Nomex® from DuPont was the original aramid fibre introduced into industry over 40 years ago. Several other manufacturers have since started to produce chemically identical products and several variants are currently available.
The manufacture of these fibres is much more complex than say for polyester and takes place from solvent, which results in more complex fibre cross sections, 2 examples being shown here:
These non circular shapes actually assist in filtration because they bring more surface area of fibre per square metre of felt. This can increase the dust holding capacity of the felt and reduce emissions. Aramids are capable of working at much higher temperatures than many other fibres.
The temperature resistance is good (up to 220°C for short periods in dry conditions), but in common with other fibres such as polyester and P84, aramids are susceptible to hydrolysis. This means that in hot moist environments water can break down the chemical from which the fibres were made turning them back to their constituent chemicals. This greatly reduces their strength and ultimately turns the fibres to powder.
Some chemical treatments can delay this onset of degradation; in particular strong fluoro-carbon treatments such as "CR1" protect the fibres from moisture, though they cannot actually prevent hydrolysis.
Typical applications for aramid needlefelts are:
| Asphalt | Quarrying | Lime | Foundries |
| Cement | Smelting | Gypsum | Chemicals |
In common with other felts, aramid needlefelts can incorporate conductive fibres to reduce problems associated with the build up of static electricity. These can take the form of Checkstatic™ conductive scrims or conductive fibres, or a combination of the two. With aramid products, it is normal to use stainless steel fibres due to the temperature and chemical conditions which are frequently encountered in the filter. Being performance fibres, aramids are produced in small volumes in textile terms and are not available in the wide range of diameters which is found for commodity fibres such as polyester. So the opportunities for design are a little restricted.
Aramid fibres lend themselves to being manufactured using our proprietary Fibrelox™ technology, exhibiting all the advantages associated with the removal of support scrims. The majority of aramid felts are heat stabilised followed by press singeing to reduce the harshness of the singe traditionally found with aramid felts. They are frequently impregnated with fluorocarbon treatments to enhance their resistance to hydrolysis and to improve cake management with certain dusts. In summary aramid felts are good all round high temperature media which need care in selection when the moisture level is high.
