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Membrane Material Sourcing For Environmental, Particle Analyses – Sourcebook

Membranes

Membranes, or synthetic artificial membrane materials, are a permeable or semi-permeable matrix made of metal, polymer or other materials. These materials are capable of separating micron and sub-micron size particles from liquids and gases by retaining particles larger than the pores on the surface of the membrane. Ultimately, a membrane is a structure, or selective barrier by which mass transfer occurs by way of some driving force.
Although there are many different types of membranes currently available in the market, the basic purpose of a membrane is to successfully control the separation of specific molecules without fundamentally changing or damaging the particles.

Membrane Classifications

Membranes can be separated into categories based on their pore sizes. Reverse osmosis (RO) membranes contain pores that are typically

There are two types of basic membrane structures: anisotropic and isotropic. Anisotropic (or asymmetric) membranes do not contain a uniform and homogeneous structure and pore sizes and distribution vary throughout the membrane. Anisotropic membranes are composed of a thin surface layer on top of a thicker, more permeable sublayer. Isotropic (or symmetric membranes) have a uniform structure and composition. Permeability characteristics can be controlled by altering the thickness of the overall membrane structure; the thicker the isotropic membrane, the less permeable it is.

One of the oldest membrane manufacturing methods still in use today is the phase inversion process. During phase inversion, a one phase (homogeneous) solution is separated into two phases, a liquid phase with a low concentration of polymer and a solid phase with a high concentration. The solid phase will eventually be used to form the permeable membrane structure while the liquid phase will be in the pores themselves. There are several techniques used to induce phase inversion to form membranes, including thermally induced phase separation and diffusion induced phase separation.

Another common membrane manufacturing method is track etching and producing membranes by track etching allows for accurate, uniform pore size and distribution. During track etching, thin films are exposed to radioactive, charged particles that create “tracks” in the film. The film is then treated with a solution that dissolves the membrane material along the tracks created, forming pores. Thus, the pore size and distribution can be regulated by controlling both the initial intensity of the charged particles and the contact time and concentration of the solution to the membrane surface.

Membranes are commonly used for filtration in a variety of industries including wastewater, food and beverage, biotech, and pharmaceutical processing. Membranes are commonly used for water and wastewater filtration due to their effectiveness in eliminating particulates, microorganisms, and bacteria. For the food and beverage industry, membranes can be utilized in dairy and wine production processes to ensure that the beverages not only possess the correct consistency, quality, and appearance but also meet all FDA requirements. Finally, membranes can be used in the biotech and pharmaceutical industry in multiple ways, including the filtration of particulates from chemical solutions and protein purification. The use of membranes in the pharmaceutical industry has seen rapid growth in recent years due to the amount of resources being diverted to novel drug development and will likely continue to expand and diversify in the future.