Abstract
We investigated the effect of gelation solvent, monomer type, and monomer concentration on the physical properties of freeze-dried poly(urethane)-poly(isocyanurate) (PUR-PIR) aerogels, with particular emphasis on their thermal conductivity. It was found that the gelation solvent considerably affects aerogel morphology and physical properties. Aerogels with the lowest thermal conductivity were obtained using a mixture of tetrahydrofuran (THF) and acetonitrile, in a 50% volume ratio. The influence on thermal conductivity of polyol and isocyanate structure and of their concentration was also investigated. Rigid precursors, phloroglucinol (POL), and an aromatic polyisocyanate based on toluene diisocyanate (Desmodur RC) yielded the lowest thermal conductivity. Our results were compared with recent work reporting on parameters that could be used as predictors of thermal conductivity and other physical properties of organic aerogels. None of these parameters were found to be satisfactory predictors of aerogel properties. For example, no systematic correlation between solvent solubility parameters and aerogel properties was observed. We also examined the role of the K-index. This index, defined as the ratio between porosity and contact angle, was shown recently to be a good predictor of the properties of polyurea aerogels. While the thermal conductivity scaled with the K-index, the scaling was different for each of the isocyanate monomers considered in our experiments. Thermal conductivity, instead, scaled well with the product of density and shrinkage of aerogels, independent of monomer type. The reasons of this dependence on shrinkage and density are discussed, and the use of these parameters to guide experimentation on other systems is discussed. Physical properties such as static and dynamic compression modulus and thermal stability of the most promising formulations were also examined.
Highlights
Aerogels are materials characterized by low density, large surface area, and extremely low thermal conductivity
Chidambareswarapattar et al [7] synthesized an array of polyurethane aerogels with a density as low as 0.094 g/cm3 and a surface area ranging from 0.5 to 241 m2/g using trifunctional isocyanates and multifunctional aromatic polyols
Desmodur ILBA is a polyisocyanate based on isophorone diisocyanate (IPDI), while Desmodur RC is an aromatic polyisocyanate based on toluene diisocyanate (TDI)
Summary
Supplementary information The online version of this article (https:// doi.org/10.1007/s10971-019-05161-6) contains supplementary material, which is available to authorized users. Institute of Polymer & Dye Technology, Lodz University of Technology, Lodz, Poland Keywords Polyurethane ● Porous materials ● Surface area ● Thermal conductivity ● Hansen solubility parameters
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