Membrane and Desalination Technologies - TCE Moodle Website

Preparation of Polymeric Membranes 55
tolerate a wider range of pH, which can be cleaned with acids or alkalis. For some membrane
preparations, the level of cyclic dimer is an important parameter for the processing efficiency
and fiber quality (11). Too much cyclic dimer can result in cloudy dope solution. UDEL
polysulfone only contains 1.20% by weight of cyclic dimer, which is very suitable for
membrane making.
3.3. Polyethersulfone
Polyethersulfone (PES) membranes also demonstrate very high chemical and thermal
stability, which chemical structure is shown in Fig. 2.6. Compared with Polysulfone’s glass
transition temperature (Tg) of 195 C, PES has a higher Tg of 230 C. Like PS material, PES
membranes also demonstrate a low tolerance of aromatic hydrocarbons or ketones. PES
membranes are mainly used in ultrafiltration, microfiltration, and dialysis membranes.
3.4. Polyacrylonitrile
Polyacrylonitrile (PAN) is mainly used to prepare ultrafiltration membranes and porous
supports of composite membranes due to its superior resistance to hydrolysis and oxidation,
which chemical structure is shown in Fig. 2.7. PAN is hydrophobic in its pure state though a
polar group is presented in the backbone of the polymer. It is usually copolymerized with
more hydrophilic monomers to improve its hydrophilicity and processability to make it less
brittle.
3.5. Polyvinylidene Fluoride
Polyvinylidene fluoride (PVDF) is a very good material for microfiltration membranes due
to its chemical resistance and thermal stability; the chemical structure is shown in Fig. 2.8.It
is resistant to most inorganic and organic acids and tolerant to a wide pH range. PVDF is
soluble in dimethyl formamide (DMF), DMAC, NMP, dimethylsulfoxide (DMSO) and
triethyl phosphate (TEP). It is a hydrophobic and semi-crystalline polymer and commonly
used for making microfiltration membranes by the phase inversion process.
* O
SO2 O
Radel A polyethersulfone
SO 2
SO 2
* O
O *
Radel H polyethersulfone
SO 2
O O SO *
2
Fig. 2.6 Chemical structure of polyethersulfone.