Thermal insulation foam is a versatile stealth material with multiple applications. It is a multiphase system composed of dispersed gas trapped in a liquid or solid phase and it exhibits unique mechanical, optical, and electrical properties that can be modified by tuning its physical and chemical structure. Foams are used for many temperature-controlled applications ranging from packaging refrigerated/frozen foods, medications and vaccines to insulation of buildings and chemical and thermal processes. Foams are lightweight materials that can be easily shaped and are also suitable for large surface areas. State-of-the-art foams are typically made from synthetic polymeric materials such as polystyrene.

There is growing interest in the use of biobased materials for thermal insulation. Biobased lignocellulosic foams, such as cellulose, hemicellulose, lignin and wood pulp are renewable and low-cost, and have the potential to provide a cost-effective alternative to existing products. However, it is important to understand how the primary constituents of these materials impact their insulation capabilities. The current literature on foams contains a great deal of data, but it is often difficult to identify the most relevant information for assessing their insulation capability.

To address this problem, the authors performed a comprehensive study of the structure-property relationship of a variety of cellulose and lignocellulosic foams. The results of this study demonstrate that structural factors, including apparent density and cell size, play a significant role in determining the thermal conductivity of foams. The authors also show that heat transfer models can be used to compare and predict foam thermal conductivity, but the results should be interpreted cautiously given the limitations of the available data.

The foaming and stability of the different lignocellulosic foams were studied with experimental design, and their ability to act as thermal insulators was assessed using response surface methodology. The influence of two surfactants (sodium dodecyl sulphate and polysorbate) and four lignocellulosic materials (bleached pulp, nanocellulose, hemicellulose and lignin) on the foaming, stability and insulation properties of the wet and dry foams were investigated. The resulting volume-optimized foams were further studied with optical microscopy and infrared imaging.

The results from this study indicate that the lignocellulosic materials can be used to produce thermally insulating foam with low apparent density, which is a critical factor for a successful application. In addition, the findings of this study suggest that the performance of a foam depends on its structure and the type of processing employed. Future research should continue to explore the nuances of this relationship and develop methods for filtering out and predicting foam thermal conductivity based on structural characteristics. This will aid in the identification of promising materials for a wide range of temperature controlled applications.