The annual EDANA Statistics have shown that the market for nonwovens as filter media has been growing consistently over the past few years. And at the forthcoming INDEX11 nonwovens show, which takes place from April 12-15th at the Geneva Palexpo in Switzerland, their ever-increasing use in this field will quickly become evident to visitors.
One reason for this growth is that nanofibre layers incorporated into the fabrics are significantly increasing their fine filtration performance – moving nonwovens beyond established meltblown media and towards being competitive with more expensive membranes in many applications.
Commercial production machinery for incorporating nanofibre layers into nonwoven filter media is now readily available, and at the same time, leading companies including Ahlstrom, Hollingsworth & Vose and Donaldson, have developed their own in-house technologies for doing so.
For water filtration and purification, nanofibre-containing nonwovens are now being employed in waste water cleaning, for the removal of contaminants such as heavy metals, and also in industrial water treatment and recycling.
Their chief benefits are high efficiency, rapid effectiveness and ability to be ‘tuned’ for selective performance. In the latter case, for example, they can be employed to capture specific molecules by immobilising an engineered capturing agent on their surface.
In the environmental industry, nanofibre nonwovens are finding applications in the decontamination and recuperation of waste streams, including the recycling of industrial water, removal of heavy metal ions, recuperation of metals, ammonia removal, the removal of radioactive substances and isotope separation, thus enabling the removal of some classes of environmental contaminants which cannot be completely eliminated by conventional purification methods.
Inorganic pollutants, such as cadmium, mercury and lead, as well as organic compounds can also be removed from waste water.
Unique among nanofibre-based products for water filtration is Ahlstrom’s Disruptor – the winner of the Nonwoven Rollgoods Innovation Award at the last INDEX show which took place in 2008.
Disruptor differs from other nanofibre-based filter media in being an electroadsorptive, rather than consisting of continuous electrospun fibres that are applied topically to a base sheet, nanofibrillated synthetic pulps and carbon nanotubes.
Produced as a wet laid nonwoven depth filter media, Disruptor can be easily converted into a wide range of pleated filter cartridges to act as a submicron polishing filter for virtually any water application.
The company explains that the technology is unrivalled in performance because it is the first material to perform submicron filtration at very low pressure drop, yet have an extremely high loading capacity. New products based on this technology containing powdered activated carbon (PAC) and silver coated zeolites to inhibit biological growth on the media have already been introduced. These additives are retained by the charge field produced by the charge field of the nanofibres, not through the use of adhesives.
This patented technology exploits the natural electrokinetic charge potential generated by the crystal structure of the nanofibres of the alumina hydroxide mineral, boehmite (AlO(OH)), to improve water quality. These nanofibres are 2 nm in diameter by 250 nm in length and attached to microglass carrier fibres to allow them to be easily incorporated into a nonwoven filter media. When used in water with a pH between 5 and 9, the nanofibres produce a positive charge field with a streaming zeta potential of over 50 millivolts at pH 7.2. Disruptor’s excellent loading capacity is due to the availability of more than 42,000 square metres of electropositive fibre surface area for each square metre of the filter media.
The technology has been proven to remove a wide range of contaminants including colloids, virus, bacteria, endotoxins, certain metals. These characteristics make it an alternative to many different types of membranes used in water treatment. It is also proving valuable as a prefilter to protect reverse osmosis membranes from biofouling.
Disruptor PAC meanwhile, contains 32% by weight of powdered activated carbon to improve the taste and odour of water by removing chlorine and humic compounds. It has also been shown to be effective at removing trace pharmaceuticals, endocrine inhibitors and pharmaceuticals.
In the latest development, Ahlstrom has partnered with Eureka Forbes to launch a ground-breaking new product to serve the growing need for clean water on the Indian sub-continent.
The device, manufactured by Eureka Forbes and to be sold under the brand name AquaSure, incorporates Disruptor and has been designed for the challenging conditions in distribution, storage and end-consumer use in developing markets like India.
The AquaSure storage water purifier removes all three types of contaminants from water – physical, chemical and microbiological -–without the use of any chemicals. As a result, it provides not just microbiologically pure, but safe drinkable water.
At the same time, the technology eliminates the need to add disinfecting chemicals about which there are public health and safety concerns and also offers consumers a simple, convenient and affordable way to purify their water that is consistent with entrenched consumer habits.
Like many of the leading nonwovens companies who will be present at INDEX11, Ahlstrom sees water purification as one of its key product areas for the future and continues to invest in expanding the capabilities of Disruptor technology.
Nonwoven filters are also widely used in providing cleaner air and the range of their applications in this field is extensive – and sometimes surprising.
Beyond being employed in conventional heating and ventilation (HVAC) systems, common applications are in industrial pollution control, catalytic and photocatalytic industrial systems and automotive cabin air purifiers.
In these roles, nonwovens provide the general benefits of high filtration efficiency, a high surface area and high permeability, which allows significant energy savings to be achieved.
In addition, of course, they are also low cost and lightweight products.
Air pollution, however, can come from many sources, and specific filter media have been introduced to combat areas which might not immediately be associated with causing it.
In an office environment, for example, laser printers emit large volumes of particulate emissions which are said to be invisible to the naked eye and can find their way into the lungs, and even the bloodstream.
To combat this, INDEX exhibitor Freudenberg has worked with fellow German company Tesa to introduce Clean Air – a new nonwoven-based particulate filter.
To illustrate the risk posed by laser printer emissions, Tesa has displayed a measurement station at recent trade shows. Working under cleanroom conditions, this measures and displays the particulate emissions and enables a comparison to be made between an unused filter and a used one, making the value of its new product clear.
Clean Air has been proven in tests by TÜV Nord to cut particulate emissions from laser printers by up to 94%.
Thanks to falling purchase prices, the number of laser printers in use has skyrocketed in recent years, with over two million sold in Germany each year. The majority of the printers are used in offices – more than 70% of German office employees work with laser printers. And most of them sit less than three metres away from the device itself.
According to one recent study, the German population associates particulate matter predominantly with car emissions, but it’s now believed the same risk exists in offices. A number of different scientific studies indicate that laser printer particulate emissions can be harmful to human health. The German Federal Institute for Risk Assessment has also been unable to rule out the risk, and is urgently recommending further medical research into the effects of exposure.
An even more specific environment is being targeted by another INDEX 11 exhibitor, 3M.
The company’s latest High Air Flow Electrostatic (HAF-E) filters have been designed in response to requests from owners of the casinos of Las Vegas.
They are designed to remove contaminants such as smoke, dust, dirt, debris and carpet fibres from the air intakes on devices such as slot machines, vending machines, arcade games, ATMs, kiosks and computers.
“The development of 3M HAF-E Filters is the result of a deep understanding of the environment the electronic devices of our gaming customers operate in,” says Chris Tsourides, Business Manager at 3M Touch Systems.
The filters employ microstructured features to increase filter surface area, allowing high air flow rates while minimising pressure drops across the filter.
In addition, filter effectiveness is maximised by the company’s proprietary electrostatic manufacturing process. This produces an electrostatic attraction from the filter surface to airborne particles to attract and remove fine particulates, which can potentially damage sensitive electronics.
The filters work to protect the air intake ducts from most contaminants, so the need to perform daily, weekly and monthly cleaning of a slot machine interior, for example, can be significantly reduced. Filter change-out can be performed in less than 30 seconds with no special tools and typically does not require taking the equipment out-of-service.
These and many more examples of just how nonwovens are helping us to clean up our environment will be on display at INDEX 11 in Geneva.
