Aerogel from Sustainably Grown Bacterial Cellulose Pellicles as a Thermally Insulative Film for Building Envelopes

Abstract

Improving building energy performance requires the development of new highly insulative materials. An affordable retrofitting solution comprising a thin film could improve the resistance to heat flow in both residential and commercial buildings and reduce overall energy consumption.Here we propose cellulose aerogel films formed from pellicles produced by the bacteria Gluconacetobacter hansenii as insulation materials. We studied the impact of density and nanostructure on the aerogels' thermal properties. Thermal conductivity as low as 13 mW/(K•m) was measured for native pellicle-based aerogels dried as-is with minimal post-treatment. The use of waste from the beer brewing industry as a solution to grow the pellicle maintained the cellulose yield obtained with standard Hestrin-Schramm medium, making our product more affordable and sustainable. In the future, our work can be extended through further diversification of the sources of substrate among food wastes, facilitating larger potential production and applications.

Biotropic liquid crystal phase transformations in cellulose-producing bacterial communities

“…When A. xylinum cells are placed into a nutrition-containing medium ( 23 , 25 , 29 ), they synthesize cellulose subfibrils of diameter 2–4 nm ejected from an array of enzymatic macromolecular sites along the bacterium length ( 18 , 22 ) ( Fig. 1 A ).…”

“…Following a procedure comprising water-to-ethanol solvent exchanges, previously used for naturally occurring pellicle hydrogels ( 25 ), we have dried our nematic gels using supercritical CO 2 , obtaining monodomain nematic aerogels ( SI Appendix , Fig. S3 ).…”

“…This would then be analogous to photopatterning of the LC order nowadays widely utilized for thermotropic LCs ( 43 , 44 ). Such patterning of nanocellulose order within hydrogels and aerogels based on them could find technological utility in applications ranging from biological cell scaffolding to directing the flow of heat within thermally superinsulating aerogel materials derived from nematic hydrogels ( 25 ). On the other hand, the active nematic LCs studied here can serve as model systems for understanding the nature and role of biotropic phase transformations, the potential role of defects and topological solitons in defining this active nematic’s behavior, including ones that can occur during the phase transformations.…”

“…Nematic LC hydrogels can be used in basic biomedical research on the artificial blood vessels ( 48 ), in tissue engineering of cartilage ( 49 ), and wound healing ( 50 , 51 ). On the other hands, the dried nematic aerogels may be utilized in applications like the loudspeakers ( 52 ), food products like edible films ( 53 ), and thermal insulation ( 25 ). As bacteria-made materials with interesting properties, nematic LC gels may be also employed in green-product applications, potentially substituting plastics and other synthetic materials that are difficult to decompose or recycle after the product’s life cycle.…”

“…A particularly interesting form of a natural LC-like organization relates to bacterial biofilms, where birefringent domains of extracellular matrix and orientationally ordered bacteria have been reported for many microbiological systems ( 7 – 21 ). For example, Acetobacter xylinum ( A. xylinum ) bacteria biosynthesize cellulose filaments which can be organized in an orderly manner at the micrometer scales while exhibiting randomly aligned domains on larger scales within the three-dimensional (3D) reticulated biofilm ( 22 – 26 ). Limitations in controlling morphology and order within such biofilms hinder potential applications of bacterial cellulose-based materials ( 15 – 19 ).…”