Synthesis and application of halogen-free epoxy resin flame retardant curing agent

In this study, the intermediate of SPDPC flame retardant curing agent was successfully synthesized through the reaction between phosphorus oxychloride and pentaerythritol under the catalysis of 4-dimethylaminopyridine. Using 1,2-propylenediamine and the prepared SPDPC, a novel phosphorus and nitrogen flame retardant curing agent named poly1,2-propylenediamine pentaerythritol diphosphate (PDS) was successfully synthesized. The target product was subjected to characterization using infrared spectroscopy, mass spectrometry, hydrogen NMR spectroscopy and thermogravimetric analysis. The molecular structure of the product was determined and its decomposition temperature curve obtained, leading to the conclusion that it could be cured at high temperatures. DDS was selected as the curing agent for epoxy E-51, the specific curing conditions were obtained by DSC test. Subsequently, E-51, DDS and PDS were mixed for high temperature curing resulting in obtaining test spline of PDS-E-51 flame retardant composite material. Then, the flame retardancy and mechanical properties of the spline were tested. It was observed that pure EP cured by DDS had an LOI of only 19.5%, indicating its flammability. However, upon addition of PDS as a flame retardant, the LOI significantly increased with 20 parts resulting in an LOI of 29.7%. The addition of 25 parts results in an increase in limiting oxygen index to 30.3%, while the tensile strength and impact strength are measured at 38.27 MPa and 5.087 kJ/m2 respectively. The CCT test shows that the addition of PDS can significantly reduce the HHR and THR of the system. CCT digital photos show that the addition of PDS can make the combustion residue of the system expand obviously, showing a good expansion and flame retardant effect. TG-FTIR gas phase infrared absorption indicates that the addition of PDS can reduce the concentration of combustible gas in the combustion process. Test results indicate that the mechanical properties of PDS-E-51 flame retardant composites experience a certain degree of decline, but with increasing amounts of PDS curing agent added, their flame retardancy is significantly enhanced.