Preparation Andflame Retardant Property Of Basic Magnesium Carbonate Based EVA

Basic magnesium carbonate has become one of mineral flame retardants with great application potential after magnesium hydroxide and aluminum hydroxide because of its low price,wide source,non-toxic and low smoke,good insulating property and so on.But the flame retardancy efficiency of basic magnesium carbonate as a single flame retardant flame retardant is low.Commonly,more than 60 wt % amount of basic magnesium carbonate is requiredin the process of preparation of composite materials to meet the requirements of flame retardancy.But the compatibility between flame retardants and inorganic materials is poor due to their different polarity.Aiming at the problems of large surface polarity of basic magnesium carbonate and low flame retardation efficiency,the mechanical and flame retardation properties of composite materials were regulated by two ideas of synergistic-effect and in-situ grafting reaction,so as to make it meet the national standards for cable sheath materials.The main research contents are as follows:(1)Firstly,the surface modification of basic magnesium carbonate powder was carried out with silane coupling agent to improve its compatibility with EVA.Then,it was compounded with magnesium hydroxide and aluminum hydroxide to achieve synergisticeffective flame retardant.The results showed that the elongation at break of modified basic magnesium carbonate increased from 105.87% to 159.43%,and the tensile strength increased from 8.75 MPa to 12.12 MPa.But the composite melt index(0.496 g / 10 min)is too low.And then according to complex formula,flame retardant compositematerialswas prepared with 155.07% elongation at break and tensile strength of 9.73 MPa,melt index of 1.00 g / 10 min,meeting the requirements of mechanical properties for cable case and flame retardant performance requirement.At the some time,melt index also achieves requirement.(2)Basic magnesium carbonate@poly-phosphoric lauryl amine(BPL)flame retardantwas synthesized through in-situ grafting method.And the results show that BPL/EVA composite exhibits ultra-high elongation at break(806%)although the adding amount of BPL reaches 60 wt %.And also it is found that the BPL displayed excellent flame retardant performance,which could be ascribe to high density,strength,quality of char layerafter combustion.(3)Based on the excellent performance of BPL,the flame retardant mechanism of BPL/EVA is further studied.The results show that BPL wouldbe decomposed to produce large amounts of inorganic phosphatewhen they are ignited.And the inorganic phosphate could quickly crosslink with EVA molecular chain segment by dehydration,so as to form tough carbon bridge between particles after rapid charring(the carbon bridge structure called "fence").And because of the restriction effect of "fence" structure as the framework,BPL particles maintained the original position in EVA matrix,presenting the structure of dislocation layer.The specific structure makes the pores fill each other,greatly enhancing the heat isolation,suppression of combustible gas and oxygen diffusion.