Effect of Zinc Borate on the Multifunctional Properties of Flame-Retardant Cross-Linked Polyolefin Cable Sheath Materials

Due to the unique application environment of new energy vehicle charging piles, the cable sheath materials are subject to stringent requirements. Enhancing the flame retardancy of cable sheath materials while maintaining their mechanical and insulation properties is important. The cross-linked high-density polyethylene (HDPE)/ethylene propylene diene monomer rubber (EPDM) blend (TPV) is considered an excellent cable sheath material, combining desirable electrical insulation and environmental shielding properties. Here, an intumescent flame retardant (IFR) composed of ammonium polyphosphate (APP) and dipentaerythritol (DPER) was combined with zinc borate (ZB) to enhance the flame retardancy of TPV, and the optimal ZB loading was investigated. The results revealed that the sample “0.10ZB” with the loading ZB of 0.1 phr reached a limiting oxygen index (LOI) value of 24.4% and a UL94 V-0 rating. Cone calorimeter tests further demonstrated that 0.10ZB effectively reduced both the heat release rate (HRR) and total heat release (THR), indicating a significant improvement in flame retardancy. Moreover, the 0.10ZB composites also exhibited excellent mechanical and insulation properties, demonstrating a balanced property profile suitable for practical cable sheath applications.