Authors:D. Berkün, D. Balköse, F. Tıhmınlıoǧlu, and S. Altınkaya
Two types of films consisting of sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropyl cellulose (HPC) as film
forming materials and glycerin as plasticizer were prepared, characterized and their water vapour sorption properties were
The water sorption isotherms of the films were measured using a magnetic suspension balance. Results show that diffusion of
water vapour in NaCMC based film is faster than that in HPC based films, due to the heterogeneous structure and larger pore
dimensions of the NaCMC films.
Authors:Maria Villanueva, I. Fraga, J. Rodríguez-Añón, J. Proupín-Castiñeiras, and J. Martín
The diffusive, calorimetric and thermal degradation behavior of different
epoxy-amine systems was investigated during water sorption at different temperatures
(23, 40 and 70°C). Experimental results showed that the water absorption
at these temperatures fitted well to Fick’s law. Influence of water
immersion during different periods of time on the glass transition temperatures
was studied by differential scanning calorimetry. Thermal degradation of saturated
samples was studied by thermogravimetric analysis. Dependence on the selected
curing cycle was also checked.
The amorphous content of different Desferal samples was quantified by recording its recrystallization using isothermal microcalorimetry in a static as well as in a flowing humid atmosphere. Furthermore water vapor sorption gravimetry was performed for the same purpose. These analytical methods result in a quantitative signal directly dependent on the content of the amorphous phase (recrystallization, water sorption equilibrium). Their sensitivity allows the detection of amorphous content below 1%. Methods are compared and advantages and disadvantages are discussed.
Authors:E. Robens, B. Benzler, H. Reichert, and K. Unger
Dry cement powder and hardened cement paste were characterised by means of laser granulometry and volumetric measurement of
the nitrogen adsorption isotherm at 77 K. Water sorption isotherms at ambient temperature were measured stepwise by means
of a gravimetric apparatus. The isotherms show a very large hysteresis loop, reaching down to zero relative pressure, which
reflects swelling of the cement gel. Thermoporometric measurements reveal that swelling of that gel consists in water take
up within the continuously growing structure; no stable pore structure could be observed.
Electronic microbalances, manufactured by CI Electronics Ltd., are used by numerous researchers to study processes and phenomena which can be followed by changes in the sample masses. Less sensitive electronic millibalances are incorporated into integrated systems for the quality control of small and valuable items such as pharmaceutical products and diamonds. A further application of microbalances is the automatic water sorption analysis of samples by the gravimetric method with the CISorp. This integrated system records kinetic and isotherm data of the changes in the relative humidity, sample masses, and temperature and allows the study of physical and chemical properties of sample surfaces.
Authors:E. T. Stepkowska, S. Yariv, J. L. Pérez-Rodríguez, A. Justo, A. Ruiz-Conde, and P. Sánchez-Soto
A dredged sludge was studied to investigate the influence of ageing and of pretreatment on its drying rate, water sorption/retention, thermal mass loss, XRD and microstructure (SEM).
Ageing caused change in particle thickness and specific surface, a gradual aggregation to form units of the size 10–50 μm, formation of macropores of similar size, unhomogeneity and fissures between aggregates and “super-aggregates”. Macropores were detectable by the initial drying rate especially at 45°C. They indicated a tendency of collapsing at a lower drying rate at 30°C. This is consistent with SEM observations. With ageing the aggregates were more compact and less sensitive to drying.
The aggregated system indicated a higher initial drying rate (higher permeability), whereas stirring induced a lower drying rate, favouring the formation of compact laminar structure.
XRD peak intensity was lowered with ageing due to decrease in crystallinity (stacking faults and/or decrease in crystallite size). The content of amorphous material was lowered as well, reducing water sorption/desorption, which indicated that the specific surface is lower.
From the suitable microstructure induced by ageing some new phases may form (feldspar, zeolites), preferably in the coarser fraction of the sludge. This is disturbed by stirring which operation expels also carbonates from the particle edges and this may reduce the structural strength of the sludge. In aged bentonite suspension a similar tendency was observed of formation of specific microstructures capable of phase transformation, e.g. to feldspar.
Authors:A. Zumailan, G. Denis, E. Dargent, J. Saiter, and J. Grenet
PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition
is studied by MDSC which allows to access the glass transition temperature Tg and the variations of ΔCp=Cp1−Cpg (difference between thermal capacity in the liquid-like and glassy states at T=Tg). Variations of Tg with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed
with regard to the structure engaged in these materials. The increments of ΔCp at Tg are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’
of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline
phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase.
Authors:Ana Brás, María Viciosa, Madalena Dionísio, and J. Mano
A detailed dielectric characterization
of the relaxation modes found in a poly(L-lactic
acid), PLLA, film containing 0.4 mass% of water is provided. The sub-glass
relaxation process is a superposition of two processes, one highly influenced
by water with activation energy of 50 kJ mol–1,
and another one, with longer relaxation times and lower intensity having activation
energy of 38 kJ mol–1. Dried PLLA exhibits
an abnormally broad secondary β-relaxation that probably corresponds to
the superposition of multiple processes. Upon water sorption the strength
of the more mobile process significantly increases being shifted to lower
temperatures which allows the detection of the underlying process. The glass
transition relaxation process is deviated to higher frequencies almost one
decade due to the water plasticizing effect. The reported results show that
small quantities of water may have a profound impact in the relaxational features
in PLLA, which should be taken in account when considering the properties
and performance of this system.
Measurements of the masses of incorporated water and of the heats of hydration have been performed at 310 K, under air atmosphere saturated with water vapour, on three differently dehydrated samples of the Saccharomyces boulardii yeast in order to evaluate differences in physicochemical properties related to the following dehydration processes: cryodesiccation (or lyophilization) and thermodesiccation (spray drying and in-fluidized-bed heating).Thermogravimetric (TG) experiments have shown that the lyophilized yeast contains less residual water than heat-treated yeasts and that it incorporates more water and more rapidly. Isothermal water sorption of a spherical yeast cell has been represented by a two-parameter equation able to take account of a maximum of the hydration rate when this is taken as a function of time. On the other hand, isothermal DSC experiments have shown that hydration-heat values are higher for the heat-treated yeasts than for the lyophilized one. The TG and DSC results have been shown to be consistent with the idea that the physicochemical properties of a dehydrated yeast are related to cell-wall behaviour during desiccation.
Authors:E.T. Stepkowska, J. Perez-Rodriguez, M. Aviles, M. Jimenez de Haro, and M. Sayagues
Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing
in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was th=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water
content, EV (110C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis
of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m2 g-1 (C-33, 1 m) to 166 m2 g-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m2 g-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m2 g-1 in C-33 (1 and 6 m) and 198-210 m2 g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m).