“The best way to predict the future is to create it” - Peter Drucker
The efficient management of energy, in all its forms and uses, is the sign of a wise and forward-thinking society. To uphold the energy efficiency, an insulation material has to be performant, but equally accessible, versatile and easily applicable. Keeping these principles in mind, we looked to the future to imagine how HESTIA should be produced, used and regulated. Here below is the framework on the implementation of HESTIA that we would suggest for the future.
When used for building insulation, aerogels are not directly applied onto the walls, as they are too fragile. Instead, they are usually embedded into insulative sheets/blankets (fibrous batting) in hydrogel form and critical-point-dried in cylinders. Then the aerogel forms inside the sheets. While the overall composite product usually has a λ-value higher than that of the normal aerogel, the increase in thermal conductivity is not detrimental (λ-values as low as 0.016 W/mK are still attested in this from on the SIA register1), and the trade off for being able to apply the material easily is generally accepted.
We would like to suggest a similar approach to this existing method: embedding the protein coated cellulose aerogel inside insulative sheets. While we initially envision the aerogel to be embedded into cellulose sheets to maintain our biodegradability and attachment approach, other insulative sheets can also be considered for higher insulative performance.
Assuming the resulting λ-value of the cellulose aerogel to be 0.020 W/mK, and assuming the λ-value of the aerogels blankets to be between 0.020 - 0.025 W/mK, a value comparable to certain existing silica aerogel products1, the blankets would be 8-10mm thick, with the ability to go higher in thickness, mirroring the current industrial approach.
The protein coating would be applied to the aerogel after it is casted and dried inside the sheets. For a coating of the sheets themselves, it would depend on the fibre type. If the fibre in question is cellulose, then the Cellulose Binding Domain within the protein coating will bind to the fibre.
For the modular protein functionalization, corresponding to the 01b (SR-Avitag) construct in our tested design, we expect different modular proteins to be present in the coating. The composition of the modular proteins and their ratios are to be determined by the desired use and the relevant regulations. The biotinylation between the Avitag and the mSA ensures a universal binding mechanism, as such any protein domain can be attached to the insulation material by a simple addition of an Avitag.
Raw Materials and Resources
Cellulose is the most abundant biopolymer on the planet3, and it can be extracted from nearly any plant-related resource. Its abundance makes the supply of cellulose relatively abundant and financially accessible compared to other aerogel-forming compounds. In addition, cellulose is recyclable, adding another stream of raw material. Assuming a similar level of efficiency in production, cellulose aerogel blankets would be much cheaper and much more environmentally friendly than their silica counterparts, simply due to the recyclability and the abundance of the biopolymer.
One of the key pillars of the HESTIA project is to contribute to a more sustainable and circular economy by improving the recycling of insulation materials in Switzerland and beyond. Through our Human Practices engagement and Sustainable Development consultations, we understood the need for material specific recycling systems. The first part of such a system is to be able to use recycled materials for production.
The purity of the recycled materials is an important concern. An important point is to re-acquire the cellulose as pure as possible. As it is possible to produce aerogels from a variety of cellulose polymers, recycled cellulose (in case it has to be dissolved) is also a valid candidate4 to form regenerated cellulose aerogels, ensuring re-iterable recycling.
To understand the application of the cellulose aerogel blankets, we need to understand who will be the end users of the finished product.
The straightforward answer is the civil engineers, thermal engineers and the architects. They have to ensure their designed buildings must be properly insulated and specific rooms to serve specific functions that can be achieved by different functions of insulation. As such, they need the tools and the materials at their disposal to be as versatile as possible. Therefore, any introduction of a new insulation material, after government approval, has to be accepted by the engineers and the architects as well.
Renovation is an interesting challenge in this regard, as the new insulation to be applied must be as thin as possible while still maintaining adequate performance. Yet the renovation is also an important point for the property owners. Through our consultation with the insulation producers and researchers, we learnt that aerogels have recently started to be used for this purpose, and that further development in this field helps contribute to that objective.
The cellulose aerogel blankets are to be applicable like any other insulation material, as most of the insulation materials are either in blanket, wool or foam structure. This assures the ease of application by not requiring any change in the current construction practices for the insulation to be used.
While applicable for a simple wall system by itself, through our consultation with architects and insulation producers, we were introduced to the double wall system (or the cavity wall system), where the insulation material is placed as a layer between two walls. If coupled with supports, the double wall system complements the insulative properties of the aerogel blanket but also relieves mechanical stress from the material.
While it is possible to completely insulate a building through aerogel blankets, there are also other possible strategic applications of the cellulose aerogel blankets. Thermal bridges are points in a system or construction where the flow of heat can take place more easily compared to the rest of the system, a weak spot on the thermal envelope. Windows are prime thermal bridge points as the surface between the window and the outer wall is hard to insulate due to a lack of space. Cellulose aerogel blankets, thanks to their low thinness, can be applied to these thermal bridges while the broader and more regular surfaces like walls can be insulated with more conventional materials, resulting in a cost-efficient yet still energy-efficient option.
Safety and Quality Considerations
Quality considerations and checks for insulation materials are mandated in Switzerland by the SIA Norm 279. According to this norm, any insulation producer declaring a λ-value for their product must derive this value from a statistical analysis based on control samples from the production line. These control samples and their λ-values must be representative of at least 90% of the product population, with a 90% confidence interval, at 10°C.
The SIA Norm 180 indicates an additional requirement for protecting the organic insulation materials from deformation: the relative humidity of the air inside the building must remain within 30% - 70% for an altitude of 800m. We have considered the city of Lausanne as our baseline locational assumption, which happens to be 526m above sea level, as such the requirement applies in default form.
Keeping all of this in mind, The SIA Norms would be an important set of requirements for the architects and the civil engineers using the HESTIA product for their designs.
For safety concerns, HESTIA has two major points to undertake, one on the safety of the material and one on the safety of the production line.
For the safety of the material, all the salts and other chemical compounds must be cleansed from the aerogel (specifically for our protocol) if they pose a danger to the end users’ health. For our protocol this mostly applies to Thiourea, a salt used in the dispersing solution to dissolve cellulose in water, even if it is not in powder form and incorporated into an aerogel. Equally, during the protein purification and the application of the protein biofilm coating onto the aerogel, it is essential that no genetically transformed E.Coli cell is present in the biofilm. Proper measures to ensure a complete lysis of the transformed cells has to be in place.
For the safety of the production line, the fact that our modular proteins are bound to the rest of the biofilm through a universal binding mechanism can be a vulnerability. It is possible that actors with malicious intent to engineer harmful/toxic proteins equipped with an Avitag. These proteins therefore could hijack the biotin-streptavidin linkage and create an insulation material with harmful substances on its surface. This might cause long term damage to the material, to the other construction materials or to the resident’s health. It is therefore important that only the final product leaves the production facility and the binding of the modular proteins be conducted under supervision.
Other Challenges and Improvements
There are yet more challenges that HESTIA has to overcome to be a truly viable insulation option, either through more tests and experiments that could’ve been conducted, or through more administrative and societal endeavours spread over years.
Upscaling Production: The upscaling of the protein and the cellulose aerogel production is a must, especially since HESTIA is a bio-manufacturing project. While we had relative success in the upscaling in both of these, the protein upscaling needs to be more reliable and the raw materials used for the aerogel should be industrial grade instead of laboratory grade.
Critical Point Dried Cellulose Aerogel: With more time and expertise in hand, the cellulose aerogel production with Critical Point Drying must be adopted. The Critical Point Drying process yields more performant, more porous5 and less thermally conductive cellulose aerogels compared to our process.
Bacterial Cellulose: Bacterial cellulose is purer than plant cellulose, and it is more inclined to polymerisation forming macrostructures while having better tensile strength6. These are relevant properties for a cellulose aerogel sample. Not only that, but the increased interest in bacterial cellulose and the current research to upscale the production further makes it even more interesting from a synthetic biology perspective. Using bacterial cellulose to produce aerogel samples was a part of our initial design, albeit it wasn’t possible to acquire the material due to shipping constraints.
Biodegradation Duration: It is crucial to know how fast the cellulose aerogel and the protein coating degrades under certain conditions. This data is useful to know how long it will take for the product to degrade in nature, if parts of it will accumulate in nature and how frequently it will require a renewal in a building. The best way to determine this is to bury the material in the earth and wait, checking it with regular intervals, an experiment usually lasting for months and unfeasible within the scope of iGEM. Nevertheless, with more time at hand, it is an experiment absolutely worth conducting.
Future Challenges and Improvements
Cellulose Aerogel Blankets: While silica aerogels are embedded/casted in blankets for industrial scale use and production, the same process is only in the development phase for cellulose aerogels, with no commercially viable process in place. While it is reasonable to assume that cellulose aerogels will have to follow the blanket-embedding process as well, it is still necessary to make it efficient enough for use in industrial scale.
Less Energy Consuming Drying: Insulation material production is an energy intensive process. This is equally true for aerogels, especially the Freeze Drying or the Critical Point Drying processes. While cellulose aerogels cannot be ambient pressure dried like their silica counterparts, if future research reveals a less energy intensive process for drying cellulose aerogels, it would be a significant step forward in the sustainability profile of the material.
Recycling System: To improve the recycling profile of the Swiss insulation sector, and to manage the decreasing waste space in the Canton of Vaud, the cellulose aerogel product must be coupled with a recycling service. This service is to take place during the renewal of the insulation, when the old insulation is taken to be separated into its raw materials of proteins and cellulose and reconstituted. While the service might require an added cost, alleviating the construction waste storage crisis in the canton is an easily acceptable trade-off.
Branching Out: We have mostly concentrated on building insulation within the scope of our project, yet the potential of insulation materials are not limited to that scope. Already, there is research on using cellulose aerogel for clothing insulation, particularly for jackets 7. Exploring the different possible applications of our project such as fireproofing cellulose fibres or using cellulose aerogel food packaging might yield interesting findings.
Overall, we aimed to integrate the knowledge we had acquired from the scientific literature, the engineering process, the stakeholder consultation, sustainability considerations and market analysis to come up with an effective, safe and realistic approach on the future implementation of our insulation material. This effort required us to think and evaluate the protein coated cellulose aerogel in all of its aspects, and shape the implementation framework accordingly to reflect the best possible use of those aspects.
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