The storage (chemical) aging of a thermoset polymer directly affects its viscosity and consequently its electrical resistance as has been experimentally shown. For liquid resins, the OptiMold system in combination with permanent sensors can be installed in a pressure pot to monitor the aging of the resin within a safety margin. Tests that were contacted by NTUA (figure 1) the storage age of a resin batch is directly related to its resistivity, so depending on the electrical resistance of a batch it is possible to decide if the batch is fresh enough, if the addition of fresh resin is necessary or the batch is too aged for use.

Figure 1. Correlation of electrical resistance with the storage age of a monocomponent resin: resin batches of same storage age correspond to the same zone of electrical resistance.

Accordingly, the storage (chemical) aging of prepregs can be also identified if a small piece of prepreg is placed on a special press for measuring its electrical resistance.

In the same way, the aging of a mixed resin in a resin bath e.g. in pultrusion or filament winding can be monitored using Optimold in combination with a pot sensor and discarded if higher resistivity is measured.