Stretching
In streching method polymer heat above their melting point to synthesis porous and
thin film shape sheet membrane (Trommer and Morgenstern 2010). Microporous
membranes are generally used in MF and UF. Stretching technique is used for
crystalline polymer. Stretching process is usually done in two stages, cold stretching
and then hot stretching. Cold stretching is used to create micropores in film and heat
stretching used to enhance or control the final pore structure of the membranes. Pores
of membrane are controlled by material’s physical properties (like crystallinity,
tensile strength, etc.).
Track Etching This method is where thin polymer film is irradiated with a highenergy heavy ion beam to create a flat, distorted track through the irradiated polymer
film. This technique is known for precise control over membrane pore size distribution. Polyamide film bombarded by heavy ions (64 Cu, 127I, 79 Br, 107Ag) then
treated in the presence of oxygen with gamma-rays. Polymer most widely used in
track etching is polycarbon and terephthalate polyethylene (Lalia et al. 2013).
Electrospinning This is a fibre production method which uses high voltage to draw
charged threads of polymer solutions or polymer melts up to fibre diameters in the
order of some hundred nanometres. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This
method ensures that no solvent can be carried over into the final product. Porous
membrane fabricates through this technique and is used in filtration and desalination
purpose (Lalia et al. 2013). Polymer concentration affects the membrane pore size
and this helps to improve salt rejection (Kaur et al. 2012).
Organic membranes have limitation of high fouling tendency due to membrane
surface hydrophobicity. Fouling is generally caused by deposition of protein microbial communities and organic and inorganic components on the membrane surface.
Other drawbacks are highly expensive and have irreproducible separation, less
lifetime performance and smaller application range.
6.4.2.2 Inorganic Membrane
J.W. McBain (1932) first time introduces inorganic molecular sieve membrane. The
inorganic membrane is classified into porous and non-porous (dense) based upon
structure and morphology. This is an important factor for membrane performance.
Porous inorganic membrane has porous ceramic and metal supports on the upper
side with structure and morphology, with additional porous sheet. This type of
membrane has various pore shapes such as conical-shaped pores, spongy pore
structure, straight pores and regular shapes. Examples of inorganic membrane
material are metal oxide, metal, alumina, zeolite, tin, zirconium, carbon (graphene,
carbon nanotube), silica, glass, silicon carbide and nitride, etc., shown in Table 6.4.
Non-porous and dense inorganic membrane contains solid electrolyte or solid layer
of metals (Ag, Pd, alloys). Electrolyte layer allows moving oxide ion and hydrogen
diffusion via membrane pores. In non-porous (pores block), block by immobilized
6 Fluoride Remediation Using Membrane Processes
185
In streching method polymer heat above their melting point to synthesis porous and
thin film shape sheet membrane (Trommer and Morgenstern 2010). Microporous
membranes are generally used in MF and UF. Stretching technique is used for
crystalline polymer. Stretching process is usually done in two stages, cold stretching
and then hot stretching. Cold stretching is used to create micropores in film and heat
stretching used to enhance or control the final pore structure of the membranes. Pores
of membrane are controlled by material’s physical properties (like crystallinity,
tensile strength, etc.).
Track Etching This method is where thin polymer film is irradiated with a highenergy heavy ion beam to create a flat, distorted track through the irradiated polymer
film. This technique is known for precise control over membrane pore size distribution. Polyamide film bombarded by heavy ions (64 Cu, 127I, 79 Br, 107Ag) then
treated in the presence of oxygen with gamma-rays. Polymer most widely used in
track etching is polycarbon and terephthalate polyethylene (Lalia et al. 2013).
Electrospinning This is a fibre production method which uses high voltage to draw
charged threads of polymer solutions or polymer melts up to fibre diameters in the
order of some hundred nanometres. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This
method ensures that no solvent can be carried over into the final product. Porous
membrane fabricates through this technique and is used in filtration and desalination
purpose (Lalia et al. 2013). Polymer concentration affects the membrane pore size
and this helps to improve salt rejection (Kaur et al. 2012).
Organic membranes have limitation of high fouling tendency due to membrane
surface hydrophobicity. Fouling is generally caused by deposition of protein microbial communities and organic and inorganic components on the membrane surface.
Other drawbacks are highly expensive and have irreproducible separation, less
lifetime performance and smaller application range.
6.4.2.2 Inorganic Membrane
J.W. McBain (1932) first time introduces inorganic molecular sieve membrane. The
inorganic membrane is classified into porous and non-porous (dense) based upon
structure and morphology. This is an important factor for membrane performance.
Porous inorganic membrane has porous ceramic and metal supports on the upper
side with structure and morphology, with additional porous sheet. This type of
membrane has various pore shapes such as conical-shaped pores, spongy pore
structure, straight pores and regular shapes. Examples of inorganic membrane
material are metal oxide, metal, alumina, zeolite, tin, zirconium, carbon (graphene,
carbon nanotube), silica, glass, silicon carbide and nitride, etc., shown in Table 6.4.
Non-porous and dense inorganic membrane contains solid electrolyte or solid layer
of metals (Ag, Pd, alloys). Electrolyte layer allows moving oxide ion and hydrogen
diffusion via membrane pores. In non-porous (pores block), block by immobilized
6 Fluoride Remediation Using Membrane Processes
185