What tests are appropriate to ensure compatibility and good performance of the internal mold release, in advance of a production trial?
Gel Time is the first property one should test for to ensure compatibility of the internal mold release and resin mixture. In pultrusion, testing gel time using a heated water batch, to measure SPI gel time, is generally recommended.
Please reference ASTM D7029 or ISO 584 for test method details.
Viscosity is another attribute which can be tested using a viscometer or similar test equipment. Internal mold releases generally reduce the viscosity of the resin mixture, which aids in impregnation of fibers and proper wetting of additives and fillers. Viscosity is also an important consideration in pultrusion processing, which impacts pull force, line speed and surface finish.
Glass transition temperature (Tg) of the cured resin is an important predictor of mechanical properties of the composite material. Tg can be measured via an analytical test such as differential scanning calorimetry (DSC). Impact on cure kinetics can also be assessed using the same technique.