in the development of real time algorithms for fertigation computers.

-cyclodextrin hydration: a calorimetric and gravimetric study

The standard heat of solvation of β-cyclodextrin (βCD) with one mole of water is determined as −10.50 kJ per mol βCD, after measurement of the heat of dissolution of βCD samples containing various amounts of water. This value is constant in the composition range βCD · n H 2 O, with 0 < n < 11 ( n is the number of water molecules attached). The thermogravimetric study of the kinetics of water absorption by βCD does not show a definite hydrate. The water content of the hydrate is controlled by the vapour pressure and temperature alone. Under ambient conditions, the number of water molecules bound to one βCD molecule lies between 10 and 12.

β-Cyclodextrin hydration: a calorimetric and gravimetric study

The standard heat of solvation of β-cyclodextrin (βCD) with one mole of water is determined as −10.50 kJ per mol βCD, after measurement of the heat of dissolution of βCD samples containing various amounts of water. This value is constant in the composition range βCD · nH 2O, with 0 < n < 11 ( n is the number of water molecules attached). The thermogravimetric study of the kinetics of water absorption by βCD does not show a definite hydrate. The water content of the hydrate is controlled by the vapour pressure and temperature alone. Under ambient conditions, the number of water molecules bound to one βCD molecule lies between 10 and 12.

Water Absorption of the Polymer Electrolyte Systems Pb ( CF 3 SO 3 ) 2 PEO n and Zn ( CF 3 SO 3 ) 2 PEO n

The water absorption behavior has been studied for poly(ethylene oxide) films (PEO) and for films of with and in the range of 9 to 24. Quantitative measurements of the kinetics of water absorption have been made. Proton nuclear magnetic resonance (NMR) spectroscopy has been used to characterize the effects of water absorption on the polymer properties, such as degree of crystallinity and polymer chain mobility. Impedance spectroscopy measurements have also been performed on humid samples. Water absorption is found to increase the mobility of the polymer chain as well as the ionic conductivity of the electrolyte, and a possible mechanism for these effects is proposed. Water absorption also causes a decrease of the amount of crystalline phase present in the sample. In addition, deuteron NMR has been used to study the mobility of the absorbed water, demonstrating the absence of liquid water surface layers on the polymer, and that the conductivity increase observed upon hydration is a property of the hydrated polymer electrolyte itself.

Development of a Novel Drug Release System, Time-Controlled Explosion System(TES). III. Relation between Lag Time and Membrane Thickness.

To describe lag time of Time-Controlled Explosion System (TES), the system's water absorption kinetics was investigated. Study of water absorption in TES with EC membrane revealed the following relations : (i) the square of water-uptake linearly increased with time in accordance with the Washburn equation, (ii) the water permeation rate correlated with the reciprocal of membrane thickness, (iii) the amount of water-uptake necessary for membrane destruction was directly proportional to the thickness of the membrane. These results suggest that lag time of TES is regulated by the function of membrane thickness. Indeed, the observed lag time was confirmed to fit with the curve expected by the above relations. When talc was included in the EC membrane in an equal weight ratio as a membrane-filler, lag time related directly to the membrane thickness. Compared with TES consisting of EC membrane only, the membrane was destroyed by a smaller amount of uptaken water owing to the weakening of membrane strength by the talc addition.

Water transport in graphite/epoxy composites

AbstractThe diffusive and mechanical behavior of tetraglycidyl diaminodiphenyl methane (TGDDM) resin‐based composites and diglycidyl ether of bisphenol‐A (DGEBA) resin‐based graphite/epoxy composites were investigated during water sorption at different temperatures. The water‐absorption kinetics in both systems at 50, 70, 90, and 100°C were fitted by a Fickian diffusion model. However, a Langmuir‐type, two‐step sorption behavior was observed for water transport in DGEBA‐based systems at 50 and 70°C. Using scanning electron microscopy, internal cracks due to water absorption were found in the DGEBA‐based samples after conditioning at 90 and 100°C in water, whereas no cracks were detected in TGDDM‐based samples conditioned in water at 100°C. Ultrasonic testing did not show significant modulus or density change of the TGDDM‐based samples conditioned in water at 100°C. No significant changes of dynamic modulus or damping factor were observed for the TGDDM‐based samples redried after immersion in 100°C water, whereas slight changes were observed above 120°C for the samples containing absorbed water. However, both water‐containing and redried DGEBA‐based samples showed a decrease of dynamic modulus and an ω‐transition around 120°C. A single‐fiber fragment test revealed that the absorbed water at 80°C reduced significantly the interfacial shear strength of DGEBA/DDA resin‐AS4 fiber samples and DGEBA/DDA resin‐AU4 fiber samples. © 1993 John Wiley &amp; Sons, Inc.