Characterisation of sorbed water molecules on neutral and ionic polysaccharides.

Ionic and neutral polysaccharides with well-defined structures were chosen to investigate the mechanism of water sorption at different relative humidities. From an experimental point of view, the freezing water was determined by DSC when the total sorbed water was obtained from thermogravimetry. The isotherms of sorption and enthalpies of interaction were determined using the combination of a microbalance and a microcalorimeter. It is shown that freezing water appears for P/P(zero) > 0.85 especially with the neutral polymers. The differential molar enthalpy of interaction is higher for P/P(zero) < 0.85 corresponding to the fixation of two water molecules forming double H-bonds; this result is confirmed by molecular modelling; saturation is obtained experimentally for 4 water molecules interacting per glucose unit. On ionic polymers, the water retention increases especially over P/P(zero) approximately 0.8 and the enthalpy of interaction is higher for the first water molecules sorbed. For P/P(zero) approximately equal to 0.8, the numbers of bound water molecules found are 2 per glucopyranosyl unit for neutral polysaccharides, 5 for glucuronan and 9-10 for carboxymethylcellulose (CMC) of DS = 2 and hyaluronan (HA).

Vapor pressure isotherms, composition and density of hyperdense bones of horse, whale and porpoise.

Water adsorption studies of three types of hyperdense bone show vapor pressure isotherms and enthalpy to be different from that for pure apatitic mineral. The mineral content of these bones varied from 80 to 98%, much greater than for the better known cortical bone. The high mineral content of all these bones and the variation of mineral content from one type of bone to the next make it possible to evaluate the contribution of the mineral component in bone to water adsorption. Both water content and the fractional shrinkage when dried decrease with increasing mineral content of the bone and increase with the organic component. The total water content of hyperdense bone is much less than the maximum water adsorbed by the equivalent pure mineral powder or by anorganic bone. It was concluded that: (1) Very little water appears to be adsorbed by the mineral in hyperdense bone; (2) It is likely that the mineral crystallites are coated with noncollagenous organic matter; (3) Water is taken up by organic matter both intra- and extrafibrillar; and (4) the enthalpy associated with the adsorption of water by HAP is higher than for hyperdense bone at all corresponding vapor pressures.