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

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.

Microcomputed Tomography for the Microstructure Evaluation of 3D Bioprinted Scaffolds

“…A Poisson’s ratio of 0.5 was assumed for hydrogels and polymers . The density, thermal conductivity, tensile yield, and ultimate strength were all assumed based on values in existing literature reports. − …”

Improvement of Heat Release Rate Measurement from Woods Based on Their Combustion Products Temperature Rise

“…A detailed procedure for calculating FIGRA by one widely accepted method is given, e.g., EN 13823:2020 + A1:2022 [5]. A more detailed overview of MARHE and FIGRA parameters and their practical applications can be found, e.g., in [6][7][8][9]. The method of estimating other fire characteristics from the HRR is described in the following scientific works [10] (prediction of reaction to fire class), [11,12] (flashover category prediction), [13,14] (flame spread rate prediction) and [15,16] (prediction of combustion products, mainly carbon monoxide yield from released heat).…”

“…The combustion products during a cone calorimeter test can be very well approximated by an ideal gas model (relatively low pressure, typically 98 to 101 kPa, and relatively high temperature, typically 300 to 400 K). The chemical amount flow rate is then calculated from the Equation of state of an ideal gas (7), 𝑝𝑉 = 𝑛𝑅𝑡 𝑐 (7) where p is the combustion products pressure (Pa), V is the combustion products volume flow rate (m 3 s −1 ), and R is the gas constant (J mol −1 K −1 ). Therefore, chemical amount flow rate of combustion products can be calculated from their volume flow rate, pressure, and temperature, according to Equation (7).…”

“…The chemical amount flow rate is then calculated from the Equation of state of an ideal gas (7), 𝑝𝑉 = 𝑛𝑅𝑡 𝑐 (7) where p is the combustion products pressure (Pa), V is the combustion products volume flow rate (m 3 s −1 ), and R is the gas constant (J mol −1 K −1 ). Therefore, chemical amount flow rate of combustion products can be calculated from their volume flow rate, pressure, and temperature, according to Equation (7). The differences between values calculated according to the state of an ideal gas (in the above-mentioned range of pressure and temperature) and according to the Van der Waals equation for real gas are deep below 1%.…”

Properties of Freeze-Dried Gelatin/Clay Aerogel Composites Crosslinked with Tannic Acid

“…Aerogels are lightweight, solid, and open-porous materials obtained from a gel in which the solvent has been replaced by air without collapsing the three-dimensional structure previously created. Their highly porous structure confers aerogels with unique features, such as low density, high specific surface area, and low thermal conductivity, making them useful for various applications, including oil absorption, thermal insulation, and flame retardancy. − Using polymers of natural origin is one way to create sustainable foamed structures with strong mechanical performance, low thermal conductivity, and fire resistance. Achieving these objectives will facilitate and promote the application of bio-based foam-like materials in sectors such as construction, transport, or packaging.…”