Study On Novel Reactive Halogen-free Flame Retardant For The Modification Of Epoxy Resin

In recent years,flame retardant containing P and N elements have been widely seen as a concern,because of their highly-efficient flame retardant properties.However,traditional P and N based flame retardants,including the derivatives cyanuric chloride,melamine,cyclophosphazene and DOPO-containing Schiff-base groups etc.,often lead to the decreased of Tg and mechanical properties of materials.In this work,based on the molecular design,halogen-free flame retardant containing P and N are synthesized,which exhibit high-efficient flame retardant and have capacity to keep the thermal and mechanical performances of epoxy resin.The main achievements of the work are shown as follows:(1)The first kind of flame retardant(denoted as PNOO)was synthesized via a one-pot procedure using N-phenyldiethanolamine,4-hydroxybenzaldehyde and DOPO as starting materials,with a yield of 89.8%.The second flame retardant(denoted as DN)was synthesized via the same procedure from 4-amino diphenylamine,phosphonitrilic chloride tirmer and DOPO with the yield of 88.8%.The molecular structures of PNOO and DN were characterized by FTIR and NMR.It was proved that the designed flame retardant was successfully synthesized.(2)Different analysis methods were employed to study the characteristics of as-formed PNOO/EP composites.The TGA analyses show that PNOO/EP has good thermal stability and PNOO can significantly improve carbon residue.For example,in the nitrogen,the char residue(700 ?)can reach 26.3%while the EPO is 18.7%.DMTA and DSC tests show that the Tg values of the PNOO/EP curing system are slightly decreased with the addition of PNOO,which are due to the decreased crosslinking density of the composites at a high loading amount of PNOO.The rubber state storage modulus(E-190?)and the values of tan8 also show that a high content of PNOO can decrease the crosslinking density.The LOI and UL-94 analyses show that the introduction of PNOO can drastically affect the flame retardant property of the composite,with the V-0 grade of UL-94 and non-dripping.When PNOO/DDM compound ratio reaches to 20:80,the LOI value increases to 41%.(3)The effect of flame retardant(DN)on the properties of DN/EP curing system were also analyzed.TGA results show that the char residue(700 ?)can reach 30.9%in nitrogen.The Tg values of the DN/EP curing system are very close to that of EPO,because there are twelve active H-N bonds in the molecular structure of DN and the reaction activity is similar to DDM,which result in a higher density of crosslinking.The values of E-190? and tan? also show that DN can participate in the curing ofepoxy and lead to a high crosslinking density.The introduction of DN can efficiently improve flame retardant property of materials,with the V-0 rating of UL-94,without reducing and 38.8%of the LOI value.