Flammability of the samples was studied by a horizontal
burning test and a limiting oxygen index test as
per ASTM D 635 and ASTM D 2863, respectively. In
the horizontal burning test, the sample was held horizontally
and a flame fuelled by natural gas was applied
to light one end of the sample. The time for the flame to
reach from the first reference mark (25 mm from the
end) to the second reference mark, which is at 100 mm
from the end, was measured. In the limiting oxygen
index test, the sample was held vertically in the glass
chamber, where there is a controlled flow of oxygen and
nitrogen. The top end of the sample was ignited and
time to burn 50 mm of the sample was measured. The
test was repeated under various concentrations of oxygen
and nitrogen to determine the minimum concentration
of oxygen needed for burning the sample