In situ observation of moisture-induced swelling of leather in an environmental scanning electron microscope

The correlation of microscopic and macroscopic effects of moisture-induced swelling of the collagen fiber structure has been investigated by measuring both mechanical stress development and stress-free deformation of leather in an environmental scanning electron microscope. Swelling of the collagen matrix is observed at microscopic scale by imaging local rearrangement of individual fibers. Microscopic swelling and macroscopic stress development exhibit the same exponential time response, when exposing the leather samples to changing water vapor pressure. The equilibrium stress levels are reached about ten times faster than observed for comparable humidity changes at ambient conditions. This acceleration is attributed to a reduced diffusion layer above the collagen surface at low pressures (≈10 Torr ).