Hydrocellulose structures

By calculations based on differences in carbon dioxide evolution, it was found that about 3% of the intact linters structure was removed in. 07 hours of prior hydrolysis. Partial confirmation of these calculations was obtained experimentally when it was found that a mixture containing 97 % of. 07-hour hydrocellulose and 3.3 % of glucose simulated... 

In this book, he emphasized the importance of the microscopic and the submicroscopic structure of fibrous high polymers. The reactions of cellulose with water, aqueous alkalis, organic bases, ammonia, and strong salt solutions were all stressed. Special attention was given to various types of cellulose esters, to cellulose xanthate, and to the cellulose ethers. The oxidation of cellulose under a variety of conditions was described, as were the hydrolysis reactions. The latter included discussions on reversion and on the kinetics of acid hydrolysis. It is interesting to note that Heuser, who earlier had criticized the terms hydrocellulose and oxycellulose, and had... 

Table I. Estimated Structural Parameters for Hydrocellulose II and Valonia...

In the present study, the role of cellulose physical structure in alkaline reactions was investigated by comparing the alkaline degradation of highly crystalline (cellulose I) fibrous hydrocellulose with that of amorphous (noncrystalline) hydrocellulose. The amorphous substrate was taken as a cellulose model the reactivity of which would most closely approximate that of alkali-soluble cellulose. The availablity of such an approximation to the inherent reactivity of cellulose allowed evaluation of the effects of the more highly ordered structure of the fibrous 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. 

During the course of the alkaline degradations, both physical and chemical structures of the hydrocelluloses were monitored. Hydroxyl accessibility (13) was determined as a practical measure of the fraction of molecules accessible to the alkaline medium. The crystalline structure was characterized by x-ray diffraction (14). 

Alkaline Degradations - Change in Physical Structure. The hydroxyl accessibility of the fibrous hydrocellulose was initially 51.4 0.8%. In contrast, the amorphous substrate had an accessibility of 99.2 1.0%. Exposure of the fibrous hydrocellulose to the alkaline media caused the accessibility to decrease slightly to 50.7 1.0% and 49.1 1.2% at 60 and 80°C, respectively, but accessibility did not change significantly during the reaction periods (0-168 hr). 

The solid-state l C-NMR spectra of the fibrous hydrocellulose also demonstrate the predominance of the cellulose I allomorph (Figure 6). All three spectra contain the sharp resonances associated with the cellulose I conformation and the broader C-4 and C-6 resonances indicative of regions of three-dimensional disorder and crystallite surfaces (16,17). The relative intensities of the sharp and broad resonances of the three spectra are similar, again demonstrating the lack of change in physical structure during degradation. 

In all cases, kp decreased with reaction time. Thus, the accessible reducing endgroups in both hydrocelluloses were more reactive initially, apparently due to their location in less ordered regions of the respective physical structures. As the less ordered material was removed, the accessible reducing endgroups occupied increasingly ordered regions of the structures and were therefore less reactive. 

Celluloses can be converted to other useful products by reorientation of their fiber structure. Paper, parchment paper, vulcan fiber, mercerized cotton, and hydrocelluloses belong in this class. 

The structure of the cellulose has a marked influence on the subsequent decomposition [73-77] and less crystalline materials decompose more readily and in terms of thermal decomposition can be rated viscose cord rayon > viscose continuous filament > viscose rayon fiber > Fortisan fiber > Cotton > hydrocellulose. However, hydrocellulose does not follow this rule. 

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