Burning behavior
The photographs in Figure 11 compared the burning
behavior of untreated and PADEP-coated cotton prepared
with 31 mM ADEP. In the experiments the
ignition time used was 10 s. Figure 11(a,c) compare
the burning behavior of the untreated and treated
fabric at the same burning time of 38 s. It can be
seen that, at this point, the untreated fabric was
burning with distinct flame, whereas in the case of
treated sample, the char area was formed on the fabric
in the burnt area with hardly noticeable flame. It
was found that, for untreated cotton, after removing
the ignition source, the flame spread quickly and
burned the entire fabric with no residue remaining
within 71 s [Fig. 11(b)]. In contrast, the PADEPcoated
cotton, after removing the ignition source, the
flame spread slowly, then extinguished in 53 s leaving
an area of char formation [Fig. 11(d)]. The flame
spread rate of the untreated cotton was found to be
2.1 mm/s, while that of PADEP-coated cotton was
1.18 mm/s. There was therefore a great improvement
in the flame retardancy of the treated cotton.
Improvement in flame retardancy with the PADEP
coating can be explained by the presence of an
adherent and insulating layer of residual char which
built up on the surface of cotton fabric during the
burning process. This layer isolates the underlying
cotton from the flame and thus makes further degradation
by combustion difficult. The flame retardancy
observed was also due to the lack of flammable volatiles
which were formed in the case of untreated
cotton. The good flame retardancy obtained with
admicellar polymerization is attributed to the successful
coating of an ultrathin uniformed film of a
phosphorus-containing flame retarding agent on the
fiber surface.