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TAPPI T 235 Alkali Solubility

Standard:

TAPPI

Method:

TAPPI T 235

Title:

Alkali solubility of pulp at 25°C

Scope

The TAPPI T 235 Alkali solubility method for determination of alkali solubility can be applied to bleached and delignified pulps only. Lignin interferes with the extraction and determination of carbohydrates, and the method cannot be applied to unbleached pulps.

Summary

Pulp is extracted with a sodium hydroxide solution of 10%, 18%, or 21.5% at 25°C for 1 h. The dissolved carbohydrates are determined by oxidation with potassium dichromate.

Significance

Low molecular weight carbohydrates (hemicellulose and degraded cellulose) can be extracted from pulps with sodium hydroxide solutions. Solubility of a pulp in alkali thus provides information on the degradation of cellulose and on a loss or retention of hemicellulose during pulping and bleaching processes.

In general, a 10% sodium hydroxide solution possesses maximum dissolving power and dissolves both degraded cellulose and hemicellulose. Resistance of pulps to 21.5% sodium hydroxide solution has been related to the rayon yield of dissolving pulps.

 

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