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. 2020 Jul 26;12(8):1661.
doi: 10.3390/polym12081661.

Thermal and Fire Behavior of a Bio-Based Epoxy/Silica Hybrid Cured with Methyl Nadic Anhydride

Aurelio Bifulco  1 , Angela Marotta  1 , Jessica Passaro  1 , Aniello Costantini  1 , Pierfrancesco Cerruti  2 , Gennaro Gentile  2 , Veronica Ambrogi  1   2 , Giulio Malucelli  3 , Francesco Branda  1
Affiliations

Thermal and Fire Behavior of a Bio-Based Epoxy/Silica Hybrid Cured with Methyl Nadic Anhydride

Aurelio Bifulco et al. Polymers (Basel). .

Abstract

Thermosetting polymers have been widely used in many industrial applications as adhesives, coatings and laminated materials, among others. Recently, bisphenol A (BPA) has been banned as raw material for polymeric products, due to its harmful impact on human health. On the other hand, the use of aromatic amines as curing agents confers excellent thermal, mechanical and flame retardant properties to the final product, although they are toxic and subject to governmental restrictions. In this context, sugar-derived diepoxy monomers and anhydrides represent a sustainable greener alternative to BPA and aromatic amines. Herein, we report an "in-situ" sol-gel synthesis, using as precursors tetraethylorthosilicate (TEOS) and aminopropyl triethoxysilane (APTS) to obtain bio-based epoxy/silica composites; in a first step, the APTS was left to react with 2,5-bis[(oxyran-2-ylmethoxy)methyl]furan (BOMF) or diglycidyl ether of bisphenol A (DGEBA)monomers, and silica particles were generated in the epoxy in a second step; both systems were cured with methyl nadic anhydride (MNA). Morphological investigation of the composites through transmission electron microscopy (TEM) demonstrated that the hybrid strategy allows a very fine distribution of silica nanoparticles (at nanometric level) to be achieved within a hybrid network structure for both the diepoxy monomers. Concerning the fire behavior, as assessed in vertical flame spread tests, the use of anhydride curing agent prevented melt dripping phenomena and provided high char-forming character to the bio-based epoxy systems and their phenyl analog. In addition, forced combustion tests showed that the use of anhydride hardener instead of aliphatic polyamine results in a remarkable decrease of heat release rate. An overall decrease of the smoke parameters, which is highly desirable in a context of greater fire safety was observed in the case of BOMF/MNA system. The experimental results suggest that the effect of silica nanoparticles on fire behavior appears to be related to their dispersion degree.

Keywords: bio-based epoxy resin; flame retardance; in-situ; methyl nadic anhydride; silica nanoparticles; sol-gel.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
FTIR-ATR spectra of (a) DGEBA, the DGEBA-based epoxy resin (DGEBA/MNA) and epoxy/silica hybrid (DGEBA/MNA_2Si), and (b) BOMF, the furan-based epoxy resin (BOMF/MNA) and epoxy/silica hybrid (BOMF/MNA_2Si).
Figure 2
Figure 2
FTIR-ATR spectra of the thermogravimetric analysis (TGA) residue of BOMF/MNA_2Si in air.
Figure 3
Figure 3
Typical TEM micrographs for (a,b) BOMF/MNA_2Si and (c,d) DGEBA/MNA_2Si at different magnifications.
Figure 4
Figure 4
(a) TGA and (b) derivative curves (DTG) thermograms of epoxy resins and epoxy/silica hybrids.
Figure 5
Figure 5
The curing of BOMF (a) and DGEBA (b) monomers leads to the formation of an ester group between the MNA and epoxy groups.
Figure 6
Figure 6
Photographs of the char residues obtained after cone calorimetry tests for (a) DGEBA/MNA, (b) BOMF/MNA, (c)DGEBA/MNA_2Si and (d) BOMF/MNA_2Si.
See this image and copyright information in PMC

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