| Polyolefin materials has been widely used in rail transportation,wires and cables,electronic appliances and other fields due to its advantages of easy processing,chemical resistance,low price.However,polyolefin is flammable,it has great significance and value to flame retardant polyolefin.Intumescent flame retardants(IFRs)are widely used to flame retardant polyolefin attributed their low smoke,low toxicity,and suppression of molten droplets.The traditional IFRs were usually prepared by mixing various components,and mainly exert the flame retardant effect in condensed phase.Therefore,the flame retardant efficiency of polyolefins needs to be improved.The mono-component IFR integrates the acid source,carbon source and gas source into one molecule,which facilitates the synergistic effect among the components.Therefore,preparing a mono-component intumescent flame retardant with high flame retardant efficiency has great significance and application value for polyolefin materials.In this paper,the intermediate named piperazine methylphosphonate borate was firstly prepared from methylphosphonic acid,piperazine and boric acid,and then the prepared intermediate esterified with neopentyl glycol.A mono-component intumescent flame retardant defined as polymethylphosphonic acid piperazine neopentyl glycol borate(MBPNE)containing phosphorus-nitrogen-boron was prepared by adjusting the molar ratio of methylphosphonic acid and boric acid.Its chemical structure was characterized by Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance spectroscopy.MBPNE melt completely during heating,and then expand to form the char layer with dense,strong surface.The results of thermogravimetric analysis(TGA)tests revealed that the residual char mass at 800℃ was 27.5 wt%,which indicated that MBPNE possessed excellent chatting capability.The synthesized MBPNE was incorporated into linear low density polyethylene(LDPE),the 1.6 mm PE/MBPNE sheets achieved UL-94 V-0 rating during vertical burning tests and the LOI value was 25.2%when only 18 wt%MBPNE was introduced.As reported,25 to 30 wt%IFR are usually required to achieve the same flame retardant level due to the large melt viscosity of PE.The sample has a good self-extinguishing phenomenon during combustion,and the char layer on the surface was not obvious,which indicated that MBPNE possessed good flame retardant effect in the gas phase.The results of thermal cracking-gas phase-mass spectrometry(Py-GC-MS)further showed that the decomposition products of MBPNE have the function of trapping free radicals,thus suppressing the chain reaction of combustion and exerting flame retardant effect in gas phase.Cone calorimeter(CONE)test indicated that the heat release rate(HRR),total heat release(THR)and other parameters reduced significantly with the introduction of MBPNE.Under the action of boron,A sticky substance was produced during combustion and adheres on the surface of the char layer,thereby strengthening the carbon layer.Therefore,a continuous,dense,hard,porous,and partially graphitized char layer was formed after the CONE test of composite.which effectively inhibited the transfer of oxygen,heat,and combustible materials between the combustion area and material,and exerting excellent flame retardant effect in gas phase.As a result,MBPNE has excellent flame retardant effects in both the condensed phase and gas phase.Therefore,the flame retardant PE materials have high flame retardant efficiency.The ethylene octene copolymer(POE)is a thermoplastic elastomer material,which drips seriously during combustion.It usually needs to add 30-35 wt%flame retardant to obtain the ideal flame retardant level.In this paper,the synthesized MBPNE was added to ethylene-octene copolymer(POE)material,the 1.6 mm sample passed the UL-94 V-0 rating and the limiting oxygen index was 25.5%,when 22 wt%MBPNE was introduced.The flame retardant POE materials have high flame retardant efficiency.Cone calorimeter test showed that HRR and THR of POE/22 wt%MBPNE composite reduced by 10.8%and 26.6%respectively,compared with pure POE.The flame retardant mechanism showed that the flame retardants play both flame retardant roles in gas phase and condensate phase,and give POE with excellent flame retardant performance... |
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