Guest Post by Dr. R. Bruce Prime Thermomechanical analysis or TMA is a simple yet very useful technique that can measure coefficient of thermal expansion, Tg and the dimensional change accompanying the relaxation of stress stored in a material. As shown in the illustration the dimensional change of a material with temperature (or time) is measured in a controlled atmosphere ... [Click to Continue...]

In our last post we described the technique called time-Temperature superposition.  Using t-T superposition, a “master curve” can be constructed that is useful in analyzing the curing of thermosets.  The requirement is to have either conversion or glass transition temperature (Tg) data as a function of time for several isothermal cure temperatures.  (Image on left courtesy of ... [Click to Continue...]

In our last post we discussed the concept of vitrification and the impact on the cure kinetics (dramatic slowing of the reaction rate in the glassy state).  When examining curing data such as the Tg versus cure time plots from the last post, it is often helpful to create a “master curve.”  Remember the Tg-time relationships had the same shape but appeared to be shifted along ... [Click to Continue...]

Vitrification, now that’s an interesting word to use in a thermoset polymer discussion.  The Merriam-Webster online dictionary defines vitrify as “to convert into glass or a glassy substance by heat and fusion.” In the case of thermosets, the definition is pretty close, since the glassy state can be obtained during cooling from the rubbery state and as we will see in this ... [Click to Continue...]

In the last two posts, Dr. Prime discussed gelation and the relationship of functional group conversion at the gel point.  Understanding the conversion at gelation has practical ramifications in many thermoset processes.  As noted in a previous post, in the case of five minute epoxy, five minutes is the gel time.  During thermoset processing, the ability to flow essentially ... [Click to Continue...]