2 SOLVENT-CELLULOSE COMPLEXES

IT HAS LONG BEEN KNOWN that organic solvents, under some conditions, can form non-stoichiometric complexes with cellulose. Mease,5 in 1933, first noted the phenomenon as an anomalous weight gain in analytical filter paper washed with ethanol. This weight gain, as high as 2.8%, was shown to cause significant errors in gravimetric analytical procedures. Other researchers have since demonstrated that virtually any organic solvent, under appropriate conditions, can be made to form complexes with cellulose.6,7,8 Moreover, many of these complexes have been shown to be stable for long periods of time at elevated temperatures or under a high vacuum.6,7,8

The highest levels of solvent retention reported in the literature have been achieved by pre-swelling the cellulose in water, or some other swelling agent, followed by a liquid exchange with an organic solvent.9,10,11 Complexes formed in this way not only retain significant amounts of solvent (as high as 10–20%), but also retain much of the swollen fiber structure of the original water-wet cellulose.8 Moreover, these cellulose complexes have been shown to be of a higher chemical reactivity in heterogeneous reactions such as hydrolysis and acetylation.8 Thus, W�chter's concern that cellulose-solvent complexes might be formed when papers are brought in contact with solvents during conservation treatment appears to be justified. If such complexes are formed and do not decompose, then one would indeed expect papers treated with organic solvents to be more reactive and to age more quickly.