13 Jul 2016
Nonwovens Magazine, 13th July 2016
A UK-based company that is continuously pushing the limits of what industrial microfiltration filter systems can achieve insists that nonwovens can realise big wins by replacing traditional materials in its new products.
Porvair Filtration Group, a subsidiary of Porvair plc, commenced operations at a new plant last year in New Milton, United Kingdom. The new facility consolidated manufacture of various industrial filtration and separation products into one location, taking advantage of and maximizing more than 40,000 square feet of space.
Various materials and end-uses
The company uses a variety of materials as filter media, including metal mesh, metal powder and sintered metal fibers, borosilicate glass fibers and various other polymerics. End-use industries meanwhile include nuclear power generation, pharmaceuticals, aeronautics, life sciences, specialty chemicals manufacture, water filtration, and food and beverage.
Nonwovens are used by Porvair across its range of microfiltration cartridge filters in two types of filter structures: prefilters and membranes. Prefilters, which may provide the complete filtration function, utilize less expensive raw materials in order to filter out a large volume of contaminants so that the more expensive membranes don't have to be swapped out as often.
In the case of the membrane, the nonwoven may be the support and drainage, with a traditional metallic or polymeric membrane material in the middle.
Opportunities for nonwovens
New Milton is one of three plants operated by the company in the UK, along with three sites in the USA and a recent additional plant in China. Nonwovens Markets spoke with New Milton General Manager Mike Hughes, and he explained how he uses nonwovens today – and how he might be able to use more in the future.
The nonwovens used by Porvair are usually a meltblown fabric. When assembled in multiple layers and pleated, the material is strong enough for the many prefilter applications. In recent times, Hughes has seen some fabrics made with nanofibers, which he called “promising” because the thinner fibres result in a higher flow and more dirt holding capacity – but he warned that these materials so far have been too weak and too expensive to use commercially.
Weak materials can be strengthened by being laminated or coproduced with support materials, but then a filtration manufacturer can run into product validation issues with its customers. Once a filter product has been extensively tested, for an application like pharmaceuticals, food or beverages, any change in the materials of construction used can require re-testing and re-validation, Hughes noted. Such costs can run from $10,000 or $15,000 for a set of lab tests, all the way up into the six figures including more lab tests as well as administrative costs, along with stretching out the schedule for getting a final product to market.
For these reasons, customers generally avoid using a product that has not been pre-approved by a relevant agency such as the US Food and Drug Administration. However, Hughes would still like to work with nonwovens suppliers to develop new materials that can be approved and be used on an ongoing basis.
What does Porvair need?
What would help it to use more nonwovens? One thing it would like to see is smaller but still uniform pore sizes for fabrics used in prefilter applications, to keep more contaminants from getting through to the membrane. The goal is to reduce the pressure drop, while increasing retention– in the actual filter – at a materials cost that is significantly lower than the materials used in the membrane.
Hughes has seen some nanoscale materials that were electrospun onto a base material, to create a filter medium with very fine pore sizes. In these cases he thought the material looked “beaten up”, raising the concern that fiber segments would shed or break off in use and clog the membrane or other downstream systems – exactly the opposite of what a user wants from a prefilter or filter.
Finer meltblown PP
Hughes has also recently seen a meltblown polypropylene fabric from a US supplier that was “encouraging” – it was not nanoscale, but the fiber diameters were finer than the normal product, and this yields a lower pressure drop for the relatively fine pore size.
Where high temperature or harsh chemicals require filtration, normally metallic media would be offered. A great opportunity that Hughes sees for nonwovens includes fabrics with more heat resistance, and resistance to oxidation with greater chemical compatibility. In some cases they may have to survive repeated steam sterilization cycles without loss of functionality.
While polypropylene is used as a raw material for many products, Porvair also works with fabrics that are either made or coated with various more exotic materials. Polyphenylene sulfide (PPS), and Halar are interesting as a potential replacement for PP in some uses. Polytetrafluoroethylene (PTFE)-coated wire mesh products are used for some hot gas filtration applications.
As one example of filters that must survive exposure to very difficult conditions without losing functionality, Porvair makes a branded filter cartridge product called Fluorofil™, using what it describes as “a highly hydrophobic ePTFE membrane. The enhanced ePTFE membrane offers exceptionally high gas flow rates at low pressure differentials. Fluorofil™ cartridges are recommended for sterile gas filtration and venting applications. The hydrophobic characteristics of the ePTFE membrane make the Fluorofil™ filter cartridge particularly suitable for wet gas sterilising applications, such as fermenter air feed.”
Aggressive chemical solutions
The company adds that, “For solvent and aggressive chemical filtration applications, Fluorofil™ cartridges offer a wide range of chemical compatibility with high thermal stability. Suitable for the most demanding microfiltration applications, the cartridges can be used for the filtration of aggressive chemical solutions including acids, alkalis, solvents and etchants.”
Fluorofil™ cartridges have also been designed and validated to be repeatedly steam sterilized at temperatures of up to 142°C for 200 cycles at 20 minutes per cycle.
Because of the validation process, the timeline to get a product from idea to market is not always a quick one, but Hughes believes that for the nonwovens producer with the patience and the ability to design for the demanding real-world conditions that require the most sophisticated filter media, filtration offers significant new product opportunities for both Porvair and its suppliers.