By Geoff Fisher, European Correspondent
Since their widespread market introduction in the 1970s, nonwoven materials have been playing a key – and growing – role in filtration. They offer a less-expensive alternative to woven textiles and often provide a technical advantage over other materials owing to their physical construction.
With the global filtration market currently valued at more than $80 billion, nonwovens account for around 37% by volume of all filter media materials employed by the industry, according to the American Filtration Society.
Recent reports suggest that the global nonwoven filter media market will reach $6.5-7.0 billion by 2023, exhibiting a compound annual growth rate of around 5-7%, with nonwovens generally replacing “older” filter media materials such as paper as other textiles.
The market is being driven by increasing applications in the transport industry, together with growing consumer awareness – and environmental legislation – regarding water and air pollution.
Transportation and water filtration are the two major applications for nonwoven filter media, together accounting for almost 45% of this segment, followed by: heating, ventilation and air-conditioning (HVAC); healthcare; food processing; industrial manufacturing; oil and gas; and electronics.
The transport sector in particular is expected to reach $1.4-1.6 billion by 2023 owing to growing demand for nonwoven filter media in automotive applications such as engine air, cabin air, and oil and fuel filtration.
Key players operating in the global nonwoven filter media market include 3M, DowDuPont, Sandler, Ahlstrom-Munksjö, Parker Hannifin, Pentair Residential Filtration, Johns Manville, Freudenberg Filtration Technologies, Hollingsworth & Vose and Berry Global.
As a result of their ability to be precisely engineered, filtration is one of the fastest growing segments of the nonwovens industry.
And of all the fiber-based materials, nonwovens are especially suitable for filtration because of their complicated, often randomized, three-dimensional (3D) structure and thickness, which results in higher filtration efficiency than either woven or knitted fabric that generally have a 2D structure.
Moreover, a nonwoven fabric can be constructed with various layers. In liquid or air filtration, for instance, an initial coarse open fabric removes larger particles, and as the fluid or airstream passes through the filter, the fibers and pores become smaller to trap ever-finer particles.
Compared with woven filters, nonwoven filters offer such advantages as:
- High filtration efficiency
- High permeability
- Less blinding tendency
- No yarn slippage
- Good cake discharge
Further, there is no limitation on thickness, and the materials can be produced at a high production rate on a continuous process line.
Synthetic fibers are particularly preferred for nonwoven filters owing to their physical properties such as resistance to chemicals, weather and ultraviolet light. They can also be made flame retardant, electrically conductive, absorbent or waterproof where desired.
Polyethylene terephthalate (PET– polyester) and polypropylene (PP) are the dominant synthetic polymers, while polyamide (PA), fiberglass, meta-aramids, fluoropolymers, polyphenylene sulfide (PPS) and other polymers can be used in certain situations owing to their specific properties.
In addition to these fibers, biopolymers such as polylactic acid (PLA) fibers from sustainable feedstocks are increasingly being utilized for disposable filters, including spunbond and meltblown fabrics used in vacuum cleaner bags, teabags and coffee filters.
According to NatureWorks, which produces compostable Ingeo PLA from starchy plants like corn, nonwovens made from PLA nanofibers exhibit “exceptional processing consistency, a range of charge capabilities and better nonwoven structure development, offering lower pressure drop.”
Needlefelt fabrics for filtration are typically made of PET fibers; PP and other polymeric fibers such as meta-aramids and PPS can also be considered.
These can be used, for example, in baghouse filters to capture particulates or contaminants from coal-fired power stations and industrial facilities, and in liquid filters to remove particulates from liquid streams and as pre-filters in a range of industries such as chemical processing and metal working.
Wetlaid PET and binder fibers are generally used as support (backing) fabrics for membranes in reverse osmosis, nanofiltration and ultrafiltration processes.
Membrane supports are highly specialized and must withstand high system pressure, lie perfectly flat across the fabric width and have no standing fibers that can penetrate a coated membrane, thereby covering the substrate’s surface.
Made on standard paper-making equipment, wetlaid filtration media are typically made from short-cut man-made, fiberglass and/or cellulosic fibers, including blends, for use in lubricant, oil and engine air-intake filters in cars and trucks.
Lighter weight spunbond fabrics made from PET, PP and PA are seeing significant growth as backings as well as for pleated filter media and cartridge applications. They are being used in such applications as pleat support separators for microporous membrane cartridges, coolant systems, and swimming pool and spa filters.
Recent spunbond developments include a PA 6.6 fabric from Cerex that prevents coolant (e.g., ethylene glycol) contamination in engine lubrication oils, unlike PET spunbond fabric that deteriorate at typical engine temperatures.
Produced in large volumes as roll goods, meltblown fabrics are used in air and liquid filtration products owing to their high dirt-holding capacity.
Berry Global recently promoted its Meltex meltblown materials, which are used in a wide range of air applications from room air purifiers and facemasks to cabin air filtration.
In blood filtration end-uses Meltex PET meltblown media is capable of removing leukocytes (white blood cells) to reduce the incidence of infection. The media acts based on size exclusion to remove white blood cells to enable leukocyte-free blood transfusions.
Meanwhile, nonwoven nanofiber filtration media are increasingly being used in micro-filtration applications, offering such benefits as enhanced air quality, reduced energy cost and longer service life.
In particular, nanofibers can be added in weights of 1–2 g/m2 to the surface of heavy wetlaid and spunbond nonwovens, principally for air filtration in dust collection cartridges or engine air-intake filters in vehicles.
Industry commentators also suggest that the use of nanofibers is closing the gap between membranes and nonwovens.
South Korea’s Finetex EnE sees immense potential in nanofibers. With existing factories in South Korea, Canada and the Philippines, and the addition of new factories in China and Europe, the company is now producing via electrospinning pure synthetic nanofiber media to E12 levels of performance (99.5% particle capture) and making them suitable for high-efficiency particulate air (HEPA) filtration applications as well as industrial liquid filtration.
Fine Dust Particulate Filter
At the Filtech 2018 conference and exhibition, held in Cologne, Germany, in March, Mann+Hummel displayed one of the first StreetScooter delivery vehicles currently being trialed in five German cities by Deutsche Post DHL Group, the world’s largest postal service.
Mann+Hummel’s fine dust particulate filters are being used in what is claimed to be the world’s first emission-neutral vehicle.
Blowers are fitted behind these filters that direct ambient air to the filters. As a result, even when the vehicle is at a standstill, it is still able to filter particulates from the ambient air, says the Germany-based filtration specialist.