Preparation Of Boric Acid Modified Expandable Graphite And Its Flame Retardancy For Polyethylene And Polyurethane Foam

In order to get the graphite intercalation compound with high expansibility and fire resistance,the synthetic method of expandable graphite modified by zinc borate?ZB?(labeled as EG_Zn)was investigated,and its influence on flame retardancy and mechanical properties of the linear low density polyethylene?LLDPE?and rigid polyurethane foam?RPUF?was carried out.First of all,the feasible reactant mass ratio of C:KMnO₄:H₂SO₄?98%?:ZB was confirmed through single factor tests.The results are determinated as follows:mass ratio of the reactants is 1.0:0.25:4.5:0.3,the used sulfuric acid should be diluted to a mass concentration of 75%,and the reaction lasts 40min at 50?.Under the above reaction conditions,EG_Znn gives an expansion volume of 520mL/g.Results of scanning electron microscope,X-ray powder diffractiometer and Fourier transform infrared spectroscopy confirm the existence of EG_Zn,Then,the influence of EG_Zn,referenced expandable graphite?labeled as EG₀,prepared with only sulfuric acid as intercalator?,ammonium polyphosphate?APP?,the mixture of EG_Znn and APP on the combustion performance,thermal stability and mechanical properties of LLDPE and RPUF were compared and investigated through limit oxygen index?LOI?,UL-94 vertical burning,thermogravimetry and mechanical property tests.The conclusions are as follows.?1?The results show that EG_znn indicates significant flame retardace for LLDPE.The 30wt%EG_Znn improves the LOI value of LLDPE from 17.6%to 26.5%.At the same time,it's2.7%higher that of EG₀.Furthermore,EG_Znn and APP present synergistic effect,and70LLDPE/20EG_Zn/10APP shows a LOI of 29.8%,and the UL-94 level reaches V-0 level.?2?Results of thermogravimetry and residual morphology show that although the residue yield of 70LLDPE/20EG_Zn/10APP is lower than that of 70LLDPE/30EG_Zn,it's more dense and compact than the later.The residue compactness presents more important effect on flame retardancy than the residue yield.The results of mechanical properties experiments confirm that the incorporation of flame retardant reduce the tensile strength of the treated LLDPE composites.?3?Addition of the tested additives increases the density of the modified RPUFs.EG_Znn and APP have different influence on foam compressive strength.The nucleation of APP improves the compression strength of RPUF to some extent.However,the addition of EG_Znn causes collapse of the pore,and then decreased compression strength.For the single flame retardant sample,EG_Znn shows the best flame retardancy than EG₀ and APP.As for the coorperation of EG_Znn and APP,there is synergistic flame retardane.70RPUF/20EG_Zn/10APP shows a LOI value of 29.3%,which is significantly higher than the theoretical value.At the same time,the vertical combustion level reaches V-0.?4?The results of thermogravimetric analysis and residual morphology show that70RPUF/20EG_Zn/10APP shows more compact and higher residual yield.The condensed phase plays more important roles in improving flame retardant performance.The high residual yield not only comes from the physical synergy between EG_Znn and APP,but also from the RPUF condensation reaction catalyzed by APP,and the phosphate produced by EG_Znn and APP.