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10.01.2023

Fraunhofer: Optimized production of nonwoven masks

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.

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.

Source:

Fraunhofer Institute for Industrial Mathematics ITWM

Foto: Pixabay
09.11.2021

NGST - Next Generation Protective Textiles

  • Efficient Production of Novel, High-Quality Infection-Protective Textiles

 
Considerable shortages of protective textiles, especially respirators, occurred during the SARS-CoV-2 pandemic, which were exacerbated by the lack of sufficient production capacity in Germany and the EU at the time. Short-term retooling at EU companies as well as importing goods often did not lead to success, as these protective textiles were of highly variable quality, which had a negative impact on safety.

The "Next Generation Protective Textiles" initiative aims to remedy this situation by researching new approaches for the production of high-quality protective textiles.

The "NGST" project is divided into several subtasks
The project includes:

  • Efficient Production of Novel, High-Quality Infection-Protective Textiles

 
Considerable shortages of protective textiles, especially respirators, occurred during the SARS-CoV-2 pandemic, which were exacerbated by the lack of sufficient production capacity in Germany and the EU at the time. Short-term retooling at EU companies as well as importing goods often did not lead to success, as these protective textiles were of highly variable quality, which had a negative impact on safety.

The "Next Generation Protective Textiles" initiative aims to remedy this situation by researching new approaches for the production of high-quality protective textiles.

The "NGST" project is divided into several subtasks
The project includes:

  • qualified selection of basic materials
  • studies on up-scaling to create the conditions for a rapid expansion of production capacities
  • development of novel antiviral coatings
  • comprehensive biological and material science analysis to verify the improved properties and also to open up new methods of quality control.

The protective textiles to be developed in the project have a wide range of applications beyond use in the medical field and in civil protection. In principle, wherever immediate cleaning and disinfection are difficult or special filtration tasks are necessary, such as in mobile or stationary filter systems for air purification or for individual personal protection.

In this project, the Fraunhofer IGCV is researching the development of a manufacturing process for nonwovens as a basis for infection protection and filtration media based on wet nonwoven technology. Compared to the state of the art (meltblown technology), this is potentially characterised by significantly increased production capacities as well as increased flexibility with regard to material variety. The main challenges here are the very high quality requirements based on low basis weights for processing the finest possible micro-staple fibres..
          
Pursuing novel approaches to increase quality and productivity in the production of protective textiles
The aim is to provide optimised nonwoven materials as a starting material for subsequent antiviral coatings, and to assess and demonstrate the high technological potential of wet nonwoven technology in this field of application.

For this purpose, an existing pilot wetlaid nonwoven line was specifically modified on a pilot plant scale. This makes it possible to produce nonwoven materials from micro-staple fibres in the required very high quality in terms of uniformity, basis weight, blending and thickness profile with high reproducibility. A standard PP nonwoven was used as a comparison system, which was produced according to the current state of the art using meltblown technology. In addition to the PP comparison variants, however, the processing of PLA, viscose and PET staple fibres, among others, was also investigated. The focus here is on maximum fibre fineness (microfibres) in each case in order to achieve the largest possible specific fibre surface or effective area in the nonwoven. In order to emphasise the significantly increased flexibility of wetlaid technology, particularly innovative variants based on modified bi-component fibres with maximised fibre surface area as well as split fibres are also being conceptually tested.

In addition to aspects of direct material and process development, the scale of the pilot plant provides a comprehensive data basis for estimating a later scaling up to an industrial series. This should create a technological starting point for the ramp-up of an efficient, national production of fleece-based infection control materials based on wet-laying technology.

Source:

Fraunhofer Institute for Casting, Composite and Processing Technology IGCV

Photo: pixabay
21.09.2021

Virtual Quality Inspection Optimizes Production of Filter Nonwovens

Nonwoven production received more attention than ever before from the general public in Corona times, because the technical textile is crucial for infection protection. The ultra-fine nonwoven products are manufactured in so-called meltblown processes. A cross-departmental team at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern is optimizing the entire production chain in the »ProQuIV« project. Simulations help to guarantee the product quality of the filter material despite fluctuations in production.

Nonwoven production received more attention than ever before from the general public in Corona times, because the technical textile is crucial for infection protection. The ultra-fine nonwoven products are manufactured in so-called meltblown processes. A cross-departmental team at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern is optimizing the entire production chain in the »ProQuIV« project. Simulations help to guarantee the product quality of the filter material despite fluctuations in production.

The abbreviation »ProQuIV« stands for »Production and Quality Optimization of Nonwoven Infection Protection Clothing«. This is because bottlenecks in the production of these materials were particularly evident at the beginning of the Covid 19 crisis. For the meltblown nonwovens, this optimization of the product quality is also particularly difficult because the textiles react very sensitively to fluctuations in the manufacturing processes and material impurities.

Digital Twin Keeps an Eye on the Big Picture
»Meltblown« is the name of the industrial manufacturing process whose ultra-fine fiber nonwovens are responsible for providing the crucial filtering function in face masks. In this process, the molten polymer is forced through nozzles into a forward-flowing, high-speed stream. It is stretched and cooled in a highly turbulent air flow.

»The overall process of filter media production – from the polymer melt to the filter medium – presents a major challenge in simulation,« explains Dr. Konrad Steiner, head of the »Flow and Materials Simulation« department. »In the project, we kept the big picture in mind and developed a completely integrated evaluation chain as a digital twin. In doing so, we take several key components into account at once: We simulate the typical production processes of nonwovens, the formation of the fiber structures and then the material properties – here, in particular, the filter efficiency. This allows us to quantitatively evaluate the influences of the manufacturing process on the product properties.« In each of these individual areas, Fraunhofer ITWM and its experts are among the leading research groups internationally.

Homogeneity of the Material – Fewer Clouds in the Simulation Sky
In the meltblown process, a key factor is the behavior of the filaments in the turbulent, hot and fast air flow. The properties of the filaments are strongly influenced by this air flow. The quality of the filaments – and thus the quality of the nonwovens – is influenced by many factors. Dr. Dietmar Hietel, head of the »Transport Processes« department, knows what this means more precisely in practice. His team has been working at Fraunhofer ITWM for years on the simulation of various processes involving filaments, threads, and fibers. »The focus of the project is the so-called cloudiness, i.e. the non-uniformity of the fiber distributions in the nonwoven,« explains Hietel. »We are investigating the question: How homogeneous is the fabric? Because the quality of the products can be greatly improved if we increase the uniformity. Our simulations help figure out how to do that.«

Objective Evaluation of the Homogeneity of Nonwovens
The researchers also use appropriate image analysis techniques to quantify this cloudiness. The power spectrum plays a special role here. »The cloudiness index (CLI) describes homogeneity complementary to local basis weight and its variance,« describes Dr. Katja Schladitz. She brings her expertise in image processing to the project. »Our CLI ensures a robust assessment of the homogeneity and can thus be used for different material classes and imaging techniques to be used as an objective measure.« The frequencies that go into the CLI calculation can be chosen so that the CLI is meaningful for the particular application area.

Filtration: How Efficient Are the Filters?
For the upscaling to industrial processes such as mask production, the ITWM expertise in filters is also included in the project. The »Filtration and Separation« team led by Dr. Ralf Kirsch has been working for years on the mathematical modeling and simulation of various separation processes.

»What's special about this project is that we calculated the efficiency of the filters for fluctuations of varying degrees in the fiber volume fraction,« emphasizes Kirsch. »This allows us to specify up to what level of cloudiness the required filter efficiency can be achieved at all.« As a current example of this, the figure depicts in the graphic the efficiency of a filter material for N95 masks as a function of the inhomogeneity of the nonwoven.

ITMW Methods Support Across the Entire Process Chain
In »ProQuIV«, digital twins and calculations from Fraunhofer ITWM support a holistic view and better understanding of the processes. The production of technical textiles thus not only becomes more efficient, but the nonwovens can be developed virtually without having to realize this in advance in a test facility. In this way, production capacities can be increased while maintaining or even increase the quality. Together with long-term partners from industry, the research can be put into practice quickly and efficiently.

Simulations save textile companies experiments, allow new insights, enable systematic parameter variations and solve upscaling problems that can otherwise lead to bad investments during the transition from laboratory plant to industrial plant. However, virtual implementation of nonwoven production also opens up new opportunities for optimization at other levels. For example, acoustic insulating nonwovens or even hygiene nonwovens can also be optimized in terms of their product quality precisely with regard to the material properties to be achieved – while taking into account the process fluctuations that occur.

The project is part of the Fraunhofer-Gesellschaft's »Fraunhofer versus Corona« program and was completed in April 2021. The results will flow into several follow-up projects with the nonwovens industry.

Photo: Pixabay
28.04.2020

Meltblown Productive: Fraunhofer ITWM vs. Corona - With Mathematics Against the Crisis

  • Meltblown Productive – ITWM Software Supports Nonwoven Production for Infection Protection

Simulations by the Fraunhofer Institute for Industrial Mathematics ITWM make processes in the manufacturing of nonwovens more efficient. Within the anti-corona program of Fraunhofer the production of infection protection is optimized.
 
Nonwovens production is currently attracting more attention than ever before from the general public, because in times of the corona pandemic, nonwovens are vital for infection protection in the medical sector and also for the protection of the entire population. Disposable bed linen in hospitals, surgical gowns, mouthguards, wound protection pads and compresses are some examples of nonwoven products.

  • Meltblown Productive – ITWM Software Supports Nonwoven Production for Infection Protection

Simulations by the Fraunhofer Institute for Industrial Mathematics ITWM make processes in the manufacturing of nonwovens more efficient. Within the anti-corona program of Fraunhofer the production of infection protection is optimized.
 
Nonwovens production is currently attracting more attention than ever before from the general public, because in times of the corona pandemic, nonwovens are vital for infection protection in the medical sector and also for the protection of the entire population. Disposable bed linen in hospitals, surgical gowns, mouthguards, wound protection pads and compresses are some examples of nonwoven products.

IEspecially in intensive care and geriatric care, disposable products made of nonwovens are used due to the special hygiene requirements. At the moment there are clear bottlenecks in the production of these materials. For the meltblown nonwovens class, however, it is difficult to increase production efficiency because meltblown processes are highly sensitive to process fluctuations and material impurities.
 
Although nonwovens are not all the same, the rough principle of their production is relatively similar to all industrially manufactured nonwovens: molten polymer is pressed through many fine nozzles, stretched and cooled down in an air stream and thus deposited into the typical white webs. "Meltblown" stands for the submicron fiber process whose nonwovens are responsible for the decisive filter function in face masks.
 
With meltblown technology, nonwoven fabrics are produced directly from granules. A special spinning process in combination with high-speed hot air is used to produce fine-fibered nonwovens with different structures. The fibers are highly stretched by the turbulent air flow. During this process they swirl in the air, become entangled and fall more or less randomly onto a conveyor belt where they are further consolidated - a very complex process. Nonwovens manufacturers around the world are striving to massively increase their production capacities.
 
Digital Twin Optimizes Meltblown Process    
This is where the software of the ITWM comes into play. "Our Fiber Dynamics Simulation Tool FIDYST is used to predict the movement of the fibers, their falling and the orientation with which they are laid down on the conveyor belt. Depending on the process settings, turbulence characteristics are generated and thus nonwoven qualities are created that differ in structure, fiber density and strength," explains Dr. Walter Arne from the Fraunhofer ITWM. He has been working at the institute for years on the simulation of various processes involving fibers and filaments.

The methodology is well transferable to meltblown processes. In these processes, one of the specific features is the simulation of filament stretching in a turbulent air flow - how the stretching takes place, the dynamics of the filaments and the diameter distribution. These are all complex aspects that have to be taken into account, but also the flow field or the temperature distribution. The simulations of the scientists at the Fraunhofer ITWM then provide a qualitative and quantitative insight into the fiber formation in such meltblown processes - unique in the world in this form when it comes to simulate a turbulent spinning process (meltblown).

Nonwoven Manufacturers benefit from Simulation
What does this mean for the industry? The production of technical textiles becomes more efficient, but the nonwovens can also be developed without having intensive productions tests in a real facility. This is because the simulations help to forecast and then optimize the processes using a digital twin. In this way, production capacities can be increased while maintaining the same product quality. Simulations save experiments, allow new insights, enable systematic parameter variations and solve up-scaling problems that can lead to misinvestments during the transition from laboratory to industrial plant.

Making a Contribution to Overcome the Crisis With Many Years of Expertise
"We want to demonstrate this in the project using a typical meltblown line as an example - for this we are in contact with partner companies," says Dr. Dietmar Hietel, head of the department "Transport Processes" at the Fraunhofer ITWM. "Within the framework of Fraunhofer's anti-corona program, we want to use our developed expertise and our network to contribute to overcome the crisis", reports Hietel. His department at the Fraunhofer ITWM has been pursuing research in the field of technical textiles for around 20 years. Due to its current relevance, the project not only got off to a quick start, but the implementation and results should now also be implemented quickly: The project is scheduled to run from April 15th 2020 to August 14th 2020. The kick-off meeting took place on April 17th 2020 via video conference.
 
The project "Meltblown productive" and the results are certainly interesting for nonwoven producers. The production of many mass products has often been outsourced to Asia in the past decades; the nonwovens manufacturers remaining in Germany and Europe tend to focus more on high-quality technical textiles. In the medium and longer term, this will also be a scientific preliminary work when production capacities in Germany and Europe are expanded by new plants. One lesson to be learned from the crisis will also be to reduce the dependence on producers in Asia, especially as a precautionary measure for crisis scenarios.

Source:

Fraunhofer Institute for Industrial Mathematics, ITWM