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Abstract

Sol-Gel Complements Conventional Strategies for the Synthesis of Self-Extinguishing Hybrid Silica-Epoxy Nanocomposites †

by
Aurelio Bifulco
1,*,
Claudio Imparato
1,
Sandro Lehner
2,
Antonio Aronne
1,
Giulio Malucelli
3 and
Sabyasachi Gaan
2
1
Department of Chemical, Materials and Production Engineering (DICMaPI), University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy
2
Laboratory for Advanced Fibers, Empa Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland
3
Department of Applied Science and Technology, Politecnico di Torino, Viale Teresa Michel 5, 15121 Alessandria, Italy
*
Author to whom correspondence should be addressed.
†
Presented at the 3rd International Online Conference on Polymer Science, 19-21 November 2025; Available online: https://sciforum.net/event/IOCPS2025.
Proceedings 2026, 136(1), 19; https://doi.org/10.3390/proceedings2026136019
Published: 14 November 2025
Versions Notes

Introduction. Growing industrial demand, together with rising pollution and the depletion of phosphorus stores, is moving the scientific community towards the development of flame-retardant (FR) epoxy nanocomposites (ENCs) containing low levels of P and more sustainable additives [1].
Methods. High-resolution transmission electron microscopy (HRTEM) analysis was carried out to study the morphology of ENCs. Cone calorimetry (CC) and UL-94 vertical flame spread tests were performed to investigate the fire responses of all ENCs.
Results. The reaction of DGEBA (Bisphenol A diglycidyl ether)- or Novolac-based resins with APTES (3-aminopropyltriethoxysilane) allowed the production of organic-inorganic silanized epoxy moieties [2,3,4]. The hybrid moieties could condense with tetraethyl orthosilicate (TEOS), a silica precursor, to form an in situ silica phase through sol-gel reactions [3,5]. HRTEM analysis revealed that in the case of DGEBA, the silica phase was composed of well-ordered multi-lamellar nanoparticles (NPs). In contrast, the investigation of Novolac highlighted that fully amorphous silica NPs were embedded in the hybrid co-continuous polymer network [3]. The incorporation of DOPO-based FRs into silica-epoxy systems based on DGEBA/Novolac resin produced aliphatic nanocomposites with high transparency, no-dripping UL-94-V0 rating, and a strong decrease (up to 80%) in the peak of the heat release rate in CC tests, with a P loading of up to 3 wt.%. Regarding Novolac, the transparency remained even at silica NP loadings beyond 4 wt.% thanks to their amorphous nature [3]. More waste-to-wealth approaches involve the use of humic acids or biochar from spent coffee grounds, together with ammonium polyphosphate and urea, in APTES-modified DGEBA-based epoxy systems to obtain no-dripping, self-extinguishing systems, with a P content of only 1 wt.%.
Conclusions. The sol-gel in situ generation of inorganic phases has been explored in combination with DOPO-based FRs, bio-wastes, and other synergists to prepare no-dripping, self-extinguishing (V-0 rating in UL-94 flammability tests) aliphatic ENCs, even while keeping P at low loadings (1–3 wt.%).

Author Contributions

Conceptualization, A.B. and S.G.; Methodology, A.B., S.L., G.M. and S.G.; Validation, A.A., G.M. and S.G.; Formal Analysis, A.B., C.I. and S.L.; Investigation, A.B., C.I. and S.L.; Data Curation, A.B., C.I. and S.L.; Writing—Original Draft Preparation, A.B.; Writing—Review and Editing, G.M. and S.G.; Visualization, A.B., C.I. and S.L.; Supervision, A.A., G.M. and S.G.; Project Administration, S.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Liu, B.W.; Zhao, H.B.; Wang, Y.Z. Advanced Flame-Retardant Methods for Polymeric Materials. Adv. Mater. 2022, 34, 2107905. [Google Scholar] [CrossRef] [PubMed]
  2. Innocenzi, P.; Kidchob, T.; Yoko, T. Hybrid Organic-Inorganic Sol-Gel Materials Based on Epoxy-Amine Systems. J. Sol-Gel Sci. Technol. 2005, 35, 225–235. [Google Scholar] [CrossRef]
  3. Lehner, S.; Arpaia, A.; Passaro, J.; Góra, M.; Pauer, R.; Rupper, P.; Russo, P.; Aronne, A.; Bifulco, A.; Gaan, S. Simultaneous Optical Clarity and Fire Protection in Novolac Resin via in Situ Amorphous Silica and a Liquid DOPO Derivative. Polym. Degrad. Stab. 2026, 244, 111839. [Google Scholar] [CrossRef]
  4. Jiao, J.; Liu, P.; Wang, L.; Cai, Y. One-Step Synthesis of Improved Silica/Epoxy Nanocomposites with Inorganic-Organic Hybrid Network. J. Polym. Res. 2013, 20, 1–8. [Google Scholar] [CrossRef]
  5. Sun, B.; Zhou, G.; Zhang, H. Synthesis, Functionalization, and Applications of Morphology-Controllable Silica-Based Nanostructures: A Review. Prog. Solid State Chem. 2016, 44, 1–19. [Google Scholar] [CrossRef]
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Share and Cite

MDPI and ACS Style

Bifulco, A.; Imparato, C.; Lehner, S.; Aronne, A.; Malucelli, G.; Gaan, S. Sol-Gel Complements Conventional Strategies for the Synthesis of Self-Extinguishing Hybrid Silica-Epoxy Nanocomposites. Proceedings 2026, 136, 19. https://doi.org/10.3390/proceedings2026136019

AMA Style

Bifulco A, Imparato C, Lehner S, Aronne A, Malucelli G, Gaan S. Sol-Gel Complements Conventional Strategies for the Synthesis of Self-Extinguishing Hybrid Silica-Epoxy Nanocomposites. Proceedings. 2026; 136(1):19. https://doi.org/10.3390/proceedings2026136019

Chicago/Turabian Style

Bifulco, Aurelio, Claudio Imparato, Sandro Lehner, Antonio Aronne, Giulio Malucelli, and Sabyasachi Gaan. 2026. "Sol-Gel Complements Conventional Strategies for the Synthesis of Self-Extinguishing Hybrid Silica-Epoxy Nanocomposites" Proceedings 136, no. 1: 19. https://doi.org/10.3390/proceedings2026136019

APA Style

Bifulco, A., Imparato, C., Lehner, S., Aronne, A., Malucelli, G., & Gaan, S. (2026). Sol-Gel Complements Conventional Strategies for the Synthesis of Self-Extinguishing Hybrid Silica-Epoxy Nanocomposites. Proceedings, 136(1), 19. https://doi.org/10.3390/proceedings2026136019

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