Effect of water on the mechanical properties of collagen films

The effect on water on mechanical properties of collagen films has been studied. The S‐shaped sorption isotherm is separated into an adsorption curve C 1 and a solution curve C 2 . From the C 2 curve, a value of 0.8 is calculated for the Flory‐Huggins interaction parameter χ 1 . The dynamic shear modulus G′ , loss modulus G″ , and loss tangent tan δ determined as functions of water content indicate two dispersions at low and at high water content. The region of water content from about 0.05 to 0.1 g/g, G′ decreases suddenly, G″ has a peak, and tan δ increases, corresponds to the region where the C 2 component of sorption becomes detectable. Another dispersion occurs at water contents above 0.2 g/g. A composite curve can be obtained by shifting stress‐relaxation curves obtained at different humidities along the log time axis. When only the C 2 component of sorbed water is taken into account, the shift factor a c is explained by a relation of Fujita and Kishimotos' based on free‐volume theory. Shift factor for the relaxation curves of wool fibers, except for an initial part at times of less than 1 sec, are described by the same equation. The parameter β in the equation has the same value of 0.16 for both collagen and wool.