Silica-Based Aerogel Composites Reinforced with Reticulated Polyurethane Foams: Thermal and Mechanical Properties

Abstract

In this work, silica aerogel composites reinforced with reticulated polyurethane (PU) foams have been manufactured having densities in the range from 117 to 266 kg/m3 and porosities between 85.7 and 92.3%. Two different drying processes were employed (ambient pressure drying and supercritical drying) and a surface modification step was applied to some of the silica formulations. These composites, together with the reference PU foam and the monolithic silica aerogels, were fully characterized in terms of their textural properties, mechanical properties and thermal conductivities. The surface modification with hexamethyldisilazane (HMDZ) proved to improve the cohesion between the reticulated foam and the silica aerogels, giving rise to a continuous network of aerogel reinforced by a polyurethane porous structure. The samples dried under supercritical conditions showed the best interaction between matrixes as well as mechanical and insulating properties. These samples present better mechanical properties than the monolithic aerogels having a higher elastic modulus (from 130 to 450 kPa), a really exceptional flexibility and resilience, and the capacity of being deformed without breaking. Moreover, these silica aerogel-polyurethane foam (Sil-PU) composites showed an excellent insulating capacity, reaching thermal conductivities as low as 14 mW/(m·K).

One-Pot Sol–Gel Synthesis of Highly Insulative Hybrid P(AAm-CO-AAc)-Silica Aerogels with Improved Mechanical and Thermal Properties

“…These results confirm that the addition of an organic polymer drastically increases the thermal conductivity of hybrid aerogels. Hence, the thermal conductivity values of the TGP_X aerogels in the present work from 22.4 to 30.6 mW/mK are comparable to those of these previously reported organic–inorganic hybrid aerogels [ 38 , 52 , 53 , 54 , 55 ], owing to the synergy among the thermally less conductive PACA polymer (60 mW/mK) [ 56 ] and the silica aerogel.…”

“…For example, Ghica et al [ 52 ] observed an increase in thermal conductivity from 31.3 to 85.4 mW/mK after the reinforcement of a silica aerogel with optimized polyamide pulps. Moreover, Merillas et al [ 53 ] analyzed that the synthesized polyurethane-reinforced silica composite aerogel exhibited enhanced thermal conductivity from 33.4 to 52.5 mW/mK. Similarly, Ilhan et al [ 54 ] and Hae-Noo-Ree Jung et al [ 55 ] reported improved thermal conductivity of hydrophobic silica aerogels to around 41 and 131 mW/mK with the addition of polystyrene and poly(methyl methacrylate), respectively.…”

“…In comparison with the previous reports, it is observed that the hybrid polymer–silica aerogel shows a higher compression modulus by sacrificing the prime properties, such as the bulk density, specific surface area, and, most importantly, thermal conductivity, owing to the crosslinking density [ 23 , 58 , 59 ]. On the other hand, despite maintaining the aforementioned prime properties, the mechanical properties of the hybrid silica aerogel deteriorated [ 13 , 27 , 47 , 53 , 60 ]. However, in the present work, the hybridized TGP_X aerogels demonstrated better thermal properties, as well as an outstanding seven-fold increase in the compression modulus compared to the pristine TGP_0 aerogel while maintaining their thermal conductivity values below 30 mW/mK ( Figure 7 ).…”

Fumed Silica-Derived, Ambient Dried, and Low-Cost Nanoporous Aerogel-like Monoliths for Thermal Insulation

“…Rao et al investigated the effect of various replacement solvents on the pore structure of silica aerogels, and the corresponding results proved that the n -heptane solvent with low-surface tension was the optimal selection for the preparation of silica aerogel in the process of ambient drying. For surface modification, the alkylated silanes are the ideal precursors, which mainly include methyltrimethoxysilane (MTMS), , methyltriethoxysilane, vinyltrimethoxysilane (VTES), trimethylmethoxysilane (TMMS), trimethylchlorosilane (TMCS), and hexamethyldisilazane, etc . For instance, Yang et al prepared highly elastic hydrophobic silica aerogels using VTES and MTMS as composite precursors.…”

Silica–Chitosan Composite Aerogels for Thermal Insulation and Adsorption

“…The obtained samples showed excellent insulating capacities, reaching values between 14.0 and 12.3 mW/m•K for the surface-modified composites that were dried under supercritical conditions. Merillas et al [24] prepared silica aerogel composites reinforced with reticulated PU foam by the sol-gel method and under both ambient and supercritical drying pressures. The carbonyl and amine groups of the polyurethane foam could establish a chemical interaction with the silica matrix, promoting an effective interaction, thus improving the mechanical properties of the silica aerogel.…”