Homogeneity or Inhomogeneity of Cured Epoxies

In an earlier analysis, it was shown that the main argument for the existence of inhomogeneous crosslinking — the appearance of nodular structure particularly when etched fracture surfaces are examined — is not at all characteristic of cured epoxies. Similar nodular structures could also be seen in other amorphous polymers. 

It is to be noted that commercial non-purifted resins were used in these studies. Another light scattering study concerned the changes occuring during the curing 

The possible inhomogeneous course of network formation should be reflected first of all in the reaction kinetics itself or, what is more relevant here, in the distribution of groups in various reaction states at conversions higher than zero. Specifically, for a 

Another proof against inhomogeneous cure in simple epoxy-amine and other systems has been supplied by gel point measurements. The critical conversion at the gel point (cf. Sect. 4) is a sensitive function of any inhomogeneity. For epoxy-amine systems, the gel point conversion has been found to agree well with the prediction of the theory assuming uniform distribution of reactive groups throughout the volume The deviation does not exceed 1 %. In contrast, for free-radical 

Therefore, it is worthwhile to examine the homogeneity of any new epoxy system using physical methods and methods of chemical kinetics. 

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