polymer is around the ambient temperature or less, we could expect pool-like fire.
Polymers with T g values >100 °C do not melt significantly and do not catch fire
easily. The melting temperatures, T g values, and decomposition temperatures can be
determined by differential scanning calorimetry (DSC) and TGA. During melting,
solid-viscous liquid phase change occurs, while during decomposition, bond
breakage occurs. In between the melt and decomposition temperatures, the viscosity
of a polymer decreases and it loses its mechanical integrity; furthermore, significant
changes may occur in other associated properties. The relationship between melt
dripping and melt viscosity of polymers and nanocomposites has been studied
[10, 11]. It has been shown that even though polymer degradation occurred to a
high extent, if the viscosity is high, then the FR activity of the polymer is high; this
is because viscosity is a parameter dependent on temperature. In the presence of
nanoparticles, the viscosity of a polymer increases, due to which the melt flow and
dripping decrease. The dripping and viscosity of polymer composite resins depend
on interactions with different FR hardeners and decomposition pathways. Schartel
et al. [2] prepared epoxy resins with different DOPO-based hardeners and the effect
of different hardeners on the dripping properties and FR properties was evaluated.
They also studied reactive and non-reactive FR additive-containing epoxy resins,
such as DGEBA/DDS, DGEBA/DDS/DOPO analogs (non-reactive) and DGEBA/
DDS/DOPO-based diamine (reactive) composites, and evaluated their FR activity.
They noticed that compared to non-reactive epoxy resins, the LOI values of reactive
epoxy resins increased from 13% to 17% and the UL-94 test results also improved
from HB to V-1 rating. Pawlowski and Schartel [1] synthesized polycarbonate/
acrylonitrile-butadiene-styrene (PC/ABS) blends with three different types of aryl
phosphates (TPP, BDP, and PTFE) and systematically conducted comparative
studies on their FR activity and melt dripping behavior. PC/ABS with BDP
achieved a V-2 rating in the UL-94 test and exhibited high deformation due to BDP
acting as a plasticizing agent. Meanwhile, a combination of BDP with PTFE in the
PC/ABS system led to a remarkable FR activity and V-0 rating in the UL-94 test
due to a synergetic effect between BDP and PTFE. In the presence of PTFE, the
condensed-phase action of BDP is enhanced with accelerating char formation.
Therefore, it is clear that PTFE strongly affects the dripping property and polymer
melt viscosity. Therefore, the PC/ABS system with PTFE achieved an HB rating in
the UL-94 test because it burns completely without dripping.
One of the most important phenomena in FR polymer synthesis is selfextinguishability or the “blowing-out effect,” which indicates the release of phosphorus radicals and non-flammable gases. This mainly involves the formation of
protective highly thermally stable carbonaceous char layers, which hinder further
polymer combustion, but at the same time, allow fast accumulation of nonflammable gases inside the char layers. A schematic model of the “blowing-out
effect” is shown in Fig. 6.1 in the initial stages, the polymer can burn plentifully and
subsequently a thermally stable char layer is formed. Inside this char layer,
non-flammable gases are accumulated, which weaken the strength of the flame. After
some time, pressure due to the non-flammable gases increases and breaks down the
char structure; once eluted, the non-flammable gases immediately extinguish the
70
6 Melt-Dripping and Char Formation
Polymers with T g values >100 °C do not melt significantly and do not catch fire
easily. The melting temperatures, T g values, and decomposition temperatures can be
determined by differential scanning calorimetry (DSC) and TGA. During melting,
solid-viscous liquid phase change occurs, while during decomposition, bond
breakage occurs. In between the melt and decomposition temperatures, the viscosity
of a polymer decreases and it loses its mechanical integrity; furthermore, significant
changes may occur in other associated properties. The relationship between melt
dripping and melt viscosity of polymers and nanocomposites has been studied
[10, 11]. It has been shown that even though polymer degradation occurred to a
high extent, if the viscosity is high, then the FR activity of the polymer is high; this
is because viscosity is a parameter dependent on temperature. In the presence of
nanoparticles, the viscosity of a polymer increases, due to which the melt flow and
dripping decrease. The dripping and viscosity of polymer composite resins depend
on interactions with different FR hardeners and decomposition pathways. Schartel
et al. [2] prepared epoxy resins with different DOPO-based hardeners and the effect
of different hardeners on the dripping properties and FR properties was evaluated.
They also studied reactive and non-reactive FR additive-containing epoxy resins,
such as DGEBA/DDS, DGEBA/DDS/DOPO analogs (non-reactive) and DGEBA/
DDS/DOPO-based diamine (reactive) composites, and evaluated their FR activity.
They noticed that compared to non-reactive epoxy resins, the LOI values of reactive
epoxy resins increased from 13% to 17% and the UL-94 test results also improved
from HB to V-1 rating. Pawlowski and Schartel [1] synthesized polycarbonate/
acrylonitrile-butadiene-styrene (PC/ABS) blends with three different types of aryl
phosphates (TPP, BDP, and PTFE) and systematically conducted comparative
studies on their FR activity and melt dripping behavior. PC/ABS with BDP
achieved a V-2 rating in the UL-94 test and exhibited high deformation due to BDP
acting as a plasticizing agent. Meanwhile, a combination of BDP with PTFE in the
PC/ABS system led to a remarkable FR activity and V-0 rating in the UL-94 test
due to a synergetic effect between BDP and PTFE. In the presence of PTFE, the
condensed-phase action of BDP is enhanced with accelerating char formation.
Therefore, it is clear that PTFE strongly affects the dripping property and polymer
melt viscosity. Therefore, the PC/ABS system with PTFE achieved an HB rating in
the UL-94 test because it burns completely without dripping.
One of the most important phenomena in FR polymer synthesis is selfextinguishability or the “blowing-out effect,” which indicates the release of phosphorus radicals and non-flammable gases. This mainly involves the formation of
protective highly thermally stable carbonaceous char layers, which hinder further
polymer combustion, but at the same time, allow fast accumulation of nonflammable gases inside the char layers. A schematic model of the “blowing-out
effect” is shown in Fig. 6.1 in the initial stages, the polymer can burn plentifully and
subsequently a thermally stable char layer is formed. Inside this char layer,
non-flammable gases are accumulated, which weaken the strength of the flame. After
some time, pressure due to the non-flammable gases increases and breaks down the
char structure; once eluted, the non-flammable gases immediately extinguish the
70
6 Melt-Dripping and Char Formation