Effect of three structurally different epoxy resins on fire resistance, optical transparency, and physicomechanical properties of intumescent fire-retardant transparent coatings


Transparent intumescent fire-retardant (IFR) coatings are the newest passive fireproofing materials which maintain structural integrity without losing aesthetic appearance of the substrate. In this present paper, effects of three IFR coatings with structurally different epoxy resins, namely aliphatic, cycloaliphatic, and aromatic, on the fire resistance, transparency, and physicomechanical properties were investigated. Different phosphate resin acids (PRA) were prepared by reacting synthesized phosphate ester acid (PEA) with aliphatic, cycloaliphatic, and aromatic epoxy resins. The chemical structures of the above PEA and PRAs were confirmed by Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance spectroscopy (1H-NMR), and 31P-nuclear magnetic resonance spectroscopy (31P-NMR). Subsequently, transparent IFR coatings were prepared by mixing these PRAs with hexamethoxy methyl melamine resin. Transparency of the coatings was confirmed by UV–Vis–NIR spectrophotometeric studies. Fire protection property and char compressive strength were done to investigate the fire protection ability of the coatings, and the quality of the char formed was analyzed by field emission scanning electron microscope. The decomposition process of prepared fire-retardant coatings was studied by thermogravimetric analysis. Results showed that aliphatic epoxy-based transparent coating produced tough and compact char, but the char height was negligible, and aromatic epoxy-based transparent coating produced soft and fluffy char having excellent char height; however, the fluffy char reduced protection for longer duration. Cycloaliphatic epoxy-based transparent coating produced tough and compact char with good char height, thereby reducing heat transfer during combustion, and also showed superior scratch, abrasion, impact, and water resistance compared to other compositions.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10


  1. 1.

    Neisius, LS, Gaan, N, “Recent Developments in Flame Retardant Polymeric Coatings.” Prog. Org. Coat., 76 1642–1665 (2013)

    Article  Google Scholar 

  2. 2.

    Mochizuki, Y, Mizutani, Y, Okoshi, M, Hamada, H, “The Flame Retardancy Study of the Furniture Made from Corrugated Cardboard.” ScienceDirect, 89 93–97 (2016)

    CAS  Google Scholar 

  3. 3.

    Alongi, J, Han, Z, Bourbigot, S, “Intumescence: Tradition Versus Novelty. A Comprehensive Review.” Prog. Polym. Sci., 51 28–73 (2015)

    CAS  Article  Google Scholar 

  4. 4.

    Arabasadi, Z, Khorasani, M, Akhlaghi, S, Fazilat, H, Gedde, UW, Hedenqvist, MS, Ebrahim Shiri, M, “Prediction and Optimization of Fireproofing Properties of Intumescent Flame Retardant Coatings Using Artificial Intelligence Techniques.” Fire Saf. J., 61 193–199 (2013)

    CAS  Article  Google Scholar 

  5. 5.

    Mariappan, T, Kamble, A, Naik, SM, “An Investigation of Primer Adhesion and Topcoat Compatibility on the Waterborne Intumescent Coating to Structural Steel.” Prog. Org. Coat., 131 371–377 (2019)

    CAS  Article  Google Scholar 

  6. 6.

    Pearce, EM, Weil, ED, Barinov, VY, “Fire Smart Polymers.” ACS Symposium Series, Washington, DC, Chapter 4, 37–48 (2001)

  7. 7.

    Gu, JW, Zhang, GC, Dong, SL, Zhang, QY, “Study on Preparation and Fire-Retardant Mechanism Analysis of Intumescent Flame-Retardant Coatings.” Surf. Coat. Technol., 201 7835–7841 (2007)

    CAS  Article  Google Scholar 

  8. 8.

    Grexa, O, Poutch, F, Mankova, D, “Intumescence in Fire Retardancy of Lignocellulosic Panels.” Polym. Degrad. Stab., 82 373–377 (2003)

    CAS  Article  Google Scholar 

  9. 9.

    Shi, YC, Wang, GJ, “The Novel Silicon-Containing Epoxy/PEPA Phosphate Flame Retardant for Transparent Intumescent Fire Resistant Coating.” Appl. Surf. Sci., 385 453–463 (2016)

    CAS  Article  Google Scholar 

  10. 10.

    Hu, X, Wang, G, Huang, Y, “Study on the Preparation and Properties of Novel Transparent Fire-Resistive Coatings.” J. Coat. Technol. Res., 10 711–726 (2013)

    Article  Google Scholar 

  11. 11.

    Wang, G, Huang, Y, Hu, X, “Synthesis of a Novel Phosphorus-Containing Polymer and Its Application in Amino Intumescent Fire Resistant Coating.” Prog. Org. Coat., 76 188–193 (2013)

    CAS  Article  Google Scholar 

  12. 12.

    Ma, Z, Wang, J, Chen, S, Li, X, Ma, H, “Synthesis and Characterization of Water Borne Intumescent Fire Retardant Varnish Based on Phosphate Resin Acid Cold Cured Amino Resin.” Prog. Org. Coat., 74 608–614 (2012)

    CAS  Article  Google Scholar 

  13. 13.

    Derakhshesh, Z, Khorasani, M, Akhlaghi, S, Keyvani, B, Alvani, AS, “Design and Optimization of an Intumescent Flame Retardant Coating Using Thermal Degradation Kinetics and Taguchi’s Experimental Design.” Polym. Int., 61 926–933 (2012)

    CAS  Article  Google Scholar 

  14. 14.

    Chen, LJ, Song, L, Jie, GX, Tai, QL, Xing, WY, Hu, Y, “A New Intumescent Flame Retardant Containing Phosphorus and Nitrogen: Preparation, Thermal Properties and Application to UV Curable Coating.” Prog. Org. Coat., 70 59–66 (2011)

    CAS  Article  Google Scholar 

  15. 15.

    Wang, G, Yang, J, “Influences of Glass Flakes on Fire Protection and Water Resistance of Waterborne Intumescent Fire Resistive Coating for Steel Structure.” Prog. Org. Coat., 70 150–156 (2011)

    CAS  Article  Google Scholar 

  16. 16.

    Han, Z, Fina, A, Malucelli, G, Camino, G, “Testing Fire Protective Properties of Intumescent Coatings by In-Line Temperature Measurements on a Cone Calorimeter.” Prog. Org. Coat., 69 475–480 (2010)

    CAS  Article  Google Scholar 

  17. 17.

    Wang, G, Yang, J, “Thermal Degradation Study of Fire Resistive Coating Containing Melamine Polyphosphate and Dipentaerythritol.” Prog. Org. Coat., 72 605–661 (2011)

    CAS  Article  Google Scholar 

  18. 18.

    Wang, GJ, Yang, JY, “Influence of Binder on Fire Protection and Anticorrosion Properties of Intumescent Fire Resistive Coating for Steel Structure.” Surf. Coat. Technol., 204 1186–1192 (2010)

    CAS  Article  Google Scholar 

  19. 19.

    Kurt, S, Uysal, B, Özcan, C, “Thermal Conductivity of Oriental Impregnated with Fire Retardant.” J. Coat. Technol. Res., 6 523–530 (2009)

    CAS  Article  Google Scholar 

  20. 20.

    Shi, YC, Wang, G, “The Novel Epoxy/PEPA Phosphate Flame Retardants: Synthesis, Characterization and Application in Transparent Intumescent Fire Resistant Coating.” Prog. Org. Coat., 97 1–9 (2016)

    CAS  Article  Google Scholar 

  21. 21.

    Yan, L, Xu, ZS, Wang, XH, “Synergistic Effect of Organically Modified Montmorillonite on the Flame Retardant and Smoke Suppression Properties of Transparent Intumescent Fire Retardant Coatings.” Prog. Org. Coat., 122 107–118 (2018)

    CAS  Article  Google Scholar 

  22. 22.

    Yan, L, Xu, ZS, Wang, XH, “Influence of Nano-silica on the Flame Retardancy and Smoke Suppression Properties of Transparent Intumescent Fire-Retardant Coatings.” Prog. Org. Coat., 112 319–329 (2017)

    CAS  Article  Google Scholar 

  23. 23.

    Xu, ZS, Chu, ZY, Yan, L, “Enhancing the Flame Retardant and Smoke Suppression Properties of Transparent Intumescent Fire-Retardant Coatings by Introducing Boric Acid as Synergistic Agent.” J. Thern. Anal. Calorim., 133 1241–1252 (2018)

    CAS  Article  Google Scholar 

  24. 24.

    Kundu, CK, Wang, X, Song, L, Hu, Y, “Borate Cross-Linked Layer-by-Layer Assembly of Green Polyelectrolytes on Polyamide 66 Fabrics for Flame Retardant Treatment.” Prog. Org. Coat., 121 173–181 (2018)

    CAS  Article  Google Scholar 

  25. 25.

    Yew, MC, Yew, MK, Saw, LH, Ng, TC, Durairaj, R, Beh, JH, “Influence of Nano Bio-filler on the Fire-Resistive and Mechanical Properties of Water Based Intumescent Coatings.” Prog. Org. Coat., 124 33–40 (2018)

    CAS  Article  Google Scholar 

  26. 26.

    Suin, S, Shrivastava, NK, Maiti, S, Khatua, BB, “Phosphonium Modified Organo Clay as Potential Nano Filler for the Development of Exfoliated and Optically Transparent Polycarbonate/Clay Nanocomposites: Preparation and Characterization.” Polym. J., 49 49–60 (2013)

    CAS  Google Scholar 

  27. 27.

    Landry, V, Blanchet, P, Riedl, B, “Mechanical and Optical Properties of Clay-Based Nanocomposites Coatings for Wood Flooring.” Prog. Org. Coat., 67 381–388 (2010)

    CAS  Article  Google Scholar 

  28. 28.

    Wang, LL, Wang, YC, Yuan, JF, Li, GQ, “Thermal Conductivity of Intumescent Coating Char After Accelerated Aging.” Fire Mater., 37 440–456 (2013)

    CAS  Article  Google Scholar 

  29. 29.

    Duquesne, S, Bachelet, P, VerineBellayer, S, Bourbigot, S, Mertens, W, “Influence of Inorganic Fillers on the Fire Protection of Intumescent Coatings.” Fire Sci., 31 258–275 (2013)

    CAS  Article  Google Scholar 

  30. 30.

    Noragaard, KP, Johansen, KD, Catala, P, Kiil, S, “Investigation of Char Strength and Expansion Properties of an Intumescent Coating Exposed to Rapid Heating Rates.” Prog. Org. Coat., 76 1851–1857 (2013)

    Article  Google Scholar 

  31. 31.

    Guffy, JC, Miller, GR, “Nuclear Magnetic Resonance Method for Analysis of Polyphosphoric Acids.” Anal. Chem. ACS, 31 1895–1897 (1959)

    CAS  Article  Google Scholar 

Download references


The authors would like to thank Dr. M. Patri, Director NMRL, and Dr. T. K. Mahato, Scientist-F for providing guidance and encouragement during the work.

Author information



Corresponding author

Correspondence to R. Baloji Naik.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary material 1 (DOCX 461 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Shree, R., Baloji Naik, R., Naik, R.S. et al. Effect of three structurally different epoxy resins on fire resistance, optical transparency, and physicomechanical properties of intumescent fire-retardant transparent coatings. J Coat Technol Res (2021). https://doi.org/10.1007/s11998-020-00422-4

Download citation


  • Polyphosphoric acid
  • Intumescent fire-retardant coating
  • FTIR
  • Epoxy resin
  • Phosphate resin acid