Lightweight lignocellulosic foams for thermal insulation

Abstract

Foams are mainly composed of dispersed gas trapped in a liquid or solid phase making them lightweight and thermally insulating materials. Additionally, they are applicable for large surfaces, which makes them attractive for thermal insulation. State-of-the-art thermally insulating foams are made of synthetic polymeric materials such as polystyrene. This work focuses on generating foam from surfactants and renewable lignocellulosic materials for thermally insulating stealth material. The effect of two surfactants (sodium dodecyl sulphate (SDS) and polysorbate (T80)), two cellulosic materials (bleached pulp and nanocellulose), and lignin on the foaming and stability of foam was investigated using experimental design and response surface methodology. The volume-optimized foams determined using experimental design were further studied with optical microscopy and infrared imaging. The results of experimental design, bubble structure of foams, and observations of their thermal conductivity showed that bleached pulp foam made using SDS as surfactant produced the highest foam volume, best stability, and good thermal insulation. Lignin did not improve the foaming or thermal insulation properties of the foam, but it was found to improve the structural stability of foam and brought natural brown color to the foam. Both wet and dry lignocellulosic foams provided thermal insulation comparable to dry polystyrene foam. Graphical abstract

Microalgae Chlorella vulgaris and kraft lignin stabilized cellulosic wet foams for camouflage

“…This phenomenon was observed when a combination of high concentrations of pulp or CNF and microalgae were foamed where also the microalgae contributed to the viscosity increase. The response surface models for neat pulp and CNF foams differ slightly from our previous study, 39 which is most likely due to minor differences in the foaming process. The role of SDS in foaming is not surprising since SDS is a surfactant designed to stabilize the interface of a bi-phase system.…”

“…Initial maximum and minimum concentrations for the different constituents were determined in previous experiments. 39 The same concentrations were used for microalgae as for lignin. A response surface model, based on the quadratic face-centered central composite (CCF) design, with three center points and two replicates, was used.…”

“…The foamability and stability of lignin-containing CNF and bleached pulp foams were investigated earlier. 39…”

“…It is possible that by going beyond the concentration limits used herein, the foam generation would have been even higher. These concentrations were initially optimized for systems with pulp/CNF, SDS, and lignin 39 and not for microalgae. The foaming was not either tested without SDS since the results shown here indicate the importance of surfactant for the foamability.…”

“…Lignin did not improve foamability, which was addressed in our previous study. 39 A detailed description of the fitting and validity of models is presented in ESI, † (Tables S1-S3). The concentration limits of SDS were not increased due to economic reasons and to obtain comparable results.…”