Degradation cellulose ether

Both the sulfite and alkaline (kraft) methods can be modified to produce high purity chemical ceUulose. These pulps, usuaUy in the form of "dissolving pulps," are not only mosdy free of lignin and hemiceUulose, but the molecular weight of the ceUulose is degraded. This increases solubUity in alkah and provides desired viscosity levels in solution. These dissolving pulps are used to make derivatives such as sodium ceUulose xanthate [9051 -13-2] via alkah ceUulose, and various esters and ethers (see Cellulose esters Cellulose ethers). 

Wirick MG. Study of the enzymic degradation of CMC and other cellulose ethers. / Polym Sci 1968 6(Part A-1) 1965-1974. Anonymous. Final report on the safety assessment of hydroxy-ethylcellulose, hydroxypropylcellulose, methylcellulose, hydroxypropyl methylcellulose and cellulose gum. / Am Coll Toxicol 1986 5(3) 1-60. 

In this study, non-isothermal thermogravimetric analysis was quite helpful in following thermal degradation of cellulose ethers and esters and also for understanding how the metal chelation affected the thermal stability of cellulose ethers and cellulose ester [14,17]. 

Complexation of cellulose ether with some transition metals does not behave in the same manner as that observed for parent cellulose ether (i.e., the number of degradation stages was increased and order of degradation were varied). This is due to the elimination of coordinated water and decomposition of cellulose ether-metal coordination bonds. 

However, the preparation of cellulose ethers is difScult in LiCl/DMAC as bases such as NaOH or KOH are insoluble in the solvent. Some success has been achieved using a 3 to 5 molar excess of reagent and powdered NaOH or KOH is slurried in the reaction mixture at 6C - 80X for 48-72 hours. As a result of the high temperatures and strong base treatment, there is considerable degradation of the cellulose. Despite these problems unique products can be prepared under homogeneous conditions. For example tiimethyl silylcellulose (D.S. ca 2) is readily prepared in LiCl/DMAC (32). 

Cellulose and its derivatives are sensitive to solar radiation and degrade rapidly under weathering conditions. Cellulose itself is among the least weather resistant substances. Cellulose ethers are less resistant than cellulose esters [32]. 

Pectin, amylose, dextran and inulin provide coatings that degrade by enzymes of colonic flora. These polysaccharides are commonly combined with cellulose ethers or esters or synthetic polymers to obtain biphasic release profiles or colon-specific release [29-31]. Drugs conjugated to dextran (linear polymer backbone of a-D-glucopyranose units) show enhanced stability in the upper part of the gastrointestinal tract, but they can be absorbed in the colon [32]. 

Cellulose is readily hydrolyzed in water at >170° at a rate that depends on the hydrogen-ion concentration, even in the range between pH 5 and 8. Because acids from the degradation of D-glucose are produced when cellulose is exposed to high temperature, the pH of the aqueous mixture drops in the absence of buffers. Earlier work had indicated that ether-soluble products could be obtained by heating cellulose in... 

---