Effect of the Coupling Agent (3-Aminopropyl) Triethoxysilane on the Structure and Fire Behavior of Solvent-Free One-Pot Synthesized Silica-Epoxy Nanocomposites

• Published in: Polymers Vol. 14; no. 18; p. 3853
• Main Authors: Branda, Francesco, Parida, Dambarudhar, Pauer, Robin, Durante, Massimo, Gaan, Sabyasachi, Malucelli, Giulio, Bifulco, Aurelio
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.09.2022; MDPI
• Subjects: Aminopropyltriethoxysilane; Coupling agents; Curing; Epoxy resins; Ethanol; fire behavior; Flammability; High resolution electron microscopy; Investigations; Micelles; Nanocomposites; nanoparticle formation mechanism; Nanoparticles; Particle size; Polyamines; Silica; silica–epoxy nanocomposites; Silicon dioxide; Size distribution; sol-gel chemistry; Sol-gel processes; solvent-free one-pot process; Solvents; Tetraethyl orthosilicate; Transformation temperature; Transmission electron microscopy; United Kingdom; United States > US
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym14183853

Uniformly distributed silica/epoxy nanocomposites (2 and 6 wt.% silica content) were obtained through a “solvent-free one-pot” process. The inorganic phases were obtained through “in situ” sol-gel chemistry from two precursors, tetraethyl orthosilicate (TEOS) and (3-aminopropyl)-triethoxysilane (APTES). APTES acts as a coupling agent. Surprisingly when changing TEOS/APTES molar ratio (from 2.32 to 1.25), two opposite trends of glass transformation temperature (Tg) were observed for silica loading, i.e., at lower content, a decreased Tg (for 2 wt.% silica) and at higher content an increased Tg (for 6 wt.% silica) was observed. High-Resolution Transmission Electron Microscopy (HRTEM) showed the formation of multi-sheet silica-based nanoparticles with decreasing size at a lower TEOS/APTES molar ratio. Based on a recently proposed mechanism, the experimental results can be explained by the formation of a co-continuous hybrid network due to reorganization of the epoxy matrix around two different “in situ” sol-gel derived silicatic phases, i.e., micelles formed mainly by APTES and multi-sheet silica nanoparticles. Moreover, the concentration of APTES affected the size distribution of the multi-sheet silica-based nanoparticles, leading to the formation of structures that became smaller at a higher content. Flammability and forced-combustion tests proved that the nanocomposites exhibited excellent fire retardancy.