Study On The Flame-retardant Performance Of Multi-element Synergistic Modified Epoxy Resin

Epoxy resin possesses low shrinkage rate,excellent mechanical properties and chemical resistance,and is being expansively applied to marine,aviation and electronic parts and other fields.Nevertheless,epoxy resin possesses combustible property that can release smoke and heat,limiting its applicable field greatly.In order to further expand the application range of epoxy resins,it is very necessary to explore the method to improve the flame-retardant properties of epoxy resin.Introducing halogen elements into the material system is the most traditional manner.Although the incorporation of halogen-containing compounds is able to get the flame-retardant performance enhanced signficantly,the gases produced by combustion are highly toxic,so the usage of compounds containing halogen gets restricted and forbidden in recent years.Some new modified systems,such as phosphorus modifier,nitrogen modifier and silicon modifier,are slowly becoming their substitute.In many modified systems,DOPO and derivatives of DOPO have been research hotspots in this field for their excellent modification effect and decreased virulence.An epoxy resin system comprising of phosphorus and silicon had been designed to explore the effect of phosphorus/silicon modification on the fire resistance as well as mechanical performance of materials.Then,for the purpose of further improvementofitsflame-retardantperformance,a phosphorus/silicon/triazine-containing flame retardant DTD was designed and modified the epoxy resin.The results showed that the phosphorus/silicon modification and the phosphorus/silicon/nitrogen modification got the flame-retardant performance of materials ameliorated as well as mechanical properties.（1）Four kinds of samples,EP-P-1（phosphorus content 0.57%）,EP-P-2（phosphorus content 0.74%）,EP-Si（silicon content 0.80%）,and EP-P/Si（phosphorus content 0.54%and silicon content 0.77%）were successfully prepared by reaction between ODOPB,PTMS and DGEBF.Studies showed that the flame-retardant performance of EP-P/Si as well as mechanical performance were superior to those of pure epoxy resin EP,EP-P-1,EP-P-2 and EP-Si.Its LOI value got 33.4%,while also acquiring V-1 level.During the cone calorimeter expriment,the PHRR and THR of EP-P/Si were 36.0%and 19.5%lower than unmodified epoxy resin.Along with the improved flame retardancy,EP-P/Si also exhibited excellent mechanical performance,with flexural,tensile,and impact strength getting imporved by 6.2%,31.8%,and369.7%.It could be explained by the fact that the introduction of ODOPB improved the stiffness of epoxy resin,and the appropriate increase in stiffness was beneficial to improve the strength.Besides,the flexible Si-O bond in PTMS enhanced the mobility of the molecular chain and increased the free volume of the cured network.It could effectively dissipate stress to suppress stress concentration when subjected to external forces.（2）The phosphorus/silicon/triazine comprised flame retardant named DTD was designed through the triglycidyl isocyanurate（TGIC）,diphenylsilanediol（DPSD）,and DOPO.Different contents of DTD were then incorporated into DGEBF to explore the effect of phosphorus/silicon/nitrogen synergistic modification on the toughness and flame-retardant properties of material.The results showed that when the DTD addition amount was 6.1 wt%,the LOI value increased from 26.8%of pure epoxy resin to 32.4%,while the UL-94 V-1 level was obtained.With the further increase of DTD content to 18.1 wt%,compared with pure epoxy resin the PHRR,THR and av-EHC of the modified resin dropped by 43.7%,45.0%and 38.0%,which indicated excellent modification of phosphorus/silicon/nitrogen.Through the analysis of char residue of modified epoxy resin,it could be found that the char residue had good stability.At the same time the·PO,·PO₂and nitrogen-containing inert gases could be found in the gas phase,which exerted the quenching and dilution effect in the gas phase.The mechanical performance of modified resins also got improved.When the DTD content was 8.8 wt%,its flexural and tensile strength were 36.0%and18.9%higher than those of neat EP.