MC² Market & Competitive Convergence

Now, there is a new patented method to directly determine permittivity. Permittivity is what remains when the thickness factor in the determination of permeability is removed. Most porous metal and plastic materials have specific thicknesses, where Darcy coefficients of permeabiltiy are applicable. Textiles, nonwovens and membranes, on the other hand, do not have specific thicknesses; therefore, permittivity is the method employed.

Permittivity is an important characteristic to measure, especially for filter media, protective clothing, biotextiles, such as vascular grafts, and geotextiles / geosynthetics. Other applications are sure to arise now that the test is easier to perform, with more accuracy and repeatability. Permittivity is specified in ISO 11058 and ASTM D 4491.

The Advanced Permittivity Testing Method (APTM):

• Determines permittivity directly over a range of pressure heads, eliminating tedious iterations while simulating field conditions
• Measures differental pressure and flow—separately and simultaneously—all under controlled conditions
• Provides precise control of head and back pressure
• Determines the point where flow turns from laminar to turbulent, if it occurs
• Allows direct observation of pore deformation under service conditions
• Fully automated, programmable test procedure
• Evaluates permittivity in the presence of silt, filter aids...
• Meets all the requirements of ASTM D 4491

APTM was developed at the National Textile Center, a research consortium of six universities: Auburn University, Clemson University, Georgia Institute of Technology, North Carolina State University, UMass - Dartmouth and Philadelphia University. A patent has been applied for, and a prototype is in use at the Advanced Textiles and Composites Laboratory, Philadelphia University.

Event: ASTM Committee D35 Geosynthetics meeting, including D4491 meeting on permittivity, January 21-24, 2002, Dallas, Texas USA