Flame-Retardation Of Poly(Ethylene-co-vinyl Acetate) Via Intumescent Flame Retardants

Poly(ethylene–co–vinyl acetate) (EVA) was widely used in the wire and cable industry as insulating materials due to its good mechanical and physical properties. However, it has a low limiting oxygen index (LOI) value and is flammable. The fateful drawback of polyethylene restricts its wider application. Therefore, how to improve its flame retardancy becomes a big challenge.This problem can be solved by using flame-retardant additives, such as halogenated compounds and inorganic hydrated compounds. Unfortunately, halogenated compounds are serious environmentally problem, and inorganic hydrated have poor efficiency. Recently, intumescent flame retardants (IFRs) have received a considerable attention because they are non-halogen, low toxicity, and low smoke release. The IFRs are designed to swell and form a porous carbonaceous char layers on the surface of materials, which act as a barrier to heat, air and flammable pyrolysis products.In this paper, a phosphorous-containing flame retardant (5,5-dimethyl-2-(2-oxo-2,6,7- trioxa-1-phosphabicyclo[2,2,2]octane-4- methyl)-1,3 dioxaphosphorinane, 2-oxide)(PEPANGP) was synthesized successfully, which was a intumescent additive (PEPANGP). The molecular structure of PEPANGP was characterized by FT-IR spectroscopy and 1H-NMR. Meanwhile, a novel intumescent flame retardant EVA system (IFR-EVA) had been obtained from EVA, PEPANGP and APP. Its thermal properties and flame retardancy were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test and cone calorimeter. The synergism between PEPANGP and APP in EVA systems was studied; meanwhile, the morphology of the intumescent char layer and its possible mechanism were investigated by scanning electron microscopy (SEM) and FT-IR spectroscopy.Ammonium polyphosphate (APP) and expandable graphite (EG) have been used to improve flame retardancy of poly(ethylene-co-vinyl acetate) (EVA). A LOI value of 31.2 and UL-94 V-0 rating can be achieved when the total loading of the two flame retardants is 30 wt.-%. The flame-retardant mechanism of EVA/APP/EG system has been investigated by TGA, SEM, FTIR and XPS. SEM is used to observe the structures of the intumescent charred layers. EG expands into a worm-like char structure when exposed to heat, and this kind of char structure could block the mass and heat transfer, and protect the underlying EVA from combustion. The chars generated at different temperatures (350℃,450℃,600℃and 650℃) have been studied by FTIR and XPS, respectively. The residues contain ammonium salt, unsaturated compounds, polyaromatics, phosphoric and ployphosphoric acids, and some EVA that was not burned completely. Based upon all the results mentioned above, a possible flame-retardant mechanism has been proposed.The mechanical properties of EVA/APP/PEPANGP and EVA/APP/EG were tested, in conclusion, the composites of EVA/APP/PEPANGP and EVA/APP/EG are applicable and are good choice to new flame retardant material.