PYROLYSIS MECHANISMS OF O-(2-HYDROXYETHYL)CELLULOSES

Primary pyrolysis mechanisms for native cellulose are more universally applicable, which is illustrated by the analyses of the characteristic pyrolysis product distributions of O-(2-hydroxyethyl)celluloses (HECs) measured by in-source pyrolysis-ammonia chemical ionisation mass spectrometry (Py-CIMS). The extent of the thermal degradation via transglycosidation, reverse aldolisation and E(i)-elimination mechanisms in these cellulose derivatives is strongly influenced by the presence of substituents and by their substitution positions. The transglycosidation mechanism, which is the main thermal degradation pathway of cellulose, is blocked if the 6-O-positions in the cellulose backbone are substituted. The formation of a series of polyethylene glycolaldehydes and polyethylene glycols is explained by the reverse aldolisation and E(i)-elimination mechanisms, respectively. The pyrolysis products of HECs have been identified by the determination of the number of hydroxyl groups in the mass peaks, which was done by the comparison of NH3 and ND3 Py-CI mass spectra. The correlation between the pyrolysis product distribution and substituents in HECs is illustrated by a multivariate analysis of the Py-CI mass spectra of 11 HECs, revealing structural information concerning the cellulose character and the average chain length of the substituents in the samples.