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Our indoor air is polluted, but new materials could provide solutions

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Frédéric Thévenet, IMT Lille Douai – Institut Mines-Télécom

We spend 80% of our lives in enclosed spaces, whether at home, at work or in transit. We are therefore very exposed to this air, which is often more polluted than outdoor air. The issue of health in indoor environments is thus associated with chronic exposure to pollutants and to volatile organic compounds (VOCs) in particular. These species can cause respiratory tract irritation or headaches, a set of symptoms that is referred to as “sick building syndrome.” One VOC has received special attention: formaldehyde. This compound is a gas at room temperature and pressure and is very frequently present in our indoor environments although it is classified as a category 1B CMR compound (carcinogenic, mutagenic, reprotoxic). It is therefore subject to indoor air quality guidelines which were updated and made more restrictive in 2018.

The sources of volatile organic compounds

VOCs may be emitted in indoor areas by direct, or primary sources. Materials are often identified as major sources, whether associated with the building (building materials, pressed wood, wood flooring, ceiling tiles), furniture (furniture made from particle board, foams), or decoration (paint,  floor and wall coverings). The adhesives, resins and binders contained in these materials are clearly identified and well-documented sources.

To address this issue, mandatory labeling has existed for these products since 2012: they are classified in terms of emissions. While these primary sources related to the building and furniture are now well-documented, those related to household activities and consumer product choices are more difficult to characterize (cleaning activities, cooking, smoking etc.) For example, what products are used for cleaning, are air fresheners or interior fragrances used, are dwellings ventilated regularly? Research is being conducted in our laboratory to better characterize how these products contribute to indoor pollution. We have recently worked on cleaning product emissions and their elimination. And studies have also recently been carried out on the impact of essential oils at our laboratory (at IMT Lille Douai) in partnership with the CSTB (French National Scientific and Technical Center for Building) in coordination with ADEME (French Environmental and Energy Management Agency).

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Emission, deposition and reactivity of essential oils in indoor air (Shadia Angulo-Milhem, IMT Lille Douai). Author provided

In addition to the primary sources of VOCs, there are also secondary sources resulting from the transformation of primary VOCs. These transformations are usually related to oxidative processes. Through these reactions, other kinds of VOCs are also formed, including formaldehyde, among others.

What solutions are there for VOCs in indoor air?

Twenty years ago, an approach referred to as a “destructive process” was being considered. The idea was to pass the air to be treated through a purification system to destroy the VOCs. These can either be stand-alone devices and therefore placed directly inside a room to purify the air, or integrated within a central air handling unit to treat incoming fresh air or re-circulated air.

Photocatalysis was also widely studied to treat VOCs in indoor air, as well as cold plasma. Both of these processes target the oxidation of VOCs, ideally their transformation into CO2 and H2O. Photocatalysis is a process that draws on a material’s – usually titanium dioxide (TiO2) – ability to  adsorb and oxidize VOCs under ultraviolet irradiation. Cold plasma is a process where, under the effect of a high electric field, electrons ionize a fraction of the air circulating in the system, and form oxidizing species.

The technical limitations of these systems lie in the fact that the air to be treated must be directed and moved through the system, and most importantly, the treatment systems must be supplied with power. Moreover, depending on the device’s design and the nature of the effluent to be treated (nature of the VOC, concentration, moisture content etc.) it has been found that some devices may lead to the formation of by-products including formaldehyde, among others. Standards are currently available to oversee the assessment of this type of system’s performance and they are upgraded with technological advances.

Over the past ten years, indoor air remediation solutions have been developed focusing on the adsorption – meaning the trapping – of VOCs. The idea is to integrate materials with adsorbent properties in indoor environments to trap the VOCs. We have seen the emergence of materials, paint, tiles and textiles that incorporate adsorbents in their compositions and claim these properties.

Among these adsorbent materials, there are two types of approaches. Some trap the VOCs, and do not re-emit them – it’s a permanent, irreversible process. The “VOC” trap can therefore completely  fill up after some time and become inoperative, since it is saturated. Today, it seems wiser to develop materials with “reversible” trapping properties: when there is a peak in pollution, the material adsorbs the pollutant, and when the pollution decreases, for example, when a room is ventilated, it releases it, and the pollutant is evacuated through ventilation.

These materials are currently being developed by various academic and industry players working in this field. It is interesting to note that these materials were considered sources of pollution 20 years ago, but can now be viewed as sinks for pollution.

How to test these materials’ ability to remove pollutants

Many technical and scientific obstacles remain, regardless of the remediation strategy chosen. The biggest one is determining whether these new materials can be tested on a 1:1 scale, as they will be used by the end consumer, meaning in “real life.”  

That means these materials must be able to be tested in a life-size room, and with conditions that are representative of real indoor atmospheres, while controlling environmental parameters perfectly. This technical aspect is one of the major research challenges in IAQ since it determines the representativeness and therefore the validity of the results we obtain.  

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Experimental IRINA room (Innovative Room for Indoor Air studies, IMT Lille Douai). Author provided

We developed a large enclosed area in our laboratory for precisely this purpose a few years ago. With its 40 square meters, it is a real room that we can go into, called IRINA (Innovative Room For Indoor Air Studies). Seven years ago, it was France’s first fully controlled and instrumented experimental room on a 1:1 scale. Since its development and validation, it has housed many research projects and we upgrade it and make technical updates every year. It allows us to recreate the indoor air composition of a wood frame house, a Parisian apartment located above a ring road, an operating room and even a medium-haul aircraft cabin. The room makes it possible to effectively study indoor air quality and treatment devices in real-life conditions.

Connected to this room, we have a multitude of measuring instruments, for example to measure VOCs in general, or to monitor the concentration of one in particular, such as formaldehyde.

Frédéric Thévenet, Professor (heterogeneous/atmospheric/indoor air quality physical chemistry), IMT Lille Douai – Institut Mines-Télécom

This article has been republished from The Conversation under a Creative Commons license. Read the original article (in French).

Corenstock Chair: a Trial Cylinder for the Heating Industry

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As 2021 begins, IMT and elm.leblanc launched the Corenstock Industrial Chair to address issues in energy and digital transition in the domestic heating industry. What is the objective? Within four years, to present a demonstrator for the hot water tank of the future: more resistant, efficient and durable. Behind this prototype lies the development of new economic models for the global transformation of the industry.

The principle of Corenstock Chair (Lifecycle design & systemic approach for energy efficiency of water heating and storage devices), launched in early 2021, is to consider an equipment of the everyday-life to be optimized and used as a model for the transformation of an entire industry. The objective is to present within four years a demonstrator for an innovative hot water tank, more energy efficient, more sustainable and more connected to its users. The project is however not limited to the design of a new domestic hot water tank: it covers the transition problematics of the heating industry as a whole. In line with new business models development, the underlying interest is to redefine the dedicated design methodologies, to generalize sustainable production and end-of-life recovery to implement new economic balances.

The Chair lead by IMT is co-funded in equal parts by the ANR (French Research National Agency) and elm.leblanc, a company specialized in the production of water heaters and boilers. The project relies on the complementary skills of the academic and industrial partners. “We are exploring two key avenues: on the one hand, technological innovation, involving design, materials and smart controls issues” says Mylène Lagardère, a researcher at IMT Lille Douai. She holds the Corenstock Chair, which is jointly coordinated with Xavier Boucher, a researcher at Mines Saint-Etienne. He is responsible for the operational management of the Chair and adds:  “on the other hand, we are working on innovation capabilities, decision-making support for new design methods and the transformation of the production chain together with the company organization”. The two researchers mention that they have “established a trusting and long-term partnership with elm.leblanc, with the goal of pursuing future projects in this area”.

What would be the tank of the future?

“The goal is to improve the energy efficiency of a product that everyone owns at home,” says Mylène Lagardère. Moreover, this equipment is crucial for various thermal systems; whether gas, oil or electricity is used as a source of energy, all of us need to store domestic hot water. To find ways to improve thermal performances, or to select materials to make the cylinder as efficient as possible, involves a significant amount and diversity of research actions. The Chair will thus benefit from the recruiting of 5 PhD students, 4 post-docs and 3 engineers.

Product durability is one of the main areas for improvement. In this sense, predictive maintenance is promising. The use of smart sensors is essential, both to better evaluate the tank performances and to foresee necessary repairs before it breaks down. Mylène Lagardère specifies that the objective is to have “the best compromise between each component, each function of the tank, while taking into account its integration in the environment and the management of the end-of-use”.

Behind the project’s targeted product, general reflection on the entire product life cycle is emerging and address the resources needed for its production, the product durability or the management valorization at the end of use. The project advancements on the improvement of the value chain are expected to be generalized to the entire industry :“The work conducted on the hot water storage tank tank is the entry point for more general work on the economic model itself,” says Xavier Boucher, and these questions are completely integrated in the Corenstock Chair program.

Evolution of the industry

Xavier Boucher emphasizes that “these hot water storage tanks are at the heart of a variable system and a transformation of this sector involves industrial actors at different levels, including the customers as well the maintenance providers”. As a result, the relations to the customers will naturally be modified. The two researchers mention: “this is part of a fairly strong phase of transition in the industries business. It is no longer simply a matter of selling a hot water storage tank, but of including the tank in a multi-actor performance contract.”

From the point of view of companies, they now need to develop customer loyalty and sustainability. “These different levers are necessary to establish a win-win relationship between the customer and the manufacturer,” says Xavier Boucher. Intelligent management offers opportunities to improve energy costs, reduce maintenance costs, and ultimately reduce the final energetic bill. This also reduces for manufacturing and maintenance internal costs.

Mylène Lagardère reports that they aim “to enlighten decision-makers on their economic transformation, particularly through the research for more sustainable indicators”. Her colleague from Saint-Etienne adds “virtualization proves to be a key tool in planning this transition”. The Corenstock Chair assumes the role of simulator of this transformation by observing the behavior of users and various partners. The project combines several routes of innovation, whether aiming towards digital, networking or what is known as digital servicing. This is a strategy converging towards a long-term customer relationship through digital services. “The challenge lies in the evolution of value creation mechanisms,” says Mylène Lagardère.

The Chair is also driven by the dissemination of the results generated and knowledge acquired towards students and future engineers in the field, but also towards the technical and innovation staff of elm.leblanc through professional trainings. Xavier Boucher notes “there are two aspects of training: short modules to increase professional skills, and a specialized master’s degree to integrate more largely the solutions into the industrial framework.” One of the objectives of the specialized master’s degree is to mutualize the skills of each school to encourage interaction between the different expertise domains required.

“Generally speaking, the Chair cannot be simply reduced to technological innovation. On the contrary it covers a global reflection on what the industry of the future is” says Xavier Boucher. This includes facilitating collaboration and opening among different sectors: industrial, technological, and economic. This collaboration is essential to ensure that these transformations are a lasting part of tomorrow’s industry. “The Chair marks what elm.leblanc is building with IMT: a new way of approaching these innovation processes, through a strong collaboration and a relationship of trust to increase the capacity for innovation,” concludes Xavier Boucher.

Tiphaine Claveau.

brominated plastics

Innovative approaches to recycling brominated plastics

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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.