| Abstrakt: |
The changes in length with time of 66 nylon yarns in water and in aqueous phenol solution have been examied, using conditioned relaxed samples and samples which previously have been treated with the swelling medium, washed and reconditioned. Yams of different filament deniers and of different degrees of longitudinal molecular orientation have been used. On immersion, there is an inhibition period during which the unpenetrated core holds the yarn at its original length. Transverse swelling of the outer layers occurs as the agent penetrates the filaments. The stresses set up by the restriction of longitudinal movement by the core cause transverse molecular orientation in these swollen outer layers. Then, when the inhibition period is long, the polymer chains approach more nearly to equilibrium in these transversely oriented positions, before the length of the yarn begins to alter. Therefore, a long inhibition period causes the ensuing change in length to be slow and small. Consequently, as the inhibition period is directly related to filament denier, the rate and the magnitude of the change in length are inverse functions of filament denier. Wetting the yarn before immersion in aqueous phenol solution increases the rate of penetration of the filaments and so virtually removes the inhibition period and increases the change in length at equilibrium. The processes which occur may be interpreted in terms of the rupture of interchain bonds up to a certain energy level. This mechanism gives a ‘mat’ of unpenetrated regions interlinked with penetrated regions and molecules of swelling agent. The polymer chains in the penetrated regions are more mobile than before penetration, because of the rupture of interchain links, and so they move readily into positions of minimum potential energy. After moving, these chains form new stronger interchain bonds from some of those broken by the swelling medium to give a ‘set’ structure. All these processes, together with the stresses present during and after the changes in length, control the characteristics of the changes in length. [ABSTRACT FROM AUTHOR] |
