Furfural and ageing: how are they related

Cellulose degradation is a complex process which is accelerated by the combined effect of temperature, water and oxygen, all of them available to the cellulose in the environment of the transformer. Several mechanisms for the thermal degradation of cellulose have been proposed, depending on whether the predominant step is pyrolysis or hydrolysis of the glucose units. In the first case, pyrolysis of glucose, the reaction proceeds via levoglucosan (1,6-anhydro-P-D-glucopyranose) a dehydrated sugar which, after a series of bond rearrangements and further losses of water and formaldehyde (or hydrogen plus carbon monoxide) yield furfuraldehyde among other products. The hydrolysis of glucose units proceeds through the formation of an epoxide or an enol followed by internal rearrangements and further dehydration and elimination of formaldehyde to yield furfuraldehyde and other products. The connection between the deterioration in the material properties and the formation of ageing products is the degree of polymerisation, the number of anhydroglucose units in the cellulose chain. The degree of polymerisation proves to be the most informative parameter for assessing the ageing or the progress of ageing of cellulose