Tuesday, June 28, 2011

SWELLING OF CELLULOSE

        In naturally occurring cellulose which may be typified by cotton cellulose the chains in the Michelle are packed closely together . Very small molecules such as water are small enough to penetrate between the chains and a process akin to capillary pressure tends to cause the chains of cellulose when immersed in water to be forced apart be penetration of water. This process can be greatly accelerated and magnified by steeping the fibers in solutions which have the effect of destroying of decreasing the partial valencies which cause the chains to adhere together .

Once the cellulose has been swollen by such solution on teneral in never returns to the former compact state and the swelling is permanent . In theory the only difference between swollen cellulose and ordinary cellulose should be in the increased spatial separation of the chains with consequent decrease in orientation and greater exposure of the O H groups to chemical action I practice there is also usually a certain amount of degradation due to a proportion of the chains becoming bro men resulting in a lowering of the mean chain length.

Swollen cellulose behaves much the same as ordinary cellulose but chemical reactions such as hydrolysis oxidation and electrification proceed faster and physical reactions such as moisture absorption (regain) dyeing staining with reagents and absorption of inorganic salts proceed father

Examples of swollen cellulose are vegetable parchment from concentrated sulfuric acid swelling followed by washing with water pandemonium rayon from solution in copper ammonium hydroxide followed by precipitation with water mercerized cotton from swelling with caustic soda followed by washing with water acetate rayon from electrification with acetic acid followed by solution in a solvent and re precipitation of the ester.

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