19—The Oxidation of Cotton Yarn by Periodate Under Mechanical Conditions that Oppose Swelling

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Abstract
The effect of preventing a cotton yarn from shrinking during its oxidation by sodium metaperiodate has been investigated. It has been found that. owing to the great swelling produced in the cotton fibres during the later stages of periodate oxidation. a high tension develops in the yarn prevented from shrinking. and a yarn of much more compact structure is produced. The yarn oxidized ‘under tension’ is stronger than the yarn oxidized to a similar extent but free to shrink. The relation between yarn breaking load and degree of oxidation is of a complex form. and this is ascribed to the separate and opposing effects of chemical modification and changing yarn structure. The effect of changing yarn structure is greatly reduced by mercerizing the yarn under tension before oxidation. since this process itself produces sufficient change of structure to cause a considerable increase in the strength of the yarn. Another effect of preventing shrinkage during oxidation is to retard the reaction in its later stages. Some differences have been detected between the fine structures of the fibres composing the yarns oxidized without shrinking and those allowed to shrink during oxidation. X-ray photographs and measurements of hygroscopicity show that the cellulose in the former suffers less disorientation during periodate oxidation than that in the latter.

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