MOISTURE SORPTION PROPERTIES OF COLLAGENS VARIED IN POLARITY AND POROUS STRUCTURE BY ALKALI-TREATMENT

Moisture sorption properties of steer hide collagen fibers treated with calcium hydroxide were investigated on the basis of sorption isotherm, differential heat of sorption, entropy of moisture sorption, and applicability of isotherm equations to elucidate the difference between untreated and treated collagens in interaction with water molecules. The alkali-treatment resulted in the occurrence of new and more active sorption sites, the increases in both number of free carboxyl and void space of collagen molecules, and also the change to a more disentangled structure. The increase in moisture content and the changes in interactive force between water molecules and various sorption sites of collagens at different ranges of water activity (Aw) were attributed to the changes in number and strength of polar groups and in inner space of collagens due to alkali-treatment. Sorption characteristics of moisture on collagen could well be explained by the strength of interaction of water with collagen and the surface hydrophobicity of collagen. The Henderson and Chung and Pfost equations fitted the moisture sorption isotherms well over a wide Aw range up to 0.90. The large values of constants in the equations to the moisture sorption isotherms of collagens indicated both unstability of the collagen structure to moisture and negative electrification due to polar groups on the surface of collagen. © 1993 by Academic Press, Inc.