Synthesis And Characterization Of Novel Nitrogen-containing/Phosphorus-nitrogen Flame Retardant Epoxy Resins

In this article, developing trends of epoxy resin, history of flame retardant technology and the necessity of flame retardant of epoxy resin were summarized. Recent progress on the flame retardant method of epoxy resin was reviewed in details. Then, a research subject on the synthesis of novel nitrogen-containing epoxy resin and nitrogen-phosphorus intumescent epoxy resin were put forward to overcome or improve the problems that existed.1. Two novel nitrogen-containing epoxy resins (DGEAZ1 and DGEAZ2), with improved fire performance, were obtained through the condensation reaction of the azomethines (AZ1 and AZ2) and epichlorohydrin in NaOH solution, respectively. Their structures were characterized with Fourier transform infrared spectroscopy (FT-IR) , nuclear magnetic resonance spectroscopy (NMR), mass spectrum (MS), element analysis (EA) and gel permeation chromatography (GPC). The curing reaction characters, thermal properties and flame retardance of them were examined by differential scanning calorimetry (DSC), thermaogravimetric analysis (TG) and UL 94V test.DSC studies showed that the reactivity of normal curing agent with DGEAZ1 was as follows: DDM>PN≈DICY>DDS, and the apparent reaction activation energy of them calculated from Kissinger's and Ozawa's models were 37.68 KJ/mol and 42.26 KJ/mol, which were close to those of the more widely used epoxy resin DGEBA(CYD-128). DGEAZ1/DDS and DGEAZ2/DDS had lower thermal degradation velocity, and higher char yield of 43.55% and 23.34% at 800℃, when compared with DGEBA/DDS. The UL 94V test showed excellent flame retardance of them, with classification of UL 94V-0.2. A novel nitrogen-phosphorus intumescent flame retardant epoxy resin PNE was synthesized and optimized basically, and characterized with FT-IR, NMR, MS. The thermal degradation properties and flame retardance was studied by DSC, TG and UL 94V.Compared with BPA/DDS and TBBA/DDS, PNE/DDS had a typically multistep thermal degradation process, with initial degradation temperature reduced greatly and third-step degradation temperature improved extremely and a relatively lower thermal degradation velocity and a high char yield of 29.98% at 700℃. The samples foamed and expanded during combustion process, and formed char on the materials surface rapidly and then extinguished, without melting and dropping and smoking. Thus the PNE epoxy resin had an excellent flame retardant up to UL 94V-0.3. Through the comparison with different epoxy resins in the same system (DGEAZ1/DDS and DGEAZ2/DDS) or different epoxy resins in the different system (DGEAZ/DDS and PNE/DDS), we know the char yield and flame retardant increased with the increasing of flame retardant element's content, and PNE/DDS system can reach to a more better flame retardant grade with relatively lower char yield because of the existence of nitrogen-phosphorus synergistic effect.