The halogen-free flame retardant principle of expandable graphite is mainly reflected in the following aspects:
Volume expansion isolates heat sources and oxygen: Expandable graphite will rapidly expand at high temperatures, with its volume reaching hundreds of times its initial size, forming an expanded carbon layer covering the surface of the substrate. This carbon layer can effectively isolate thermal energy radiation and oxygen, preventing the further spread of flames. The internal structure of the expanded graphite sheet is loose, which has an efficient insulating effect on energy and reduces the damage to the material structure caused by high temperature.
Heat absorption and cooling: During the expansion process, expandable graphite will absorb a large amount of heat, thereby reducing the temperature of the combustion system. This endothermic effect helps to slow down or prevent the thermal degradation and thermal oxidation degradation processes of materials.
Promoting carbonization: The interlayers of expandable graphite contain acid radical ions, which are released during the expansion process, promoting the carbonization of the substrate. The carbonized layer has higher thermal stability and barrier performance, which can effectively prevent the continuous progress of combustion.
Interrupting the chain reaction: During the expansion process of expandable graphite, the acid radical ions released can also combine with the free radicals produced by combustion, thereby interrupting the chain reaction of combustion.
