32—The Influence of Heat and of Swelling Agents on 66 Nylon Yarns

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Abstract
The changes in length, at equilibrium, of drawn and undrawn 66 nylon yarns on heating and on immersion in swelling agents, have been investigated. Both treatments produce reversible and irreversible changes. On heating, the reversible change in length is caused by an increase in entropy; the length of drawn yarn decreases and the length of undrawn yarn increases. A swelling agent gives a reversible increase in length which is a reflection of the increase in volume caused by uptake of the agent. The irreversible changes in length are believed to be caused by the rupture of some interchain bonds followed by the relaxation of chain segments associated with these bonds; some of the broken interchain bonds then re-form to give a ‘set’ structure which is stable under the conditions of treatment. The mechanism of setting by heat is essentially the same as that of a swelling agent and the actions of the two treatments are supplementary. Increase in the severity of a treatment causes rupture of more interchain bonds and hence an increase in the irreversible change in length. The distribution of phenol between water and nylon has been investigated at different phenol concentrations, at different temperatures, and with yarns annealed under various conditions.

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