High-performance low-smoke halogen-free flame-retardant composites for Fuxing electric multiple units via synergistic effects of char formation and anti-dripping of clay-based organic sheet silicates

The polyethylene (PE)-based low-smoke halogen-free flame-retardant composites by introducing clay-based organic sheet silicates (COSS) into PE and ethylene–vinyl acetate copolymer (EVA) blends were prepared by melt blending method. COSS with hydroxyl and organic functional groups on the surface had a good compatibility with the polymer matrix, which favored their uniform dispersion in the polymer matrix. The introduction of COSS restricted the movement of molecular chains and raised the thermal decomposition temperature of the polymer. Meanwhile, the storage modulus and complex viscosity of the materials were raised, and the internal plastic deformation of the materials was enhanced. When the COSS content was 1 wt %, the tensile strength reached 14.7 MPa, and the elongation at break was 596%. The introduced COSS could weaken the regularity of the molecular chain, generate many holes and carriers, and reduce the crystallization ability and volume resistivity of the material. Significantly, a low addition of 3 wt % COSS could improve the density and uniformity of the carbon layer and greatly alleviate the dripping phenomenon during the burning process of the material. With the addition of 7 wt % COSS, the limiting oxygen index (LOI) of the material could reach 28.8%, and the material had a good stiffness balance and significant anti-drip effect.