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. 2022 Sep 15;14(18):3853.
doi: 10.3390/polym14183853.

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

Francesco Branda  1 , Dambarudhar Parida  2 , Robin Pauer  3 , Massimo Durante  1 , Sabyasachi Gaan  4 , Giulio Malucelli  5 , Aurelio Bifulco  1
Affiliations

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

Francesco Branda et al. Polymers (Basel). .

Abstract

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.

Keywords: fire behavior; nanoparticle formation mechanism; silica–epoxy nanocomposites; sol-gel chemistry; solvent-free one-pot process.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
FTIR spectra of EPO_WH, EPO, and of the nanocomposites containing (a) 2 wt.% of silica and (b) 6 wt.% of silica, at different TEOS/APTS ratios.
Figure 1
Figure 1
FTIR spectra of EPO_WH, EPO, and of the nanocomposites containing (a) 2 wt.% of silica and (b) 6 wt.% of silica, at different TEOS/APTS ratios.
Figure 2
Figure 2
HRTEM micrograph of EPO_6%Si_2.32.
Figure 3
Figure 3
Tg vs. TEOS/APTES molar ratio for the nanocomposites at 2 (blue labels) and 6 wt.% (orange labels) of silica. In particular, blue squares represent the samples containing 2 wt.% of silica; orange circles indicate samples containing 6 wt.% of silica. The dotted blue line highlights the Tg values of all formulations containing 2 wt.% of silica at different TEOS/APTES ratios, while the dotted orange line identifies the Tg values of all formulations containing 6 wt.% silica at different TEOS/APTES ratios.
Figure 4
Figure 4
Tg vs. APTES/epoxide weight ratio. In particular, blue squares represent samples containing 2 wt.% silica; orange circles indicate samples containing 6 wt.% silica and the black triangle displays pristine resin.
Figure 5
Figure 5
Typical HRR curves vs. time for EPO and some nanocomposites containing (a) 2 wt.% of silica and (b) 6 wt.% of silica, at different TEOS/APTS ratios.
Figure 6
Figure 6
HRR vs. TEOS/APTES molar ratio for the two investigated series containing (a) 2 wt.% of silica and (b) 6 wt.% of silica.
Figure 6
Figure 6
HRR vs. TEOS/APTES molar ratio for the two investigated series containing (a) 2 wt.% of silica and (b) 6 wt.% of silica.
Figure 7
Figure 7
Typical HRR curves vs. temperature for EPO and some nanocomposites containing (a) 2 wt.% of silica and (b) 6 wt.% of silica, at different TEOS/APTS ratios.
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