Expandable Graphite in Polyethylene: The Effect of Modification, Particle Size and the Synergistic Effect with Ammonium Polyphosphate on Flame Retardancy, Thermal Stability and Mechanical Properties

ABSTRACT

Four different sizes of tripolyphosphate modified expandable graphite (EG_p) are prepared and incorporated into linear low density polyethylene (LLDPE). Its size effect on the material combustibility, thermal stability, and mechanical properties are investigated, respectively. The interactions between each EG_p and ammonium polyphosphate (APP II) are also examined. Results confirm that EG_p can significantly improve the flame retardancy and thermal stability of LLDPE composites than the normal expandable graphite. A 13% dose of EG_P50 can ensure that 87LLDPE/13EG_P50 meets the flame retardant requirement. There is a positive correlation between EG_P size and LOI and high temperature thermal stability. Especially, the combination of EG_p and APP produces a significant synergistic effect in improving the LOI value and the vertical burning level. The peak value of heat release rate of 87LLDPE/8.7EG_P50/4.3APP can be remarkably reduced by 83.9%. However, addition of the tested additives causes a decline of LLDPE mechanical performance. With the size of EG_P increases, the effect becomes more obvious.

KEYWORDS:

• Modified expandable graphite
• tripolyphosphate
• particle size effect
• flame retardancy
• polyolefin
• synergistic effect

Additional information

Funding

This work was supported by the Natural Science Foundation of Hebei Province (CN) under Grant (number B2015201028).