An investigation of the surface and bulk nitration of cellulose
Modern analytical techniques have been employed to investigate the nitration reaction of cellulose. The nitronium ion, NO(_2)(^+), is shown to be the important nitrating species of cellulose in the nitrating media employed. In mixes of high nitronium ion concentration, nitration at the cellulose surface is observed, by ESCA, to be extremely rapid, while in mixes of low nitronium ion concentration it is observed to be comparatively slow. It is shown that the degree of substitution (DOS) achieved at the fibre surface is equilibrium controlled. However, it is also shown that cellulose morphology plays an important role in determining the final bulk DOS achieved by nitration. The surface and bulk nitration of cellulose in dichloromethane/nitric acid mixes has been investigated by a variety of techniques. (^13)C solution state nmr has been employed to monitor the partial DOS established at the individual sites of the anhydroglucose residues. The substitution distribution patterns observed for materials in the DOS range 1.8 → 2.4 are very dependent on the nitrating media employed. Further, the differences in the substitution distribution pattern are reflected in the d(l0l) mean interchain spacing. A possible explanation for these differences is forwarded. The plasma etching of cellulose nitrate has been investigated as a function of DOS. The influence of sulphate ester residues on etch rate is also considered.