Improving the flame retardancy efficiency and mechanical properties of the intumescent flame retarded low-density polyethylene by the dual actions of polyurea microencapsulation and aluminum hypophosphite

The use of intumescent flame retardants to retard polyethylene usually had the disadvantages of low flame retardancy efficiency and poor compatibility between intumescent flame retardants and low-density polyethylene (LDPE), which led to the reduction of mechanical properties of materials. In order to solve these issues, the microencapsulated ammonium polyphosphate (MAPP) and microencapsulated aluminum hypophosphite (MAHP) with polyurea were prepared through the interfacial polymerization of water-in-oil (W/O) microemulsions. The flame retarded polyethylene composites with MAPP and MAHP were manufactured. The LDPE composites with 17.3 wt% of MAPP and 3.9 wt% of MAHP possessed a LOI value of 27.3% and achieved the V-0 standard. The PHRR and THR were remarkably decreased by 30.3% and 31.1% compared with that of the LDPE. Furthermore, the tensile strength of LDPE/MAPP-MAHP was 19.1% higher than that of LDPE/APP-AHP because of good dispersion and compatibility of MAPP and MAHP with LDPE. This work provides a new method to prepare flame-retardant LDPE with high performance and the related mechanisms were discussed in detail.