Characterizing the decay of ancient Chinese silk fabrics by microbeam synchrotron radiation diffraction

Scanning synchrotron radiation microdiffraction with an approximately 1 x 1 microm(2) beam has been used as a novel method for characterizing the decay of several T'ang dynasty (618-907 AD) silk fabrics. The crystalline fraction could be visualized based on beta-sheet 210 reflection intensities, extracted by recursive peak fits from several thousand diffraction patterns recorded during mesh scans. The azimuthal width of the 210 reflection, which is related to the orientation distribution of the crystalline domains within nanofibrils and the macroscopic orientation of the fibers traversed by the beam, was found to be sensitive to the overall state of decay of the fabric. The fine structure of the histogram of azimuthal width was related to the fiber hierarchical microstructure and the fabric morphology. SAXS/WAXS analysis supports the assumption of an initial loss of the random chain network with decay. At a subsequent state of aging, decay proceeds into the nanofibrils and the silk fibers break up into even smaller fractions.