Botswana Medical composite film

The materials used in medical composite membranes encompass any conceivable material combination, such as a ceramic layer deposited on a metal oxide or an aromatic polyamide thin film coated onto a polysulfone microporous membrane. Both flat-sheet and spiral-wound membranes are reinforced with nonwoven fabrics to enhance the pressure resistance of the microporous layer, whereas hollow-fiber membranes do not require such reinforcement.

The preparation methods are classified into four categories: (1) the lamination method, in which a very thin, dense, homogeneous membrane is first fabricated and then laminated onto a microporous support membrane; (2) the dip-coating method, in which a polymer solution is dip-coated onto a microporous membrane and subsequently dried; alternatively, an active monomer or prepolymer solution may be dip-coated onto the microporous membrane and cured by heat or radiation; (3) the plasma vapor deposition method, in which a dense, homogeneous membrane is formed on the surface of the microporous support membrane via plasma glow discharge; (4) the interfacial polymerization method, in which interfacial polymerization is carried out on the surface of the microporous support membrane using an active monomer.

Medical composite membranes are primarily used in separation processes such as reverse osmosis, gas separation, and pervaporation.

Using two different membrane materials, a composite membrane is fabricated, comprising a dense separation layer that performs the separation function and a porous support layer that provides structural integrity.

Medical composite membranes are produced by laminating geotextile fabric to one or both sides of a thin film, resulting in a composite geomembrane. They come in two configurations: one‑fabric‑one‑membrane and two‑fabric‑one‑membrane. With a width of 4–6 m and a basis weight ranging from 200 to 1500 g/m², these products exhibit excellent physical and mechanical properties, including high tensile strength, tear resistance, and puncture resistance. They also offer superior strength, good elongation, a high modulus of deformation, resistance to acids and alkalis, corrosion resistance, aging resistance, and outstanding impermeability. These characteristics make them well suited to meet the demands of civil engineering applications such as seepage control, isolation, reinforcement, and crack‑prevention in water conservancy, municipal works, construction, transportation projects, subways, tunnels, and other infrastructure developments. Thanks to the use of advanced polymeric materials and the incorporation of anti‑aging additives during manufacturing, they can be deployed in non‑conventional temperature environments. They are commonly employed for seepage control in embankments and drainage channels, as well as for pollution prevention in waste‑disposal sites.

Processing method

1. Dry lamination: This method involves applying an adhesive to the surface of a substrate using a laminating machine, followed by heat‑induced pressure bonding to another film.

2. The wet lamination process involves coating water-soluble or water-dispersible adhesives onto the surface of a substrate while it is in a wet state, laminating it with other materials, and then applying roll‑press bonding followed by drying.

3. Extrusion Lamination This is a commonly used method in composite processing, in which an extruder produces thin films of PP, PE, EVA ionomer resins, and other materials, which are then coated with adhesives and laminated onto various films containing processing aids, followed by cooling and curing.

4. The hot-melt lamination method involves coating a hot-melt adhesive—composed of adhesives such as rosin, xylene resin, and styrene resin, along with wax-based release agents—onto the surfaces of films, paper, or aluminum foil, and then immediately laminating it to another substrate while cooling.

5. Co-extrusion lamination: This method uses two or three extruders operating simultaneously to produce multilayer films. It can be implemented using either a T-die head or an extrusion blow‑molding process, enabling a wide range of laminates and the production of ultra‑thin films.