| The ceramifying polymer composites ideally have the dual performance characteristics of polymer at room temperature and ceramics at elevated temperatures.The ceramifying polymer composites are widely used in the preparation of electric cable,due to its excellent fire prevention.Silicon-based polymers such as silicone rubbers with high bond strength Si-O had been proven to promote the ceramifying process during combustion.And silicone rubber with less smoke,slow speed flame propagation,and electrical insulation,etc,is an ideal material for the preparation of cable material.However,it is difficult to achieve a strong,hard ceramic material because silicone decomposes to powder at 300600 oC,while the liquid phase formed from eutectic reaction does not occur.Glass frits are added into silicone polymer composites with the aim to improve the mechanical strength at the low temperature,but could decline the electrical conductivity due to the ionic conduction of the glass phase,limiting use as a fire-resistant cable material.Therfore,the mechanism of ceramifying process of ceramifying polymer composites is the interactions in the inorganic substances essentially.The ceramifying process is designed by inorganic reactions innovatively in the paper.The silicone rubber ceramifying composites with high flexural strength from low to high temperatures and high self-supporting,is prepared by the combination of ceramifying of mica and synergistic flame retardance between ammonium polyphosphate and aluminium hydroxid in this paper.The mechanical properties is improved by phosphates via reaction of ammonium polyphosphate and aluminium hydroxide in meso-low temperature and enhanced by the reactions in the phosphates and mica at high temperature,which can improve the flame retardant of composites.Firstly,the phase and microstructure evolution of ammonium polyphosphate/mica/aluminium hydroxide compounds during thermal reaction were investigated.The thermal decomposition products of APP react with AlOOH to NH4AlP2O7,which can improve the flexural strength from 4.68 MPa at room temperature to 15.39 MPa at 600 oC.The reactivity of mica is increased by eliminating hydroxyl at temperature up to 600 oC,and then the chemically interactions between active mica and phosphates are able to generate Al2O3·2SiO2,and AlPO4 compounds improving the flexural strength.The residues exhibit relatively high flexural strength,which can reach 26.85 MPa when the calcined temperature is 1000 oC and reactions between mica and phosphates could generate KAlSi3O8 and 3Al2O3·2Si O2.The apparent activation energy of APP/mica/Al?OH?3 is less than the apparent activation energy of APP/mica,which is helpful to form ceramic.The ammonium polyphosphate/mica/aluminium hydroxide compounds with high flexural strength from low to high temperatures is expected to be a kind of excellent inorganic additive of ceramifiable polymer with wide temperature range for using.Secondly,the effect of the content of ammonium polyphosphate,mica and aluminium hydroxide on the mechanical properties of ammonium polyphosphate/aluminium hydroxide/mica/silicone rubber composites were investigated by orthogonal experimental design.The composite(hereinafter referred to as APP25Al20M25SiR30)is produced when the content of ammonium polyphosphate,mica and aluminium hydroxide is 25%,25%and 20%,respectively,which is optimized by orthogonal experimentent.The ceramifying process and mechanical properties of APP25Al20M25SiR30 are investigated.The mass loss rate of composites between 251324 oC is highest,which is caused by the degradation of Al?OH?3,APP and the rupture of SiR.And there is no interactions between the SiO2 from the rupture of SiR and phosphates at temperature up to 500 oC.Then the chemically interactions between SiO2,active mica and phosphates are able to generate Al2O3·2SiO2,and KAlP2O7 compounds at 600 oC.Further reactions between SiO2,mica and KAlP2O7could generate KAlSi3O8 to form relatively dense structure at 1000 oC.SiO2 can inhibit the conversion of Al2O3·2SiO2 to 3Al2O3·2SiO2.It was concluded that ceramifying process is formed by eutectic reactions between the rupture of SiR,ammonium polyphosphate,aluminium hydroxide,and mica at high temperatures.Moreover,the mechanical properties of APP25Al20M25SiR30 at room temperature,in the muffle furnace and naked flame were investigated.The results suggest that the tensile strength and tear strength of APP25Al20M25SiR30 are less than those of SiR30 at room temperature,which reach to 3.1 MPa and 8.7 MPa,respectively.The mechanical properties of the composites are affected by the temperature,heating rate and holding time in the muffle furnace.With the temperature increasing,the mechanical properties of composites increase in the muffle furnace,and the flexural strength of the composite is 9.46 MPa at 1000 oC.The composites with high flexural strength and good self-supporting from low to high temperatures could come ture.The flexural strength of the composite are enchanced with temperature increasing.The flexural strength of APP25Al20M25SiR30 residues in naked flame using alcohol blast burner are higher than in using alcohol lamp during the same buring time duo to the more phosphates.The flexural strength of composites is 8.26 MPa,when the composites burned in alcohol blast burner for 10 min.Finally,the flame retardant properties and combustion products of APP25Al20M25SiR30 composite during the cone calorimeter test were investigated in this work.Results from cone calorimeter indicate that the addition of APP and Al?OH?3 reduces the mHRR of composites from 46.7 kW/m2 to 22.2 kW/m2,the tPHRR from 110 s to 130 s and the THR from 25.3 to 14.4 MJ/m2.The addition of APP and mica prolong the TTI of composites from 57 s to 106 s and enhance the residue from 51.9%to 74.3%.The addition of APP,mica and Al?OH?3 prolong the TTI of composites and reduces the THR to 13.9 MJ/m2,which could improve the flame retardant performance of APP25Al20M25Si R30.The synergistic effect of APP,Al?OH?3and mica may be explained by a flame retarding mechanism under combustion.The APP25Al20M25SiR30 composite exhibit good flame retardant properties due to gas evolution from the endothermic thermal decomposition of APP and Al?OH?3 in the early stages of combustion.The thermal decomposition products of APP react with Al?OH?3 to NH4AlP2O7,which can improve the flame retardant properties with temperature increasing.The flame retarding mechanism belongs to the typical condensed phase flame retardant.Further reactions between SiO2,mica and phosphates could form relatively dense structure to further improve the flame retardant performance in the later stages of combustion. |
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