Interview with Marta Muñoz Hernández, Professor and Researcher, Materials Science and Engineering Faculty, Rey Juan Carlos University
What is Materials Science?
Materials Science is the scientific branch that studies the structure of matter, both at microscopic and macroscopic levels. This atomic structure is closely related to the properties exhibited by the materials.
This science is also linked to materials engineering, which involves properties, structure and different processing techniques, i.e., the different manufacturing technologies that allow the design of new products with different applications.
Materials are used in many areas of society – in transportation, medicine, energy, mechanics, ecology, nanotechnology, to name but a few. Materials science permeates our daily lives: where we live, where we work, our modes of transport, the clothes we wear, etc. Everything is made of materials and it is important to study their structures, properties and uses.
What types of materials exist?
Although there are many classifications of materials, one of the most common ones divides them into four main groups:
One of these groups is metallic materials. With a specific atomic structure and characteristic properties such as high conductivity (both electrical and heat), high hardness and strength, and low corrosion resistance. These typical properties of metals are a direct consequence of their microscopic structure, i.e. how the atoms are arranged in space.
Another group is ceramic materials. These have a different structure and, therefore, a different atomic and molecular organization. As a result, they have different properties: they are hard and rigid but fragile materials, as they do not deform and are highly resistant to corrosion.
We also have the group of polymeric materials or plastics. Then there is the polymeric or plastic materials group. We often use both terms interchangeably, although there are some differences between them as we will see below. Polymers are long chains of mostly carbon and hydrogen bonded together. Their structure consists of the joining of many monomers, as if they were the beads of a long necklace, and each of the beads is a monomer unit. When one monomer is joined to another, a dimer is formed; if another monomer is added, a trimer is formed, and so the number of monomeric units increases until a polymer is formed, which is a chain of thousands or even millions of monomers. Polymers are light, soft, easily deformed and not very resistant. They do however resist corrosive environments very well.
Finally, composite materials are manufactured by combining any of the materials of the previous groups. One of the best known composite materials are those in which the matrix – the main component – is polymeric. Thus, for example, we have the polymer matrix composites reinforced with glass fiber or carbon fiber, widely used in the aeronautics field, where, thanks to their exceptional properties, they have managed to displace metals. Composite materials have superior performance, but are nevertheless more difficult to recycle, since each component must be separated to ensure proper treatment.
How can materials science contribute to the fight against climate change?
Materials science and engineering is studying new materials with interesting properties in many different fields.
For example, in construction, the design and manufacture of new materials can contribute to curbing climate change, with the use of ecological bricks that incorporate part of recycled plastic, photovoltaic tiles that save energy, and self-repairing and self-cleaning materials that also reduce water consumption.
Thanks to the development and design of materials, much more efficient lighting systems have been achieved that allow considerable energy savings. LEDs are replacing traditional tungsten bulbs or sodium lamps.
Work is also being done on new materials to make batteries of greater capacity that are more efficient, to manufacture electric cars, and new materials to use hydrogen as a form of energy, and so on.
The manufacturing processes of these materials are also being studied to minimize waste generation.
Why is plastic so harmful and are all plastics equally “bad”?
Environmentally speaking, plastics (which are polymers to which an additive has been added to improve some of their properties) offer a very attractive property, which is their durability, but in the long run it becomes their worst enemy. These materials are so durable that once the product’s useful life cycle is over, they are not easily assimilated by nature. In other words, they take so long to degrade that they end up becoming persistent waste.
The use of microplastics in the cosmetics industry is one such example, as is the very process of plastic degradation, which, although slow, can generate microplastics that end up in the waters of oceans and rivers, becoming part of the trophic chain and the human food system. However, the main problem with plastics is that, once their useful life cycle is over, they persist in nature without degrading, and can take between 400 and 1000 years to disintegrate.
The Chinese government used to buy all plastic waste from many industrialized countries, up until 2018, when this practice was banned. Why? Because this waste has a very high value, both material and energy. Polymers come from petroleum, and this petroleum value remains in any processed plastic product. For example, if we have a plastic bottle, we can reverse the process and turn it back into petroleum or any other fuel fraction. The result is that, as of 2018, we have an increased accumulation of plastic waste in most countries and this requires an urgent solution.
Plastic waste is the new gold. We can transform it into fuels or new value-added products. In this sense, it is a very useful raw material requiring us to extract both its material and energetic value.
You are working with MIT on the “Plastic waste to alternative fuels” project, what does this project consist of?
The idea we proposed was somewhat disruptive and risky because it attempted to unify two very different areas of science: plastic recycling and electromagnetism. On the one hand, we proposed to use magnetic nanoparticles that would generate heat under the action of alternating high-frequency electromagnetic fields, and, on the other hand, to use this heat in the cracking or decomposition processes of plastics.
The idea was to use this large amount of energy released by these magnetic nanoparticles under radiofrequency fields to break the bonds of plastics and transform them into different fuel fractions. This idea caught the attention of Alan Hatton, Director of the Chemical Engineering department at MIT, and we were awarded a collaboration grant in January 2019, starting a student and faculty exchange program between MIT and Rey Juan Carlos University.
The proposed technology also proved appealing to companies such as Cepsa, and two postdoctoral researchers with Marie Curie grants from the European Union have also participated in the project.
We have now been awarded a research project as part of the Ecological and Digital Transition 2021 call for proposals, coordinated with the Institute of Applied Magnetism, with which we intend to move from the laboratory scale to the semi-industrial scale. This project will provide the funding to develop this innovative technology and allow its scaling, since it has been proven that it is a technology that works, is efficient on a small scale, and can be a good alternative in these times of ecological transition.
Is the overall objective of this research to replace fossil fuels?
The objective of this project is to gradually replace fossil fuels; the use of fossil fuels cannot be eradicated overnight. The objective is to transform plastic waste into fuels, minimizing and eliminating the accumulation of this type of waste and reducing the current dependence on oil. At the same time, however, plastics can also be transformed into new products that can be used as raw materials for other processes. To understand this, we need to delve a little deeper into the concept of plastic waste recycling.
There are two types of plastics recycling. On the one hand, physical recycling, in which those polymers that are recyclable, the thermoplastics, are melted and given a new shape and a new life cycle. For example, by melting a plastic bottle we can turn it into a canvas and this in turn, at the end of its useful life cycle, can be transformed into a hose, and so on. In this type of link, only operations of a physical nature are performed.
On the other hand, chemical recycling, which is the technology we are working on, is based on breaking and forming new bonds through chemical reactions, thus altering the nature of matter. By shortening the long polymer chains, we can return to the initial raw material or to new building blocks to manufacture new products.
If chemical recycling breaks the polymeric chains into very short chains, we have very light petroleum fractions, obtaining methane, ethane, propane or butane, gaseous fractions, made up of few carbon atoms. If we cut the polymers into slightly heavier fractions, we obtain gasoline, with around 8 carbon atoms, which is where the term octane comes from. If it is fractionated into somewhat larger chains, we obtain diesel or kerosene.
So, basically, this chemical recycling consists of cutting the long polymer chains into shorter chains to obtain different fractions of the oil or new raw materials. To do this, we need catalysts to govern the mechanism by which the molecules are broken down, under certain conditions of pressure and temperature, and with a very high energy input. It is in this energy input that the innovation of the project lies. Instead of resorting to traditional heating methods based on resistive heating with electrical energy, we propose to use a new heating system based on magnetic induction to perform this chemical recycling of plastics using radiofrequency fields and magnetic nanoparticles.
These two types of recycling, both physical and chemical, complement one another. First, physical recycling must be used to maximize the material life of the plastic, and once this material pathway has been exhausted, chemical recycling must be used to exhaust its material value and extract and recover its energy content.
Do you think we will ever completely replace fossil fuels with alternative fuels?
I would like to think so, although joint action is required on a global scale by all countries, both industrialized and those in the process of becoming industrialized. We need to unify policies globally and help these less industrialized countries to be able to manage their waste properly.
Waste policies in Europe differ greatly from those in Asian countries, for example. In Europe plastic waste is collected, sorted, treated and managed correctly, while many other countries in the world do not even have waste collection policies, let alone waste treatment technologies.
A more global approach to the problem is needed, international regulations are needed together with equal collaboration from all countries.
What are the keys to ending climate change?
Policies are fundamental, but investment in both basic and applied research is also key. This needs to take place via collaborations between universities and companies, between the public and private sectors and between different countries. Funding is needed to research and find solutions to this problem.
We must also focus on scientific outreach, communicating and informing society about what is being researched in universities and research centers. Awareness must also be raised among the population regarding the key role played by the citizens themselves in the fight against climate change. Each of us, from our homes and workplaces, can make a decisive contribution.
For recycling to be carried out correctly, we, the citizens, are the ones who must initiate the whole process in our homes, classifying and cataloging the different waste streams and depositing them in the different containers provided. This in turn allows us to start the most appropriate treatment.
Moreover, there are many small actions that can be done to be more environmentally friendly, from reusing packaging, aluminum foil, recycling used oil, transforming it into natural soaps made by ourselves, etc. There are many measures that we can implement as citizens and society needs to be made aware of the important role it plays.
Bringing back the concept of repairing in our society is also vital. Nowadays we do not repair damaged products. It is easier to throw it away and buy a new one, even if it lasts less and less, since products have shorter and shorter life cycles. We are thus engaging in an unstoppable wheel of consumerism, buying and discarding products. We must abandon this linear “use and discard” philosophy and move towards circularity, i.e. “use and recycle”. Even if we do not close the circle, we should at least try to achieve a spiral that resembles it.
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