Research On Properties Of Phosphorus/Nitrogen/Silicon/Graphene-containing Synergic Flame-retardant Epoxy Resin

Epoxy resin?EP?is one of the most common thermosetting polymer materials with many excellent properties.However,the inherent flammability of EP greatly limits its further application,so it is necessary to conduct flame-retardant treatment on EP.Given the outstanding flame-retardant effects of P,N,Si-based flame retardants,and nanomaterials,this thesis selects P-N-based synergic phosphazene compounds,Si-based silica?SiO₂?and polyhedral oligomeric silsesquioxane?POSS?,as well as graphene nanofillers,to prepare flame retardants and EP composites by using four methods:microencapsulation technology,the synergistic flame-retardant technology,and nanotechnology.The thermal properties,mechanical properties,flame retardancy and mechanisms of flame retardants added EP composites are systematically investigated.The main contents are as follows:?1?Based on P-N effectively synergistic flame retardancy of phosphazene and compatibility of polymethyl methacrylate?PMMA?with EP,P?H?microcapsules with core-shell structure was prepared by microencapsulation technology with hexaphenoxycyclotriphosphazene?HPCTP?as the core and PMMA as the shell,and used to prepare EP composites.After P?H?microcapsules was added to EP network,the glass transition temperature?T_g?values of the composites increased significantly,and the system achieved a limit oxygen index?LOI?value of 30.5%and a vertical burning tests?UL-94?V-1 rating with improved flame retardancy.Compared with the pure EP,the peak value of heat release rate?PHRR?of P?H?/EP composite decreased by 18.6%,which was restrained by the flammable PMMA.The P-N synergistic flame-retardant mechanism of P?H?microcapsule includes:the quenching effect of P-containing free radicals and diluting effect of N-containing incombustible gases in the gas phase,and the charring effect of P-containing char residues in the condensed phase.However,the charring effect in the condensed phase was inapparent,so the flame retardancy can be further improved.?2?In order to further improve the flame-retardant efficiency,based on the condensed function of SiO₂ particles,P-N-Si synergistic flame-retardant Si?H?microcapsules with core-shell structure was prepared by microencapsulation technology and synergistic flame-retardant technology with HPCTP as the core and SiO₂ particles as the shell,and used for flame-retardant modification of EP composites.Two silane coupling agents?KH550 and KH560?were used to enhance the interface between the fillers and the substrate.Compared with the pure EP,the fire hazard of Si?H?/EP composites was greatly reduced,and PHRR decreased by 34.1%and 44.7%,which implying a further improvement of flame retardancy.The P-N-Si synergistic flame-retardant mechanism of Si?H?can be summarized as:the quenching effect of P-containing free radicals and diluting effect of N-containing incombustible gases in the gas phase,and the charring effect of P-containing char residues and barrier effects of Si-containing components in the condensed phase.The barrier effect in the condensed phase was proved to play an important part in flame-retardant system with a high efficiency.?3?In order to detect the effect of nanoscale flame retardant in condensed phase,based on the structural characteristics of graphene nanosheets and Si-based flame retardant octa?propyl glycidyl ether?polyhedral oligomeric silsesquioxane?OGPOSS?,flame-retardant functionalized graphene oxide?GO?nanofiller FGO nanosheets was prepared by nanotechnology with KH550 as a bridge,and used for flame-retardant modification of EP composites.Due to the good dispersion and interfacial interaction of FGO nanofillers in EP matrix,the prepared FGO/EP nanocomposites exhibited good thermal resistance and tensile property.The thermal conductivity of FGO/EP composites was reduced due to the tortuous effect of FGO nanosheets in EP matrix,which prolonged the thermal conduction path.The increase of char residues and the decrease of volatile gases proved that the protective carbon layer structures formed on the surface of EP matrix by FGO nanomaterials can effectively inhibit smoke release and mass loss.and increased char residues.Compared with the pure EP,the PHRR of FGO/EP composites decreased by 37.2%,which implying a great improvement of flame retardancy.The flame-retardant mechanism of FGO can be summarized as:tortuous effect and barrier effect of graphene sheets and Si-components in condensed phase.The flame-retardant effect of graphene-based materials was proved to be prominent in the condensed phase.However,FGO contained system lacked the mechanisms in the gas phase,which implied a possibility of further improvement of flame retardancy.?4?Base on the effects of P-N synergistic phosphazene in the gas phase and the mechanisms of graphene-based materials in the condensed phase,hexakis?4-aminophenoxy?-cyclotriphosphazene?HANPCP?was synthesized and grafted on GO sheets to prepared flame-retardant functionalized fGO nanosheets by nanotechnology and synergistic flame-retardant technology,and used for flame-retardant modification of EP composites.In fGO/EP composites,fGO nanofillers exhibited excellent interfacial adhesion and improved dispersion and compatibility in the system,and endowed EP composites with better thermal stability,lower thermal conductivity and good dynamic mechanical properties.The compact char structure and inhibited volatile gas products indicated that fGO nanofiller promoted the formation of protective char residue structures,which can inhibit the transfer and exchange of heat,oxygen and mass.Compared with the pure EP,the PHRR of fGO/EP composites decreased by 49.0%,which implying a further improvement of flame retardancy.The P-N synergistic and nanoscale flame-retardant mechanisms of fGO nanofiller in EP composite can be summarized as:the quenching effect of P-containing free radicals and diluting effect of N-containing incombustible gases in the gas phase,and the charring effect of P-containing char residues and tortuous effect and barrier effect of graphene sheets in the condensed phase.This system combined the gas and condensed mechanisms of phosphazene and graphene-based materials,which can provide significant improvement of flame retardancy of EP composites at a low additive content.The systems in this work were designed based on the flame-retardant mechanisms of gas and condensed phase,and provided effective methods to improve the flame retardancy of EP composites at low additive contents,which can enhance the comprehensive properties,expand the applications,and promote the fire safety of EP composites.