Influences of Talc on Fire Performance of Low Density Polyethylene

In this paper the effects of talc on the ignition time, the burning rate and the downward flame spread rate of low density polyethylene were studied through the cone calorimeter test, the modified UL 94 vertical burning test and a designed downward flame spread experiment. Cone calorimeter tests show that the mass loss rate (MLR) and the heat release rate (HRR) decrease with increasing the talc content, which is ascribed to the residue formed by talc. When the loading of talc is low, talc powders aggregate to form separate talc tablets during burning, leading to the slight decrease of MLR and HRR. When the mass fraction of talc is higher than 20%, possibly the percolation threshold for barrier effect of talc, an integral crust covering the whole specimen surface is generated to act as a good heat and mass barrier, resulting in the significant drop of MLR and HRR. However, no evidence of char in the residue is found. The ignition time in both the cone calorimeter test and the modified UL 94 test initially decreases and then increases with increasing the talc content. It is supposed that the wick effect of talc aggregations reduces the ignition time while the dilution effect and the barrier effect delay the ignition time. The downward flame spread rate initially increases and then decreases with increasing the talc content, which is suspected to be related with the reduction of ignition time and melt flow rate during burning caused by talc.