Fire parameters of recycled plastic pellets

During the recycling process, waste plastic undergoes various processes that change its geometry. The thermal properties and fire behaviour of plastic in different geometries has not been widely studied. This paper aims to determine critical thermal properties of plastic pellets made of recycled plastic. For this paper, cone calorimeter tests of various volumes of recycled plastic pellets of low- and high-density polyethylene and polypropylene were conducted. During these tests, the heat release rate (HRR), mass loss rate and time-to-ignition were measured, thereafter the heat of combustion (HOC) was calculated. A calibration of suitable time-to-ignition equations is carried out. The average HRR is between 353 and 581 kW/m² with an external heat flux of 50 kW/m². The measured time-to-ignition values ranged between 27 s at 50 kW/m² and just more than 90 s at 25 kW/m². Values obtained analytically from the thermally thin time-to-ignition equations for these materials describe ignition well, which appears to be due to the particulate nature of the samples. The HOC (40–41 MJ/kg) shows good agreement with the HOC for virgin plastic found in literature. These properties can be used as a basis for material characterisation, and further testing will be done before using this as simulation inputs to determine how bulk stored plastic pellets will behave in the event of a fire.