EFFECTS OF PHYSICAL STRUCTURE ON THE ALKALINE DEGRADATION OF HYDROCELLULOSE (REGENERATED CELLULOSE, ENDGROUP ANALYSIS)

Fibrous cotton hydrocellulose (predominantly cellulose I) and amorphous hydrocellulose (non-crystalline) were degraded in 1.0M NaOH at 60 and 80(DEGREES)C. Degradative and stabilizing reactions were characterized by monitoring yield loss and endgroup composition. Changes in physical structure were evaluated from hydroxyl accessibility, x-ray diffractograms, and Raman and solid-state ('13)C-NMR spectra.;Peeling was drastically inhibited by the cellulose I domains of the fibrous hydrocellulose and the cellulose II domains that formed in the amorphous hydrocellulose. Thus, crystalline domains physically impede the peeling reaction, even if the reducing endgroup is accessible to the alkaline medium. In contrast, chemical stopping was significantly more inhibited by cellulose I than by cellulose II. Therefore, the reactivity of a reducing endgroup toward chemical stopping is dictated by both the degree and type of structural order. The rate of chemical stopping relative to peeling increased with increasing temperature, consistent with chemical stopping having a higher activation energy than peeling.;"Physical stopping" of the peeling reaction occurred when the reducing endgroups became inaccessible to the alkaline medium. Due to the larger fraction of molecules extending into crystalline domains, the fibrous hydrocellulose contained more potential physical stopping sites and exhibited more rapid and extensive physical stopping. Consequently, the dominant stabilization mechanisms for the fibrous and amorphous hydrocelluloses were physical and chemical stopping, respectively.;During degradation, the physical structure of the fibrous hydrocellulose was not significantly altered, while the amorphous hydrocellulose underwent partial recrystallization (cellulose II) and preferential loss of amorphous material. Initially, endwise depolymerization (peeling) and formation of stable acidic endgroups (chemical stopping) occurred more rapidly in the amorphous hydrocellulose. In addition, random chain cleavage occurred only in the amorphous hydrocellulose. These findings indicate that the reducing endgroups and glycosidic linkages of amorphous cellulose are more reactive than those of the fibrous cellulose. Therefore, it is postulated that the fibrous hydrocellulose contains slightly distorted cellulose I domains rather than amorphous regions. Preferential removal of a limited quantity of material from such distorted regions would not significantly increase the crystalline fraction, because the material removed would exhibit some cellulose I characteristics.