The effect of expanded graphite on the flammability and thermal conductivity properties of phase change material based on PP/wax blends

The study reports on the flammability, thermal stability, impact properties and thermal conductivity of shape-stabilized phase change materials based on a soft Fischer-Tropsch paraffin wax blended with polypropylene (PP). The blends were melt-mixed with expanded graphite (EG) up to 9 wt% to improve the thermal conductivity and flammability resistance of the material. The thermal stability and flammability results show an increase in thermal stability and flame resistance of PP in the presence of EG, with the flammability further increasing in the presence of wax, probably because of the smaller and better dispersed EG particles in the PP/wax/EG composite that gave rise to a more compact char layer. Although the thermal degradation mechanism did not change in the presence of EG, the EG particles retarded the evolution of the volatile degradation products. The storage modulus of the PP/wax/EG composite was lower than those of PP and PP/EG, and decreased with increasing in wax content because of the softening effect of the wax. The impact strength of the PP/wax/EG composites increased with increasing EG content in all the samples, but decreased with increasing wax content.