brominated plastics

Innovative approaches to recycling brominated plastics

/0 Comments/in , /by

Recovering untreated plastic materials and putting them back into the recycling loop through a decontamination line is the challenge of thesis research by Layla Gripon, a PhD student at IMT Lille Douai. These extraction methods contribute to a comprehensive approach to recovering plastic materials, in particular brominated plastics.

High consumption of electronic devices implies a significant amount of waste to be processed. While waste electrical and electronic equipment (WEEE) is often seen as a gold mine of silver and rare earths, plastic materials represent 18% of these deposits. This was equivalent to 143,000 tons in France in 2018 according to a report by Ademe (Ecological Transition Agency) published in 2019. But not all this plastic material is created equal. Some of it contains atoms of bromine – a chemical compound that is widely used in industrial flame retardants. These substances meet requirements for reducing flammability hazards in devices that may get hot while in use, such as computers or televisions. There’s just one problem: many of these substances are persistent organic pollutants (called POP). This means that they are molecules that can travel great distances without being transformed, and which are toxic to the environment and our health. The amount of these molecules contained in devices is therefore regulated in the design stage, as well as in the end-of-life processing stage. In 2019, the European Union set the threshold at which waste containing bromine can no longer be recycled at 2 grams per kilo. Beyond this limit, it is destroyed through incineration or used as fuel. But couldn’t it still be recycled, with the right processing? For her thesis co-supervised by researchers at IMT Lille Douai and The Alençon Institute of Plastics and Composites (ISPA), Layla Gripon has set out to identify a method for separating brominated flame retardants from plastics. “We seek to maximize recycling by limiting the loss of unrecoverable material, while complying with regulations,” says the PhD student.

Finding the right balance between extraction efficiency and respect for the environment

Approximately 13% of WEEE plastics are above the legal threshold for brominated flame retardants, which is equivalent to 17,500 tons in France. Samples tested in the laboratory reached a concentration of bromine up to 4 times higher than the legal threshold. In order to process them, Layla Gripon tested a number of methods that do not degrade the original plastic material. The first was highly efficient, removing 80% of the bromine. It was an extraction method used diethyl ether, an organic solvent. But since it uses a lot of solvent, it is not an environmentally-friendly solution. Another technique based on solvents is dissolution-precipitation. Through this technique, plastic is dissolved in the solvent, which retains the flame retardants. “In order to limit the environmental impact of this process, we subcontracted the German Fraunhofer Institute to carry out a test. Their patented process (CreaSolv) allows them to reuse the solvents. In the end, the bromine was no longer detected after processing and the environmental impact was reduced,” she explains.

In addition, a method that is more environmentally-friendly – but less efficient, for now – uses supercritical CO2, a green, non-toxic and non-flammable solvent. This process is already used in the agri-food industry, for example, to remove caffeine from coffee. In the supercritical state, carbon dioxide exists in an intermediate state between liquid and gas. To achieve this, the gas is heated and pressurized. In practice, the closed-loop system used by Layla Gripon is simple. Shredded plastic is placed inside an autoclave in which the supercritical fluid circulates continuously. When it leaves the autoclave, the recovered gas brings various additives with it, including a portion of the flame retardants.

To improve the yield of the second method, Layla Gripon planned to use a small amount of solvent. “The tests with ethanol improved the yield, with a rate of 44% of bromine removed, but this wasn’t enough,” says the PhD student. Other solvents could be considered in the future. “The supercritical CO2 method, on the other hand, works very well on the brominated flame retardant that is currently the most widely-used in industry (tetrabromobisphenol A – TBBPA),” she adds. But the most difficult brominated plastics to process are the ones that have been prohibited for a number of years. Although they are no longer available on the market, they are still accumulating as waste.

A large-scale approach to recovering recycled plastic  

These promising processing techniques must still evolve to respond fully to the needs of the recycling industry. “If these two processes are selected for applications beyond the laboratory, their environmental impact will have to be minimized,” says the PhD student. Such methods could therefore be incorporated in the pre-processing stage before the mechanical recycling of WEEE plastics.

At the same time, manufacturers are interested in the benefits of this research initiated through the Ecocirnov1 Chair. “They’ve joined this project because the laws are changing quickly and their products must take into account the need to recover materials,” explains Éric Lafranche, a researcher who specializes in plastic materials at IMT Lille Douai and is Layla Gripon’s thesis supervisor. The objective of maximizing recycling is combined with an ambition to create new products tailored to the properties of the recycled materials.  

Read more on I’MTech: A sorting algorithm to improve plastic recycling

“Recycling today is different than it was 10 years ago. Before, we sought to recover the material, reuse it with similar properties for an application identical to its original use. But the recycled product loses some of its properties. We have to find new applications to optimize its use,” says Éric Lafranche. For example, French industrial group Legrand, which specializes in electrical installations and information networks, seeks to use recycled plastic materials in its electrical protection products. In collaboration with researchers from IMT Lille Douai, the company has implemented a multilayer injection system based on recovered materials and higher-grade raw materials on the surface. This offers new opportunities for applications for recycled plastics – as long as their end-of-life processing is optimized.

By Anaïs Culot.

1 Circular economy and recycling chair created in 2015, bringing together IMT Lille Douai, and the Alençon Institute of Plastics and Composites and Armines.

Photographie d'un train Regio2n, même modèle que le démonstrateur en résine thermoplastique développé par le projet Destiny

Trains made with recyclable parts

/0 Comments/in , /by

The Destiny project proposes a new process to manufacture parts for the railway and aeronautical industries. It uses a thermoplastic resin, which enables the materials to be recycled while limiting the pollution associated with manufacturing them.   

 

It is increasingly critical to be able to recycle products so as to lower the environmental cost of their production. The composite parts used in the railway sector have a service life of roughly 30 years and it is difficult and expensive to recycle them. They are mostly made from thermosetting resins — meaning they harden as the result of a chemical reaction that starts during the molding process. Once they have reached a solid state, they cannot be melted again. This means that if the parts cannot be repaired, they are destroyed.

The Destiny project brings together several industrial and academic partners[1] to respond to this need. “The goal is to be able to migrate towards recyclable materials in the railway and aeronautical industries,” says David Cnockaert, head of the project at Stratiforme Industries, a company that specializes in composite materials. Destiny won an Innovation Award at JEC World 2020 for two demonstrators made from recyclable composite materials: a regional train cabin and a railway access door.

A resin that can be melted

“An easy solution would be to use metal, which is easy to recycle,” says David Cnockaert “but we also have to take into account the requirements for this sector in terms of mass, design, thermal and acoustic aspects.” The purpose of the Destiny project is to develop a solution that can easily be tailored to current products by improving their environmental qualities . The materials used for reference parts in the railway industry are composites, made with a resin and fiber glass or carbon fiber. During the stratification stage, these fibers are impregnated with resin to form composite materials.

“In the Destiny project, we’re developing thermoplastic resins to create these parts,” says Eric Lafranche, a researcher at IMT Lille Douai who is involved in the Destiny project. Unlike thermosetting resins, thermoplastic resins develop plasticity at very high temperatures, and change from a solid to a viscous state. This means that if a train part is too damaged to be repaired, it can be reprocessed so that the recyclates can be reused.

The resin is produced by Arkema in a liquid form, with very low viscosity. “A consistency close to that of water is required to impregnate the fiberglass or carbon fibers during polymerization,” explains Eric Lafranche. “Polymerization takes place directly in the mold and this process allows us to avoid using certain components, namely those that release volatile organic compounds (VOC),” he adds. The production of VOC is therefore greatly limited in comparison with other resins. “People who work in proximity to these VOCs have protective equipment but they are still a source of pollution, so it’s better to be able to limit them,” says Eric Lafranche.

Read more on I’MTech: What is a Volatile Organic Compound (VOC)?

Tailored innovation

This thermoplastic resin provides properties that are virtually equivalent to thermosetting resins, “or even better resilience to shocks,” adds the researcher. In theory, this resin can be recycled infinitely. “In practice, it’s a bit more complicated – it can lose certain properties after being recycled repeatedly,” admits the researcher. “But these are minimal losses and we can mix this recycled material with pure material to ensure equivalent properties,” he explains.

The aim of the project is to be able to offer manufacturers recyclable materials while limiting the pollution associated with their production, but to do so by offering parts that are interchangeable with current ones. “The entire purpose of the project is to provide manufacturers with a solution that is easily accessible, which may therefore be easily tailored to current production lines,” says David Cnockaert. This means that the recyclable parts must comply with the same specifications as their thermosetting counterparts in order to be installed. This solution could also be adapted to other industries in the future. “We could consider applications in the energy, defense or medical industries, for example, for which we also manufacture composite parts,” concludes David Cnockaert.

 

Tiphaine Claveau for I’MTech

[1] Accredited by the i-TRANS and Aerospace Valley competitiveness clusters, the Destiny FUI project brings together Stratiforme Industries, STELIA Composite, ASMA, CANOE, Crépim, ARKEMA and an ARMINES/IMT Lille Douai research team.

 

Temporary tattoos for brain exploration

/0 Comments/in , , /by

A team of bioelectronics researchers at Mines Saint-Étienne has developed a new type of electroencephalogram electrode using a temporary tattoo technique. As effective as traditional electrodes, but much more comfortable, they can provide extended recordings of brain activity over several days. 

 

The famous decalcomania transfer technique – made popular in France by the Malabar chewing gum brand in the 1970s – has recently come back into fashion with temporary tattoos. But it does not serve solely to provide fun for people all ages. A new use has been developed with the invention of temporary tattoo electrodes (TTE) designed to record electrophysiological signals.

Originally developed to pick up heart (electrocardiogram, ECG) and muscle signals (electromyogram, EMG), the technique has been refined to reach the holy Grail of bioelectronics: the brain. “Electroencephalographic signals (EEG) are the hardest to record since their amplitudes are lower and there is more background noise, so it was a real challenge for us to create flexible epidermal electronic devices that are as effective as standard electrodes,” explains Esma Ismailova a bioelectronics researcher at Mines Saint-Étienne.

From Pontedera to Saint-Étienne

The process for printing tattoo electrodes was developed by an Italian team, led by Francisco Greco, at the Italian Institute of Technology in Pontedera. The next step for preclinical application was carried out at the Saint-Etienne laboratory. Laura Ferrari, a PhD student who worked on TTE with Francisco Greco for her thesis, chose to carry out postdoctoral research with Esma Ismailova in light of her experience in the field of wearable connected electronics. In 2015, the Mines Saint-Étienne team had developed a connected textile, derived from the technique used to print on kimonos, intended to record an electrocardiogram on a moving person, with fewer artifacts than traditional ECG electrodes.

The sensors of the tattoo electrodes, like the textile electrodes, are composed of semi-conductive polymers. These organic compounds, which were the topic of the 2000 Nobel prize in chemistry, act as transistors and offer new possibilities in the field of surface electronics.  The conductive polymer used is called PEDOT:PSS. It is mixed with ink and projected on a paper sold commercially for temporary tattoos, using a regular inkjet printer. The back layer is removed at the time of application. A simple wet sponge dissolves the soluble layer composed of cellulose, and the tattoo is transferred to the skin. The materials and techniques used in the microfabrication process for TTEs make it suitable for large-scale, low-cost production.

Esma Ismailova and her team worked extensively on the assembly and interconnection between the electrodes and electronic signal recording devices. An extension ending in a plastic clip was manufactured through 3D printing and integrated in the decalcomania. The clip makes it possible to attach a wire to the tattoo: “We had to solve the problem of transmitting the signal to transfer the data. Our goal is now to develop embedded electronics along with the electrodes, a microfabricated, laminated board on the patch to collect and memorize information, or transmit it through a mobile phone,” says the Saint- Étienne researcher.

a: multi-layer structure of a TTE allowing for the transfer of the top film on which the electrode is printed b: exploded view of a TTE with integrated flat connection c: TTE transferred to the scalp in the occipital region d: close-up of a TTE 12h after application with hair regrowth

Electrodes that are more comfortable for patients…

The dry electrodes composed of a one-micron thick polymer film conform perfectly to the surface of the skin due to their flexibility. This interface makes it possible to dispense with the gel which is necessary for traditional electrodes, which dries out after a few hours, making the electrodes inoperative.  The transfer must be done on shaved skin, but a study has shown that hair regrowth through the film does not stop them from being effective. This means that they can be used for 2 to 3 days, provided they do not get wet, since the principle of temporary tattoos is that they are broken down by washing with soap and water.  Research is currently underway  to replace the regular transfer layer by a more resistant, water-repellent material, which would extend their lifetimes.

For Esma Ismailova, this technology is a huge step forward, for both the field of clinical research and patient care: “These new flexible, stretchable, very thin electrodes are ergonomic, conformable, virtually imperceptible, and are therefore much more acceptable for patients, particularly children and elderly people, for whom certain exams can be stressful.”  Indeed, to perform an EEG, patients must normally wear a headset that attaches below the chin, composed of electrodes on which the technician applies gel.

… and more effective for doctors

Another advantage of these temporary tattoo electrodes is their compatibility with  magnetoencephalography (MEG). Since they are composed entirely of organic materials and therefore do not contain any metal, they do not disturb the magnetic field generated by the device and do not create artifacts, so they can be used to perform EEGs coupled with MEGs. These two techniques for exploring neuronal activity are complementary and refine information about the  starting point of epileptic seizures,  the review of systems for certain tumors before their ablation, and neurodegenerative diseases.

The clinical assessment of TTE in the field of neurophysiology was carried out in collaboration with Jean-Michel Badier from the Institut de Neurosciences des Systèmes at the University of Aix-Marseille. This study was recently published in the journal Nature, and confirmed that their performance was similar to traditional electrodes for standard EEG, and superior for MEG, since they do not produce any shadow areas.

“We’ve done a proof of concept, now we’re trying to develop a device that can be used at home. We plan to do a study with epileptic or autistic children, for whom comfort and acceptability are very important,” explains Esma Ismailova. These tattoo electrodes – like other connected technology –will generate a great amount of data. For the researcher, “it’s essential to collaborate with researchers who can process this data using specialized algorithms. It’s a new era for smart wearables designed for personalized, preventive medicine, in particular through the early detection of abnormalities.”

 

Sarah Balfagon

masks

Protective masks: towards widespread reuse?

/0 Comments/in , , , /by

How can protective masks be recycled and reused without risking safety? Scientists, medical practitioners and manufacturers have teamed up to explore different treatment methods. As part of this consortium, IMT Atlantique researchers are studying the impact of decontamination processes on mask performance.

 

Surgical and FFP2 masks are intended for single use. Thrown away after just a few hours of use, they are designed to protect the wearer from inhaling infectious agents spread through the air. The question of recycling these masks has not been raised before, but high demand for masks to protect healthcare workers and the general public has been a game-changer. To help find a solution to the current shortage, an interdisciplinary consortium bringing together nearly 25 laboratories and manufacturers throughout France was created in early March, led by professor Philippe Cinquin from Grenoble University Hospital, the CNRS and the CEA. Its goal is to find a treatment process that makes it possible to reuse masks.

Currently, various decontamination methods recognized for both their virucidal and bactericidal effects are being explored: among others, gamma or beta irradiation, thermal decontamination with steam at 121 °C; an ethylene oxide treatment, and wet or dry heating methods at 70°C or higher. These methods must able to reduce the bioburden of protective masks, without reducing filtration efficiency or breathability.

At IMT Atlantique, which is a member of the research consortium, Laurence Le Coq and her colleagues Aurélie Joubert and Yves Andrès are working mainly on this second aspect of the project.  The researchers are drawing on their research on filtration applied to air treatment — for industrial waste applications, for example, or indoor air treatment in ventilation networks. The team has been able to quickly shift its focus and adapt its expertise to work on recycling used masks. “The contribution and dedication of researchers and technical staff, who were called on to respond to an urgent need to develop technical solutions and establish experimental conditions, has been instrumental,” says Laurence Le Coq.

By mid-March, the scientists had set up an initial test bed to closely reflect the AFNOR standards for masks in order to test their performance following decontamination. “If the masks are normally intended for single use, it’s also because they first undergo a treatment process which gives them a certain level of efficiency, as well as their mechanical strength and specific shape. When they are decontaminated, part of this pre-treatment is removed, depending on the type of decontamination and its conditions. What’s more, depending on how a mask has been put on, worn and taken off, it may be damaged and its structure could be altered,” explains the researcher.

Preliminary findings    

So, how can effective decontamination be combined with a sufficient level of protection?  “We compare how performance is maintained between new treated masks and used treated masks. More precisely, we measure the changes brought about by decontamination treatments, in particular their level of breathability and their filtration efficiency for particles with a diameter ranging from 0.3 to 3 µm, since the virus is spread by microdroplets,” explains Laurence Le Coq.

After ruling out certain methods, the scientists were able to determine favorable treatment conditions for decontaminating the masks without having too much of an effect on their inherent qualities. “Dry heat treatments, for example, are promising but we can’t move forward for the time being. Certain findings are encouraging following irradiation or washing at 95°, but only for surgical masks. For now, our findings do not allow us to converge on a single treatment, a single protocol. And most importantly, there is a huge difference between what we do in good laboratory conditions and what could be done on a greater quantity of masks in a hospital environment, or at home,” says Laurence Le Coq.

The researchers are currently trying to clarify and confirm these preliminary findings. Their goal is now to quickly establish treatment conditions that are effective for all surgical and FFP2 masks, regardless of the manufacturer.

Is widespread mask recycling possible?

The majority of masks provided for the “general public” during the lockdown are reusable after being washed at 60°C for 30 minutes. This is not yet the case for professional masks.

Lockdown measures have been accompanied by efforts to raise public awareness about the importance of wearing masks. In French departments classified as red due to a high number of cases, masks intended for the “general public” are mandatory on public transportation and in high schools. These fabric masks are less effective than professional protective masks, but they are easily reusable and can be washed at least five times. “What is lost in effectiveness is made up for by widespread mask-wearing and ease of use,” says Laurence Le Coq.

For the researcher, this unprecedented research project could also be an opportunity to consider recycling protective masks in the long term, even when there is not a shortage. “Is it really appropriate to have single-use masks if at some point we are required to use them to a greater extent, or even on a daily basis? How should the environmental costs of this medical waste be weighed? Of course, what happens next will depend on the treatment we’re able to develop.”

 

By Anne-Sophie Boutaud

tribology

What is tribology?

/0 Comments/in , , , /by

The science of friction: this is the definition of tribology. Tribology is a focal point shared by several disciplines and an important field of study for industrial production. Far from trivial, friction is a particularly complex phenomenon. Christine Boher, a tribologist at IMT Mines Albi[1], introduces us to this subject.

 

What does tribology study?

Christine Boher: The purpose of tribology is to understand what happens at the contact surface of two materials when they rub, or are in “relative movement” as we call it. Everyone is aware of the notion of friction: rubbing your hands together to warm up is friction, playing the guitar, skiing, braking, oiling machines, all involve friction. Friction induces forces that oppose the movement, resulting in damage. We are trying to understand these forces by studying how they manifest themselves, and the consequences they have on the behavior of materials. Tribology is therefore the science of friction, wear and lubrication. The phenomenon of wear and tear may seem terribly banal, but when you look more closely, you realize how complex it is!

What scientific expertise is used in this discipline?

CB: It is a “multiscience”, because it involves many disciplines. A tribologist can be a researcher specializing in solid mechanics, fluid mechanics, materials, vibratory behavior, etc. Tribology is the conjunction of all these disciplinary fields, and this is what makes it so complex. Personally, I specialize in material sciences.

Why is friction so interesting?

CB: You first need to understand the role of friction in contact. Although it sounds intuitive, when two materials rub together, many phenomena occur: the surface temperature increases, the mechanical behavior of both parts is changed, particles are created due to wear, which have an impact on the load and sliding speed. As a result, material properties arise which would not have happened without friction. Tribology focuses on both the macrometric and micrometric aspects of the surfaces of materials in contact.

How is the behavior of a material changed by friction?

CB: Take for example the wear particles generated during friction. As they are generated, they can decrease the frictional resistance between the two bodies. They then act as a solid lubricant, and in most cases they have a rather useful, desirable effect. However, these particles can damage the materials if they are too hard. If this is the case, they will accelerate the wear. Tribologists therefore try to model how, during friction, these particles are generated and under what conditions they are produced in optimal quantities.

Another illustration is the temperature increase of parts. In some cases of high-speed friction, the temperature of the materials can rise from 20°C to 700°C in just a few minutes. The mechanical properties of the material are then completely different.

Could you illustrate an application of tribology?

CB: Take the example of a rolling mill, a large tool designed to produce sheet metal by successive reductions in thickness. There is a saying in the discipline: “no friction, no lamination”. If problems arise during friction, that is, if there are problems of contact between the surface of the sheets and those of the cylinders, the sheets will be damaged. For the automotive industry, this means body sheets are damaged during the production phase, compromising surface integrity. To avoid this, we are working in collaboration with the relevant industrialists either on new metallurgical alloys or on new coatings to be put on the rollers. The purpose of the coating is to protect the material from wear and to slow down the damage of the working surfaces as much as possible.

Who are the main beneficiaries of tribology research?

CB: We work with manufacturers in the shaping industry, such as ArcelorMittal, or Aubert & Duval. We also have partnerships with companies in the aeronautics sector, such as Ratier Figeac. Generally, we are called in by major groups or subcontractors of major industrial groups because they are interested in increasing their speeds, and this is where friction-related performance becomes important.

 

[1] Christine Boher is a researcher at the Institut Clément Ader, a joint research unit
of IMT Mines Albi/CNRS/INSA Toulouse/ISAE Supaero/University Toulouse III Paul Sabatier/Federal University Toulouse Midi-Pyrénées.

earth

The world’s oldest building material is also the most environmentally friendly

/0 Comments/in , /by

The original version of this article was published on The Conversation. 
By Abdelhak Maachi and Rodolphe Sonnier, IMT Mines Alès.

[divider style=”normal” top=”20″ bottom=”20″]

[dropcap]D[/dropcap]espite the recommendations of IPCC experts, who in 2018 recommended that greenhouse gas emissions be reduced by 40 to 70% by 2050 in an attempt to limit the impacts of the climate crisis, global CO2 output increased by 0.6% in 2019.

Among the efforts made towards reducing the CO2 emitted through human activity, earth, the world’s most widespread raw material, has an essential role to play. Let’s not forget that the building sector alone generates nearly 40% of annual greenhouse gas emissions.

An ancient and global history

11,000 years ago, Homo sapiens was already building with earth in the region of present-day Syria. This age-old eco-material is still one of the world’s main building materials today. It is estimated to represent more than a third in the countries of the South.

Examples of earthen architecture, from the most modest to the most monumental, can be found on all continents and in all climates. 175 sites, wholly or partially built using this material, are classified by UNESCO as World Heritage Sites, highlighting the durability of this construction method.

 

In orange, the regions where earth is used in construction. The dots indicate the main architectural sites on the UNESCO World Heritage List. Source: Craterre.

 

Examples include the Grand Mosque of Djenné in Mali, built in 1907. It remains one of the largest mud brick buildings in the world and is one of the emblems of the country’s culture. In China, the Great Wall has sections several kilometers long built from earth where stone was not available locally. Also worthy of note is the 16th-century town of Shibam in Yemen, the world’s first dense, vertical town with high-rise buildings about 30 meters high, built entirely of molded mud bricks (called “adobes”). Due to the ongoing civil war in the country, the city is now on the UNESCO World Heritage in Danger list.

In Morocco, the four imperial cities – Fez, Marrakesh, Meknes and Rabat – are also classified as World Heritage Sites because of their traditional medinas built of adobe and rammed earth (pisé). The country also features prodigious fortresses made from ochre earth, called ksars and kasbahs. The Ksar of Ait-Ben-Haddou is an emblematic example of the traditional Amazigh architecture of southern Morocco.

earth

Shibam (Yemen) and its brick towers. Source: Kebnekaise/Flickr, CC BY-NC-SA

 

earth

In Marrakesh (Morocco). Source: Luca Di Ciaccio/Flickr, CC BY-NC-SA

 

In Europe, earthen constructions are not restricted to rural environments. In Granada, the dazzling Alhambra palace (meaning “red” in Arabic, in reference to the color of the earth), was largely built from rammed earth in the 13th century, in particular its ramparts.

France is one of the few countries featuring earthen heritage buildings using the 4 main traditional techniques – rammed earth (pisé), adobe, torchis cob and bauge cob – and where the majority of the earthen buildings often date back more than a century. Lyon is home to some remarkable examples of earthen architecture. In the Croix-Rousse neighborhood, people have been living in 4 and 5-floor rammed earth buildings since the 1800s.

Les tours défensives de l’Alhambra, à Grenade (Espagne). Source : Moli Sta Elena/Flickr, CC BY-NC-SA

The defense towers of Alhambra in Granada (Spain). Source: Moli Sta Elena/Flickr, CC BY-NC-SA

Building with what is under our feet

The earth is made up of minerals, organic matter, water and air. These minerals, composed mainly of silicates – quartz, clays, feldspars and micas – and carbonates, are the result of physical and chemical alteration of a source rock. The earth used for building (the raw material), which is essentially mineral, is easily removed from the ground, underneath the layer of soil that is rich in organic matter (humus) and is used for plant production.

After extraction using rudimentary or more elaborate tools, the earth (consisting of clay, silt, sand and possibly gravel and pebbles) is transformed into building material using traditional or more contemporary methods. The methods can be grouped into four main categories.

  • Compacted earth, not saturated with water: to make rammed earth walls (pisé) and blocks of compressed earth.
  • Stacked or molded earth: to make bauge cob walls and adobes.
  • Earth mixed when wet with plant fibers: to make torchis cob (to fill a wooden framework), straw earth, hemp earth, etc.
  • Earth poured in a liquid state into framework, such as fluid or self-consolidating concrete.

Cycle de vie de la terre crue : extraction, construction, utilisation, démolition et recyclage. Arnaud Misse

Life cycle of earthen building materials: extraction, construction, use, demolition and recycling. Source: Arnaud Misse.

Pisé : la terre peu humide est compactée à l’aide d’une dame (pisoir) dans des coffrages en bois (banches). Source : Arnaud Misse.

Rammed earth (pisé): earth containing little moisture is compacted with the help of a tamper into wooden formwork. Source: Arnaud Misse.

Blocs de terre comprimée (BTC) : la terre peu humide est comprimée dans des moules à l’aide d’une presse. Source : Arnaud Misse.

Blocks of compressed earth: earth containing little moisture is compressed in molds using a press. Source: Arnaud Misse.

Bauge : la terre malléable est empilée pour former un mur. Arnaud Misse

Bauge cob: malleable earth is piled up to form a wall. Source: Arnaud Misse.

Adobe : la terre est moulée à l’état plastique et séchée à l’air libre. Arnaud Misse

Adobe: earth is molded while it is malleable and dried in the open air. Source: Arnaud Misse.

Torchis : la terre, mélangée à de la paille, recouvre une ossature en bois. Arnaud Misse

Torchis cob: earth is mixed with straw, then used to cover a wooden frame. Source: Arnaud Miss

Easy to work with, healthy and environmentally friendly

There are a lot of advantages to using earth: it is a natural material, abundantly and locally available (transport is often nil), with low embodied energy (energy consumed throughout the life cycle of a material) and infinitely recyclable. It is raw and diversified, and offers a variety of granularities, natural colors and lively textures, for a minimalist aesthetic.

Earth also provides hygrothermic natural comfort, optimal acoustics and a healthy indoor atmosphere. It provides hygrometric regulation and solid walls provide good thermal inertia and sound insulation. It emits no VOCs (volatile organic compounds) and absorbs odors. These virtues have been empirically understood for thousands of years, but have now been confirmed scientifically.

Unlike industrialized and globalized materials, earth is easy to work with and poses no health risk. It thus helps to promote participatory building sites and self-built constructions (especially for the most disadvantaged), to value the diversity of construction cultures and to stimulate local development.

Earthen construction also contributes to the recovery of excavated land in large cities considered as waste. While the Greater Paris Express construction site will generate 40 million tons of earth by 2030, the “cycle terre” project aims to transform part of this “waste” into eco-materials for construction in a circular economy.

These eco-responsible advantages make earth a building material of the future, an alternative to energy-intensive and polluting building materials such as fired brick or cement (nearly 7% of global CO2 emissions), and a solution to be promoted in the building industry to respond to the global housing crisis (affecting one billion people) and the climate emergency, as hoped by the signatories of the “Manifesto for a Happy Frugality”.

Ordres de grandeur d’énergie grise de différents matériaux de construction. Abdelhak Maachi

Orders of magnitude of embodied energy of different building materials. Source: Abdelhak Maachi.

earth

Earth offers natural hygrothermal comfort. Source: Antonin Fabbri.

Limitations to be overcome

But earth also has its limits. The main problem is its sensitivity to water. To overcome this, mud walls are traditionally protected, especially in rainy climates, with a base (made of stone for example) to prevent moisture soaking up through capillary action, and a roof overhang to protect against erosion due to rain.

A small amount of cement is sometimes added to limit sensitivity to water and to increase, albeit modestly, mechanical properties. However, this “stabilization” technique is open to criticism because it impacts the ecological advantages and penalizes the life cycle of the material.

Répartition du patrimoine architectural en terre crue. En orange : torchis, en marron : pisé, en jaune : bauge et en rouge : adobe. Craterre

Distribution of architectural heritage made from earth. In orange: torchis cob, in brown: rammed earth (pisé), in yellow: bauge cob and in red: adobe. Source: Craterre.

Earth represents 15% of French buildings. However, the percentage of new buildings made of earth remains close to zero at the national level, although it is on the increase. The omnipresent reign of concrete, the hyper-industrialized context of construction, lobbying, inappropriate regulations, unfavorable prejudices (it is often seen as a primitive material for poor countries!), the lack of knowledge among decision-makers, engineers and project owners, are all reasons that explain the marginalization and ostracism from which this material suffers.

To overcome these barriers, earthen construction requires appropriate specific regulations for its implementation and maintenance, as well as adapted tests taking into account its specificities and complexity; evaluating its physical properties and durability. The development of earthen construction also requires scientific research, education, appropriate training of future designers and builders and promotion.

But earth, along with other ecomaterials such as wood, stone and bio-based insulators (such as hemp and straw), should undoubtedly contribute to building the resilient and autonomous city of tomorrow.

earth

Construction of Terra Janna in Marrakesh (Morocco): an earthen construction training center (Centre de la Terre) and a guest house built entirely using the adobe technique. This is an example of contemporary environmentally responsible earthen architecture. Source: Denis Coquard.

[divider style=”dotted” top=”20″ bottom=”20″]

Arnaud Misse (CRAterre), Ecole nationale supérieure d’architecture de Grenoble), Laurent Aprin, Marie Salgues, Stéphane Corn, Éric Garcia-Diaz (IMT Mines Alès) and Philippe Devillers (Ecole nationale supérieure d’architecture de Montpellier) are co-authors of this article.

Abdelhak Maachi doctoral student in material science, Mines Alès – Institut Mines-Telecom and Rodolphe Sonnier, assistant professor at the Ecoles des Mines, Mines Alès – Institut Mines-Telecom

This article was republished from The Conversation under the Creative Commons license. Read the original article here (in French).

 

 

ERC

Twin ERC grants for research on the aorta

/0 Comments/in , , /by

In 2015, the Mines Saint-Étienne engineering and health center was awarded two grants by the European Research Council (ERC). This funding was for two five-year projects on ruptured aortic aneurysms in the Sainbiose laboratory[1]. Pierre Badel received a €1.5 million starting grant (young researcher grant), and Stéphane Avril received a €2 million consolidator grant (for putting together a research team). 2020 marks the end of their grants and the related research projects. On this occasion, I’MTech conducted a joint interview with these two researchers to discuss their results and the impact of these ERC grants on their work.

 

Your two ERC grants were awarded in 2014 and started in 2015, focusing on similar topics: the biomechanics of the aorta in the context of ruptured aneurysms. What were the particularities of each of your projects?

Pierre Badel: The starting point for my project, AArteMIS, was to better explain the resistance of the walls of the aorta. In 2014, we had just developed in vitro tests to study the mechanical strength of this artery. The ERC grant was used to add experiments on the microstructure. In concrete terms, developing protocols to draw on these materials and study the structural properties when the wall breaks.

Stéphane Avril: My Biolochanics project had a degree of overlap with AArteMIS. We had recovered aneurysm tissue from real patients through our partnership with Saint-Étienne University Hospital, and we wanted to characterize the mechanical stresses in these tissues in order to understand how an aneurysm develops and how it ruptures. The two projects were not designed to work together, it is not common to have two ERC grants in the same team. However, the evaluation committees for the starting grant and the consolidator grant applications are different, which meant that the two projects were judged independently and both ended up receiving grants. The connection between the two projects was made afterwards.

Reproduction in vitro d'une dissection aortique pour l'étude de la rupture d'un anévrisme. Ici, l'image est réalisée par tomographie à rayons X sur une artère de lapin.

In vitro reproduction of an aortic dissection for the study of aneurysm rupture. Here, the image is made by X-ray tomography on a rabbit artery.

 

How did you adapt the research in each of the projects to what was being done in the other?

SA: When we learned that we had been awarded the two scholarships, I redesigned my project. I turned my focus towards the mechanical and biological aspects of the research. Rather than studying the mechanical reasons for aneurysm rupture and their relationship to artery wall structure – which the AArteMIS project was already doing – I focused on early aortic wall changes and their relationship to the environment. For example, the study looked at how blood flows through the aorta and how this affects the development of the aneurysm. We also launched a new protocol in the project to include patients with very small aneurysms. We are still monitoring these patients today, and this gives us a better understanding of the development of the pathology.

PB: For my part, I stayed fairly close to the planned program, i.e. the mechanical study of the material of the artery. The only difference with the original project is that we were able to look further into the structural aspect in the rupture of walls. We had the opportunity to use a new technique: X-ray tomography. This is like a CT scan, but suitable for very small samples. This allowed us to work on each layer of the vessels that make up the wall of the aorta, which have different properties.

These two projects have gone on for five years and will come to an end in a few months. What are the key findings?

PB: For AArteMIS, we now have experience that proves that even if we know the precise thickness of an aneurysm, we cannot predict where it will break. We are very proud of this result because a material will usually break at its thinnest point. However, this approach is wrong. This result helps in the diagnosis of aneurysms by explaining to practitioners that there is more involved than just looking at the thickness of the aortic wall when deciding whether an aneurysm is at risk of rupture.

What about the results of the Biolochanics project?

SA: There are two things I’m very happy about. The first is having finished a scientific article that took 5 years to write. It concerns the development of a method to reconstitute the elasticity map of vessels. It’s a very interesting technique because no one had managed to make an elasticity map of the vessels in the aorta before us. We have filed a patent, and the technique could be used in pharmacological research. The second result is that we have developed a digital model to simulate the accelerated aging of the aorta according to biological parameters. This is a step towards the development of a digital twin of the aorta for patients.

The research conducted under Stéphane Avril’s ERC grant has led to the development of a digital model to simulate the development of an aneurysm (in red on the right) based on biological parameters of the initial artery (left).

 

Read on I’MTech: A digital twin of the aorta to prevent aneurysm rupture

An ERC grant provides major funding over five years. How do these funds help you to develop a research project in concrete terms?

PB: First of all, an ERC grant means that for a few years we don’t have to waste time looking for money. This is a great comfort for researchers, who constantly have to apply for funding to conduct their work. Specifically for my project, the grant allowed me to recruit three PhD students and three post-docs. A whole team was put together, and that has given us greater research power. In our discipline, there are also many experiments involving expensive tools and equipment. The grant makes it possible to acquire state-of-the-art equipment and to set up the experiments that we wish.

SA: It’s similar for me: we were able to hire nine post-docs for Biolochanics. That’s a considerable size for a research team. The financial comfort also means that you can devote time to scientific resourcing and collaborations. I have been able to spend one to two months each year at Yale University in the United States, where there is also a very good team in specialized biomechanics of the aorta, led by Jay Humphrey.

Read on I’MTech: How Biomechanics can Impact Medicine – Interview with Jay Humphrey

How does being responsible for a project funded by an ERC grant affect your life as a researcher?

SA: There’s a lot of time spent managing and organizing. It’s demanding, but you can see the benefits for the laboratory directly. It is time that is well spent, and that is the main difference from having to spend time looking for funding, where the outcome is more uncertain. It also means a lot of recognition for the work. As researchers, we are solicited more often, we receive invitations that probably would not have come without the ERC grant. In terms of international interaction, it makes a significant difference.

As you approach the end of the projects – the end of December for you Stéphane, and the end of October for you Pierre – how do you envisage the future of your research?

PB: Right now we’re at full throttle! We still have several scientific articles in progress. The project officially ends in the fall, so I’m slowly starting to look for funding again. For example, I have a local project that is about to start up on soft tissue rupture for abdominal wall repair, funded by the Rhône-Alpes Region, Lyon University Hospital, Insa Lyon, and Medtronic. But the next few months will still be very busy with the end of the AArteMIS project.

SA: During the ERC grant period, we have little time to initiate and coordinate other projects. For the last five years, my approach has been to jump on trains without driving them. This has involved associations with other academic partners to submit projects, but without being a leader. Recently, one such project was accepted for funding under a Marie Curie International Training Network Action, European funding for the recruitment of cohorts of doctoral students. The laboratory is thus participating in the supervision of 6 theses on the digital twin for aneurysms in the aorta starting in the spring of 2020. In addition, I plan to take advantage of the end of this project to see what is being done elsewhere in my field of research. For one year, I will have a position as a visiting professor at the Vienna University of Technology in Austria. It’s also important to give yourself time in your career to open up and build relationships with your peers.

 

[1] The Sainbiose laboratory is a joint research unit of Mines Saint-Étienne/Inserm/Jean Monnet University

 

Interview by Benjamin Vignard, for I’MTech.

 

tactile perception

I like this, I don’t like that

/0 Comments/in , /by

We like the soft feel of a cat’s fur, but we don’t like mud, which is slimy, nearly as much. Why is this? We are told that everyone’s tastes are different. But that does not keep scientists from trying to find answers. Jenny Faucheu, a researcher at Mines Saint-Étienne, has studied tactile perception, a highly original subject.

 

“We’re used to defining what is beautiful or pleasant from a visual perspective,” explains Jenny Faucheu, a materials engineering researcher[1] at Mines Saint-Étienne, “but it is less common to think about these questions in terms of other senses, such as touch.” A Research Group name GDR TACT 2033 was formed on 1 January 2018 to study the complexity of tactile perception across a wide range of disciplines.

A better understanding of the sense of touch would provide a wide range of benefits. On one hand, medical examination focused on the possible causes of tactile deficiency or applications focused on rehabilitation. And on the other hand, efforts to develop and design products geared to tactile interfaces and simulators, or innovation in e-commerce. To make this possible, insight must be gained into a sense that is often considered of secondary importance, after sight or hearing.

Who likes what

“Our goal is not to define a human standard and a perfect material,” says Jenny Faucheu, “we’re trying to create links between different aspects through tactile perceptions.”  The researchers therefore take the material’s texture and substance into account by using sensors to detect finger vibrations on a surface. They also study cerebral activity through electroencephalograms and collect behavioral information using psycho-sensory questionnaires. “For example, we wondered if it bothered people that they couldn’t feel the fabric when buying an item such as a sweater online.” explains Jenny Faucheu.

Other questionnaires were focused on the surfaces themselves. In a multiple-choice format, participants had to sort surfaces into four categories ranging from “I like it a lot” to “I really don’t like it.” Another focused instead on how surprising or familiar participants found a surface to be. They were then asked to sort the materials based on their similarities. Then, they were asked to name them and attribute labels for their characteristics. “These mechanisms allow us to create correspondences,” explains Jenny Faucheu, “so we can then say, if this person likes sample 22, they should like sample 45.”

Still, some materials win a consensus. People generally like smooth materials and like rough materials much less. And a surprise can be either positive or negative. But the cultural impact must be kept in mind. “This study was carried out with French participants,” she explains, “it is highly likely that the results would be different for a different culture.”

Liking without touching

To carry out this study, the research team made special surfaces. The various textures were created by distributing small cylindrical dots of varying heights, diameter and spacing on polyurethane surface. Certain samples were perceived as smooth, rough, vibrating or sticky.

“When we rub a sample, vibrations are generated and travel through our finger to the mechanoreceptors,” explains Jenny Faucheu. The sensors used by the research team make it possible to study the vibrations received by these sensory receptors in our fingers. The lowest frequencies correspond to rough materials, which are generally disliked. And, conversely, the higher the frequencies are, the more the materials are perceived as smooth and tend to be well-liked. But it would also appear that a high amplitude intensifies the feeling of roughness.

All fifty or so samples look alike from a visual perspective, with their whitish color, and the naked eye cannot make out the small bumps on some of them. “We also decided to perform the study in a room that was dark enough to limit the influence of sight,” says the Mines Saint-Étienne researcher. Visual information is omnipresent and can therefore interfere with our perception. But hearing can too, although in a more discreet manner.

“We wanted to know whether tactile perceptions would be modified by associating more or less enjoyable sounds,” adds Jenny Faucheu. The same experiments are therefore repeated but with soundproof headphones. When the tester runs his finger along the surface, various sounds are sent to the headphones. It would therefore seem to be conceivable to reverse the perception of a surface by adjusting the ambient sound. “That said, we’re talking about an unpleasant feeling, not a painful one,” she says.

The loss of tactile sensation may appear with age or following an accident. Tactile simulation exercises can be performed to help slow down this loss or regain this sensation. It is possible that an unpleasant feel could slow rehabilitation by requiring additional effort. Therefore, relying on the sense of hearing to transform the perception of a surface could facilitate this process. “It’s the principle of gameification, ” says Jenny Faucheu, “the more fun and enjoyable the process, the more the patient is engaged and the rehabilitation is effective.” An idea that requires fundamental research on the sense of touch and new protocols for analyzing and understanding.

The same principle applies to tactile interfaces. On a tablet or smartphone, there is usually tactile feedback to emphasize a selection: a tool that improves interaction with the object. “Tactile simulators try to simulate real renderings of surfaces,” adds Jenny Faucheu. Projects such as StimTact aim to develop an augmented tactile screen that gives people the impression that they are touching the material displayed. We could therefore imagine buying a sweater on an online shopping website and caressing the real surface of the fabric, from right in front of our computer.

[1] Jenny Faucheu is a researcher at the Georges Friedel laboratory, a joint research unit between CNRS and Mines Saint-Étienne.

Tiphaine Claveau for I’MTech

 

building

Recovering knowledge of local, traditional building materials

/0 Comments/in , , /by

Why is an old country farmhouse more pleasant in summer than a modern city building? Traditional building materials and natural stone provide old buildings with better thermal and hygrometric properties. Unfortunately, they often lack the technical characterizations they need to find their place in the construction industry. The European regional development project OEHM has set out to resolve this problem. It brings together IMT Mines Alès, the University of Montpellier and the National School of Architecture of Montpellier. Aymeric Girard, a materials researcher at IMT Mines Alès, gives us an overview of the project and the challenges involved.

 

You’re studying natural building materials through the OEHM project. Why is this?

Aymeric Girard: All building materials require technical characterization. It’s important, since proposals for buildings are always simulated by computer nowadays as a first step. But traditional building materials, which are not produced by industry, lack technical characteristics. By studying local, traditional materials through the project, we are striving to fill this gap.

If the construction industry doesn’t use these materials, is it interested in this knowledge?

AG: Yes, since one of the major observations about current buildings is that they rely too heavily on internal insulation. The main reason for this is a lack of thermal mass in modern buildings, meaning a mass of materials that serves as a heat regulator. In a new building made with conventional building materials, you’re hot in the summer and cold in the winter. So you need heat and air conditioning. But this is far less of a problem in old buildings built with traditional building materials. In Seville, which is one of the hottest cities in Europe, old churches and cathedrals remain cool in the summer.   The construction industry is now seeking to model new buildings after these traditional structures.

Read more on I’MTech: In Search of Forgotten Cements

There’s also a second benefit. The construction industry is a sector that contributes heavily to greenhouse emissions. This is partially due to the environmental footprint of transporting materials. Using local stones encourages short supply chains, thereby reducing the environmental impact.

What materials are we talking about?

AG: For the OEHM project, we’re working with a clay brick factory and four natural stone quarries: one for granite and three for limestone. Some of these stones are truly local, since they come from the Occitanie region where IMT Mines Alès is located. Others are local in the sense that they come from France at least.

What aspects of these stones and bricks do you study?

AG : We conduct two main analyses of these stones: a thermal analysis and a hygrometric analysis. Hygrometry allows us to study a material’s ability to absorb humidity. That’s important because in winter, for example, the windows in a house are usually closed and you cook, take showers, sweat etc. All of these things increase the humidity level in rooms, which affects quality of life. Certain stones with very low porosity will not absorb this humidity at all, while others with high porosity will have a buffering effect and provide greater comfort.

How do you obtain the technical characteristics you’re seeking?

AG: The quarries send us small five-centimeter cubes to be analyzed. We use the hot-wire method to study heat transfer. This involves taking two cubes of the same stone, and putting a sensor the size of a post-it note between them. We heat one side and observe the speed at which the stone on the other side heats up. We also study the stones’ heat capacity, by putting even smaller samples measuring 5 mm per side in a mini-oven. This provides us with information about how long it takes to raise the stone’s temperature and about how it behaves.

In terms of humidity, we have a sort of refrigerator where we apply a constant amount of moisture, then we compare the weight of the dry stone with the saturated stone above, and deduce its capacity to absorb moisture. It’s a very long process that can take up to four months.

With whom are you working on this project?

AG: On the industrial side, we’re only working with the quarries for now. They’re interested in the technical characteristics we’re producing in order to provide their partners and customers with data about the materials. It’s important knowledge, just as when you buy glass wool to renovate your home, or when you compare offers to decide what to buy. On the research side, the project is part of a long collaboration between IMT Mines Alès, the University of Montpellier, and the National School of Architecture of Montpellier.

What will the project produce besides these technical characteristics?

AG: We plan to use the data we recover to develop our own material simulation software. And we’re also going to carry out real-site testing in collaboration with the National School of Architecture of Montpellier. They have a replica of a house that can be adapted to test materials. This will give us the opportunity to test our results and share insights with architects about the opportunities offered by natural materials suited to the Mediterranean climate.

plastics

A sorting algorithm to improve plastic recycling

/0 Comments/in , , /by

Producing high-quality raw materials from waste is contingent on effective sorting. Plastics from waste electrical and electronic equipment (WEEE) are no exception. To help solve this problem, researchers at IMT Mines Alès have developed a selective automation algorithm designed for these plastics. It can be integrated in new industrial-scale sorting machines.

 

How will your coffee maker be reincarnated after it dies? This electrical appliance composed primarily of plastic, metal and glass falls into the category of waste electrical and electronic equipment (WEEE). Your smartphone and washing machine are also included in this category. After it is thrown away, the coffee maker will find itself drowning in what amounts to over 750,000 tons of WEEE collected every year in France, before it is recovered by a specialized recycling center. There, it is dismantled, crushed and separated from its ferrous and non-ferrous metals, such as copper or aluminum, until all that’s left of the machine is a heap of plastic. Plastic is the second-largest component of WEEE after steel, so recycling it is a major concern.

And successful recycling starts with effective sorting. 20% of plastic materials are recovered through flotation after being placed in a tank filled with water. But how are the remaining 80% be processed? “Samples measuring 1 cm² are placed on a converyor belt equipped with an infrared camera at the end, which scans the material and determines what type of plastic it’s made of,”  says Didier Perrin, a physical chemist at IMT Mines Alès. The radiation excites the atomic bonds of the molecules and creates a spectral signature that characterizes the plastic to be identified. A technique using a near infrared source (NIRS) is especially rapid but cannot be used to identify dark plastics, which absorb the radiation. But black plastic, which holds up over time better than colored plastic, represents nearly 50 % of the waste. “Accurate and effective identification of the material is therefore crucial to generate high-quality raw material to be recycled, combining purity and mechanical performance,” adds the researcher. However, this method does not always make it possible to determine the exact type of plastic contained within a sample.

An automated sorting algorithm

Researchers at IMT Mines Alès have therefore developed an automated method for sorting plastic by working with SUEZ and Pellenc ST, a company that develops smart, connected sorting machines. The focus of their collaboration was on establishing a classification of the plastics contained in WEEE. The researchers generated a database in which each plastic has its own clearly-defined spectral identity. WEEE were therefore divided into four major families: ABS (acrylonitrile butadiene styrene), a polymer commonly used in industry which represents 50 to 60% of plastic waste (cases, covers, etc.); HIPS (high-impact polystyrene), which are similar to ABS but less expensive and with lower mechanical performance (refrigerator racks, cups); polypropylene (material which is more ductile than ABS and HIPS (soft covers for food containers, cups)); and what is referred to as ‘crystal’ polystyrene (refrigerator interior, clear organic glass).

Their first step was to better recognize the plastics to be sorted. “We used a supervised learning method on the data measured in the laboratory and then analyzed the same samples in industrial conditions,” explains PhD student Lucie Jacquin. Nevertheless, it is not always easy to characterize the type of plastic contained in waste. First of all, plastic degrades over time, which modifies its properties and makes it difficult to identify. And second, industrial conditions — with 3,000 kg of waste analyzed per hour — often result in incomplete spectral measurements.

Beyond the uncertainties of the measurements, the most traditional sorting methods also have their flaws. For example, they are based on probabilistic classification algorithms, which are used to determine how similar a sample is to those in a reference database. Except that these algorithms do not distinguish between equiprobability and ignorance. In the event of equiprobability, the spectrum of a sample is 50% similar to the spectrum of plastic A and 50% similar to that of plastic B. In the event of ignorance, even though the spectrum of a sample is not similar to any element within the database, the algorithm gives the same result as in the event of equiprobability (50% A and 50% B). So how can it be determined whether the information provided by the algorithm reflects uncertainty or ignorance? The researchers’ aim is therefore to better manage uncertainty in measurements in real conditions.

Understanding the material to recycle it better

“We approached this problem using modern uncertainty theories, which allow us to better represent uncertainty in the classification of a sample, based on the uncertainty in its spectrum obtained in real conditions. Belief functions can distinguish between equiprobability and ignorance, for example,” explains computer science researcher Abdelhak Imoussaten. The algorithm attempts to determine the class of plastic to which a sample belongs. When there is a doubt, it determines the set of classes of plastic to which it may belong and eliminates the others. For example, we can be sure that a sample is either ABS or HIPS, but definitely not polypropylene. “In this way, we use ‘cautious’ machine learning to control what the machine will send to the sorting bins,” adds Abdelhak Imoussaten. Since that’s the real goal: determining to which sorting bin these small bits of plastic will be sent in an automated way.

“Each category of plastic accepts a certain quantity of other plastics without affecting the matrix of the recycled material,” says Didier Perrin. In practice, this means that it is possible to send a plastic to a sorting bin with some certainty, even if the exact type of plastic is unclear (A or B but not C). While completing his PhD at IMT Mines Alès under the supervision of Didier Perrin, Charles Signoret studied all the possible mixtures of the various plastics and their compatibility. For example, ABS may only contain 1% polypropylene in its structure in order to maintain its mechanical properties, but it may contain up to 8% HIPS.

While the presence of impurities is inevitable in recycling, the researchers consider a sorting  method to be effective when it results in materials with 5% impurities or less. One thing is certain: the collaborative work of the researchers, SUEZ and Pellenc ST has proved to be effective in terms of sorting quality. It has already resulted in a demonstration machine which will subsequently be implemented in the production of new sorting machines.

Improving the effectiveness of sorting systems is crucial to the economic viability of the recycling industry. The ADEME estimates that 1.88 million tons of household appliances are brought to the market every year in France. These products will eventually have to be sorted in order to provide high-quality material to produce future equipment for this ever-growing market. “Our goal is also to ensure that the term ‘recycled,’ when referring to plastics, does not mean low-quality, as has already been achieved with glass and steel, two recycled materials whose quality is no longer questioned,” concludes Didier Perrin.

 

Article written in French by Anaïs Culot for I’MTech