The Physical Ageing of Epoxy Polymers

It is known that the properties of polymers can be changed essentially because of their physical (heat) ageing. This process is considered as a transition to a thermodynamically more equilibrium state [89] and different parameters were used 

Let us note the following in respect to description of the physical ageing process within the frameworks of fractal analysis. The study of the dynamics of reactions in disordered systems showed [96] that allowance for both types of disorder was necessary. The majority of the subordination takes place over large durations for the reactions, expressed by the common relationship [96]  

In respect to the physical ageing process the change of structure with time can be described, proceeding from the common Relationship 6.35, as follows [97]  

As has been shown in Chapter 5, for polymers the quasi-equilibrium state exists which the polymer structure tries to attain with growth of its thermodynamic equilibrium degree, characterised by an approximate condition d = 2.5. This condition corresponds to a fully relaxed polymer with a narrow distribution of sizes of free volume microvoids [100] and, hence, to the least temporal disorder, characterised by the spectrum width relaxation times (see Section 5.5). Therefore the following approximation will be used further [97]  

For characterisation of structure in the quasi-equilibrium state the approximate condition d = 2.5 was accepted above (see Equations 6.37 and 6.38). The authors of papers [101-103] carried out a more precise definition of conditions at which the quasi-equilibrium state was reached and they compared estimations of the different modes of those conditions. 

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