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Effect of a novel aflame retardant based on silane-modified nanosepiolites functionalized with expandible graphite on the reaction kinetics, cellular structure and physical properties of rigid polyurethane foams

Thursday (08.10.2020)
11:50 - 12:10

Rigid polyurethane (RPU) foams are one of the most important thermal insulating materials, since they can be used simultaneously as structural materials, due to a unique combination of low weight, low thermal conductivity and good mechanical properties. Due to this, RPU foams are nowadays extensively used in buildings, transportation insulation, refrigeration systems and pipelines, as well as in other applications [1]. However, these materials have a great disadvantage, their high flammability and their fast flame-spreading rate in case of a fire. For this reason, many investigations are focused on improving the flame resistance of RPU foams in order to achieve the strict requirements on the flame retardancy, especially in the field of building and construction. For this, different types of flame retardants (FRs) are proved to improve the thermal stability of PU foams: halogen-containing FRs, halogen-free FRs (such as layered silicate, phosphonium salt, expandable graphite, ammonium polyphosphate, and SiO2) and reactive FRs (such as polyols modified by phosphorous-, nitrogen-, and silicon-containing compounds) [2, 3].


In this research, we have used a novel FR based on silane-modified nanosepiolites functionalized with expandable graphite (SFEG) (80 wt% nanosepiolites- 20 wt% expandable graphite) in order to have a synergistic effect mainly on the thermal stability of water-blown RPU foams. Density, cellular structure, thermal stability, thermal conductivity and mechanical properties are investigated for four RPU foams with different contents of SFEG (0, 2, 4 and 6 wt%). Moreover, the effect of SFEG on the blowing and gelling reactions involved in the foaming process is evaluated by FTIR spectroscopy and the resulting modifications of the chemical composition are related to the final properties of the studied materials.


Additionally, foams containing only silane-modified nanosepiolites, foams containing only EG and foams containing silane-modified nanosepiolites and EG are studied; and their properties are compared with those of foams with SFEG.


[1] M. Szycher, Szycher's Handbook of Polyurethanes, Second ed., CRC Press Boca Raton, Florida, USA, 2012.

[2] D. Liu, A. Hu, Materials, 13 (2020).

[3] W. Zhou, S.J. Hao, G.D. Feng, P.Y. Jia, X.L. Ren, M. Zhang, Y.H. Zhou, Polymers (Basel), 12 (2020).

Ph.D. Mercedes Santiago-Calvo
University of Valladolid
Additional Authors:
  • María Carracedo-Pérez
    University of Valladolid
  • Dr. María Luisa Puertas
    Tolsa S.A.
  • Dr. Antonio Esteban‐Cubillo
    Tolsa S.A.
  • Julio Santarén
    Tolsa S.A.
  • Prof. Dr. Fernando Villafañe
    University of Valladolid
  • Prof. Dr. Miguel Ángel Rodríguez-Pérez
    University of Valladolid