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 °C have been examined by 13C high-resolution solid-state NMR spectroscopy. Chemical reactions for the samples started around 300 °C 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 °C due to their difference in molecular weight, pH or structural modification. However, the reaction pathway was similar. Above 400 °C, the starch structure was destroyed and the product appeared structurally similar to thermally cross-linked/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 °C and identical carbon structures were generated at 600 °C.