Transparent Polyisocyanurate-Polyurethane-Based Aerogels: Key Aspects on the Synthesis and Their Porous Structures

Abstract

The effect of the catalyst concentration on the synthesis and textural properties of polyisocyanurate-polyurethane aerogels is analyzed. The use of different catalyst amounts allows obtaining low-density aerogels (0.10−0.16 g/cm 3 ) with high porosities (85−91%). Their porous structures were analyzed by scanning electron microscopy and nitrogen adsorption−desorption isotherm. A noticeable decrease in the size of the scattering centers, particles and pores, was achieved when reducing the catalyst amount. In some samples, the small size of these features, much smaller than the wavelength of visible light, causes a bare light dispersion, leading to the first transparent polyisocyanurate-polyurethane aerogels. Light transmittance measurements at 532 nm have been made showing high values (ca. 76% for 1 mm thick samples) for the formulations with the smallest particle and pore sizes. These aerogels presenting optical transparency have many potential applications such as solar collectors, glazing systems for insulating windows, and sensors, among others.

Super-Insulating Transparent Polyisocyanurate-Polyurethane Aerogels: Analysis of Thermal Conductivity and Mechanical Properties

“…Moreover, the combination of excellent thermal insulation with adequate mechanical [ 29 , 30 ] and optical properties has recently been attracting attention [ 31 , 32 ]. In our previously published works, we synthesized for the very first time PUR-PIR aerogels with tunable optical properties, ranging from opaque to transparent aerogels [ 33 , 34 ]. In the present study, we analyze in depth their mechanical and insulating properties reaching, as far as the authors know, the lowest thermal conductivity values up to now for aerogels based on a PU-PIR matrix.…”

Improving the Insulating Capacity of Polyurethane Foams through Polyurethane Aerogel Inclusion: From Insulation to Superinsulation

“…when light passes through them owing to the gel transparency [23,34], as observed in Fig ure 3b. This supports the notion that the foam pores are completely filled with the aeroge which forms a continuous network with the polymeric skeleton of PU foam.…”

“…Their reticulated structure can be differentiated A reference polyurethane aerogel was synthesized as described in the Experimental Section. After the corresponding CO 2 supercritical drying, the measurement of the aerogel bulk density gave a value of 129 kg/m 3 , which implies a high porosity of 89% (taking as solid density a value of 1170 kg/m 3 [23]). Its textural properties were analyzed by means of nitrogen sorption (Figure 2b), reaching a high internal surface area of 242 m 2 /g and a pore size of ca.…”

“…Examples of the PU F -PU A gel composites obtained are depicted in Figure 3a. Their reticulated structure can be differentiated when light passes through them owing to the gel transparency [23,34], as observed in Figure 3b. This supports the notion that the foam pores are completely filled with the aerogel, which forms a continuous network with the polymeric skeleton of PU foam.…”

“…Herein, we report the synthesis of novel composites in which polyurethane reticulated foams (a special type of flexible foams in which the polymer forms a continuous network of struts and ribs) are filled with an organic aerogel. The selected organic aerogel was polyurethane aerogel [23], due to its promising properties and to the expectable good interaction with the PU foam. The obtained composites showed lower densities and shrinkages than the monolithic PU aerogel while keeping excellent insulation capacities as well as high mechanical strength, in comparison to the initial foams.…”