Combustion behavior of bioplastic in high-temperature airflow

The effects of airflow temperature and velocity on the combustion of a cylindrical bioplastic (PLA) were investigated. The combustion characteristics of polymethylmethacrylate (PMMA) were also investigated for comparison. The diameter and length of the PLA and PMMA fuel cylinders were 10 mm and 40 mm, respectively. After the upper end of the vertically placed fuel cylinder was ignited with a pilot flame, air was supplied from above. The airflow temperature T were set at 15, 100, and 400 ℃. As the airflow velocity increased, the fuel was widely covered by the flame, promoting the preheating and pyrolysis of the fuel. However, when the airflow velocity exceeded a certain value, local extinction was observed at the leading edge of the fuel. The heat release rate (HRR) increased with increasing airflow temperature and velocity. At T = 400 ℃, the HRR of the PLA, which has a low calorific value, was comparable to that of PMMA. Only flaming combustion was observed with PMMA, and the CH radical emission intensity due to flaming combustion was found to be correlated with the HRR. In contrast, in the PLA, surface combustion was observed in addition to flaming combustion, and the former became more pronounced as the airflow temperature and velocity increased. As a result, the HRR increased with increasing airflow velocity; however, the CH radical emission intensity did not increase monotonically as a result of surface combustion. The amount of PLA residue after combustion was smaller than that of PMMA, especially when the airflow temperature was below the pyrolysis temperature of the fuel. The heat release rate and residue amount suggested that PLA is also a plastic suitable for thermal recycling.