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 i ndividual fibers. Microscopic swelling and macroscopic stress development e xhibit the same exponential time response, when exposing the leather sample s to changing water vapor pressure. The equilibrium stress levels are reach ed 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 (approximate to 10 Torr). (C) 2001 American Institute of Physics.