Chapter 5
Flame-Retardant Polyurethanes
In 1937, the German scientist Otto Bayer and his team discovered poly addition
reactions [1–3]; the poly addition of diols and diisocyanates forms PUs under
suitable conditions and completely avoids the formation of undesired by-products.
PUs can basically be prepared by two methods, of which the most often used
method is the reaction between polyols and diisocyanates under appropriate conditions (Scheme 5.1). In a single-step process, the two monomers, polyol and
diisocyanate, react together to form PU. Using this method, it may be possible to
obtain linear PUs, given that the starting compounds are linear. Under similar
conditions, in the presence of excess diisocyanates, a pre-PU polymer is formed.
Subsequently, in the next step, a calculated amount of chain extender is added for
the complete formation of PUs. Chain extenders contain hydroxyl, amine, or other
functional groups capable of reacting with isocyanate groups [4, 5].
PUs are considered versatile polymeric materials and their physical and chemical
properties depend on the choice of starting materials; further, their properties can be
tailored by varying the composition of the monomers and monomer compounds.
Accordingly, depending on the application, the required chemicals for PU synthesis
can be chosen. Unfortunately, most PU polymers are highly flammable and release
toxic smoke while burning. Therefore, it is important to study parameters that can
improve the FR activity of PU polymers for customized applications. In this
respect, melting temperature (T m ), glass transition temperature (T g ), viscosity, and
degree of crosslinking are the important factors affecting the FR activity of a
polymer. Most of the early established studies on segmented PUs suggest that
segmental phase separation increases T g and T m ; further, the T g values of hard
segments (HS) and soft segments (SS) are different [6–8]. The responsible factors
are the –NCO/–OH ratio, the size of HS and SS domains, and reaction conditions
[4, 9–13].
© 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_5
47
Flame-Retardant Polyurethanes
In 1937, the German scientist Otto Bayer and his team discovered poly addition
reactions [1–3]; the poly addition of diols and diisocyanates forms PUs under
suitable conditions and completely avoids the formation of undesired by-products.
PUs can basically be prepared by two methods, of which the most often used
method is the reaction between polyols and diisocyanates under appropriate conditions (Scheme 5.1). In a single-step process, the two monomers, polyol and
diisocyanate, react together to form PU. Using this method, it may be possible to
obtain linear PUs, given that the starting compounds are linear. Under similar
conditions, in the presence of excess diisocyanates, a pre-PU polymer is formed.
Subsequently, in the next step, a calculated amount of chain extender is added for
the complete formation of PUs. Chain extenders contain hydroxyl, amine, or other
functional groups capable of reacting with isocyanate groups [4, 5].
PUs are considered versatile polymeric materials and their physical and chemical
properties depend on the choice of starting materials; further, their properties can be
tailored by varying the composition of the monomers and monomer compounds.
Accordingly, depending on the application, the required chemicals for PU synthesis
can be chosen. Unfortunately, most PU polymers are highly flammable and release
toxic smoke while burning. Therefore, it is important to study parameters that can
improve the FR activity of PU polymers for customized applications. In this
respect, melting temperature (T m ), glass transition temperature (T g ), viscosity, and
degree of crosslinking are the important factors affecting the FR activity of a
polymer. Most of the early established studies on segmented PUs suggest that
segmental phase separation increases T g and T m ; further, the T g values of hard
segments (HS) and soft segments (SS) are different [6–8]. The responsible factors
are the –NCO/–OH ratio, the size of HS and SS domains, and reaction conditions
[4, 9–13].
© 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_5
47