Evaluating Models That Predict Epoxy Conversion Using Rheological Properties

Simultaneous rheology and conversion measurements of neat and composite epoxy resins reveal that conventional models neither accurately nor fully describe the relationship between rheology and conversion. We find that models predicting thermoset conversion based on mixing rules of rheological properties are quantitatively inaccurate and do not account for chemical gelation. Models based on percolation theory and the divergence of the viscosity at the gel point are more accurate but valid only before the gel point. Here, we propose the use of the generalized effective medium (GEM) model, which incorporates the divergence of the rheological properties on both sides of the critical gel point. We show that the GEM model works well for both neat resins and filled systems, and the resulting parameters estimate the gel point and scaling behavior on either side of the sol-gel transition.