Combustion and free burning behaviour of recycled plastic pellets

Abstract

This paper details the behaviour of plastic pellets under various fire conditions. Plastic pellets made of recycled plastic materials namely, low density polyethylene (LDPE), high density polyethylene (HDPE) and polypropylene (PP) are the subject of this paper. Recycled plastic has contaminants not present in virgin plastic, and the geometry has been adjusted, whereby the latter has a significant impact on fire phenomena. Cone calorimeter tests were conducted at 25, 35 and 50 kW/m2. At 35 kW/m2the average heat of combustion (HOC), average time to ignition (TTI) and average heat release rate (HRR) over all three materials tested are 44 MJ/kg, 39 s, and 560 kW/m2 respectively. Behaviour observed during experiments is described based on the cone calorimeter tests as well as non-standardised free burn tests – for illustrative purposes. These observations include ease of ignition and initial flames spread, mass involved in burning, burning in layers, formation of solidified layers and whether the material will remain burning after the removal of the external heat source. During combustion the material flows, potentially leading to flaming pools, but would also solidify during the application of water making suppression of deep-seated fires difficult. Although recycled plastic pellets are difficult to ignite, once ignited they burn intensely making them a much larger fire risk than an ignition risk. Early detection of such fire is imperative for fire extinguishment.