M-Tech supply a wide range of filtration equipment supplied by Advantec MFS. Membrane filters are microporous plastic films made from a variety of polymers. Since the commercial introduction of membrane filters 30 years ago, they have become widespread for use in industrial/process and research applications. The versatility and unique physiochemical properties of membrane filters have made "membrane filter" a common phrase.

Membrane filters, microporous filters, screen or sieve filters are all synonyms for filters with specific pore ratings which retain particles or microorganisms larger than their pore size by surface capture and some particles smaller than the stated pore size by other mechanisms. Such filters usually have a rated pore size within the range of 0.1-5µm. This type of filter is refered to as a membrane.

Advantec MFS membranes (with the exception of PTFE and PCTE) are reverse phase, solvent cast membranes. Here, controlled evaporation or removal of the complex solvent systems forms the porous structure. Reverse phase membranes are available in Nitrocellulose, Cellulose Acetate, Mixed Cellulose Esters and Nylon. PTFE membranes are made by a patented process where the membranes are stretched biaxially to form the porous structure. PCTE filters are track etched.

Important performance characteristics of Advantec MFS membranes

• Thin, high porosity - Typically, a single layer of membrane is approximately 150µm thick with a porosity of approximately 80%. Pore ratings represent mean values around which there is a distribution of pores. These porous filters exhibit high liquid flow rates and high gas flow rates per unit area. In addition, one must consider there is a very high surface area available for selective adsorption or nonspecific binding.
• Strength - Advantec MFS membranes are monitored for both burst (longitudinal) and tensile (lateral) strength. Supported Acetate and Nylon are the strongest reverse phase membranes are available from Advantec MFS, followed by Cellulose Acetate. All membranes will withstand autoclaving. Consult the specifications for more complete information.
• Chemical and Biological Cleanliness - Membrane cleanliness is affected by the raw materials that are used in the manufacturing process, membrane treatments and by the way the membrane is handled after the casting operation. To assure membrane cleanliness, Advantec MFS uses only high purity reagents and raw materials. All materials are carefully screened to meet production specifications and filtered prior to use. Once cast, the membranes are handled in a class 100 clean room to minimise ambient contamination. Some membranes will contain 0.1-3(wt%) of an aqueous wetting agent. Cellulose Acetate membranes have a lower aqueous extractable, 0.1(wt%), nitrocellulose the highest 3.0(wt%). Nylon is inherently hydrophilic with no added wetting agents or surfactants. All Advantec MFS membranes are Triton Free and pyrogen free (<0.005ng/cm² filter area).
• Thermostability - All Advantec MFS membranes can be sterilised by autoclaving. Advantec MFS membranes can be used over a broad range of temperatures. Cellulosic membranes can withstand 130ºC, Nylon will withstand 180ºC. Specific maximum temperature limits can be found in the catalog (contact us for one). In addition, these membranes exhibit minimal shrinkage at elevated temperatures. Cellulose Acetate membranes should be pre-wet prior to loading then in the holder and autoclaving.

Choosing the correct membrane filter for your needs:

1. Determine what liquid or gas will be filtered
2. Determine the maximum pore size required to achieve the results you want
3. Using the chemical compatability chart, determine which polymer types are available
4. Identify any unusual process conditions that would otherwise limit your choice of membrane
5. Choose your prefered pack size