Amorphous hydrocellulose

Experimental Approach. The experimental study was a comparison of the alkaline degradations of fibrous and amorphous hydrocelluloses in oxygen-free 1.0 NaOH, at 60 and 80 C. The fibrous hydrocellulose was predominantly crystalline (cellulose I) and therefore served as a substrate which would undergo alkaline reactions with significant physical structure effects. In contrast, the amorphous hydrocellulose was noncrystalline (9,10). Thus, it was a substrate which would experience substantially less structural constraint during its alkaline reactions. 

The accessibility of the amorphous hydrocellulose, however, did decline, both upon exposure to the alkaline media and during the reaction periods (Figure 1). This Indicates both recrystallization and selective removal of amorphous material. 

Figure 1. Hydroxyl accessibility of the amorphous hydrocellulose during degradation in l.OM NaOH.

The increase in cellulose II character and decrease in accessibility of the amorphous hydrocellulose upon exposure to the alkaline medium and during the reaction interval definitely indicate partial recrystallization. However, selective removal of amorphous cellulose may have occurred simultaneously. This additional possibility is consistent with the alkaline reaction data. 

In both the 60 and 80 C reactions, the fibrous hydrocellulose exhibited higher kpg values than the amorphous hydrocellulose (Table V). This appears to be due to the involvement of more molecules in crystalline domains of the fibrous substrate. The greater inhibition of chemical stopping by cellulose I than cellulose II domains may also have contributed to this effect by allowing more molecules in the fibrous hydrocellulose to peel to a point where the reducing endgroup would be inaccessible. 

Except for the later period of the 80°C reactions, the fibrous hydrocellulose exhibited a higher value of kpg (Table V) than k(-g (Table IV). Consequently the degradation of a majority of the molecules in the fibrous hydrocellulose was terminated by physical rather than chemical stopping processes. In contrast, chemical stopping was the dominant mechanism of stabilization in the amorphous hydrocellulose. 

Rate coefficients for random chain cleavage in the 60 C amorphous hydrocellulose reaction decreased gradually from 8 to 168... 

The rate of chemical stopping increases with temperature relative to peeling in both fibrous and amorphous hydrocellulose. This observation is consistent with previous findings ( )>... 

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