Study On Preparation And Properties Of The Halogen-free Flame Retardant EPDM/PP Dynamic Vulcanizates

EPDM/PP dynamic vulcanizates(EP-TPV)is one of the most widely used polyalkene thermoplastic elastomers.It has excellent mechanical properties,weatherability,processability,low cost and recyclable,etc,which makes it widely used in the automobile,construction,electronics and daily necessities field.However,EPTPV is highly combustible,and thus its application is greatly restricted in the field of high flame-retardant requirements.In this paper,EP-TPV was first prepared by one step method,and the effects of rubber and plastic ratio,content of crosslinking agent as well as oil filling on the microstructure,gel content,dynamic and static mechanics,crystallization,thermodynamics and rheological properties were investigated.Also,the best process conditions and formula were explored.Then,PER and MP were used to prepared intumescent flame retardant EP-TPV using compound method and reactive extrusion method,respectively.The effect of FR on the properties of EP-TPV were studied,and the flame retardant EP-TPV prepared by two methods were compared.Finally,zinc borate,organic montmorillonite and expandable graphite were selected as synergist to establish a synergistic flame retardant system.The paper focused on the influence of synergists and their contents on mechanical properties and flame retardancy of the aforementioned flame rerardant EP-TPV.Meanwhile,the mechanism of synergist was also discussed.The conclusions are as follows:(1)EPDM particles refine and evenly distribute in the PP resin during dynamic vulcanization.The gel content and complex viscosity of EP-TPV increases with increasing rubber and plastic ratio,while the permanent compression deformation,storage modulus and hardness decreases.When,the rubber and plastic ratio is 40/60,the tensile strength and elongation at break reached the maximum value of 20.5 MPa and 554%,respectively.The content of DCP can affect the crosslinking density of EPTPV and the mechanical properties are the best when DCP is 1.2 wt%.The naphthenic oil could promote the motion of EPDM and PP molecular chains,and thus the complex viscosity,storage modulus and loss modulus reduce.Moreover,the vulcanization of EPDM is promoted and the elongation at break increases,while the tensile strength and hardness of EP-TPV decreases.In addition,EPDM and naphthenic oils can hinder the the crystallization of PP,and DCP can also play the same role by causing partial crosslinking or degradation of PP molecular chains.(2)When the molar ratio of MP/PER is 1.8,the yield of the reactive extrusion reaches the maximum value of 75.45%,and the flame retardant masterbatch prepared has good thermal stability and high carbon residue with the MP/PER molar ratio of 1.6 or 1.8.When FR content is more than 25 wt%,FR particles tend to agglomerate,and the mechanical properties the flame retardant EP-TPV decreases significantly.Also,FR particles can impede the motion of EPDM and PP molecular chains,and thus the rigidity is improved as well as the complex viscosity,storage modulus and loss modulus,while the crystallization of PP decreases.Then,the thermal stability enhances with increasing FR content,and a continuous and compact carbon layer is formed with improving the flame retardancy of EP-TPV.When FR is 35 wt%,the flame retardancy of the system is better and the UL-94 test reaches V-0.In addition,compared with the reactive extrusion method,FR prepared by the compound method showes low carbon forming efficiency and poor flame retardancy.(3)The rigidity,storage modulus and bending strength of the flame retardant EPTPV are further improved with the addition of synergists,while the elongation at break decreases obviously.ZB and OMMT have relatively low effect on the mechanical properties of the system when the addition amount is low,while EG is not.Then,the synergists enhances the thermal stability and the carbon residual carbon of the system significantly.The OMMT synergistic system showes a poor flame retardancy due to the carbon layer with low stability is formed.The addition of a small amount of EG can effectively delay the combustion of EP-TPV and decrease the HRR and SPR obviously.The compact carbon layer in the combustion process is formed with the addition of ZB,which showes good synergistic effect.Also,when ZB content is 6 wt%,the system reached V-0 with a slight decrease of mechanical properties,and thus ZB is suitable for the synergistic flame retardancy of EP-TPV.