Other Cellulose Solvent Systems
In each and every instance of dissolution of cellulose ... thermodynamic factors can be delineated and shown to have a significant and controlling effect on the success of the dissolution process. In each case the solvent system swells the cellulose and then modifies the molecule either by derivatizing, proton weakening or removal, or by complexing, to give a new intermediate specie that can more readily react with the liquid solvent system.
Thus, all cellulose solvent systems can be categorized under 4 mechanisms:
a) Cellulose as an acid
b) Cellulose as a base
c) Cellulose unstable derivative
d) Cellulose stable derivatives
This chapter will review selected solvent systems involving areas a, b, and c. Stable derivatives (d) will not be discussed. All compounds can be considered to be acids or bases relative to some other stronger specie. For example;
(A) is an Acid relative to Base (B)
HCl, H2SO4 Carboxylic Acids
Phosphoric Acetic, Cellulose
Phenol NaOH, Sodium Carbonate
Alcohol NaOH, sodium Metal
Cellulose NMMO, N2N4
Li(+)/DMAc Cellulose
Cellulose-OH Unsolvated anhydrous Cl(-)
Hydrocarbons,(isobutane) NaNH2
It may seem odd to realize that cellulose can act either as an acid or a base, yet this is exactly the case; especially in anhydrous or limited aqueous systems .
Water is an excellent swelling liquid for cellulose and opens millions of internal pores in the cellulose microfibrillar structure . However, H2O is itself both an acid or a base depending on the other molecular specie. Therefore, water normally reacts more rapidly than the cellulose with incoming molecules and this totally disrupts the effectiveness of the incoming potential dissolving moiety.
See Also "Solvent Spun Rayon" and "Regenerated Cellulose Fibres"
See Also "Solvent Spun Rayon" and "Regenerated Cellulose Fibres"
No comments:
Post a Comment