Chapter 6
Melt-Dripping and Char Formation
This chapter reports the fundamental understanding of melt-dripping and how this
characteristic of polymeric materials link with fire properties.
6.1 Relationship Between the Melting Dripping
Characteristics of Polymer Films and Fire Properties
Dripping is also considered as an important parameter that needs to be analyzed
while evaluating the FR properties of polymers; in the UL-94 test, polymers are
characterized based on their dripping behavior [1, 2]. Dripping may lead to flame
propagation due to spreading of flames on the surface of the polymer and surroundings. Many researchers carried UL-94 test to quantify the dripping behavior
during combustion [3–6]. If a polymer melts easily, it obviously exhibits high
dripping, which is one of the main reasons for the spreading of fire. The melt flow
and dripping of polymers mainly depend on the polymer viscosity. At particular
temperatures, solid polymer films melt, where there is no solid phase, is called
melting point or melting temperature. This is a physical phenomenon and phase
change occurs from solid to liquid, which in turn affects the efficiency of heat
diffusion, particle size, and heating rate. Crystalline polymers exhibit a sharp
melting point and at this temperature they lose their ordered structure. The melting
of some compounds or polymers may be accompanied by simultaneous decomposition, similar to sublimation [7]. It is well known that the T g , polymer degradation, and viscosity of the polymer melt affect its melt dripping behavior [8].
Generally, the dripping of polymers depends on their melting behavior, which is
dependent on the T g and melting temperature. Zhang et al. [9] studied the effect of
T g and melting point on the flammability of polymers and they observed that the
degree of melt flow or melt drip is directly proportional to T g . Therefore, polymers
with low T g values melt easily, while those with higher T g do not. In case the T g of a
© Springer Nature Switzerland AG 2020
S. Sinha Ray and M. Kuruma, Halogen-Free Flame-Retardant
Polymers, Springer Series in Materials Science 294,
https://doi.org/10.1007/978-3-030-35491-6_6
69
Melt-Dripping and Char Formation
This chapter reports the fundamental understanding of melt-dripping and how this
characteristic of polymeric materials link with fire properties.
6.1 Relationship Between the Melting Dripping
Characteristics of Polymer Films and Fire Properties
Dripping is also considered as an important parameter that needs to be analyzed
while evaluating the FR properties of polymers; in the UL-94 test, polymers are
characterized based on their dripping behavior [1, 2]. Dripping may lead to flame
propagation due to spreading of flames on the surface of the polymer and surroundings. Many researchers carried UL-94 test to quantify the dripping behavior
during combustion [3–6]. If a polymer melts easily, it obviously exhibits high
dripping, which is one of the main reasons for the spreading of fire. The melt flow
and dripping of polymers mainly depend on the polymer viscosity. At particular
temperatures, solid polymer films melt, where there is no solid phase, is called
melting point or melting temperature. This is a physical phenomenon and phase
change occurs from solid to liquid, which in turn affects the efficiency of heat
diffusion, particle size, and heating rate. Crystalline polymers exhibit a sharp
melting point and at this temperature they lose their ordered structure. The melting
of some compounds or polymers may be accompanied by simultaneous decomposition, similar to sublimation [7]. It is well known that the T g , polymer degradation, and viscosity of the polymer melt affect its melt dripping behavior [8].
Generally, the dripping of polymers depends on their melting behavior, which is
dependent on the T g and melting temperature. Zhang et al. [9] studied the effect of
T g and melting point on the flammability of polymers and they observed that the
degree of melt flow or melt drip is directly proportional to T g . Therefore, polymers
with low T g values melt easily, while those with higher T g do not. In case the T g of a
© Springer Nature Switzerland AG 2020
S. Sinha Ray and M. Kuruma, Halogen-Free Flame-Retardant
Polymers, Springer Series in Materials Science 294,
https://doi.org/10.1007/978-3-030-35491-6_6
69