Glass fiber filter media is made from 100% micro-fine borosilicate glass fibers. Glass fiber filters are used where high flow rate and micron/sub-micron filtration is required. The filter media can be used for both liquid and air filtration. In the highest purity form, HI-Q offers a binderless 'AE' grade glass filter media. With its' excellent purity, using the FPAE-XX series filter paper reduces the overall possibility of extractable organics commonly found in cellulose filter paper.

Where greater structural strength filter papers are needed (high pressure drop, vacuum applications), either a spun polyester backing is used, Type FP5211, or a minimal amount of acrylic resin binder is used, Type FP2063 & FP2061, to keep up the integrity of the glass fibers during and after sampling/analysis. Some PM-10 sampling applications specifically call out for Whatman's 'EPM-2000', HI-Q part number FP2000. FP2000 was developed and produced specially for use in high volume PM-10 air sampling equipment that collects atmospheric particulates and aerosols.

Properties of Glass Fiber Media: The borosilicate glass fibers are inert and resistant to all but strongly alkaline bases or acids such as hydrofluoric acid. The fibers are heat resistant and will only begin to soften at over 600°C. The borosilicate glass has a refractive index of 1.51, and when immersed in a solvent of a similar refractive index like benzene, the fibers will be transparent. Particles collected on the media then become easier to visibly identify.

Particle Retention: For air and gas filtration, collection of sub-micron (less than one micrometer in aerodynamic diameter) particles is sometimes required. In nuclear environmental air testing, the protocol is for sub-micron collection. Use of glass fiber media is therefore recommended. The test procedure for determining the effectiveness of particle retention is known as the DOP smoke test. In this test, DOP (dioctyl phthalate) is heated, the vaporized compound is dispersed into the air where it is cools and condenses into mono-molecular particles of 0.3 micron size. By drawing these airborne particles through the filter media and measuring the amount of breakthrough particle, a retention efficiency is established (see ASTM method D-2986 for the complete procedure.) See tabular results in 'Typical Performance Summary on Glass Fiber Filter Media'.