Synergistic Flame Retardant Effect Of Ammonium Polyphosphate/Theic Modified Miamine Resin/Siliceous Ore In PP

Intumescent flame retardant（IFR）is an environmentally friendly green flame retardant,and charring agent is an important component of IFR.At present,the commonly used charring agent is a macromolecular triazine derivative synthesized from cyanuric chloride,but it has serious environmental and safety problems.In view of the above problems,our research group has developed a nevel macromolecular triazine charring agent-THEIC modified melamine resin（THEIC modified resin）.The charring agent has some advantages such as simple process,no waste discharge and no safety hazard,but the flame retardant efficiency of IFR consisted of it and ammonium polyphosphate（APP）is significantly lower than that of the existing triazine charring agent.Synergistic flame retardant technique is a common means to improve the flame retardant efficiency of IFR,and siliceous ores are a type of natural and cheap synergistic agent.Therefore,in this paper,the synergistic flame retardant effect of six siliceous ores such as perlite,bentonite,diatomite,wollastonite,sepiolite and organic montmorillonite,and APP/THEIC modified resin in polypropylene（PP）,and the flame retardant mechanism of the flame retardant system and the synergistic mechanism of siliceous ores were a studied.The synergistic flame retardant effect of siliceous ores and APP/THEIC modified resin was studied by vertical combustion test and limiting oxygen index（LOI）measurement.The results show that perlite,bentonite and organic montmorillonite have a good synergistic effect with APP/THEIC modified resin,and the synergistic effect of wollastonite is weak,while diatomite and sepiolite have antagonistic effect.For example,when the addition amount of APP/modified resin is 26.0%,the flame retardant grade of the flame retardant PP reachs V-0,and the LOI value is 26.6%.When the loading of APP/THEIC modified resin and bentonite is 23.0%and 3.0%,respectively,the flame retardan PP also reachs V-0 level,but the LOI value increase to 27.7%。At the same dosage,APP/THEIC modified resin/wollastonite/PP only passes V-1 level,but the LOI value is 26.7%,while APP/THEIC modified resin/sepiolite/PP can only reach V-1 level,but the LOI value is reduced to 25.9%.In addition,the flame retardant properties of the PP composites increase first and then decrease with the increased loading of siliceous ores.The influence of siliceous ores on the combustion behavior of APP/THEIC modified resin/PP were studied by cone calorimeter test（CCT）.The results show that the combination of a small amount of bentonite and wollastonite can significantly improve the inhibition ability of APP/THEIC modified resin on flame propagation and fire intensity during PP combustion,while the impact of organic montmorillonite is not obvious.Perlite,diatomite and sepiolite significantly reduce the inhibition ability of APP/THEIC modified resin.For example,compared with APP/THEIC modified resin/PP,the peak of heat release rate of flame retardant PP combined by bentonite and wollastonite decreases by 11.9%and 15.4%,while that of flame retardant PP compounded by perlite,diatomite,sepiolite and organic montmorillonite increases by9.7%,7.7%,5.7%and 1.6%.The flame retardant mechanism of the flame retardant system and the synergistic mechanism of siliceous ores were studied by the thermogravimetric analysis（TGA）and thermogravimetric-mass spectrometry（TG-MS）of the flame retardant PP,and combining the characterization of the morphology and composition of CCT residues and the effect analysis of heat treatment on the composition of flame retardant PP.The results show that the flame retardant effect of APP/THEIC modified resin is mainly imparted through condensed phase.During the combustion process,firstly,APP is decomposed into polyphosphoric acid,etc.,and esterified with the modified resin and its cracking products;after that,the system gradually melts and is foamed by gaseous products such as N₂ and water vapor.When the system temperature further increases,polyphosphoric acid is dehydrated into polymetaphosphoric acid,which dehydrates and crosslinks the esterification product to forms an intumescent charing layer with a barrier effect.The layer can isolate oxygen and heat,protect the substrate from further decomposition,which thereby reducs fire intensity and inhibits flame propagation.Bentonite and wollastonite can improve the char residual and strength of the charing layer,which is advantageous to inhibit the decomposition of PP,so results in an exceptional synergism.Perlite and organic montmorillonite reduce the residual and strength of the char layer,which is not conducive to inhibiting PP cracking,so brings about a poor synergistic effect,diatomite and sepiolite even have an antagonistic effect.