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. 2022 Jul 5;8(7):419.
doi: 10.3390/gels8070419.

Ice-Template Crosslinked PVA Aerogels Modified with Tannic Acid and Sodium Alginate

Lucía G De la Cruz  1 , Tobias Abt  1 , Noel León  1 , Liang Wang  2 , Miguel Sánchez-Soto  1
Affiliations

Ice-Template Crosslinked PVA Aerogels Modified with Tannic Acid and Sodium Alginate

Lucía G De la Cruz et al. Gels. .

Abstract

With the commitment to reducing environmental impact, bio-based and biodegradable aerogels may be one approach when looking for greener solutions with similar attributes to current foam-like materials. This study aimed to enhance the mechanical, thermal, and flame-retardant behavior of poly(vinyl alcohol) (PVA) aerogels by adding sodium alginate (SA) and tannic acid (TA). Aerogels were obtained by freeze-drying and post-ion crosslinking through calcium chloride (CaCl2) and boric acid (H3BO3) solutions. The incorporation of TA and SA enhanced the PVA aerogel's mechanical properties, as shown by their high compressive specific moduli, reaching up to a six-fold increase after crosslinking and drying. The PVA/TA/SA aerogels presented a thermal conductivity of 0.043 to 0.046 W/m·K, while crosslinked ones showed higher values (0.049 to 0.060 W/m·K). Under TGA pyrolytic conditions, char layer formation reduced the thermal degradation rate of samples. After crosslinking, a seven-fold decrease in the thermal degradation rate was observed, confirming the high thermal stability of the formed foams. Regarding flammability, aerogels were tested through cone calorimetry. PVA/TA/SA aerogels showed a significant drop in the main parameters, such as the heat release rate (HRR) and the fire growth (FIGRA). The ion crosslinking resulted in a further reduction, confirming the improvement in the fire resistance of the modified compositions.

Keywords: aerogel; crosslinking; fire resistance; lyophilization; tannic acid.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM micrographs of uncrosslinked aerogels (a) P5T2A1, (b) P5T3A2, (c) P5T3A3, and (d) P5T2A1 crosslinked aerogel; EDS images for (e) boron and (f) calcium dispersion in P5T2A1 crosslinked aerogel.
Figure 2
Figure 2
Schematic representation of the aerogels’ preparation process and the possible reactions between PVA/TA/SA aerogels and post-ion-crosslinking with CaCl2 and H3BO3 (Created with Biorender.com Agrmt. No. EV240EKOH).
Figure 3
Figure 3
FTIR-ATR spectra of PVA, TA, SA, P5T3A3 uncrosslinked and crosslinked aerogels.
Figure 4
Figure 4
(a) Compressive behavior of aerogels; (b) comparison of the specific moduli obtained in each composition of aerogels in different states (uncrosslinked, crosslinked, and dried crosslinked).
Figure 5
Figure 5
(a) TGA weight loss; (b) Derivative thermogravimetric curves of PVA/TA/SA aerogels. For the sake of clarity, only P5T3A3 crosslinked aerogel has been represented. See Figure S4 for the rest of the studied samples.
Figure 6
Figure 6
Flame behavior of (a) P5, (b) P5T3A3 uncrosslinked, and (c) crosslinked aerogels under Bunsen burner. (d) Diagrammatic scheme of combustion cycle and the flame retardant mechanism (Created with Biorender.com Agrmt. No.HF242VFEC0).
Figure 7
Figure 7
(a) Main representative HRR curves from uncrosslinked and crosslinked PVA/TA/SA aerogels; (b) digital photographs from P5T3A3 uncrosslinked and crosslinked aerogels before and after combustion at 50 kW/m2.
See this image and copyright information in PMC

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