Microgel Formation in the Curing Process of Epoxy Polymers

3 Microgel Formation in the Curing Process of Epoxy Polymers 

The first theory of gel formation of crosslinked polymers, elaborated by Carothers and Flory, considered the gel formation point as formation of an infinite network of chemical nodes [19]. Since this theory does not always agree with experimental data then the gel formation period concept was proposed. According to the indicated concept two gel formation points exist. The first corresponds to an appearance moment in a reactive medium of crosslinked clusters (microgels), characterised by non-fusibility 

In Table 3.5 the experimental values of gel formation time for the first gel formation 

If we suppose that time tf corresponds to the percolation threshold of spherical microgels, closely filling reactive space, then x = 0.19 and /= 0.79. Such a value of / actually corresponds to close packing of spheres of approximately equal diameter [65]. From this it follows that the first gel formation point is characterised by the stopping of growth of the microgels, closely filling the reactive space at their contact. 

From Relationship 3.7 at the condition = const, and = const, it can be written [62]  

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