Effects of post-curing on the thermo-mechanical behavior and the chemical structure of highly filled phenolic molding compounds

Abstract

AbstractDue to their excellent thermomechanical properties, as well as their good media resistance, phenolic molding compounds are outstanding materials for high temperature applications, such as components for the engine compartment. An additional post-curing process, after injection molding, shifts the glass transition temperature towards high temperatures up to 300 °C. The objective of this work is to analyze the influence of the post-curing process on the chemical structure of the material. This structure is responsible for the mechanical and thermal properties of the material. Therefore tensile test bars were molded with a highly filled phenolic molding compound and different post-curing cycles under different atmospheres were done. The tensile properties and the glass transition temperatures (TMA) were measured. To get detailed information of the chemical structure ATR-FTIR and NMR analyses were done. The mechanical properties decreased up to 25 % with higher post-curing temperature (under air atmosphere) although the glass transition temperatures (TMA) and the grades of curing (NMR) increased. Furthermore, in the ATR-FTIR measurements, oxidation products were detected on the surface of the sample which were post-cured under air atmosphere. In comparison, no oxidation products could be detected on the samples post-cured under nitrogen atmosphere and the mechanical properties just decreased about 4 %. Oxidation processes could be provided by post-curing under nitrogen atmosphere which led to higher mechanical properties, in connection with a high grade of cure and a higher glass transition temperature in comparison with post-curing under air atmosphere.