Preparation Of Sodium Tripolyphosphate Modified Expandable Graphite And Its Flame Retardancy For Polyethylene And Polyurethane

Sodium tripolyphosphate(STPP)modified expansible graphite(EGP)was prepared with 80,100,150 mesh graphite as materials,respectively,through chemical oxidation-intercalation method.The products were written as EGP80,EGP100 and EGP150.The influence such as mass ratio of graphite to KMnO4,STPP and H2SO4,H2SO4 concentration,reaction time and temperature on EGP dilatability was tested.The feasible reaction conditions were detected as follows:(1)As for the EGP80,mass ratio of C80:KMnO4:H2SO4(98%):STPP was controlled as 1.0:0.2:5.0:0.6,H2SO4 diluted to 75 wt.% before intercalation reaction,and the reaction lasted 40 min at 40?.Expanded volume(EV)and initial expansion temperature(T0)of the prepared EGP80 reached 583mL/g(at 800?)and 186?,respectively.(2)As for the EGP100,mass ratio of C100:KMnO4:H2SO4(98%):STPP was controlled as 1.0:0.3:5.0:0.5,H2SO4 diluted to 75 wt% before intercalation reaction,and the reaction lasted 30 min at 40°C.EV and T0 of the prepared EGP100 reached 500mL/g(at 800?)and 218°C,respectively.(3)As for the EGP150,mass ratio of C150:KMnO4:H2SO4(98%):STPP was controlled as 1.0:0.4:5.0:0.5,H2SO4 diluted to 70 wt% before intercalation reaction,and the reaction lasted 20 min at 35?.EV and T0 of the prepared EGP150 reached 266mL/g(at 800?)and 320°C,respectively.There was a linearship between every EGP size and the EV.Scanning electron microscopy(SEM),X-ray diffraction spectroscopy(XRD)and Fourier transform infrared spectroscopy(FTIR)analysis characterized the structure,and confirmed the intercalation reaction.The influence of prepared EGP flame retardants and ammonium polyphosphate(APP II)on flame retardancy and mechanical properties of linear low density polymer ethylene(LLDPE)and high density polymer ethylene(HDPE)was investigated.Combustion behavior was characterized by limiting oxygen index(LOI)and UL-94 vertical combustion.Thermogravimetric(TG)and differential thermogravimetric analysis(DTG)were used to characterize sample thermal stability.Tensile tests were carried to detect composite mechanical strength.The results showed as follows:(1)When the mass ratio of EGP to APP controlled as 2:1,70LLDPE/20EGP/10 APP and 70HDPE/20EGP/10 APP all presented the highest LOI value and vertical combustion UL-94 level than the others.(2)LOI value and UL-94 level reduced with the decreasing of EGP particle size.(3)The maximum weight loss rate and residual yield decreased with the decreasing of EGP particle size.(4)Compatibility and dispersion of flame retardant with substrates became better with the decrease of EGP particle size.(5)70 LLDPE/20EGP100/10 APP possesses not only the best flame retardance,but also has well mechanical property.With different mass ratio,APP and the prepared EGP were added into rigid polyurethane foam(RPUF).The results showed that:(1)when only the EGP was added,there was a proportional relationship between EGP dosage and the RPUF density.On the contrary,a negative relationship was observed as for the compressive strength.(2)When a part of EGP was replaced by APP,there was a proportional relationship between APP amount and the RPUF density,compressive strength.(3)When the mass ratio of APP to EGP was controlled as 1:1,80RPUF/10EGP/10 APP composite showed high LOI value,low heat release rate and the total heat release.While,the burning time lengthened.(4)Thermal stability of 80RPUF/10EGP/10 APP was bad in the low temperature zone,and it was good in the high temperature zone.It also presented maximum residual yield at 800 ?.(5)Thermal conductivity of 80RPUF/10EGP/10 APP was less than 0.03 W/m·K,belonging to highly efficient insulation material.(6)80RPUF/10EGP/10 APP showed better hydrophobic property than pure RPUF.The influence of EGP particle size on RPUF properities showed:(1)EGP50 indicated obvious damage on RPUF cell structure,and the cell integrity of 80RPUF/10EGP80/10 APP was the best.Replacement of EGP with APP could reduce the influence.(2)When the mass ratio of EGP to APP was controlled as 1:1,density of 80RPUF/10EGP/10 APP decreased with the decreasing of graphite particle size.While,the compressive strength increased with the decreasing of particle size at first,and then it decreased.80RPUF/10EGP80/10 APP presented the maximum strength.(3)Although the LOI value decreased with the decreasing of EGP size,they all made the RPUFs indicate the property of flame retardant material.(4)In the low temperature zone,EGP with small size showed better thermal stability.While,EGP with big size indicated better thermal stability in high temperature.(5)The maximum heat release rate and combustion intensity increased with the decreasing of EGP size.(6)The final residual yield,residue density gradually reduced with the decreasing of EGP size,and it became easily fall off.