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24.08.2021

Air, Water, Oil: What PLA bioplastic can filter well - and what not

Air filters have been discussed so often in recent days in the fight against the pandemic. With filter material made of nonwoven fabric, they block the way back into rooms for aerosols containing viruses. But how can these devices not only protect health, but also be operated with filter material that is as environmentally friendly as possible?

Air filters have been discussed so often in recent days in the fight against the pandemic. With filter material made of nonwoven fabric, they block the way back into rooms for aerosols containing viruses. But how can these devices not only protect health, but also be operated with filter material that is as environmentally friendly as possible?

Under clearly defined conditions, the bioplastic polylactide (PLA), also known as polylactic acid, is suited for this purpose. This can be deduced from results obtained by researchers from the Zuse community in the recently completed "BioFilter" research project. The key question for this and other potential applications of biofilters is: How do the special properties of PLA affect the filter performance and durability? After all, PLA can have practical disadvantages compared to its fossil-based competitors. Its material tends to be brittle and it doesn't particularly like high temperatures beyond 60 degrees Celsius. As a biogenic material, polylactic acid is also potentially more susceptible to abrasion and organic degradation processes. This can play an even greater role in the use of filters, e.g. in sewage treatment facilities, than in air filters. Industrial customers, however, naturally want a durable, reliable product.

From monofilament to nonwoven
Against this background, the researchers studied the PLA properties in order to test nonwovens for biofilters on this basis. The German Textile Research Center North-West (German Textile Research Center North-West - DTNW) and the Saxon Textile Research Institute (STFI), where the nonwovens were produced, were involved. Granules from various commercially available manufacturers were used. However, the research did not start with nonwovens, in which the fibers are deposited close together in different layers, but with so-called monofilaments, i.e. fibers made of PLA that are comparable to threads. DTNW and STFI initially carried out tests on these monofilaments, e.g. in a climate chamber for aging and durability.

As can be seen in the picture, the monofilaments became brittle after only two weeks at higher temperatures from 70 degrees Celsius, as the DTNW authors recently reported in the Journal Applied Polymer Materials. Under normalized conditions, however, the monofilaments showed no measurable reduction in stability even after almost three years, and the PLA nonwovens were in no way inferior to their fossil-based counterparts in terms of filter performance. "In my opinion, the focus for the use of PLA as a filter material will be on applications where relatively low temperatures are present, with which PLA copes very well," says DTNW scientist Christina Schippers.

Besides temperature and humidity consider other factors
For the researchers, however, the project, which was funded by the German Federal Ministry for Economic Affairs and Energy, was not just about the suitability of polylactide for air filters, but also for other applications, such as filtering water. In addition, the research revealed that when evaluating filter media made from bio-based and biodegradable nonwovens, it is important to consider other influencing factors, such as mechanical loads caused by air currents, in addition to temperature and humidity. "The innovative core of the project was to evaluate the possibilities and application limits of PLA nonwovens as filter media with sufficient mechanical properties and long-term stability," says project leader Dr. Larisa Tsarkova. Like her colleagues at STFI, DTNW is involved in the Zuse Community's Bioeconomy Cluster, in which researchers from nonprofit institutes cooperate under the guiding principle of "Researching with Nature." "For us, the bioeconomy is a top cross-industry topic that connects numerous institutes of the Zuse Community and is lived through collaborations such as with the 'Bio-Filter'," explains the future STFI managing director Dr. Heike Illing-Günther.

Cooperation in the Bioeconomy Cluster
With the results obtained from the "Bio-Filter" project, DTNW and STFI now want to continue working in order to be able to make derivations for clearly described areas of application for PLA nonwoven filters in the future. These possible fields of application extend far beyond room air filters and thus beyond the pandemic. For example, the water-repellent property of PLA is potentially interesting for filters in large-scale kitchens for water-oil filtration or also in the industry for engine oils.

The research is also so important, because PLA is already quite well established in individual consumer-related segments - keyword: carrier bags. Traditionally, lactic acid was used to preserve food, for example in sauerkraut. Today, PLA is obtained via a multi-stage synthesis from sugar, which ferments to lactic acid and polymerizes this to PLA, as Kunststoffe.de explains. PLA is one of the best-known bioplastics, but has not always been readily available due to strong demand in recent years. The Netherlands-based company Total Corbion has announced plans to start up a PLA plant with an annual capacity of 100,000 tons in Grandpuits, France, by 2024. It would be the largest plant of its kind in Europe, with Asia leading the way so far.

Source:

Deutsche Industrieforschungsgemeinschaft Konrad Zuse e.V.

(c) Fraunhofer IAP
08.06.2021

Fraunhofer IAP: Recyclable, Fiber-reinforced Material made from Bio-based Polylactic Acid

"Packaging made from bio-based plastics has long been established. We are now supporting the further development of these materials for new areas of application. If in the future the market also offers plant-based materials for technically demanding tasks such as vehicle construction, the bioeconomy will take a decisive step forward," explained Uwe Feiler, Parliamentary State Secretary at the Federal Ministry of Food and Agriculture, in Potsdam. The occasion was the handover of a grant to the Fraunhofer Institute for Applied Polymer Research IAP. The Fraunhofer IAP wants to develop a composite material that consists entirely of bio-based polylactic acid (PLA) and is significantly easier to recycle than conventional fiber composites.

"Packaging made from bio-based plastics has long been established. We are now supporting the further development of these materials for new areas of application. If in the future the market also offers plant-based materials for technically demanding tasks such as vehicle construction, the bioeconomy will take a decisive step forward," explained Uwe Feiler, Parliamentary State Secretary at the Federal Ministry of Food and Agriculture, in Potsdam. The occasion was the handover of a grant to the Fraunhofer Institute for Applied Polymer Research IAP. The Fraunhofer IAP wants to develop a composite material that consists entirely of bio-based polylactic acid (PLA) and is significantly easier to recycle than conventional fiber composites.

The German Federal Ministry of Food and Agriculture (BMEL) is intensively promoting the development of biomaterials as part of its Renewable Resources funding program. More than 100 projects are currently underway, covering a wide range of topics: from plastics that are degradable in the sea to natural fiber-reinforced lightweight components for the automotive sector. The projects are supported by the Agency for Renewable Resources, the BMEL project management agency responsible for the Renewable Resources funding program.

Easier recycling of fiber-reinforced plastics
PLA is one of the particularly promising bio-based materials. The global market for this polymer is growing by around 10 percent a year. PLA is also used, among other things, as a matrix in fiber-reinforced plastics. In these mechanically resilient plastics, reinforcing fibers are embedded in a plastic matrix.

The Fraunhofer IAP project is now focusing on these reinforcing fibers: "We are further developing our PLA fibers in order to transfer them to industrial scale together with partners from industry. These fibers are ideally suited for reinforcing PLA plastics. The resulting self-reinforcing single-component composite promises great recycling benefits. Since the fiber and the matrix of PLA are chemically identical, complex separation steps are not necessary," explains Dr. André Lehmann, expert for fiber technology at Fraunhofer IAP.

Novel PLA fibers and films are more thermally stable
The challenge with this approach is that conventional PLA has a relatively low temperature resistance. Technical fibers can be produced most economically using the melt spinning process. The Fraunhofer IAP team is now using more thermally stable stereocomplex PLA (sc-PLA) for the fibers. The term stereocomplex refers to a special crystal structure that the PLA molecules can form. Sc-PLA fibers have a melting point that is 40 - 50 °C higher and can therefore withstand the incorporation process in a matrix made of conventional PLA. In the project, the researchers are developing and optimizing a melt spinning process for sc-PLA filament yarns. The partner in this work package is Trevira GmbH, a manufacturer of technical and textile fiber and filament yarn specialties that are in demand from automotive suppliers and contract furnishers, among others. Furthermore, the development of a manufacturing process for sc-PLA reinforced flat films is planned. The international adhesive tape manufacturer tesa SE is participating in this task, and will test the suitability of sc-PLA films as adhesive foils. In a third work package, the Fraunhofer IAP will finally process the filaments in a double pultrusion process to produce granules suitable for injection molding.

Bio-based solutions for the automotive and textile industries
The scientists led by Dr. André Lehmann are certain that the self-reinforced PLA material can conquer many new areas of application. The automotive and textile industries are already showing interest in bio-based materials that are also easier to recycle. In terms of price, PLA would already be competitive here, and now the material is also to be made technically fit for the new tasks.

Professor Alexander Böker, head of Fraunhofer IAP, says: "The steadily growing demand from industry for sustainable solutions underlines how important it is to develop biobased and at the same time high-performance materials. With our research, we are also actively driving the development of a sustainable and functioning circular economy and therefore very much welcome the support from the federal government."

Information on the project is available at fnr.de under the funding code 2220NR297X.