2.5.1. Limiting Oxygen Index (LOI) Test

The limiting oxygen index test was carried out on a Dynisco Limiting Oxygen Index Analyzer (Franklin, TN, USA). After specimens with the size of 80 mm, 10 mm, and 4 mm were inserted, the concentration of oxygen within the device was adjusted to the desired test value by adding nitrogen, and the tube was flushed for 30 s. The specimens were exposed to a 3 cm methane flame for 30 s in a top surface ignition, and the time until extinction was recorded. If the sample burned continuously for more than 180 s or the flame burned more than 50 mm in length, the test was considered failed. Iteratively, the oxygen content was examined and repeated twice for the highest possible value passed.