Study On Instumescent Flame Retardant In Ethylene-vinyl Acetate Rubber

Ethylene vinyl-acetate thermoset rubber (EVM) with high vinyl acetate content is knownfor its excellent resistance to aging，outstanding weathering/ozone/UV resistance, lowcompression set at high temperatures and good processability. EVM is currently found inmany rubber products, including the cable sector, adhesives and in the modification ofthermoplastics. It is increasingly being used in the automotive industry for seals and gasketsdue to the more stringent high temperature requirements. However, EVM is flammable anddrips when burning, hence flame retardant (FR) systems have to be incorporated into thepolymer to reduce fire hazards and to meet the legislation required standards. In order toachieve an acceptable degree of flame retardancy, metal hydroxides have been extensivelyused as smoke and toxic-free additives in halogen-free flame-retardant (HFFR) polymericmaterials. But their fatal disadvantages are low FR efficiency and very large usage amount,which causes the mechanical properties of the FR polymeric materials to decrease sharply.Among the flame retardants, intumescent flame retardants (IFRs) have aroused greatattention in recent years because they are more environmentally friendly than the traditionalhalogen-containing flame retardant. Ammonium polyphosphate（APP） is an importantcomponent in intumescent halogen-free flame retardant, which does not generate additionalsmoke.In this thesis, APP was used as an acid agent and dipentaerythritol (DPER) as acarbonization agent. Further investigations on retardancy of EVM were listed as followed:Ⅰ. The IFR system containing EG, APP and DPER was prepared. It improved the flameretardancy and reduced the dripping tendency of EVM rubber. LOI values above40%and theUL-94test V-0level could be obtained. However, the mechanical properties of the EVMdecreased slightly when the DPER/APP/EG retardant system was added.Ⅱ. Thermal analysis showed that EG treated rubber could form more residual char andrelease less heat than untreated rubber. SEM photographs indicated the residual char ofsample treated with APP, DPER and EG was continuous and compact. It was concluded thatthis IFR system could improve the char formation which is the key factor in drippingresistance and improve the material properties of the product.Ⅲ. Microencapsulated ammonium polyphosphate coating layer (MMT-MF-APP) with a montmorillonite-melamine formaldehyde resin coating layer was successfully prepared by insitu polymerization. The product was characterized by Fourier transform infrared, Energydispersive X-ray spectroscopy and scanning electron microscopy. Water absorption analysisshowed that the microencapsulation of APP with the MMT-MF resin leads to a decrease in theparticle’s water solubility.Ⅳ. Compared to the untreated APP, the obtained microcapsules also exhibited bettermechanical properties and higher flame retardancy in the ethylene-vinyl acetate copolymerwith high vinyl acetate content（EVM）rubber compared with the common ammoniumpolyphosphate. Moreover, thermogravimetric analysis (TGA) results showed that the EVMcomposites with MMT-MF-APP and Dipentaerythritol (DPER) as flame ratardants possesshigher thermal stability than those with common APP and DPER as flame retardants.