Which tests should be done before starting production to make sure the internal mold release works well with the resin?

The first thing to check is the Gel Time, which measures how long it takes for the resin and mold release to gel. In pultrusion, it’s recommended to use a heated water batch to test the Gel Time and measure it with SPI gel time.

You can find detailed testing methods in ASTM D7029 or ISO 584.

Another important thing to test is viscosity, which can be done using a viscometer or similar equipment. Internal mold releases usually lower the resin’s viscosity, helping it soak into fibers and properly coat additives and fillers. Viscosity also affects pultrusion processing, influencing pull force, line speed, and surface finish.

The Glass Transition Temperature (Tg) of the cured resin is crucial for predicting the composite material’s mechanical properties. You can measure Tg with tests like differential scanning calorimetry (DSC). The impact on cure kinetics can also be evaluated using the same technique.