Thermal conductivity of hygroscopic foams based on cellulose nanofibrils and a nonionic polyoxamer

Abstract

Nanocellulose-based lightweight foams are promising alternatives to fossil-based insulation materials for energy-efficient buildings. The properties of cellulose-based materials are strongly influenced by moisture and there is a need to assess and better understand how the thermal conductivity of nanocellulose-based foams depends on the relative humidity and temperature. Here, we report a customized setup for measuring the thermal conductivity of hydrophilic materials under controlled temperature and relative humidity conditions. The thermal conductivity of isotropic foams based on cellulose nanofibrils and a nonionic polyoxamer, and an expanded polystyrene foam was measured over a wide range of temperatures and relative humidity. We show that a previously developed model is unable to capture the strong relative humidity dependence of the thermal conductivity of the hygroscopic, low-density nanocellulose-and nonionic polyoxamer-based foam. Analysis of the moisture uptake and moisture transport was used to develop an empirical model that takes into consideration the moisture content and the wet density of the investigated foam. The new empirical model could predict the thermal conductivity of a foam with a similar composition but almost 3 times higher density.Accurate measurements of the thermal conductivity at controlled temperature and relative humidity and availability of simple models to better predict the thermal conductivity of hygroscopic, low-density foams are necessary for the development of nanocellulose-based insulation materials.

Compostable, fully biobased foams using PLA and micro cellulose for zero energy buildings

“…It was observed that the inclusion of micro cellulose fibrils in PLA influenced the density of the unfoamed composites leading to a linear increase in effective thermal conductivity as the weight concentration of the inclusions increased as shown in Table 3 below. The thermal conductivity of unfoamed PLA gave a value of 0.191 W/m∙K that falls in the (0.1–0.5) W/m∙K documented range for non-conducting polymers due to their amorphous and defective internal structure 120 , 121 . The reduction in the thermal insulation property of the PLA-Af foam could be attributed to a drop in its density which is due to the poor interfacial interaction between the amorphous regions of the fibrils and PLA which reduced the Van der Waals forces between them 122 .…”

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

“…the drawbacks for their practical application [54]. Figure 3b shows that the thermal conductivity of the pure CNF aerogel significantly increased from 44 at 5% RH to ~ 76 mW m −1 K −1 (72% increase) at 80% RH.…”

Sclerotization-Inspired Aminoquinone Cross-Linking of Thermally Insulating and Moisture-Resilient Biobased Foams

“… 4 , 5 However, most biobased materials, including nanocellulose, are hygroscopic, water uptake at humid and wet conditions can result in a very large reduction of strength, and replacement of air with water in aerogels and foams can increase the thermal conductivity. 6 , 7 …”