A method to assess downward flame spread and dripping characteristics of fire-retardant polymer composites

A method is described to assess the flame retardancy of polyethylene composites by measuring both their downward flame spread rates as well as their combined melting and dripping rates on rectangular rods, ignited at their top. The composite materials were produced by mixing pulverized polymer with organic additives of differing particle sizes, shapes, and mass fractions. The resulting mix was melted in a mold, and then it was solidified into rods. The additives were carbonaceous solids with particle sizes spanning from tens of nanometers to tens of micrometers. The mass fraction of the additives in the polymer matrix varied from 1 to 5wt%. Upon ignition of the upper tips of the polymer composite rods, the downward flame spread rate and the melting and dripping rate were separately assessed by measuring their mass loss and their heights. The addition to polyethylene of finely sized carbonaceous additives at mass fractions of 4 to 5wt% proved effective at significantly slowing down its downward flame spread by drastically hindering its dripping tendency. The effectiveness of the additives increased with increasing their mass fraction and decreasing their particle size. High mass fractions of carbon additives resulted in wicking, which can enhance radiatively the heat transfer.