Synthesis And Mechanism Of Flame Retardants Based On Furan Ring

The flame retardancy of polymeric materials is an important issue to ensure its safety in use.With people's increasing environmental awareness,development of halogen-free flame retardants obtains more and more attention.Among all,the combination of bio-based materials and flame retardant factors is an effective and sustainable way to achieve halogen-free flame retardants.However,with the variety of bio-based materials,design of high-efficient bio-based flame retardants and its efficient application in polymeric materials become difficult.Meanwhile,disperse of bio-based flame retardants and its compatibility with matrix is also severe issues leading to the poor mechanical properties of flame-retardated composites.In view of these problems,this thesis concentrates on the synthesis of three phosphorus-containing flame retardants based on bio-based platform compounds furan and its derivatives,with the purpose of combination of phosphorus and furan ring and improvement of polymeric materials'comprehensive properties.The phosphorus-containing flame retardants were used in poly(lactide acid),nylon 6 and epoxy resins respectively,and the comprehensive properties and flame retardant mechanism of composites are investigated in detail.The detailed researches are as follows:(1)A furan-phosphamide derivative(POCFA)was synthesized using furfurylamine(FA)and phosphorus oxychloride(POC),and used as a flame retardant and nucleating agent in poly(lactide acid)(PLA).The flame retardancy of PLA/POCFA compounds were investigated by the UL-94 vertical burning tests,limited oxygen index(LOI)and cone calorimeter tests.A small 2 wt%loading of POCFA increases the LOI of PLA from 19.4 vol%to 29.6 vol%and achieves the UL-94 V0 rating.According to the results from thermogravimetric analysis linked with infrared spectrometry(TG-IR)and Q-TOF mass spectrometer,the flame retardant mechanism of POCFA can be deduced into interruption of heat exchange:POCFA can catalyze the random esterification of PLA to form more low-molecular-weight oligomers leading to more serve melting droplet during burning.Moreover,the isothermal crystallization and non-isothermal crystallization behavior of PLA/POCFA composites indicate that POCFA is a good nucleation agent to improve the crystallization rate and crystallinity of PLA and decrease its negative effect on mechanical properties of PLA.(2)POCFA was used also in Nylon 6(PA6).With 5 wt%loading of POCFA can make PA6 pass UL-94 V0 rating and increase the LOI value of 27.2 vol%.The results of TG-IR indicate its flame retardant mechanism is still to interrupt heat exchange.After melt-blending,the increasing viscosity-average molecular weight of PA6/POCFA composites reveals the reaction between PA6 chains and POCFA,and the same trend of elongation at break can also been observed.The model reaction between?-caprolactam(CPL)and POCFA at 240°C in nitrogen was simulated to explain this trend.The results indicated that phosphate acid compounds from decomposition of POCFA can catalyze degradation of PA6,leading to sharply decreased molecular weight and toughness of PA6/POCFA composites.In addition,POCFA can successfully react with PA6 molecular chain in forms of phosphate ester,alkyl-substituted phosphamide and phosphamide.According to the results of differential scanning calorimetry(DSC)and FTIR,Diels-Alder addition reactions or amide exchange reaction between these phosphorus-containing chains and double-bonded chains appeared leading to the crosslink of PA6 chains and the increased molecular weight.(3)A novel bio-based flame retardant(FAFD)synthesized from furfuryl amine(FA),furaldehyde(FD)and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide(DOPO)was used in flame retardant of bisphenol-A epoxy resin(EP)with common curing agent of 4,4'-diamino diphenyl methane(DDM).It reveals that only 6 wt%loading of FAFD can make EP achieve UL-94 V0 rating and increased LOI value of34.6 vol%.The results of cone calorimeter test indicate that heat release rate(HRR),total heat release(THR)and total smoke release(TSR)of epoxy resin composites(EPs)have significantly decreased with 6 wt%loading of FAFD.Furthermore,the compatibility between matrix and flame retardant was improved by adding itaconic acid epoxy(EIA)with slight decrease of fire resistance.As to the addition of EIA,the interfacial adhesion between matrix and flame retardant was increased,and the mechanical properties of flame-retarded EP composites were significantly increased.According to the results of FTIR and ~1HNMR after the reaction of FAFD and EIA,the connection of EIA was thought to be the curing reaction of epoxy groups and Diels–Alder reaction between FAFD and EIA leading to the improved compatibility and tensile strength of EP composites.(4)A reactive phosphorus-containing epoxy(E-TFD)was synthesized by epichlorohydrin(ECH)and bio-based flame retardant(TFD),and TFD was firstly synthesized from FD,tyrosine(Tyr)and DOPO.E-TFD was used in flame retardant of bisphenol-A epoxy resin with common curing agent of DDM.The flame retardancy of EPs was investigated by LOI,UL-94 vertical burning tests and cone calorimeter tests.With 2.0 wt%phosphorus content,EPs can pass UL-94 V0 rating,and the LOI value can be increased to 34.3 vol%.The results of cone calorimeter test indicate that heat release rate(HRR),total heat release(THR)and total smoke release(TSR)of epoxy resin composites(EPs)have significantly decreased with 1.5 wt%phosphorus content.In addition,thermal properties,flame retardant mechanism and toughness of the composites were also investigated by TGA,DSC,TG-IR and impact tests.It revealed that due to the aliphatic structure of E-TFD,glass transition temperature(T_g)and thermal stability of EP composites was decreased,wheras the impact strength was increased.Due to the DOPO structure and aromatic ring of E-TFD,the gaseous phase flame retardant mechanism and condensed phase flame retardant mechanism in EP composites were deduced from the results of TG-IR.