Synergistic effects of expandable graphite with some halogen-free flame retardants in polyolefin blends

The synergistic effects of expandable graphite (EG) with some halogen-free flame retardant (HFFR) additives in the polyolefin (PO) blends have been studied by cone calorimeter test (CCT), thermal analysis (TGA. and DTA), limiting oxygen index (LOI), and mechanical properties measurements etc. The results in this work show that EG combined with some HFFR additives, such as ammonium polyphosphate, zincborate, phosphorus-nitrogen containing compound NP28, and microcapsulated red phosphorus, can apparently increase the LOI values and improve the flammability properties of PO blends. The data obtained from the CCT indicate that the heat release rate (HRR) and effective heat of combustion (EHC) decrease and the residues of carbonaceous chars increase remarkably with addition of EG and/or the other HFFR additives. The TGA and DTA data give the positive evidence that the decreases of HRR and EHC Values of the retarded PO materials are due to the increase of oxidative degradation temperature and the decrease of oxidization heat. By optimizing the formulation system and using ethylene vinylacetate copolymer as a compatilizer, the PO/EG/HFFR blends with good flame-retardant and mechanical properties have been obtained in this study. (C) 2001 Elsevier Science Ltd. All rights reserved.