Simultaneous multi-frequency dielectric analysis of the polymerization process of anionic polyamide 6

The demand for sustainable material concepts is increasing more and more. One possible concept is the use of thermoplastic fiber reinforced composite components. The processing of anionic polyamide 6 offers both advantages in the processing of low-viscosity melts and improved material properties due to a very high degree of crystallization and simultaneously very long molecular chains. The processing of this anionic polyamide 6 (aPA6) in thermoplastic resin transfer molding (T-RTM) is already state of the art. Due to the extremely high sensitivity to moisture the material is only processed under inert gas atmospheres. Because moisture decreases the reactivity of the chemicals involved in the curing process there is demand for a measuring method to determine the state of cure during the production process. A well-known method is the measurement of the temperature curve during anionic polymerization. Due to the exothermic characteristics of the reaction this method allows a statement about the conversion. However, this method is only used on a laboratory scale. An integration of this method into the T-RTM process has not been successful so far. Dielectric Analysis (DEA) provides the means to perform online measurements inside the melt to determine the state of the material. By the use of a newly developed advanced measurement system it is possible to acquire measurement results of multiple excited frequencies simultaneously. This provides unprecedented depth of information compared to state of the art DEA analysis. In this paper the proposed technology was applied to a generic processing method and the results compared to conventional temperature measurements. The results and findings of these trials are discussed in detail and a new method for analyzing the curing process is proposed. After successful testing the dielectric measurement system was also used in a real-world production environment to show the capabilities of the new measurement system.