THE I-ALPHA-]I-BETA TRANSFORMATION OF HIGHLY CRYSTALLINE CELLULOSE BY ANNEALING IN VARIOUS MEDIA

The I-alpha --> I-beta-conversion of cellulose was investigated by annealing Valonia and bacterial cellulose in a series of mediums ranging from helium gas to organic solvents of various polarities. The annealing treatment was followed by C-13 CP/MAS NMR and infrared spectroscopy together with electron diffraction analysis. These techniques revealed that when annealing conditions ranging from 260-degrees-C and 30 min to 280-degrees-C and 60 min were selected, around 80% of the I-alpha-phase could be converted into the I-beta, whereas a residual 20% remained unmodified. With polar solvents such as glycol, glycerol, etc., the transformation occurred at temperatures lower than with nonpolar mediums such as dibenzyl ether, heptane, helium, etc. Also, samples of lower crystallinity, e.g. bacterial cellulose, were converted more easily than specimens of high crystallinity such as Valonia.