The kinetics of stress aging are markedly increased by H2O additions to nylon. This increase in rate is taken as evidence that the aging process takes place in amorphous regions of the polymer. The breakup of the stress‐aged structure is also greatly accelerated by H2O. The activation enthalpy ΔH* and shear activation volume V* for breakup are constant up to ∼0.7 wt% H2O, and then decrease to about one‐half their dry values at ∼2.0 wt% H2O. These changes in the activation parameters are consistent with the activated step in breakup being the synchronous shear of stress‐induced microcrystals, the size of microcrystals which nucleate during stress aging being limited by the average spacing between H2O molecules in the amorphous regions.

Topics
Polymers
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Some time was saved here by extrapolating linear log10td‐vs‐log10ta plots, determined for aging times between 10 min and 24 h under the more nearly dry conditions, to the longest aging times necessary for the comparison.
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The essence of this argument is that if the same delay time is measured under the same breakup conditions for two different samples, this indicates that the starting structures in the neck are the same. It would thus require aging ∼44 days at 0.3% H2O to duplicate the structure (obtain the same td⁠) produced by aging 1 day at 1.15% H2O and drying 2 days. If the sample is assumed to be close to 0.3% H2O during most of this drying time, aging 1 day at 1.15% H2O is equivalent to aging ∼42 days at 0.3% H2O. One can then show that ∼97% of the total delay time is due to wet aging and that only ∼3% developed during drying. This argument is even better at 1.8% H2O where it would take 190 years aging under dry conditions to duplicate the structure produced by 1 day wet aging and 6 days drying.
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The originalexpression in Ref. 4 for γ̇(∞), which is proportional to l̇, has been modified by assuming that the temperature and water dependence of the secondary (more amorphous) flow unit jump frequency f2 is proportional to Da.
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© 1971 The American Institute of Physics.
1971
The American Institute of Physics
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