and achieved a V-0 rating in the UL-94 test. Meanwhile, neat EP did not pass the
UL-94 test and burns vigorously for a longer time period with dripping until
clamping. This observation clearly indicates that DTA exhibited efficient FR activity
and was remarkable in decreasing flame dripping and combustion time; furthermore,
auto extinguishability was observed in EP/DTA resins. In the initial stage, flame
propagation slowly increased up to 0.5 s then slowly decreases the flame and at 3 s,
the flame was extinguished as shown in Fig. 6.2, due to the “blowing-out effect,”
which means that in the initial stage, non-flammable gases are accumulated inside
the char layer and once released, they extinguished the flame. These observations
indicate that FR activity in such cases depends on the fast accumulation and release
of non-flammable gases as well as strong char formation. From literature, it can be
inferred that that triazole and tetrazole-containing DOPO derivative compounds and
condensed compounds of p-di-substituted amine derivatives with DOPO show a
blowing out effect which contributes to their FR activity; the synthesis of these
compounds is illustrated in Scheme 6.1. In addition, some phosphazene derivative
compounds also exhibited this behavior. In such compounds, the P-moieties aid in
the formation of a char layer, whereas N-moieties release non-flammable gases.
During polymer burning, with time, the volume of non-flammable gases increases
and at a certain pressure, the char layer breaks and the gases are released into the
flame zone and immediately extinguish the flame. Therefore, new synthesis methods
and techniques should be developed for efficient P and N-containing FRs, which are
inexpensive and are capable of fast accumulation and release of high volumes of
non-flammable gases and strong char formation. Matzen et al. [19] systematically
studied the effect of dripping on the FR activity of different thermoplastic polymers,
such as PBT, PP, PP-EP, and PA6, in different thermal conditions with different
flame retardants. They reported that a high melt viscosity is imperative to improve
the dripping property; in addition, dripping can be reduced by high crosslinking
Fig. 6.1 Schematic of the blowing-out effect [13]. Reproduced with permission from Elsevier
Science Ltd
72
6 Melt-Dripping and Char Formation
UL-94 test and burns vigorously for a longer time period with dripping until
clamping. This observation clearly indicates that DTA exhibited efficient FR activity
and was remarkable in decreasing flame dripping and combustion time; furthermore,
auto extinguishability was observed in EP/DTA resins. In the initial stage, flame
propagation slowly increased up to 0.5 s then slowly decreases the flame and at 3 s,
the flame was extinguished as shown in Fig. 6.2, due to the “blowing-out effect,”
which means that in the initial stage, non-flammable gases are accumulated inside
the char layer and once released, they extinguished the flame. These observations
indicate that FR activity in such cases depends on the fast accumulation and release
of non-flammable gases as well as strong char formation. From literature, it can be
inferred that that triazole and tetrazole-containing DOPO derivative compounds and
condensed compounds of p-di-substituted amine derivatives with DOPO show a
blowing out effect which contributes to their FR activity; the synthesis of these
compounds is illustrated in Scheme 6.1. In addition, some phosphazene derivative
compounds also exhibited this behavior. In such compounds, the P-moieties aid in
the formation of a char layer, whereas N-moieties release non-flammable gases.
During polymer burning, with time, the volume of non-flammable gases increases
and at a certain pressure, the char layer breaks and the gases are released into the
flame zone and immediately extinguish the flame. Therefore, new synthesis methods
and techniques should be developed for efficient P and N-containing FRs, which are
inexpensive and are capable of fast accumulation and release of high volumes of
non-flammable gases and strong char formation. Matzen et al. [19] systematically
studied the effect of dripping on the FR activity of different thermoplastic polymers,
such as PBT, PP, PP-EP, and PA6, in different thermal conditions with different
flame retardants. They reported that a high melt viscosity is imperative to improve
the dripping property; in addition, dripping can be reduced by high crosslinking
Fig. 6.1 Schematic of the blowing-out effect [13]. Reproduced with permission from Elsevier
Science Ltd
72
6 Melt-Dripping and Char Formation