Textination Newsline

Producing infection control clothing requires a lot of energy and uses lots of material resources. Fraunhofer researchers have now developed a technology which helps to save materials and energy when producing nonwovens. A digital twin controls key manufacturing process parameters on the basis of mathematical modeling. As well as improving mask manufacturing, the ProQuIV solution can also be used to optimize the production parameters for other applications involving these versatile technical textiles, enabling manufacturers to respond flexibly to customer requests and changes in the market.

Nonwoven infection control masks were being used in their millions even before the COVID-19 pandemic and are regarded as simple mass-produced items. Nevertheless, the manufacturing process used to make them needs to meet strict requirements regarding precision and reliability. According to DIN (the German Institute for Standardization), the nonwoven in the mask must filter out at least 94 percent of the aerosols in the case of the FFP-2 mask and 99 percent in the case of the FFP-3 version. At the same time, the mask must let enough air through to ensure that the wearer can still breathe properly. Many manufacturers are looking for ways to optimize the manufacturing process. Furthermore, production needs to be made more flexible so that companies are able to process and deliver versatile nonwovens for a wide range of different applications and sectors.

ProQuIV, the solution developed by the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern, fulfills both of these aims. The abbreviation “ProQuIV” stands for “Production and Quality Optimization of Nonwoven Infection Control Clothing” (Produktions- und Qualitätsoptimierung von Infektionsschutzkleidung aus Vliesstoffen). The basic idea is that manufacturing process parameters are characterized with regard to their impact on the uniformity of the nonwoven, and this impact is then linked to properties of the end product; for example, a protective mask. This model chain links all relevant parameters to an image analysis and creates a digital twin of the production process. The digital twin enables real-time monitoring and automatic control of nonwoven manufacturing and thus makes it possible to harness potential for optimization.

Dr. Ralf Kirsch, who works in the Flow and Material Simulation department and heads up the Filtration and Separation team, explains: “With ProQuIV, the manufacturers need less material overall, and they save energy. And the quality of the end product is guaranteed at all times.”

Nonwoven manufacturing with heat and air flow
Nonwovens for filtration applications are manufactured in what is known as the
meltblown process. This involves melting down plastics such as polypropylene and forcing them through nozzles so they come out in the form of threads referred to as filaments. The filaments are picked up on two sides by air flows which carry them forward almost at the speed of sound and swirl them around before depositing them on a collection belt. This makes the filaments even thinner: By the end of the process, their thickness is in the micrometer or even submicrometer range. They are then cooled, and binding agents are added in order to create the nonwoven. The more effectively the temperature, air speed and belt speed are coordinated with each other, the more uniform the distribution of the fibers at the end and therefore the more homogeneous the material will appear when examined under a transmitted light microscope. Lighter and darker areas can thereby be identified — this is referred to by experts as cloudiness. The Fraunhofer team has developed a method to measure a cloudiness index on the basis of image data. The light areas have a low fiber volume ratio, which means that they are less dense and have a lower filtration rate. Darker areas have a higher fiber volume and therefore a higher filtration rate. On the other hand, the higher air flow resistance in these areas means that they filter a smaller proportion of the air that is breathed in. A larger proportion of the air flows through the more open areas which have a less effective filtration effect.

Production process with real-time control
In the case of ProQuIV, the transmitted light images from the microscope are used to calibrate the models prior to use. The experts analyze the current condition of the textile sample and use this information to draw conclusions about how to optimize the system — for example, by increasing the temperature, reducing the belt speed or adjusting the strength of the air flows. “One of the key aims of our research project was to link central parameters such as filtration rate, flow resistance and cloudiness of a material with each other and to use this basis to generate a method which models all of the variables in the production process mathematically,” says Kirsch. The digital twin monitors and controls the ongoing production process in real time. If the system deviates slightly from where it should be — for example, if the temperature is too high — the settings are corrected automatically within seconds.

Fast and efficient manufacturing
“This means that it is not necessary to interrupt production, take material samples and readjust the machines. Once the models have been calibrated, the manufacturer can be confident that the nonwoven coming off the belt complies with the specifications and quality standards,” explains Kirsch. ProQuIV makes production much more efficient — there is less material waste, and the energy consumption is also reduced. Another advantage is that it allows manufacturers to develop new nonwoven-based products quickly — all they have to do is change the target specifications in the modeling and adjust the parameters. This enables production companies to respond flexibly to customer requests or market trends.

This might sound logical but can be quite complex when it comes to development. The way that the values for filtration performance and flow resistance increase, for example, is not linear at all, and they are not proportional to the fiber volume ratio either. This means that doubling the filament density does not result in double the filtration performance and flow resistance — the relationship between the parameters is much more complex than that. “This is precisely why the mathematical modeling is so important. It helps us to understand the complex relationship between the individual process parameters,” says ITWM researcher Kirsch. The researchers are able to draw on their extensive expertise in simulation and modeling for this work.

More applications are possible
The next step for the Fraunhofer team is to reduce the breathing resistance of the nonwovens for the wearer without impairing the protective effect. This is made possible by electrically charging the fibers and employing a principle similar to that of a feather duster. The electric charge causes the textile fabric to attract the tiniest of particles which could otherwise slip through the pores. For this purpose, the strength of the electrostatic charge is integrated into the modeling as a parameter.

The Fraunhofer researchers’ plans for the application of this method extend far beyond masks and air filters. Their technology is generally applicable to the production of nonwovens — for example, it can also be used in materials for the filtration of liquids. Furthermore, ProQuIV methods can be used to optimize the manufacture of nonwovens used in sound-insulating applications.

A significant part of carpet waste consists of petroleum-based polypropylene. As a non-recyclable product, disposing of it has previously meant incineration or landfill. However, a new solvent is now making it possible to recover virgin-standard polypropylene from carpet waste — with no perceptible reduction in quality. Developed by the Fraunhofer Institute for Building Physics IBP and its partners, the process also involves costs that are quite competitive. The development has taken place as part of the ISOPREP EU project.

The EU alone produces around 1.6 million tons of carpet waste every year. The majority of this ends up being sent to landfill or incinerated, as carpet is a composite material that is not suitable for purely mechanical recycling methods. With carpet waste analysed in the project consisting of around a quarter polypropylene, a petroleum-based plastic, the result is a great deal of resources going to waste.

Carpet recycling now possible thanks to a new process
A team of researchers, including from Fraunhofer IBP, has now developed a new recycling process as part of an EU project named ISOPREP (see logo). “For the first time, this is making it possible to recover polypropylene from carpet waste — and the outcome is virgin-quality,” says Maike Illner, a researcher at Fraunhofer IBP. Not only does this allow the recovered polypropylene to be used in lower-quality products (in a process known as downcycling), but it also means that the quality is similar to that of newly manufactured polypropylene, making the material suitable for high-quality products too.

The process is based on a special solvent in the form of an ionic liquid. With the right components, it is able to selectively extract polypropylene from carpet fibers. Before the team of experts applies the solvent, the carpet waste is cleaned — something which involves removing as much of the backing as possible — and broken down. Once the pretreatment is complete, the waste is fed into a reactor in which it undergoes treatment using the solvent. The polypropylene is selectively dissolved in the solvent, a method that provides an effective way of removing dyes and other additives. The process is already being used on an extensive laboratory scale involving several liters of the solvent — and now, the research consortium has set its sights on scaling the process up to a pilot plant with the ability to recycle a ton of carpet waste per day. The pilot plant is set to commence operation by the end of the project in March 2022.

Costs and environmental impact
A recycling process can only be deployed on a large scale if its costs are competitive. For this application, this means retaining as much of the expensive ionic liquid as possible in the cycle. “If loss rates can be kept to one percent or less, there is potential for the costs of the process to rival those of producing new polypropylene,” explains Illner. “We know this thanks to a preliminary economic analysis that we conducted at Fraunhofer IBP.” The analysis involved the Fraunhofer researchers investigating the quantities of material and energy that would be required for the process and what kind of product would be output, and then calculating the associated costs. The team also considered how the costs would develop over the long term.

Fraunhofer IBP is focusing on the ecological aspects of carpet recycling. It is able to draw conclusions from factors including a lifecycle assessment, which sheds light on the emissions that are produced during the recycling process, for example. If the consortium is able to achieve its aim of keeping solvent loss rates to one percent or less in this case too, primary energy requirements and greenhouse gas emissions will remain on a similar scale to those involved in producing new polypropylene.

Potential for transfer to other polypropylene waste streams
While carpet waste is the focus of this particular project, the process that has been developed has potential applications far beyond it. The experts involved believe that it could be transferred to a whole host of waste flows that contain polypropylene and are unsuitable for conventional recycling methods. “One example is polypropylene products that contain dyes and additives,” says Illner. “Until now, it has been difficult to extract them from plastic, which means that the recycled polypropylene has only been suitable for use in lower-quality products.” The new process separates the polypropylene not only from other materials, but also from dyes and other additives, allowing it to be used in high-quality applications.

This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 820787.

Coveted awards for active insulation and sustainable hybrids

The awards presented at PERFORMANCE DAYS are coveted trophies in the world of functional textiles. The winning fabrics or technologies are always truly pioneering innovations. In Fall 2016, the "Oscars of Function" go to Imbotex and Pontetorto.

PERFORMANCE AWARD for the insulation "TWINS" from Imbotex
The Italian company Imbotex is well known for its high quality insulations. The latest generation is called "TWINS" and does not merely hold the warmth, it applies intelligent technology to create heat on demand. This is made possible by the two "faces" of the twin design. The patented, bonded fleece material consists of a lining made from a blend of polyacrylic and polyester that transports moisture quickly away from the skin. On the outside, hydrophobic polypropylene rapidly releases the moisture into the environment. The water vapor formed at the level of "insensible perspiration" is quickly transported to the outside and the body stays dry. During this process, the kinetic energy of the water vapor converts to heat energy and the inner lining of the garment remains pleasantly warm, even in the low temperatures of winter. "TWINS" from Imbotex was the winner of the PERFORMANCE AWARD for this intelligent solution that produces additional warmth and ensures a dry feeling.    

ECO PERFORMANCE AWARD for the hybrid design "ECO HYBRID" from Pontetorto
Engineered hybrids, that is, hybrid solutions that combine multiple zones and fibers in one fabric length are the future of functional clothing. Through such hybrid engineering, sports styles are given the added value of such useful features as thermal retention, climate management, durability, lighter weight, and elasticity; and, all of these at the exact position where it is desirable to have the function. Another advantage of this fabric design is the elimination of irritating seams, which means increased comfort for the wearer. Nevertheless, to manufacture these hybrids requires much experience with jacquard production. The new fabric "ECO HYBRID" introduced by fleece specialist Pontetorto represents not only a sophisticated and highly functional jacquard hybrid with different zones – it is entirely produced with absolutely sustainable methods. The fibers used, in this case polyamide and merino wool, are both quickly degradable and environmentally friendly. The fact that merino wool is degradable is not unusual as it is a natural product. The special aspect of this concept is the polyamide fiber used exclusively by Pontetorto, which is fully degradable within three years! For so much "green" innovation, Pontetorto was selected as the winner of the ECO PERFORMANCE AWARD.
 
All of the newest trends for Winter 2018/19 and our FOCUS TOPIC are on display on November 16-17, 2016 at PERFORMANCE DAYS in the Munich MTC. For all those who cannot wait, a lot of information is already provided for you online at: https://www.performancedays.com

About PERFORMANCE DAYS
PERFORMANCE DAYS — The “functional fabric fair” launched in 2008, is the first and only event created especially for functional fabrics for sports and work clothing. The aim of the semi-annual trade fair is to give leading and innovative textile manufacturers, suppliers and service providers the opportunity to present their functional fabrics, membranes plus treatments, laminates, paddings, finishes, and accessories such as yarns, tapes, prints, buttons and zippers.
No entry fee and free admission to all events for industry visitors.
Detailed information and advanced registration online at: www.performancedays.com