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Ray Rogers FAQ

8. Rate of Cellulose Decomposition vs Impurities Found on the Shroud

J. L. Banyasz, S. Li, J. Lyons-Hart, and K. H. Shafer [Fuel 80 (2001) 1757-1763] studied real-time evolution of formaldehyde, hydroxyacetaldehyde, CO, and CO2 from pure microcrystalline cellulose by EGA/FTIR (effluent gas analysis and Fourier transform infrared spectrometry). They detected 10 compounds simultaneously in the gas phase by FTIR. The cellulose decomposition is very complex. The quantity of formaldehyde produced is a function of heating rate, so decomposition mechanisms change depending on how fast you heat the cellulose. That is important in considering image-formation mechanisms and long-term stability vis-à-vis scorching processes.

According to A. G. W. Bradbury, Y. Sakai, and F. Shafizadch, [J. Appl. Polym. Sci. (1979) 23, pp. 3271-3280], the induction process in cellulose can be neglected above 300ºC. They observed two major decomposition mechanisms with the following constants:

E1 = 47.3 kcal/mole                   Z1 = 3.2 X 1014 s-1

E2 = 36.6 kcal/mole                   Z2 = 1.3 X 1010 s-1

They assumed that 65% of the products in the char-forming chain of reactions went to gas.

Glucose decomposes by a multi-step process. As with all of the other saccharides, the first is a dehydration/condensation reaction. The condensation processes yield carbon-carbon double bonds, which ultimately lead to color formation. Bruce Waymack of Philip Morris measured the kinetics of the first reaction as E = 23.9 kcal/mole and Z = 1.26 X 107 s-1. The low-molecular-weight polysaccharides are much less stable than cellulose.

I measured the kinetics of vanillin elimination from lignin as E = 23.6 kcal/mol and Z = 3.7 X 1011 s-1. It is much less stable than crystalline cellulose.

Results of kinetics studies support a low­temperature image-formation process. The temperature was not high enough to change cellulose within the time available for image formation, and no char was produced




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