Influence of the Fiber Structure on the Nitration of Native Cellulose

Abstract

The nitration of native cotton cellulose has been investigated under both rate- and equilibrium-controlled conditions and in a manner that caused the least possible changes in the original fine structure of the fiber. By successive extractions the nitrates were subdivided into a number of fractions, which were examined for chemical composition and molecular weight, the fractionation being continued until swelling became noticeable. The results indicated that the specimens studied were chemically nonuniform and more so the lower the average degree of substitution. Products formed in an equi librium-controlled reaction or regenerated from solution were more homogeneous than similar ones obtained under rate-controlled conditions or with the original fiber structure left intact. The nitration involved an initial, rapid but only partial conversion of the surface and outer regions of the microfibrils of the cellulose, followed by a slower but more complete esterification of the interior, more crystalline portions, the easily ac cessible, short-chain parts being less substituted than the remainder of the material. In this respect nitrates were accordingly found to be different from most other cellulose derivatives.