Conversion of cellulose Iα to Iβ via a high temperature intermediate (I-HT) and other cellulose phase transformations

The observation that the hydrothermal conversion of cellulose I alpha to cellulose I beta is irreversible has been assumed to be due to the relative free energy of these polymorph phases. We propose an alternative explanation: when cooling the high temperature phase, the barrier to forming I beta is much smaller than the barrier to forming I alpha, so kinetics favor the formation of I beta. This explanation is consistent with all available experimental data, and is consistent with the general observation of polymer solid-solid phase transformations via metastable intermediate states. While cellulose I beta may be lower in free energy than I alpha, this has not been shown experimentally. Phase transformations of other cellulose polymorphs may be subject to similar kinetic effects when converted via metastable intermediate states.