Preparation Of Polyphosphazene Derivative Flame Retardant And Its Flame Retardant Properties For PET

Polyethylene terephthalate(PET)is a typical polymer material,which is extensively used in engineering plastics and textile materials due to its excellent thermal stability,corrosion resistance and low cost.However,PET is easy to burn extremely.It is necessary to improve its flame retardant performance in order to further expand its market.In addition,PET can produce melt-dripping during combustion that will cause secondary damage and pose a great threat to people's daily life safety.Therefore,it is an urgent problem to solve the flame retardant and anti-dripping effect of PET materials.However,the flame retardant finishing of PET always causes a decrease in the mechanical properties of the material.In this paper,poly(cyclotriphosphazene-co-resveratrol)(PRS)microspheres and polyphosphazene modified zeolite-like imidazole skeleton(ZIF-8@PZS)submicron particles were successfully prepared by using the unique P-N alternate structure of polyphosphazene materials as monomer,then these two flame retardants were applied to PET to explore its flame retardant effect and its influence on the mechanical properties of PET.PRS microspheres flame retardant system: PRS microspheres were synthesized through template method.It was incorporated into PET to prepare PET/PRS composites by melt blending process.Thermogravimetric analysis,limit oxygen index,vertical combustion,cone calorimetry and mechanical tensile test were used to investigated the flame retardancy,fire safety and mechanical properties of the composites.The results showed that PRS microspheres have excellent flame retardant effect.Adding 2 wt% PRS microspheres to PET,the limiting oxygen index of PET/PRS2.0 increased to 28.3% and passed UL-94 V-0 rating.In addition,the heat release rate(HRR)and total heat release(THR)of PET/PRS2.0 composites were reduced by31.1% and 13.5%,respectively.It effectively improved the fire safety of PET materials.Compared to the pure PET,the tensile strength and elongation at break of PET/PRS2.0 composites decreased slightly,while the tensile modulus increased by 10.5%.The char residual structure of the composites after combustion was studied by scanning electron microscopy(SEM).The results demonstrated that the PET/PRS composites will rapidly generate dense and continuous carbon layers during combustion,which protected the internal material from further cracking.At the same time,incombustible gases such as ammonia were also generated during burning process,which can dilute the concentration of oxygen around the material and slow down the flame combustion.ZIF-8@PZS submicron particles flame retardant system: ZIF-8 was synthesized by stirring at room temperature.The ZIF-8@PZS submicron particles(ZIF-8@PZS)were prepared through surface modification with PZS.SEM images showed that the particle diameter was about 300-400 nm.PET/ZIF-8@PZS composites were prepared by melt blending with PET.The thermal stability,flame retardant and anti-dripping properties,mechanical properties and flame retardant mechanism of the composites were investigated.The experimental results showed that the oxygen index of PET/FR6.0 can reach 29.2% after adding 6 wt% ZIF-8@PZS submicron particles,and achieved UL-94 V-0 rating in the vertical combustion test.Additionally,the heat release rate of PET/FR6.0 was reduced by 41.24%,which greatly reduced the combustion risk of the material.It should be noted that the mechanical properties of PET/ZIF-8@PZS composites decreased.The flame retardant mechanism exhibited that ZIF-8@PZS submicron particles had great catalytic ability for carbon formation,which can promote the formation of stable carbon layers in the combustion process of polymer materials.The carbon layers can effectively isolate oxygen and inhibit the release of heat and combustibles.On the other hand,nonflammable gases such as SO2 and NOx will be produced around the materials during degradation process,which could dilute the concentration of oxygen on the surface of the material.Under the synergistic effect of gas phase and condensed phase,PET/ZIF-8@PZS composites showed excellent flame retardant and anti-dripping effect.