The Mechanism of Setting and the Release of Set in Water

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Abstract
The rates of release of wool yarns set under a variety of conditions have been measured. There is a rapid initial loss of set followed by a slower loss that is linear with the logarithm of time of release. Partial destruction of free thiol groups in the set yarns decreases the extent of the rapid phase, but has no effect on the rate of the slow phase. These effects are similar to those produced by prolonged setting. If free thiol groups are completely destroyed or if the set yarns are released in Acid. even the rate of the slow phase is decreased. In order to, explain these and other results, we have postulated that two different types of contractile structures arise during setting. These are disorganized (but extended) regions, and β-crystallites. Contraction of the former causes loss of set in the rapid phase, whereas collapse of β-crystallites is responsible for the slow logarithmic loss of set. The rapid phase may be divided into two stages, only one of which requires thiol/disulfide interchange. The slow phase also requires thiol disultide interchange, but in this case does not normally limit the rate of release.