Guest Post by Dr. R. Bruce Prime In the last post we introduced the concept of gelation. Since gelation is the practical endpoint during thermoset processing, it is important to understand how the chemistry and stoichiometric ratios impact the conversion at the gel point.   First to review, gelation is the point during cure where a viscous liquid becomes a ... [Click to Continue...]

Guest Post by Dr. R. Bruce Prime As a result of the chemical reactions discussed in earlier posts thermosets cross-link and become “set”. At a well-defined point in the cure reaction the thermoset transforms from a viscous liquid to a cross-linked gel or rubber, i.e. it gels. Gelation is the incipient formation of a cross-linked network, and it is the most distinguishing ... [Click to Continue...]

Guest Post by Dr. R. Bruce Prime A thermoset cures due to the chemical reactions discussed in earlier posts. The figure on the left shows how the chemical reaction (conversion of reactive groups) can be monitored over time.  Note the time scale on the plot!  A very patient scientist named Harvey Bair at Bell Labs made samples for a cure study and then left them on his desk ... [Click to Continue...]

Guest Post By Dr. R. Bruce Prime DSC can quantitatively measure the rate of cure, da/dt, from the exothermic heat flow, dH/dt, produced by the chemical cure reaction. As illustrated in the figure below, DHrxn is the total heat liberated from an uncured thermosetting system and can be measured in a DSC heating experiment. DH is expressed as heat per mole of reacting groups ... [Click to Continue...]

Guest Post by Dr. R. Bruce Prime. Differential scanning calorimetry or DSC is the most widely used analytical technique to characterize thermoset cure, due its ability to quickly and accurately measure the glass transition temperature Tg and conversion or degree of cure. Tg is the temperature where on heating the thermoset changes from a rigid glass to a liquid, or to a rubber ... [Click to Continue...]