The influence of trehalose–maltodextrin and lactose–maltodextrin matrices on thermal and sorption properties of spray-dried β-lactoglobulin–vitamin D3 complexes

In the study, the effect of lactose–maltodextrin and trehalose–maltodextrin matrices on the glass transition temperatures and moisture sorption characteristics of spray-dried β-lactoglobulin–vitamin D₃ complexes was investigated. Incorporation of sugars into complexes can influence the thermal properties and moisture sorption characteristics of powders. The glass transition temperature as an important physiochemical parameter that determines the processing conditions, product quality and stability of the final product was studied with the use of modulated differential scanning calorimetry method. Moisture sorption isotherms, water activity and moisture content as parameters related to sorption properties, were also investigated. Additionally, particle size, wettability and insolubility index were studied to characterise newly synthesized products. For the samples tested, two well-separated glass transitions were found. The dominant effect of maltodextrin on the glass transition temperatures was observed. An increase in the percentage of maltodextrin added resulted in increasing T _g value of studied complexes. At low water activity all powdered complexes showed typical sorption behaviour of food systems. Trehalose as a carbohydrate component of powdered complexes, in comparison to lactose, delayed the occurrence of crystallization.     

Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

Dilation and plasticization of polystyrene by carbon dioxide

We have used an optical interference technique to measure the dilation of polystyrene films in the presence of carbon dioxide or helium at pressures up to 20 atm. Dilation isotherms (plots of dilation versus gas pressure at constant temperature) were obtained for three samples of polystyrene which had widely differing molecular weights. The dilation isotherms have the same general shape as sorption isotherms, which means that all of the sorbed gas molecules contribute to volume dilation and non can be thought of as occupying molecular-sized voids in the polymer. Using sorption results from the literature we show that the partial molar volume of CO₂ at 35°C is about 39 cm³ mol^?1 and appears to be independent of polystyrene molecular weight. For a polystyrene sample with M_n = 3600, the partial molar volume of sorbed CO₂ increases to 44 and 50 cm³ mol^?1 at 45 and 55°C, respectively. The sorption of CO₂ in polystyrene is shown to depress the glass transition temperature of the mixture, consistent with theoretical predictions. The shape of the dilation and sorption isotherms are consistent with the depression of the glass transition temperature.     

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (H.B.K.) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25°C over saturated salt solutions in order to obtain water activities (a_w) between 0.11–0.90. Samples with a_w>0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon–Taylor model was able to predict the plasticizing effect of water. In samples, with a_w>0.90, the glass transition curve exhibited a discontinuity and T^’_g was practically constant (–58.8°C), representing the glass transition temperature of the maximally concentrated phase(T_g ).     

Sorption and dilation in poly(ethyl methacrylate)–carbon dioxide system

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low-pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO₂ in PEMA were obtained from sorption and dilation data, which were described well by the extended dual-mode sorption and dilation models developed recently. The temperature dependence of the dual-mode parameters and the isothermal glass transition are discussed.     

The glass transition and crystallization of ball milled cellulose

Samples of ball milled cellulose were prepared by ball milling pulps from eucalyptus and softwood (spruce/pine). Water sorption isotherms were obtained by both dynamic vapor sorption and equilibration over saturated salt solutions, in the water content range of 5–42% db (db = dry basis; water as a % age of total solids). Dynamic mechanical analysis using a pocket technique showed a water content dependent thermal transition occurring at the same temperature for the two pulp samples, which was interpreted as a glass transition. Fitting the data to a Couchman–Karasz relationship predicted a value for T _g of the dry cellulose of approximately 478 K, which was similar to values previously reported for other dry polysaccharides. No clear glass transition could be observed calorimetrically, although an endotherm at approximately 333 K was measured, which in polymers is normally attributed to enthalpic relaxation, however the lack of dependence of this endotherm on water content suggests that the melting of some weak associations, such as residual hydrogen bonds, could be a more credible explanation. An exotherm was also observed on heating, which was dependent on water content and which was attributed to partial crystallization of the cellulose. This was confirmed by Wide angle X-ray diffraction and cross polarization magic angle spinning ¹³C NMR (CPMAS NMR). The recrystallisation was predominantly to form I of cellulose. This was thought to be caused by a small amount of residual form I (probably less than 5%) acting as a template for the crystallizing material. Differential scanning calorimetry reheat curves showed the appearance of freezable water for water contents higher than 20%, as a result of a transfer of water to the amorphous phase following crystallization. The increase in cellulose rigidity following crystallization was also confirmed by CPMAS NMR relaxation. Low resolution proton NMR T ₂ relaxation suggested the presence of proton water/cellulose exchange, which was active at water contents of 20% and above.     

Influence of Moisture on the Glass Transition of A Spray-Dried Compound Using the Isosteptm Method

The interaction among moisture content, solvent loss and glass transition temperature is relevant for processing of spray-dried pharmaceuticals, since the glass transition temperature determines the application range of a compound. Conventional Differential Scanning Calorimetry (DSC) does usually not allow to separate glass transitions from common kinetic effects like evaporation or crystallization. Based on classical DSC methods, the IsoStep^TM method allows the independent determination of heat capacities and kinetic effects, and thus, the separation of kinetic effects from effects arising from heat capacity changes. This technique is used to separate glass transition and evaporation processes, and to find the relation between moisture content and glass transition temperature for a pharmaceutical sample based on a modified Gordon–Taylor equation. This revised version was published online in August 2006 with corrections to the Cover Date.     

The determination of isosteric heats of sorption of leather: Experimental and mathematical investigations

Knowledge of sorption isotherms of leather products is necessary to control rehydration/dehydration and storage processes and it is valuable tool for prediction of the stability and shelf life of products but the impact of the controlled climate on moisture sorption isotherms of leather remains unclear. The aim of this work is to predict moisture desorption isotherms of leather of bovine variety. The static gravimetric method was used to determine sorption isotherms at four temperatures (30, 40, 50 and 60 °C) and the equilibrium moisture content of leather samples was measured within the range of 5–90% relative. All the curves exhibited type II behavior, according to Brunauer’s classification. Equilibrium moisture contents are observed to drop as the temperature is enhanced. Many models available in the literature were used to describe the experimental data. The agreement between experimental and calculated sorption isotherms is seen to be satisfactory (correlation coefficients from 0.93 to 0.99). Furthermore, DENT model is found to be the most appropriate for describing the relationship between the equilibrium moisture content, the water activity and temperature. On the other hand, the isosteric heats of desorption were determined from sorption isotherms and then correlated with corresponding equilibrium moisture contents. Besides, the isosteric heats of desorption decreased continuously with increasing of the equilibrium moisture content.     

Sorption of water vapor by poly(vinyl acetate)

Summary The sorption property of water vapor by poly(vinyl acetate) (PVAc) of relatively low glass transition temperature (T _g) was studied at temperatures nearT _g.Tc_g of humidity-controlled samples of various moisture contents was measured and its variation with the moisture content was determined.T _g of the dry sample was estimated by dilatometry and DSC methods, and to confirm the value, the temperature dependence of mutual diffusion coefficient of the system of water vapor + PVAc was determined. A difference between the sorption mechanisms of water vapor by PVAc at 20 and 30 °C was observed: two sorption mechanisms are involved at 30 °C, while three mechanisms at 20 °C are involved which include the above two and another intermediate one. In earlier stage of sorption, at both 20 and 30 °C, water molecules sorbed by PVAc showed a tendency towards aggregation, while a mixing effect was found at higher stage of the sorption.

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Zusammenfassung In der Arbeit werden Wasserdampfsorptionseigenschaften von Polyvinylacetat mit relativ niedriger Glastemperatur (T _g) in der Nähe vonT _g untersucht. Es wurden Plastizitätseinflüsse und Veränderungen vonT _g mit dem Wassergehalt studiert. Es wurde gefunden, daß bei 30 °C ein 2-Stufen-Sorptionsmechanismus, bei 20 °C ein 3-Stufen-Mechanismus existiert.

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With 7 figures     

Sorptive dilation of polysulfone and poly(ethylene terephthalate) films by high-pressure carbon dioxide

Dilation of polysulfone (PSUL) and crystalline poly(ethylene terephthalate) (PET) films accompanying sorption of carbon dioxide is measured by a cathetometer under high pressure up to 50 atm over the temperature range of 35–65°C. Sorptive dilation isotherms of PSUL are concave and convex to the pressure and concentration axes, respectively, and both isotherms exhibit hysteresis. Each dilation isotherm plotted versus pressure and concentration for the CO₂-PET system shows an inflection point, i.e., a glass transition point, at which the isotherm changes from a nonlinear curve to a straight line. Dilation isotherms of PET below the glass transition point are similar to those of the CO₂-PSUL system, whereas the isotherms above the glass transition point are linear and exhibit no hysteresis. Partial molar volumes of CO₂ in these polymers are determined from data of sorptive dilation. On the basis of the extended dual-mode sorption model and the current data, primitive equations for gas-sorptive dilation of glassy polymers are proposed.     

Sorption charateristics of methane among various rank coals: impact of moisture

Enhanced coalbed methane (ECBM) in deep coal seams is being actively investigated around the world. Since the in situ coal seams are always saturated with water, methane sorption behavior on coal in the presence of water can help accurately assess the amount of recoverable methane. Thus, methane sorption isotherms have been measured on a high-rank anthracite, a low-volatile bituminous, a middle-volatile bituminous and a high-volatile bituminous coal with the manometric technology at 30 °C under six different moisture contents. The Dubinin–Astakhov (D–A) equation was used to fit the experimental sorption isotherm data. In all cases, the moisturized coals exhibited lower sorption capacity than the corresponding dry materials and moisture has a significant effect on CH₄ sorption capacity. The maximum sorption capacity, V ₀, displays a linear decline with the moisture content for the Changcun and Malan samples, but it is nonlinear for the other two coal samples. The net heat of CH₄ sorption, βE, is also reduced by the presence of water, but varies only slightly between a relatively small span of about 8.8 and 10.0 kJ mol^?1 for the dry samples studied, despite the difference in coal rank. In addition, the maximum sorption capacity of CH₄ in dry coals presents the typical “U-shape” trend with coal rank. Moisture has a greater impact on the sorption capacity in low-rank coals than that in high-rank coals. The mechanisms responsible for the effect of moisture on CH₄ sorption among various rank coals are also presented. The pore-blocking effect is the main influencing factor for high-rank anthracite, whereas, the competition sorption is dominant for low-rank coals.     

The Thermal Characteristics,Sorption Isotherms and State Diagrams of the Freeze-Dried Pumpkin-Inulin Powders

Powders based on plant raw materials have low storage stability due to their sorption and thermal properties and generate problems during processing. Therefore, there is a need to find carrier agents to improve their storage life as well as methods to evaluate their properties during storage. Water adsorption isotherms and thermal characteristics of the pumpkin powder with various inulin additions were investigated in order to develop state diagrams. Differential scanning calorimetry (DSC) was used to obtained glass transition lines, freezing curves and maximal-freeze-concentration conditions. The glass transition lines were developed using the Gordon–Taylor model. Freezing data were modeled employing the Clausius–Clapeyron equation and its development–Chen model. The glass transition temperature of anhydrous material (Tgs) and characteristic glass transition temperature of maximum-freeze-concentration (Tg′) increased with growing inulin additions. Sorption isotherms of the powders were determined at 25 °C by the static-gravimetric method and the experimental data was modeled with four different mathematical models. The Peleg model was the most adequate to describe the sorption data of the pumpkin–inulin powders. Guggenheim-Anderson-de Boer (GAB) monolayer capacity decreased with increasing inulin concentration in the sample.     

CO2 sorption in wet ordered mesoporous silica kit-6: effects of water content and mechanism on enhanced sorption capacity

The sorption isotherms of CO₂ in wet ordered mesoporous silica KIT-6 with different amounts of pre-adsorbed water were firstly collected experimentally using a volumetric method in the temperature range of 275–281 K. The isotherms show an inflection point indicating CO₂ hydrates form in the pore spaces which is proofed by the enthalpy change calculated at the inflection pressure, and the quantity of water content shows considerable effect on the sorption capacity of CO₂. The highest enhancement of sorption capacity in the presence of water is observed in wet KIT-6 sample with water loadings of 2.48, which is about 12.80 mmol/g and 1.86 times than that on dry sample. However, the saturation capacity is still far less than that what can be stored merely in the form of hydrates due to the low ratio of water utilization because of the large pore and the polar surface of KIT-6.     

Argon sorption and partial molar volume in poly(ethyl methacrylate) above and below the glass transition temperature

Sorption and dilation isotherms for argon in poly(ethyl methacrylate) (PEMA) are reported for pressures up to 50 atm over the temperature range 5–85°C. At temperatures below the glass transition (T_g=61°C), sorption isotherms are well described by the dual-mode sorption model; and isotherms above T_g follow Henry's law. However, isotherms for dilation due to sorption are linear in pressure at all temperatures over the range investigated. Partial molar volumes of Ar in PEMA are obtained from these isotherms. The volumes are approximately constant above T_g (about 40 cm³/mol), whereas the volumes below T_g are smaller and dependent on both temperature and concentration (19–26 cm³/mol). By analyzing the experimental data according to the dual-mode sorption and dilation model, the volume occupied by a dissolved Ar molecule and the mean size of microvoid in the glass are estimated to be 67 129 ų, respectively. The cohesive energy density of the polymer is also estimated as 61 cal/cm³ from the temperature dependence of the dual-mode parameters.     

Swelling and sorption in polymer–CO2 mixtures at elevated pressures

Experimental data on gas sorption and polymer swelling in glassy polymer—gas systems at elevated pressures are presented for CO₂ with polycarbonate, poly(methyl methacrylate), and polystyrene over a range of temperatures from 33 to 65°C and pressures up to 100 atm. The swelling and sorption behavior were found to depend on the occurrence of a glass transition for the polymer induced by the sorption of CO₂. Two distinct types of swelling and sorption isotherms were measured. One isotherm is characterized by swelling and sorption that reach limiting values at elevated pressures. The other isotherm is characterized by swelling and sorption that continue to increase with pressure and a pressure effect on swelling that is somewhat greater than the effect of pressure on sorption. Glass transition pressures estimated from the experimental results for polystyrene with CO₂ are used to obtain the relationship between CO₂ solubility and the glass transition temperature for the polymer. This relationship is in very good agreement with a theoretical corresponding-states correlation for glass transition temperatures of polystyrene-liquid diluent mixtures.     

Thermal behaviour of some mixture of collagen hydrolysates with vinylic polymers

The thermal behaviour was studied by DSC and TG methods for some mixtures of poly(ethyl acrylate) and poly(vinyl alcohol) with collagen to examine compatibility, glass transition temperature and thermal degradation. The mixtures of collagen hydrolysates with poly(ethyl acrylate) have a single glass transition temperature. The mixtures with poly(vinyl alcohol) show a glass transition temperature independent of composition and a melting temperature dependent on composition. The DSC and T_g data reveal partial compatibility at low temperature. By heating above 200°, the mixture separates into the two components which behave independently.     

Moisture absorption and diffusion in an underfill encapsulant at T > T g and T < T g

Moisture absorption and diffusion behavior of an underfill material used for electronic packaging with a glass transition temperature (T _g) slightly above room temperature have been investigated by the sorption thermogravimetric analysis technique. It has been found that moisture diffusion in this material follows the Fick’s diffusion model, and moisture absorption–desorption is reversible and repeatable. Based on moisture-induced mass gain versus time curve, the diffusion constant can be determined. It was found that below T _g, moisture diffusivity exhibits an Arrhenius temperature dependence, which changes to a different Arrhenius temperature dependence as the temperature increases to T > T _g. The change in diffusivity from T < T _g to T > T _g is accompanied by a significant decrease in the energy barrier for moisture diffusion. Results shed light on the change in moisture diffusion in polymer-based materials in the glassy and the rubbery state.     

Thermodynamic analysis of sorption isotherms of bentonite

Sorption isotherms of water vapour on commercial bentonite clay are determined at T = (303, 323, and 343) K. The sorption isotherms have a sigmoid shape (Type II). At a given water activity, moisture content decreases with increasing temperature. Hysteresis between adsorption and desorption isotherms is shown over most the range of water activity varying from 0.1 to 0.9. The fitting of the experimental data by using two theoretical models (Guggenheim–Anderson–DeBoer (GAB) and Henderson) shows that the two models reproduce experimental data with acceptable accuracy. The GAB model, however, is largely superior. The isosteric sorption enthalpy is determined and its dependency on the amount of water retention is investigated. It is found that the enthalpy reaches a maximum value when a monolayer of water covers the adsorbant surface. The enthalpy decreases asymptotically to a finite value when the amount of adsorbed water increases.     

Effect of penetrant-induced isothermal glass transition on sorption,dilation, and diffusion behavior of polybenzylmethacrylate/CO2

The effect of a penetrant-induced isothermal glass transition on sorption, dilation, and diffusion behavior was studied in a single experimental run for CO₂ in cast polybenzylmethacrylate films. The dual-mode type sorption isotherms below the glass transition temperature of the polymer changed to linear ones above a certain concentration. Meanwhile, partial molar volume of CO₂ determined from the dilation of the films above the concentration gave a value very close to the one reported for rubbery polymers, and diffusion coefficients became less concentration-dependent. The results were conformable to the concept of unrelaxed volume in glassy polymers. © 1996 John Wiley & Sons, Inc.     

Effect of relative humidity on mechanical properties of a woven thermoplastic composite for automotive application

The purpose of this work is to characterise the influence of moisture content in a woven glass fibre reinforced polyamide 6,6 composite. Two different stacking sequences are studied: [(0/90)₃] and [(±45)₃] as well as the neat PA6,6 matrix. Samples have been conditioned through three ways: either water immersed, left at ambient temperature and humidity or dried in 35 °C oven. A one dimensional Fick's law has been used to model the water uptake in immersed samples. The glass transition temperature is highly affected by the presence of water and has been measured using modulated DSC technique. Finally, the effects of water on these composite materials have been investigated through tensile tests instrumented with acoustic emission monitoring (AE). Mechanical properties are highly affected by the presence of water in the composite. This result is even more visible on [(±45)₃] sample because of the preferential loading of the matrix.