Improved flame retardancy and ceramifiable properties of PE composites by the combination of aluminum hypophosphite and zinc borate

Ceramifiable polyolefin materials protect circuits by forming compact ceramic layers under fire conditions, and can have an excellent application prospect in the refractory cable field. In this paper, Aluminum hypophosphite (AHP) and zinc borate (ZB) were added to further improve flame retardancy and ceramifiable properties of polyethylene (PE)/silicon powder (SP)/wollastonite (WS)/glass frits (GF) composites. The LOI values of composites with AHP/ZB can reach 23.5%, significantly higher than that of PE/SP/WS/GF composites (19.6%). The thermal stability behavior and char yield behaviors of composites could also be characterized by the TG test. The incorporation of AHP/ZB enhances the flexural strength of residue formed at 1000°C from 0.1 to 20.5 MPa. In addition, a new crystal is formed at high temperatures and is identified as the calcium aluminum phosphate phase CAP, Ca₉Al (PO₄)₇] by XRD analysis. The flow of molten ZB accelerates the reaction of AHP and WS, and this eutectic reaction promotes the formation and stability of ceramics. Furthermore, the SEM analysis reveals the fluxing effect of ZB at low temperatures and AHP at high temperatures. The incorporation of AHP/ZB with a ratio of 1:1 could effectively avoid the vitrification of ceramics and improve their dimensional stability.