Preparation And Properties Of Epoxy Resin Modified By Phosphorus-nitrogen Derivatives Containing Hydroxy/aromatic Groups

Epoxy resin was a thermosetting resin which was widely used in electronic equipment,aerospace,adhesives and other industries due to its excellent chemical resistance and its mechanical,electrical,and adhesion properties.Unfortunately,epoxy resin was extremely flammable,which limited its application in the field requiring high fire resistance.Hence,it was necessary to develop flame retardant of epoxy resin.Flame retardants containing phosphorus-nitrogen were used to improve the fire resistance of EP because of their good flame retardant effect.In this paper,two kinds of flame retardants containing hydroxyl/aromatic ring phosphorus-nitrogen derivatives were synthesized and used to prepared flame retardant modification EP.The main contents were as follows:(1)To prepare modified epoxy resin with excellent flame retardant and mechanical properties,a novel containing aromatic ring phosphorus-nitrogen imidazole derivatives(PNB)was synthesized from diaminobenzene,imidazole phosphoryl chloride(NBZ)and phosphorus oxychloride(PPDC),and its chemical structure was confirmed by NMR and FT-IR.Then,PNB was added into the epoxy resin to prepare PNB flame retardant modified epoxy resin.The results showed that PNB can effectively reduce the flammability of epoxy resin.For example,when 10 wt%of PNB was added,the LOI value of PNB was 37.9%,and V-0 rating in the UL-94 test.In addition,curing kinetic equation of EP-10%PNB was (?)=6.3×10~5exp(?).Furthermore,the flexural,tensile and impact strength were increased by 34.5%,47.1%and 22.5%,respectively,which was because the PNB structure contains aromatic ring and amine group can enhance the interaction with epoxy resin.(2)By using PNB as flame retardant,DDM as curing agent and carbon fiber as reinforcement,carbon fiber/EP-PNB composites were prepared by hand lay-up molding and hot pressing.The LOI value of the composites increased from 29.6%to 34.2%,which was attributed to the fact that PNB can promote the formation of a complete and dense carbon layer.In addition,the impact and flexural strength of CF/EP-10%PNB were increased to 127.8 k J/m~2and 328.5 MPa,which was because the amine group in the PNB structure can react with both the epoxy group and the OH group on the carbon fiber to play group and the OH group on the carbon fiber to play a bridging role,thus enhancing the binding force between the carbon fiber and the epoxy resin.(3)In order to simultaneously improve the flame retardant,mechanical and transparent properties of EP.1,2-dihydroxyethylenediamine and DOPO were used as materials to synthesize containing hydroxyl and DOPO based phosphorus nitrogen flame retardant(DOPO-AEEA).The structure of DOPO-AEEA was characterized by NMR and FT-IR.The epoxy resin was prepared by using DDM as curing agent under the condition of 100?/2 h+150?/2 h condition.The results showed that the transmittance of epoxy resin modified by DOPO-AEEA was the same as that of EP-0,both of which were above80%,indicating that the addition of DOPO-AEEA had no effect on the transparency of the epoxy resin.The reason was that the addition of DOPO-AEEA did not change the amorphous structure of epoxy resin and the-OH,-NH contained in DOPO-AEEA structure can improve the dispersion of DOPO-AEEA in epoxy resin.LOI of EP-2 was 44.5%and reached V-0 grade.This was because DOPO-AEEA contains P and N flame retardant elements,and these P and N elements played a synergistic flame retardant role.In addition,the flexural,tensile and impact strength were 31.5%,59.6%and 22.5%,which were attributed to that the hydroxyl and amine groups in DOPO-AEEA structure can improve the dispersion of DOPO-AEEA in the resin system.