Water Sorption Properties

Water uptake is usually used to study the humidity diffusion through the composite films. To determine the water uptake [92, 94, 95], the composite films used were thin rectangular strips with dimensions of 10 mm x 10 mm x 0.2 mm. Ihe films were supposed to be thin enough so that the molecular diffusion was considered to be onedimensional and were vacuum-dried at 90°C overnight After weighing, they were conditioned at 25°C in a desiccator containing sodium sulfate in order to ensure a relative humidity (RH) of 95%. They were then removed at specific intervals and gently blotted with tissue paper to remove the excess of water on the surface, and the water uptake was calculated with Eq. 1, as follows  

In a multi-component biopolymer system (like starch-cellulose films), each biopolymer engages in biopolymer-biopolymer interactions contributing each one and both to the system properties. Occasionally, these interactions are more important than individual actions. A neat starch film will always display high water absorbency properties, this fact impeding the its application for most water resistance applications. 

This behavior can be explained by the formation of a more tight structure after starch crosslinking which prevents the swelling of starch and also restricts the movement of macromolecular chains, leading to a decrease of the amount of absorbed water in agreement with mechanical properties. 

The tensile strength of the films was influenced by the polymer components. By addition of cellulose fillers, the tensile strength values were improved. Elongation at break for CMSt/St/C film samples was reduced than that for CMSt/St sample. However, as a result of more compact structure due to high intermolecular hydrogen bond 

Composite sample Tensile strength (MPa) Young s modulus (MPa) Elongation at break (%) 

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Khan KA, Rhodes CT. Water-sorption properties of tablet disintegrants. / Pharm Sci 1975 64(6) 447 51. 

White, W.A., 1958. Water sorption properties of homoionic clay minerals. Ill. State Geol. Surv., Rep. Invest. 208, 46 pp. 

Biomaterial films can be used to prevent water sorption by low moisture foods or pharmaceutical solids and, thus, to maintain product quality, and to improve shelf life and storage stability. For many biomaterials water acts as a plasticizer and therefore affects stability and quality (Roos and Karel, 1990, 1991). Hence, it is important to control water sorption properties of low moisture foods or pharmaceutical products. Edible films can be used as barriers or retarders of water sorption of low moisture products. 

Water-sorption properties of various films were determined gravimetri-cally after storage of freeze-dried samples in vacuum desiccators at a relative humidity ranging from 11 to 86% at 25°C. Water-sorption behavior was modeled with the Guggenheim-Anderson-de Boer (GAB) Equation 24.1 in which water content is m, monolayer moisture content is wXm, water activity is flw/ arid K and C are constants. 

Much deeper insights into the water sorption properties of polyelectrolytes can be provided by evaluating the (nNa)p term directly. By the use of the activity coefficient of Na+ ions in the PA A polyelectrolyte phase, (yNa)p, (aNa)p can be expressed as (aNa)p = (yNa)P [Na]p. Two concentration terms, i.e., (1) Na+ ions present in the polyelectrolyte phase to neutralize free car-boxylate groups and (2) Na+ ions imbibed in the polyelectrolyte phase in the form of NaCl, contribute the [Na]p term. Escape of Na+ ions from the polyelectrolyte phase due to their thermal motion, which produces a site vacancy of the polyion, should also be taken into consideration. The fraction of site vacancy of polyelectrolytes is available as a practical osmotic coefficient, c/>p-Na, which can simply be related to the linear charge separation of the PAA polyion. It has been revealed that PiNa is not affected by the change in the polyion concentration nor Cs, which is known as an additivity rule [16,17]. Thus the (aNa)p term can finally be expressed as... 

The water sorption properties of polystyrene sulfonate (PSS) exchangers with different degrees of cross-linking have been observed to coincide in the lower water activity region where the Vh O 5 negligibly small (6 ). There is coincidence as well... 

J. Kajaks and S. Reihmane. Thermal and water sorption properties of polyethylene and linen yarn production waste composites. In 2nd International Wood and Natural Fibre Composites Symposium, Universitat Gesamthochschule Kassel, Institut fur Werkstoff-technik, Kassel, Germany, 1999, pp. 39/1-39/5. 

Linko, P., Pollari, T., Harju, M., and Heikonen, M. (1981). Water sorption properties and the effect of moisture on the structure of dried milk products. Lebensm. W/w. Technoi 15(1), 26. 

Liu C, Komarneni S. Nitrogen and water sorption properties of ethyl substituted silica aerogels and xerogels. Mat Res Soc Symp Proc. 1995 371 217-22. 

White WA, Pichler E (1959) Water Sorption Properties of Clay Minerals. In III. State Geol Surv Circ No. 266, Champaign, 111 Johnson AL, Norton FH (1941) Fundamental Study of Clay n. Mechanism of Deflocculation in the Clay-Water System. J Amer Ceram Soc 24 189-203... 

White WA, Pichler E(1959) Water Sorption Properties of Clay Minerals. In 111. State Geol Surv Circ No. 266, Champaign, 111... 

Z. Palacha and A. Danak, Effect of temperature on water sorption properties of osmo-convection dried pumpkin and carrot. In Properties of Water in Foods (P.P. Lewicki, ed.), Warsaw Agricultural University Press, Warsaw, Poland, 1997, p. 130. 

Data on Water Sorption Properties of Selected Pharmaceutical Materials... 

Demir H, Atikler U, Balkose D, Tihmmhoglu D (2006) The effect of fiber surface treatments on the tensile and water sorption properties of polypropylene-luffa fiber composites. Compos A 37 447 56... 

A. GuiUermo, G. Gebel, H. MendH-Jakani, E. Pinton, NMR and pulsed field gradient NMR approach of water sorption properties in nafion at low temperature, J. Phys. 

Water sorption isotherm is itseful for predicting water sorption properties of polymer and allowed to provide little insight into the interaction between water molecules and polymer tested. 

The ion exchange capacities and water sorption properties of 400EW and 600EW polymer films are listed in Table... 

FIGURE 9.1 Water content change of Nafion 112 as a function of the ambient temperature at different initial k>. (Reprinted with permission from Guillermo, A. et al. 2009. NMR and pulsed field gradient NMR approach of water sorption properties in Nafion at low temperature. /. Phys. Ghent. B 113 6710-6717. Copyright (2009). American Chemical Society Publications.)... 

Z. Palacha and A. Danak, Effect of temperature on water sorption properties of osmo-convection dried... 

The key objective of PEM research is to rationalize and eventually predict the impact of variations in thermodynamic conditions and fuel cell current density on (i) chemical structure and composition, (ii) water sorption properties, (iii) proton conductivity, (iv) water flux mechanisms and parameters, (v) electrochemical... 

The main assumptions of the simple bulk conductivity model are valid at high water contents. This wording implies that a lower characteristic value of water content exists, below which the model is invalid. This value emerges as an important membrane characteristic. It will be discussed below, based on an assessment of water sorption properties and dynamics of proton and water transport. 

How does the primary chemical architecture of ionomer molecules determine ionomer aggregation, formation of water containing pathways in the PEM, and water sorption properties of the PEM ... 

The self-organized structure and mechanical properties of ionomer aggregates determine the water sorption properties and the stability in PEMs. These properties in turn are the key to PEM operation in PEFCs they govern water distribution and transport, proton density and conductivity, and the membrane response to mechanical stressors. 

Satterfield MB (2007) Mechanical and water sorption properties of Nation and Nation/ Titanium dioxide membranes for polymer electrolyte membrane fuel cells. In Chemical Engineering. Princeton University, Princeton, NJ, p 208... 

Wang, Y, and Padua, G. (2004). Water sorption properties of extruded zein films./ Agricfood Chem., 52,3100-3105. doi 10.1021/jf035329t. 

Antonucci et attributed the enhanced performance of the composite membrane to the hygroscopic properties of silica. Watanabe et investigated silica- and titania-impregnated Nation composite membranes in H2/O2 proton-exchange membrane fuel cells operating at 100 °C with minimal external humidification. They reported that the silica particles were superior to titania particles in terms of water retention qualities within the Nafion membrane, and attributed this to the higher water sorption properties of silica. Adjemian et reported that the performances of silica and titania composites at 130 °C and 75% RH are comparable (0.33 Qcm and 0.35 Qcm cell resistivities) while recast Nafion -based composites present high cell resistivity (0.9 Qcm ). 

Snoeck, D., L. F. Velasco, A. Mignon, S. Van Vlierberghe, P. Dubruel, P. Lodewyckx and N. De Belie (2014). The influence of different drying techniques on the water sorption properties of cement-based materials . Cement and Concrete Research 64 54-62. 

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