Preparation And Properties Of Ethylene-propylene-diene Monomer/Chloroprene Foams With Halogen-free Flame Retardants

Ethylene-propylene-diene monomer(EPDM)foams are widely used in automotive,construction,electrical and electronic industries and other fields as synthetic rubber foam with excellent comprehensive performance.However,EPDM is flammable material with an oxygen index of about 20 %.Because of bigger specific surface area,EPDM foams become easier to burn and harder to flame retardant.That limits the scope of its application to expand.With the increase of the content of flame retardant,the content of matrix rubber which can be used for foaming will be reduced correspondingly,and that foam is difficult to form small and uniform cell,resulting in poor performance of the materials used.Therefore,in this paper,chloroprene rubber(CR)was used instead of part of EPDM to reduce contents of flame retardants and to ensure the content of matrix rubber used for foaming.And then,the co-curing property and compatibility of EPDM phase and CR phase in EPDM/CR blends were improved by changing the content of accelerators Na-22 and TMTD and the compatibilizer EPDM-g-MAH.At present,the halogen flame retardant is still one of the main flame retardants of EPDM foam material,but it will release a lot of toxic fumes in the combustion process,which are not conducive to personal safety and environmental protection.So a new type of highly efficient halogen-free flame retardant will become the new darling of future market demand.As far as we know,there are no literatures focused on synergistic flame retardant properties and mechanism of expansible graphite(EG),organic montmorillonite(OMMT)and magnesium hydrate(MH)together as halogen-free flame retardants in preparation of EPDM/CR foams.In this subject,the EPDM/CR foams containing 20 to 25 wt.% inorganic halogen-free flame retardants can reach the flame retardant grade and the V-0 grade of UL-94,and has a relatively uniform cell structure.That material is in line with China's policy guidance of flame retardant industry from the development of high-performance products to the development of both high-performance and environmentally friendly products.This topic has great practical significance.The curing rate,mechanical properties,dynamic mechanical properties,thermal stability,microstructure and flame retardancy were tested,respectively.The results are as follows:1.In this project,sulfur and zinc oxide were used as the vulcanization system of EPDM/CR blends,and the basic formula was designed according to the optimum effective sulfur ratio.By changing the contents of accelerator Na-22 and TMTD,the differences of vulcanization rate and crosslinking density between EPDM and CR phases were effectively reduced,which improving the co-vulcanization and compatibility of two-phase.By changing the content of compatibilizer EPDM-g-MAH,the compatibility of EPDM and CR phases was improved effectively,but the vulcanization rate and crosslinking density of EPDM/CR were reduced.When the content of Na-22,TMTD and EPDM-g-MAH was 1.5 phr,2.1phr and 10 phr respectability,the mechanical properties of EPDM/CR vulcanizate were optimized,especially the tensile strength was 17.84 MPa,the elongation at break was 483.75 % and the tearing strength was 28.38 kN/m.2.In this paper,OMMT/EPDM nano intercalation composite material was prepared in the mixer with the process condition of 160 ? and 110 r/min.The layer spacing of OMMT increased 2.78 nm than that of pure OMMT in the composite,which was about 5.04 nm.3.The EPDM/CR foams containing 5 wt.% EG,5 wt.% OMMT and 5 wt.% MH could obtain a LOI value of 29.1 % and a UL-94 V-0 rating.EG combined with OMMT remarkably improved the fire retardant property and thermostability,and when MH was used as the third co-retardant unit,the new system could achieve better fireproof performance.Flame retardant system consisting of EG and OMMT increased the LOI values and UL-94 rating,considerably decreased the second peaks of heat release rates(HRR)and smoke production rates(SPR),formed more complete charred residues,and reduced the thermal degradation rates and mass loss percentages compared to the control samples.In addition,the fire retardancy was further improved when MH,EG and OMMT coexisted in the rubber foams,especially,there was no second peaks in the HRR and SPR curves.Moreover,the observation from scanning electron microscopy(SEM)revealed the synergistic flame retardant mechanism of EG and OMMT.In condensed-phase,EG and OMMT left over after combustion formed a complete,compact and rigid charred layer with a mosaic structure by expanded graphite embedded in cortical-honeycomb layers of OMMT,thus effectively weakened the transfer of heat,oxygen and volatiles.4.The smaller OMMT contributes to the formation of a more complete cell structure in EPDM / CR,while EG with larger particle size can severely damage the foam structure of the material.