Preparation and properties of flame retardant modified polyethylene terephthalate by in-situ polymerization
Objective Polyethylene terephthalate(PET)is widely used because of its excellent comprehensive properties,but PET has poor flame retardancy,which greatly limits its application.Traditional halogenated flame retardants have great impact on the environment during combustion and cause damage to people's eye sight.Hence,the research of new halogen-free flame retardants is imperative.Method In this study,flame retardant polyester(DDP-gCDs-PET)was prepared with[(6-oxo-6H-dibenzo[c,e][1,2]oxahex-6-yl)methyl]succinic acid(DDP)and gelatin-based carbon dots(gCDs)as flame retardant by in-situ polymerization.To explore the flame retardant properties of PET,a study was conducted using limiting oxygen index(LOI),vertical combustion(UL-94)and cone calorimetry to assess the influence of gCDs with varying mass fractions.Results gCDs are quasi-spherical in structure,with an average particle size of about 3.34 nm and good dispersion.FT-IR spectra demonstrated the presence of amino groups and carboxyl groups on the surface of gCDs.In addition,FT-IR spectra also demonstrated the successful introduction of gCDs,DDP into PET molecular chains.When DDP was 8％and gCDs were 1.0％(named DDP-1.0gCDs-PET),the glass transition temperature of DDP-1.0gCDs-PET was increased by 9.33％compared with that of pure PET.The temperature at which ester mass decreases by 5％of DDP-1.0gCDs-PET was increased by 10.32 ℃ compared to that of DDP-PET.Compared with PET,the peak heat release rate of DDP-1.0gCDs-PET was reduced by 39.77％,the total heat release was reduced by 25.00％,and the time to ignition was delayed by 25 s compared with that of PET.UL-94 and LOI studies show that DDP-1.0gCDs-PET had a LOI of up to 35％,and UL-94 was upgraded from V-2 to V-0.After the combustion of flame-retardant polyester,a continuous dense carbon layer was formed,which effectively hinders the spread of heat and gas and improves the flame retardant performance of the matrix.It is evident that DDP promoted the decomposition of the matrix and played the role of quenching free radicals when the matrix was burned.The addition of gCDs significantly reduced the concentration of CO2 and CO in meteorological products and improved the quality of the carbon layer.Conclusion Compared with pure PET,the flame retardant effect of DDP-gCDs-PET is significantly improved.The flame retardant mechanism of DPP and gCDs in PET system is understood.During the combustion process,gCDs absorb heat to form a heat conduction network,so that the heat diffuses rapidly and evenly in the matrix and delays the combustion of the matrix.DDP promotes decomposition of the matrix,while producing P=O to quench free radicals in the gas phase and dilute combustible groups in the gas.gCDs promote the retention of P in DDP in the carbon layer,forming a large number of dense and continuous high-quality carbon layers in the solidified phase to achieve the purpose of flame retardancy.
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