Flame retardant performance
LOI values of the fabric samples are presented in Fig. 6. It indicates
that LOI values of the grafted samples are higher than that of
ungrafted sample (19.8). AM-g-nylon-6,6 sample with DP of 32.5%
has the highest LOI value of 26.2, which is 6.4 higher than that of
the ungrafted sample. Fig. 6 also shows the effect of monomer
concentration on LOI. DP increases from 9.6% to 32.5% with the
increase of monomer concentration, while the LOI value increases
from 21.8 to 26.2 with the increase of monomer concentration. The
vertical burning test results are shown in Table 2. Compared to the
ungrafted sample, the samples with DP of 32.5% and 16.9% have
shorter after-flame time, shorter char length and no melt dripping
in the vertical burning test. Shrinkage of the grafted samples is
more obvious than that of the ungrafted sample, and the spread
speed of flame on the grafted sample is retarded. Therefore,
combustion of the grafted samples could not be self-sustained in
air. These phenomena could be explained by the earlier decomposition
of AM-g-nylon-6,6 fabric sample and the release of
nonflammable gas which finally prevents fire from spreading,
which is also supported by the results from thermal analysis, cone
calorimetry and SEM. These results show that the flame retardancy
of nylon-6,6 fabric can be enhanced by photografting with acrylamide.
Meanwhile, compared to the treated fabric from two step
method in our previous study, although the LOI value (26.2) of the
grafted fabric obtained from the one-step photografting is lower
than that (29.1) of the grafted fabric obtained from the two-step
surface modification, AM-g-nylon-6.6 fabric has no melt dripping
in the vertical burning test while MAn-g-PA fabric sample reacted
with triethanolamine has the melt dripping. This phenomenon
could be attributed to the different flame retardant used for nylon-
6,6 fabric.