Enhancing Flame Retardancy, Thermal Stability, Physical and Mechanical Properties of Polyethylene Foam with Polyphosphate Modified Expandable Graphite and Ammonium Polyphosphate

Abstract The method of preparing polyolefin foam with good flame retardancy, thermal stability, and physical and mechanical properties was investigated. Foaming condition of linear low density polyethylene (LLDPE) was investigated with triphenyl phosphate (TPP) as plasticizer, NaHCO 3 as foaming agent. The influence of modified expandable graphite (EG P ) and ammonium polyphosphate (II) on foam density, compression strength, combustion characteristics and thermal stability was explored. Results verified that EG P presented better dilatability and flame retardancy than the normal expandable graphite. Addition of EG p improved the limiting oxygen index (LOI) of 15NaHCO 3 /100 LLDPE TPP /30EG p foam from 18.8% to 24.6%. Furthermore, the combination of EG p and ammonium polyphosphate (II) (APP) at the mass ratio of 2:1 improved the LOI of 15NaHCO 3 /100 LLDPE TPP /20EG p /10APP sample to 27.9%, and the vertical burning UL-94 level reached V-0, indicating that this material was flame retardant. Although these additives made 15NaHCO 3 /100 LLDPE TPP /20EG p /10APP composite exhibit a high density of 142.5 kg m −3 , which was increased by 12.3 wt% relative to the 15NaHCO 3 /100 LLDPE TPP foam, it could improve the compressive strength to 0.4747 MPa, which was about 2.7 times that of the matrix. The thermal stability of the material was also enhanced.