The world is witnessing a growing trend towards a bioeconomy, which utilizes living organisms to create safer, more sustainable materials. This movement aims to replace conventional synthetic products that are toxic to make or use, difficult to recycle, and have a significant carbon footprint. A concept that goes hand in hand with bioeconomy is “green chemistry” which focuses on a set of principles that aim to design chemical products and processes while minimizing or eliminating the use and generation of hazardous substances. Although the bioeconomy / green chemistry movement is still relatively small on a global scale, the drive to turn successful research into sustainable products via sustainable manufacturing processes is gaining momentum.
At LIST, within the Materials Research and Technology (MRT) department, researchers are working on transforming all available residues, such as agricultural and wood waste, un-utilized plants like bamboo and fungi, as well as industrial and mass consumption waste into sustainable bio-based and chemical products.
“Bio-based compounds can be engineered from natural resources. We can use seemingly unimportant materials to create functional products”, says Jean-Sebastien Thomann, who heads the Powder and Colloids Engineering group at LIST-MRT. Thomann’s team is working with one such material. “Our focus is on the use of materials derived from wood, specifically lignin,” adds Thomann.
Lignin, a biomass waste, can be transformed into a smart additive or filler to reinforce other polymer matrices. “For example, we have successfully modified rubber composite to be softer or harder by incorporating lignin particles with specific properties,” says Thomann. “By modifying lignin, we can create colloids and particles of different sizes, which can be used for various applications. For example, we have found that smaller lignin particles can be used to reinforce tyres. Additionally, these particles have antibacterial properties, which we have encapsulated into fibres for use in smart textiles.”
Cellulose, another “waste product”, is also a material of predilection within Thomann’s group. Specifically, cellulose nanocrystals (CNC) and micro fibrillated cellulose (MFC), which can be as stiff as glass, are used to reinforce polymers.
MFC consists of fibrils, explains Thomann, which can be extracted from the larger structure and then purified to preserve the most robust parts. This material can be used to create liquid crystals, which diffract light and can generate so-called “structural colour” of the same type found in butterfly wings. “We have also been able to chemically modify cellulose particles, which can be used to alter the mechanical properties of polymers.”
Complementing the work on cellulose and lignin, vitrimers, a class of self-healing, reworkable polymers are stars in their own right when it comes to sustainable manufacturing. These materials resemble traditional thermosets – the epoxy resins one can find at any hardware store being one common example. Initially liquids or pastes, such materials solidify and harden due to chemical reactions that induce the creation of a crosslinked polymer network. With conventional thermosets, this process is irreversible, generating robust materials with excellent properties but which cannot be melted, dissolved or recycled.
In contrast with conventional thermosets, vitrimers possess chemical bonds that become dynamic when heated and undergo rapid exchange with one another, enabling repair, reshaping, recycling and reuse.
“This makes vitrimers extremely attractive as a basis for fibre composites used in wind turbine blades, boats, cars and aircraft,” says Daniel Schmidt, head of the Sustainable Polymeric Materials group at LIST. Fibre composites promise high mechanical performance with minimum weight and represent a key technology for reducing greenhouse gas emissions as a result, but conventional systems cannot be repaired or recycled. Vitrimers can solve this problem.
Schmidt explains that both mechanical and chemical recycling are possible in this context. In the former case, both pure and particle-reinforced vitrimers can be ground up and hot pressed back together multiple times, without losing their properties. In the latter case, the matrix of vitrimer composites can be cleanly and easily removed, enabling high value reinforcing fibres to be reused.
“We also do work on bio-based vitrimers,” adds Schmidt, “an example of such a material developed by one of my group members, makes use of compounds derived from apple peels, among other things. Another impressive capability of vitrimers is that you heal these materials as well. If you've got a scratch, you can heal it just by heating the material up. It welds itself back together!”
When it comes to the process itself of manufacturing, a major trend both in the Grand Duchy and globally, is the production of goods in a manner which is both economically and environmentally sustainable. This requires manufacturers to carefully scrutinize every aspect of their product's lifecycle, from design and sourcing to manufacturing, delivery, and even service. Henri Perrin, the Composite Manufacturing Platform lead at LIST, and whose expertise is in designing and producing sustainable composites, says, “At LIST, we are trying to enable the processing of sustainable fibres through sustainable manufacturing approaches. Specifically, we are adapting existing processes to produce bio-composites using both natural fibres and bio-based resin systems.”
The focus is also on developing sustainable processes by reusing production waste within the manufacturing process, thereby avoiding extensive waste management steps. “As part of an M-ERA.NET (an EU funded network established to support and increase the coordination of European research programmes and related funding in materials science and engineering) project Natalina, we are developing an in-process production approach that reuses off-cuts of materials to enhance formability properties, specifically using flax fibres based semi-products,” adds Perrin.
He explains that a joint task force has been formed that leverages the synergy effect of combining the competencies of both green chemistry and advanced manufacturing, the goal being to showcase innovative proof-of-concept solutions that have the potential to open up perspectives for real-scale industrial applications.
“Currently, we are working on a number of projects with major national and European industrial stakeholders,” continues Perrin. “One example is Vitrispace, a project we are working on with Thales Alenia Space for space applications.” Funded by the European Space Agency, the project involves pre-qualifying the use of bio-composites and biobased vitrimers, that are synthesized at LIST, in a simulated space environment. Perrin’s team is also developing solutions compatible with 3D winding of bio-composites in collaboration with the Luxembourgish based company Gradel, as part of an FNR (Luxembourg National Research Fund) funded project called Greenshaper. Within this initiative, biobased vitrimers made at LIST are coupled with sustainable basalt fibres.
“There is a strong interest from industry in bio-composites in general,” concludes Perrin, “However, before a wider industrial deployment, we need to first demonstrate the ability of these materials to be used in representative applications such as in space, automotive, or hydrogen storage. Additionally, we need to develop and validate sustainable processes that will enable us to produce the targeted material and the parts at full scale, compliant with the technical and economical specifications and reducing significantly the global environmental impact.”
Collaboration is crucial when it comes to binding and elevating all these research efforts. For instance, Jean-Sebastien Thomann’s group provides lignin nanoparticles for a project in the group of Daniel Schmidt that is focused on making porous bio-based polymer networks for wastewater treatment. “We have also been able to further refine the MFCs to produce NFCs (nanofibrillated cellulose) in support of an EU Horizon project focused on open innovation in the area of bio-based polymeric materials,” adds Schmidt.
Likewise, the vitrimers developed in Schmidt’s group are used as the matrix material for various sustainable composites that Henri Perrin’s group uses and adapts for industrial production.
Schmidt emphasizes that, “While we each have our expertise and do creative and innovative work on our own, it’s when we combine our capabilities that we can really maximize our impact and generate the most exciting results!"
Talking about the importance of collaboration, Damien Lenoble, director of the MRT department adds, "It is inherent in the DNA of our department to assemble multiple research expertise and outcomes in a relevant approach to achieve well-defined goals. This is a strong demonstration of the valuable benefits brought about by focusing MRT research on their core technologies. In 2018, an overarching strategy was set and launched, leading to truly impactful and disruptive technologies that contribute to solving some of the most pressing challenges related to resource scarcity and the carbon footprint of our modern society."
All three experts agree that the time is ripe for new impulses in biobased and green chemistry research. They add in a word of advice saying that there are many paths to sustainability, and it's important to recognize that simply using bio-based materials does not necessarily make a solution sustainable.
The green chemistry principles, for example, that recommend using agents that are not toxic and leaving no harmful residues, “may seem intuitive,” says Daniel Schmidt, “but historically, industry has not always been successful in implementing them, leading to costly waste and environmental harm.” When working towards sustainable processes, it is thus crucial to carefully consider the positive and negative aspects of any solution, regardless of whether it's bio-based or not.
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