Reaching a near zero radiative heat transfer by the inclusion of modified multiwalled-carbon nanotubes (MWCNTs) in polyurethane-polyisocyanurate aerogels

Abstract

This article studies the effect of adding different contents of surface-modified multiwalled carbon nanotubes (CNTs) on the structure and final properties of polyisocyanurate-polyurethane aerogels. The produced samples were characterized in terms of density, porosity, shrinkage, textural properties, mechanical behavior, ultrasonic behavior, and thermal conductivity. Low-weight aerogels were obtained with densities between 89 and 95 kg/m3. The inclusion of homogeneously dispersed carbon nanotubes protected the aerogel structure during supercritical drying decreasing the final shrinkage of these samples and, therefore, increasing their porosity. The porous structure of the aerogels containing CNTs was modified, and slightly larger pores were formed. The structural modifications contribute to decrease the stiffness of the samples while improving their resilience and elasticity. Finally, a significant enhancement on the insulating performance of the aerogels has been found when CNTs were added reaching values as low as 12 mW/mK. These fillers were proved to act as infrared opacifiers by absorbing and scattering the infrared radiation, a relevant contribution in these lightweight materials. In fact, the radiation contribution was strongly reduced when the content of CNTs reached 3 wt%, being this contribution near zero. Thus, this content was considered as the optimum for the final properties-balance in these aerogels.