Thermal decomposition chemistry of starch studied by 13C high-resolution solid-state NMR spectroscopy

The chemical structure and thermal reaction pathway of four native and modified starch samples after being heated up to 600 degreesC have been examined by C-13 high-resolution solid-state NMR spectroscopy. Chemical reactions for the samples started around 300 degreesC to generate ether and ethylene segments via thermal condensation and dehydration mechanisms. Heating at increased temperatures generated substituted phenol/benzene and furan structures with methylene or ether linkages between these aromatic rings. Varied thermal reactivity was observed for starch samples around 300 degreesC due to their difference in molecular weight, pH or structural modification. However, the reaction pathway was similar. Above 400 degreesC, the starch structure was destroyed and the product appeared structurally similar to thermally crosslinked/decomposed phenolic/furfuryl alcohol resins, thereafter, the thermal reaction of the systems followed a similar pathway as these resins. No significant difference of chemical structures was obtained for the four samples after heating above 350 degreesC and identical carbon structures were generated at 600 degreesC. (C) 2002 Published by Elsevier Science Ltd.