Synergistic effects of ammonium polyphosphate and red phosphorus with expandable graphite on flammability and thermal properties of HDPE/EVA blends

In this work, the flame-retardant high-density polyethylene/ethylene vinyl-acetate copolymer (HDPE/EVA) composites have been prepared by using expandable graphite (EG) as a flame retardant combined with ammonium polyphosphate (APP) and red phosphorus masterbatch (RPM) as synergists. The synergistic effects of these additives on the flammability behaviors of the filled composites have been investigated by limiting oxygen index, UL-94 test, cone calorimeter test, thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), and scanning electron microscopy. The results show that APP and RPM are good synergists for improving the flame retardancy of EG-filled HDPE/EVA composites. The data from TGA and FTIR spectra also indicate the synergistic effects of APP and RPM with EG considerably enhance the thermal degradation temperatures but decrease the charred residues of the HDPE/EVA/EG composites because the flame-retardant mechanism has changed. The morphological observations present positive evidences that the synergistic effects take place in APP and RPM with EG in flame-retardant EG-filled HDPE/EVA/EG composites. The formation of stable and compact charred residues promoted by APP and RPM with EG acts as effective heat barriers and thermal insulations, which improves the flame-retardant performances and prevents the underlying polymer materials from burning. Copyright (C) 2015 John Wiley & Sons, Ltd.