Properties Of Nitrogen-sulfur-phosphorus Organically Modified Magnesium-Aluminum Hydrotalcite And Their Flame Retardant In Polypropylene

Polypropylene(PP)is one of the most commonly used thermoplastics.However,its limiting oxygen index(LOI)is only 17-18%.In case of fire,it is quickly ignited,spreads fast,releases a lot of heat,and is accompanied by severe combustible droplets,which is easy to cause fire accidents and severely restricts the application of PP in the field with higher flame retardant requirements.In order to improve the flame retardancy of PP,the addition of flame retardants is considered to be the most effective method.Among them,hydrotalcite(LDHs)is an environmentally friendly halogen-free compound.Its typical layered structure,layer controllability and interlayer ion exchangeability have attracted the attention of experts and scholars at home and abroad in the field of flame retardant polymers.However,to obtain a good flame retardant effect,the high filler content(>40 wt%)in the polymer leads to a decrease in mechanical properties,and its laminate has more hydroxyl groups making them exhibit strong polarity and hydrophilicity.As a result,there is a serious incompatibility between the LDHs and the polymer matrix material,resulting in low flame retardant efficiency and reduced mechanical properties of the polymer matrix material.Therefore,how to effectively improve the compatibility and dispersion of hydrotalcite in polyolefin matrix,and further improve its flame retardant and mechanical properties,is the key to the preparation of hydrotalcite-based high-efficiency flame retardants.In view of this,the main research content of this article had the following aspects:1.Based on the high-efficiency flame retardant performance of triazine-based compounds and sulfur-containing flame retardants,and the improvement of the dispersion of hydrotalcite-based flame retardants in polyolefins caused by interlayer modification.A new type of nitrogen-containing sulfur anion(triazine sulfonate NNS)was designed and synthesized,and introduced into the layers of magnesium aluminum hydrotalcite(LDH-NS).Studies had shown that at the same addition amount,LDH-NS was more effective than LDH-C in improving the flame retardancy and thermal stability of PP matrix.The LOI value of PP/LDH-NS composite and corresponding UL-94 rating were higher than LDH-C,while the peak heat release rate,total heat release and total flue gas release decreased by 69.7%,43.1% and 75.0% compared to the unmodified hydrotalcite composite materials,respectively.Triazine sulfonate and LDH had a significant synergistic effect in improving the fire resistance of PP matrix by promoting the carbon formation of PP/LDH-NS composites.2.With the help of the synergistic effect of nitrogen and sulfur elements on the hydrotalcite flame retardant polypropylene,guanidine sulfamate(GS),which is cheap and easily available and has good flame retardant properties,was introduced as a flame retardant modifier between LDH laminates to prepare the guanidine sulfamate modified magnesium aluminum hydrotalcite(LDH-GS).Studies had shown that the PHRR,THR and TSR of PP/LDH-GS composites decreased by 62.0%,51.9% and 56.1% respectively compared to the unmodified hydrotalcite composites.Furthermore,the residual carbon rate of PP/LDH-GS at 600 ? was doubled more than that of PP/LDH-C,which may be mainly due to the fact that LDH-GS could promote the formation of denser carbon,thereby playing the role of flame retardant effect of condensed phase in PP composites.3.Take advantage of that hexachlorocyclotriphosphazene(HCCP)has the dual identity of "surface modifier" and "synergistic flame retardant",the surface modification of hydrotalcite(LDH@HCCP)was carried out by chemically grafting the phosphazene flame retardant to the surface of hydrotalcite.Researches shown that organically modified hydrotalcite had significantly increased hydrophobicity,which was beneficial to improve the compatibility between LDH@HCCP and matrix material PP,resulting in better dispersion.Since the firmly interconnected functionalized LDHs can maintain the PP matrix for a longer period of time during thermal degradation,the thermal stability of PP/LDH@HCCP was higher than that of PP/LDH-C.