Fire property and charring behavior of high impact polystyrene containing expandable graphite and microencapsulated red phosphorus

High impact polystyrene (HIPS) flame retarded by expandable graphite (EG) alone or in combination with microencapsulated red phosphorus (MRP) was prepared by melt compounding and investigated in terms of its fire property and charring behavior by limiting oxygen index, UL-94, cone calorimeter test, thermal analysis and scanning electron microscopy. It has been shown that EG itself has some flame-retarding and good smoke-suppressing effect on HIPS, but the flame retardant efficiency is rather low. The addition of a small amount of MRP can improve the flame retardancy and smoke suppression of the HIPS/EG composite and decrease the loading of flame retardant considerably. The HIPS/EG/MRP composite with a mass ratio of 80/15/5 produces more char yield and exhibits good flame retardancy and smoke suppression simultaneously. The thick and thermally stable intumescent char residue covered on the surface of the HIPS/EG/MRP composite can serve as an effective barrier against heat transfer and mass exchange between flame area in the gas phase and the polymer in the condensed phase. The temperature inside the HIPS/EG/MRP (80/15/5) composite is decreased more than that inside the HIPS/EG (80/20) composite upon burning. Due to a lower effective heat flux, the pyrolysis rate of the polymer is decreased. Moreover, fuel release rate is reduced because of the increasing thermal insulation property and char yield. As a result, the flame retardancy of the HIPS/EG/ MRP composite is increased noticeably. The burnt residue of the HIPS/EG/MRP composite in cone calorimeter test is not homogeneous and contains much undecomposed polymer beneath the expanded char layer. (C) 2015 Elsevier Ltd. All rights reserved.