Preparation Of Highly Transparent Flame-retardant Epoxy Resin And Study Of Its Flame-retardant Mechanis

Epoxy resin（EP）is widely used in electronic and electrical appliances,adhesives,coatings,furniture,life and other fields because of its excellent mechanical strength,strong corrosion resistance and low curing shrinkage.Unfortunately,epoxy resin is extremely flammable and poses a potential threat to the safety of people’s lives and property,thus limiting its application in a wider range of fields.Therefore,it is necessary to improve its flame retardancy.In this thesis,three kinds of flame retardants（FRs）containing phosphorus/nitrogen/sulfur were synthesized through molecular design,and EP/FRs thermosets were prepared using 4,4’-diaminodiphenylmethane（DDM）as the curing agent.The effect of the FRs on the thermal stability,flame retardancy,curing kinetics,combustion behaviors,mechanical properties and transparency of the flame-retardant EPs（FREPs）were investigated on detail,and the possible flame retardant mechanism was disclosed.The main subjects are as follows:（1）4-（（diphenylphosphoryl）amino）benzenesulfonamide containing P/N/S（named as DPABSA）was synthesized by the nucleophilic reaction using diphenylphosphinyl chloride（DPPC）and 4-aminobenzenesulfonamide as raw materials.With the addition of 5.0 wt%DPABSA,the FREP achieved the UL-94 V-0 rating and the LOI value of36.7%.As compared to the pure EP,the peak heat release rate（PHRR）,total heat release（THR）and total smoke production（TSP）of EP/5wt%DPABSA were decreased by 38.6%,48.2%and 51.3%,respectively.Meanwhile,the EP/5wt%DPABSA also gave the lowest value of fire growth index（FGI）,indicating that the DPABSA can effectively improve the fire safety performance of the EP.The analysis of the curing kinetics and（dynamic）mechanical measurements showed that the incorporation of DPABSA promoted the curing process of EP while decreased the crosslinking density.At the same time,the mechanical properties（including tensile strength and flexural strength）were also deteriorated due to the bad compatibility between DPABSA and EP matrix.The comprehensive analysis of the pyrolysis gases and the carbon residues demonstrated that the DPABSA exerted synergistic flame retardant effect in the gas phase and condensed phase.（2）Sulfonyl bis（3,1-phenylene）bis（diphenylphosphonate）（marked as SBPDPP）was synthesized by the nucleophilic reaction of DPPC with 4,4’-Sulfonyldiphenol（BPS）.At loading level of 6.0 wt%SBPDPP,the FREP passed UL-94 V-0 rating and gained LOI value of 38.8%.The PHRR,THR and TSR of FREP containing 6.0 wt%SBPDPP were reduced by 40.0%,42.0%and 26.3%as comparison with the pure EP,respectively.The TG-FTIR spectra of the pyrolysis gases demonstrated that the decomposition of SBPDPP produced non-flammable gas（SO₂）to dilute the combustible volatiles and P-containing compounds to capture the highly active radicals（H.and OH.）as radical scavenger,thus interrupting the burning process of the EP matrix.In the condensed phase,P-or S-containing acids which produced from the thermo-oxidative degradation of SBPDPP could esterify and dehydrate the EP resin,consequently promoting the carbonization of EP resin to form continuous and compact char residues,thus isolate the isolate the transfer of the combustible volatiles and heat.Additionally,the SBPDPP became compatible with EP due to its polyphenyl ring structure,and dispersed uniform within EP phase.The optical transparency,tensile strength and flexural strength of the FREP kept almost the same as the pure EP..（3）A P/N/S-containing N,N-bis（diphenylphosphoryl）-4-toluenesulfonamide（DPPBSA）was synthesized by the nucleophilic reaction of DPPC with p-toluenesulfonamide.The FREP containing 5.0 wt%DPPBSA achieved UL-94 V-0 rating with a LOI value of 35.4%,its PHR and THR values were reduced by 51.0%and 40.5%as compared to the pure EP,respectively.It revealed that the DPPBSA displayed better flame retardant effect and heat suppression.Furthermore,the DPPBSA exerted dual flame retardant effect in the gas and condensed phase.In the gas phase,the released non-flammable gaseous products（SO₂ and NH₃）diluted the flammable gases meanwhile the PO.radicals captured the highly active radicals（H.and OH.）during combustion.In the condensed phase,the produced compounds including phosphates and sulfates promoted the dehydration of the EP matrix to carbonize and crosslink,and thus constituting continuous and compact carbon layers which acted as solid physical barriers to isolate the transfer of the combustible volatiles and heat.Additionally,the FREPs showed high optical transparency with 95%transmittance of the pure EP and better mechanical properties which are comparable to the pure EP.