Influence Of Water Sorption Research Articles

The influence of water sorption on the microstructure of a hydro-sensitive granular material (couscous) deduced from simultaneous neutron and X-ray tomography

The effects of water on the behaviour of granular materials can be significant. Besides capillary bridges, several other chemo-hydro-mechanical processes can affect the response of hydro-sensitive granular assemblies, when water sorption critically alters the individual particles properties (i.e., swelling, deterioration of mechanical properties). It is very common to find such materials in food and pharmaceutical industries, where water sorption can often lead to important resources waste while processing or storing the product. It is therefore necessary to understand the phenomena that affect the material’s functionality, often related to particle agglomeration and degradation. However, despite the relevance of the problem, our knowledge about these phenomena is still relatively poor. With this study we aim to explore the link between water content increase and particle, contacts and assembly scale phenomena. Simultaneous neutron and X-ray tomography allows us to investigate respectively the water uptake and microstructure evolution of two couscous assemblies exposed to high relative humidity while subjected to constant stress, a configuration chosen to simulate the conditions in an industrial silo-storage. We acquire a data-set of images, from which we follow and quantify the variations of water content distribution and the resulting volumetric response of thousands of particles through bespoke algorithms. Despite the abundance of water provided, we observe spatial gradients in water content distribution and consequently in particle swelling. We find that the relation between these two variables can be described as (quasi-)linear. The contact area growth also seems to follow a similar trend.Graphic abstract

VFT to Arrhenius crossover at the dynamic glass transition of an epoxy network as revealed by dielectric experiments in continuous immersion

The influence of water sorption on the α-relaxation of an epoxy network was studied by performing impedance measurements in continuous immersion (in aqueous solution) at various temperatures in the range [20; 80] °C. Relaxation times associated with the α-relaxation were found to shift towards lower temperatures as a result of plasticization, accompanied by a decrease in the relaxation strength. The most striking feature of the impedance measurements was a crossover from a Vogel-Fulcher-Tammann (VFT) to an Arrhenius dependence of the relaxation times upon cooling, in the vicinity of the glass transition of the epoxy network. Complementary experimental techniques (namely differential scanning calorimetry, dielectric spectroscopy, thermally stimulated currents) were used on dry and wet epoxy samples to better understand the physical origin of this crossover. Various scenarios were discussed; the most convincing involved confinement-like effects. The deviation from VFT behaviour below Tg was possibly due to long-living H-bonds between the epoxy network and water molecules, which limited the cooperativity of the α-relaxation. The water molecules H-bonding to the network localized the mobility of the main chain, as confirmed by thermally stimulated currents performed on a wet sample.

Effects of plasticizers on water sorption and aging stability of whey protein/carboxy methyl cellulose films

Influence of water sorption and phase transitions requires clarification to understand plasticizer mechanisms on the physico-chemical properties of biodegradable and edible films. The effects of plasticizers as glycerol, xylitol, sorbitol, polyethylene glycol 400 (PEG 400) and oleic acid were investigated on water sorption, phase transitions and properties in whey protein concentrate and carboxy methyl cellulose blend films (WPC-CMC). Stability after aging at different humidity (50% RH and 75% RH for 30 days) was determined. Sorption isotherms of glycerol-plasticized films showed the highest water affinity and binding sites led to the lowest glass transition temperature (Tg). Xylitol showed similar water sorption behavior to sorbitol but higher plasticization effect. An increased C-atom of glycerol, xylitol and sorbitol gave identical infrared spectra. Conversely, oleic acid modified protein secondary structures contributed to the lowest water sorption and highest Tg as indicated by amide I and amide II bands in the infrared spectra. Highly hydrophilic plasticizers as glycerol, xylitol and sorbitol showed less sensitivity to water-induced Tg reduction. Water sorption greatly improved plasticization effects in PEG 400 and oleic acid which contained non-polar components. Aging accelerated the Maillard reaction in WPC-CMC and led to physico-chemical changes and destabilized films. Light transmission decreased concurrently with increased brown pigments that improved the water barrier and stiffness. Higher humidity accelerated molecular mobility and facilitated physico-chemical changes of the polymer blends. Oleic acid showed the least stability during aging, while sorbitol greatly enhanced water barrier properties and stability of the blend films. Molecular structures of plasticizer greatly influenced water sorption, modified molecular orientation of biopolymers which subsequently impacted properties and stability of the films.

Evolution of surface micro-structure and moisture sorption characteristics of spray-dried detergent powders

The role of water is critical to the solid state behaviour of complex formulated products such as spray-dried detergent powders. Understanding changes in water sorption behaviour due to interactions within the solid allows the influence of water sorption on the surface micro-structure to be better elucidated. This work investigates the effect of relative humidity (RH) on the micro-structural evolution and moisture sorption behaviour of model detergent powders containing the sodium salt of linear alkylbenzene sulphonate (NaLAS) and sodium sulphate. Scanning electron microscopy showed significant changes to surface morphology when the powders were exposed to 75% RH. However, the addition of sodium silicate to the formulation made the powders more susceptible to humidity-induced morphological changes. Surface crystal growth was seen at 54% RH and dramatic changes in structure were seen at 75% RH due to the emergence of the hydrated phase of sodium sulphate, i.e. mirabilite, which was confirmed by the X-ray diffraction. These differences are thought to be due to the increased hygroscopicity and water mobility conferred by the silicate and observed via sorption isotherm measurements and FTIR analysis, which suggest a change in structure due to a moisture-induced glass transition. Considerable differences in moisture absorption were observed between samples produced from the slurries differing in water content, highlighting the importance of micro-structure on moisture sorption behaviour. The experimental sorption isotherms were fitted to three mathematical models: Brunauer-Emmett-Teller (BET), Guggenheim-Anderson-de Boer (GAB) and Oswin. In nil-silicate powders, all three models presented a good fit to the experimental data with R2 ∼ 99%. However, in silicate containing powders, the GAB and Oswin fits were unsuccessful; the influence of the phase transition on the isotherm not being captured by the models.

Dental Resin Cements-The Influence of Water Sorption on Contraction Stress Changes and Hydroscopic Expansion.

Resin matrix dental materials undergo contraction and expansion changes due to polymerization and water absorption. Both phenomena deform resin-dentin bonding and influence the stress state in restored tooth structure in two opposite directions. The study tested three composite resin cements (Cement-It, NX3, Variolink Esthetic DC), three adhesive resin cements (Estecem, Multilink Automix, Panavia 2.0), and seven self-adhesive resin cements (Breeze, Calibra Universal, MaxCem Elite Chroma, Panavia SA Cement Plus, RelyX U200, SmartCem 2, and SpeedCEM Plus). The stress generated at the restoration-tooth interface during water immersion was evaluated. The shrinkage stress was measured immediately after curing and after 0.5 h, 24 h, 72 h, 96 h, 168 h, 240 h, 336 h, 504 h, 672 h, and 1344 h by means of photoelastic study. Water sorption and solubility were also studied. All tested materials during polymerization generated shrinkage stress ranging from 4.8 MPa up to 15.1 MPa. The decrease in shrinkage strain (not less than 57%) was observed after water storage (56 days). Self-adhesive cements, i.e., MaxCem Elite Chroma, SpeedCem Plus, Panavia SA Plus, and Breeze exhibited high values of water expansion stress (from 0 up to almost 7 MPa). Among other tested materials only composite resin cement Cement It and adhesive resin cement Panavia 2.0 showed water expansion stress (1.6 and 4.8, respectively). The changes in stress value (decrease in contraction stress or built up of hydroscopic expansion) in time were material-dependent.

Effect of Water Sorption on the Electronic Conductivity of Porous Polymer Electrolyte Membrane Fuel Cell Catalyst Layers

A method is described for measuring the effective electronic conductivity of porous fuel cell catalyst layers (CLs) as a function of relative humidity (RH). Four formulations of CLs with different carbon black (CB) contents and ionomer equivalent weights (EWs) were tested. The van der Pauw method was used to measure the sheet resistance (RS), which increased with RH for all samples. The increase was attributed to ionomer swelling upon water uptake, which affects the connectivity of CB aggregates. Greater increases in RS were observed for samples with lower EW, which uptake more water on a mass basis per mass ionomer. Transient RS measurements were taken during absorption and desorption, and the resistance kinetics were fit using a double exponential decay model. No hysteresis was observed, and the absorption and desorption kinetics were virtually symmetric. Thickness measurements were attempted at different RHs, but no discernible changes were observed. This finding led to the conclusion that the conducting Pt/C volume fraction does not change with RH, which suggests that effective medium theory models that depend on volume fraction alone cannot explain the reduction in conductivity with RH. The merits of percolation-based models were discussed. Optical micrographs revealed an extensive network of "mud cracks" in some samples. The influence of water sorption on CL conductivity is primarily explained by ionomer swelling, and its effects on the quantity and quality of interaggregate contacts were discussed.

Influence of water sorption on mechanical properties of injection-molded thermoplastic denture base resins

Objective. This study investigated the influence of water sorption on certain mechanical properties of injection-molded thermoplastic denture base resins. Materials and methods. Six thermoplastic resins (two polyamides, two polyesters, one polycarbonate, one polymethylmethacrylate) and a polymethylmethacrylate (PMMA) conventional heat-polymerized denture-based polymer, selected as a control, were tested. Specimens of each denture base material were fabricated according to ISO 1567 specifications and were either dry or water-immersed for 30 days (n = 10). The ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of the denture base materials were calculated. Results. Water sorption significantly decreased the ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of one of the polyamides and the PMMAs. It also significantly increased the ultimate flexural strength of the polycarbonate. Conclusion. The mechanical properties of some injection-molded thermoplastic denture base resins changed after water sorption.

Influence of water sorption on resin composite color and color variation amongst various composite brands with identical shade code: An in vitro evaluation

Objective The aim of this study was to evaluate the influence of 1 week water storage on color stability of A2 enamel and dentine shade of 13 resin composites intended for anterior restorations and to evaluate the interchangeability of different composite brands of equal color shade. Methods 6 samples per shade were prepared as 1 mm thick discs of 10 mm diameter. L* a* b* and contrast ratio (CR) were measured immediately after light curing and after 1 week storage in water at 37 °C, in the dark. Then all samples were compared against each other. Results The greatest color change was found for Enamel A2 Artemis (Δ E 3.13) with white background whilst the smallest was Dentine A2 Filtek and Voco (Δ E 0.20) with black background. Significance Most of resin composite brands showed statistically significant differences between initial and post immersion color values. Some of post ageing dentine and enamel CR values was statistically different amongst them. The color differences in-between all the A2 enamel and dentine composite shades were highly statistically different.

Influence of water sorption of the underlying abutment on fracture resistance of zirconia copings

Objective. To investigate the influences of abutment water sorption and various aging parameters on the fracture resistance of zirconia copings. Methods. Using a master die, identical replicas were made from three resin materials. The first was a melamine resin with very high water sorption (n = 48), the second an experimental resin core build-up composite with moderate water sorption (n = 40) and the third a commercially available core build-up composite with low water sorption (n = 40). On the abutment replicas, zirconia copings (n = 128) were made using a computer-aided design–computer-aided manufacturing system. The copings were luted onto the abutments using zinc oxide phosphate cement. In the melamine group, a subgroup of samples (n = 8) was cemented with a composite cement as controls. The forty specimens in every abutment material group were randomly divided into one of five subgroups, as follows: (i) not aged; (ii) mechanically (dry) loaded only (50 N; 1.2 × 106 cycles); (iii) stored for 10 days in water; (iv) thermally cycled (TC; 6000 × 5/55°C); and (v) TC and mechanically loaded (TCML; 50 N, 1.2 × 106; 6000 × 5/55°C). After aging, all copings were loaded to fracture. Results. A statistically significant difference was found between the three abutment–die groups if the samples were aged by TCML. The zirconia copings cemented on abutments with high water sorption fractured during TCML, and the subgroup with moderate water sorption had significantly lower fracture resistance. A change of luting material had no impact on this behavior. Conclusion. Only the simultaneous combination of all chosen aging factors (TCML) was able to detect a difference in fracture behavior of a zirconia coping luted on abutments with varying water sorption.

The effect of ethylene content on the interaction between ethylene-vinyl alcohol copolymers and water—II: Influence of water sorption on the mechanical properties of EVOH copolymers

This paper deals with the influence of water on the mechanical performance of ethylene-vinyl alcohol copolymers. A comparative study on the mechanical properties of six EVOH food packaging commercial grades with different ethylene contents has been carried out as a function of relative humidity by DMA and tensile testing. Two different cooling rates, i.e. fast and slow cooling, were used in order to study the effect of cooling speed on water/EVOH interactions. In agreement with the water transport results of a previous study, the current results indicate that there is a surprising anomalous antiplasticization regime for some mechanical properties below 30% RH, and that beyond this point further moisture sorption acts as the well reported effective plasticization agent for the mechanical properties.

Influence of Water Sorption on Fluorinated Polyimide Waveguide

The influence of water sorption on the refractive index of a fluorinated polyimide was investigated. The change in refractive index as much as 10-3 reflected a one order smaller change in volume than that in weight due to water sorption. We confirmed the dependence of refractive index on water sorption using optical switch fabricated by fluorinated polyimide waveguide.

Influence of water sorption on refractive index of fluorinated polyimide

The influence of water sorption on refractive index of a fluorinated polyimide was demonstrated by measuring water uptake and change in volume due to water sorption. The refractive index of the fluorinated polyimide increased with increasing the water uptake. The change as much as 10 −3 in refractive index was observed at the temperature of 25 °C. These results reflected a one order smaller change in volume than that in weight due to water sorption. A loose intermolecular packing structure of the fluorinated polyimide mainly induced this small change in volume due to water sorption. We confirmed this dependence of refractive index on water uptake using a Mach-Zehnder Interferometer type switch fabricated using the fluorinated polyimide waveguide.

Influence of water sorption on acrylic polymer waveguide loss

The influence of water sorption on acrylic polymer waveguides was studied by measuring the loss changes in the atmosphere at 13 to 98% RH. The absorption peak at 1.41 /spl mu/m increased from 0.5 to 2 dB/cm due to water sorption. This peak resulted in a small loss change of 0.03 dB/cm at 1.3 /spl mu/m, which was successfully measured using a 57 cm waveguide with a loss of around 0.1 dB/cm. Relationships between loss change and water sorption were also revealed by measuring the water content of the polymers. >

Creep and recovery of composites for use in posterior teeth during static and dynamic compression

The deformation behavior of 8 different posterior composites under uniaxial static and dynamic compression have been investigated. The influence of water sorption on the mechanical properties was also assessed. The static creep behavior during a 2 h period and the creep recovery for the following 2 h were determined. Stress/strain curves were recorded during cyclic loading at a frequency of 0.25 Hz for 2 h. Water sorption increased the creep and decreased the creep recovery. Both static and dynamic creep values were higher for the microfilled materials than for the other types of composite materials.

木材のレオロジーに関する研究 (第6報)

It is well known that the mechanical properties of wood are very much affected by temperature and by relative humidity. In the light of the results previously considered of these effects, we expect that an investigation of the effects of moisture content and temperature on creep and stress relaxation of wood would be of interest. Of course, it is necessary first to establish the fundamental creep or relaxation behavior of wood under given conditions, and so we have investigated the static viscoelasticity of wood within low stress range in bending of Buna wood (Fagus crenata) beam. The results are as follows:Within the range of strain observed in this experiment, the stress-strain relation is linear and creep compliance, recovery compliance and relaxation modulus are independent of magnitude of loads. This facts suggests that wood behaves as a linear viscoelastic material.The scale factor of wet wood parallel to grain amounts to as much as four times of air dry wood. Such an influence of water sorption on creep behavior is discussed in connection with the variation in moisture effects on dynamic behavior of Buna wood and on stress relaxation of Hinoki wood treated by formaldehyde.The curves of D(t) or E(t) vs. logt of wood that are determind at different temperatures have been tried to be superposed by means of a horizontal translation along the logarithmic time axis and the result was found uncomplete. But when these curves are smoothed out and differentiated by logt, the shape of the curves obtained are analogous to the relaxation time spectra measured for long time scale. The temperature dependency of the shift factor is hereby discussed.