Composite theory and the effect of water on the stiffness of horn keratin

-keratin is a hydrogen-bond dominated composite material. The dry -keratin (0% regain) of the horns of an oryx has a stiffness of 6.1 GPa. Water interacts only with the amorphous matrix of -keratin to break down structural hydrogen bonds and reduce stiffness to 4.3 GPa at 20% regain and 1.8 G Pa at 40% regain. The effect of water on the stiffness of horn -keratin is not modelled by the Voigt estimate at high to moderate regains. Water interacts probably with the disordered regions within the fibres which reduces the effective fibre length. As a result the reinforcing effect of the fibres is reduced and the stiffness and strength of hydrated horn keratin are less than that predicted by the simple Voigt estimate. If the Voigt estimate is modified to take into account a short fibre length of 40 nm, the stiffness and tensile strength of horn -keratin can be modelled successfully.