Plasma Processing Changing Filtration

By Stephen Coulson, Ph.D., Chief Technical Officer, P2i

Plasma processing of filtration media can increase oil and water repellency while maintaining pore size distribution and airflow.
Plasma processing of filtration media can increase oil and water repellency while maintaining pore size distribution and airflow.

Membrane and nonwoven filters are widely used by the industry to separate solids from liquids or gases. Filters can range from the conventional, such as simple dust filters for air intakes, to the critical, such as dialysis filters to prevent kidney failure. In fact, there are more than 50 filters in a single car. The worldwide filter industry is expected to expand 5.6% through 2010 to a value of $45 billion.

Filtration media is generally selected based on reasons of cost, ease of processing and performance r equirements. Many different materials can be used, but where filters are intended for repeated use, it is vitally important that integrity and consistency of pore size is retained throughout a product’s lifetime despite the often harsh environments they are exposed to, including cleaning processes.

In order to achieve this level of reliability, reusable filtration media have traditionally been made from highly resistant and rigid polymers, such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). However, these materials tend to be fairly costly and would still benefit from complex chemical finishes to add further performance benefits. A more desirable scenario, therefore, would be to use cheaper, easily formed filter media and then modify the surface using an additional process to impart the desired liquid resistance.

Thanks to the pioneering work of P2i and its revolutionary liquid repellent nano-coating, it is now possible to enhance alternative, more sustainable filtration media – such as cellulose or nylon – to a level that matches, or exceeds, the performance of traditional, more expensive materials that are more difficult to work with. Indeed, using the widely accepted American Association of Textile Chemists and Colorists conventions, P2i’s nano-coating has been shown to create filters with the maximum levels of liquid repellency in both the AATCC 193-2007 water repellency test (resisting 100% isopropyl alcohol) and the AATCC 118-2007 oil repellency test (resisting n-heptane).

Using a special pulsed ionized gas (plasma), which is created within a vacuum chamber, the patented P2i technology attaches a nanometerthin polymer layer over the entire surface of a product. This dramatically lowers the product’s surface energy, so that when liquids come into contact with it, they form beads and simply run off. In filtration media, the P2i nanocoating increases oil and water repellency without affecting the material’s bulk properties or pore size distribution and, therefore, airflow. It has also been shown to exhibit improved cake release, no pressure drop or decrease in water entry pressure and a lower replacement frequency, meaning less waste. This allows products to perform at a much higher level in a wide range of application sectors, including biosciences, industrial processing, laboratory testing, food & beverage, electronics and water treatment, as well as opening up new applications altogether.

A Problem Solved

P2i’s technology is genuinely revolutionary for filtration because it solves so many of the industry’s traditional challenges. For example, until now the choice of filter material has usually been dictated principally by desirable bulk physical properties and ease of processing. In many cases, however, this has led to a compromise in material surface properties, which may not be ideal for the intended use, requiring treatment with complex chemical formulations and high curing temperatures. In turn that has led to manufacturing processes that are power hungry, time consuming, and limited to specific materials that will withstand the chemicals and high curing temperatures involved. These processes are expensive and can have significant environmental impacts.

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