Sustainable hydrophilic membranes to filter water
In order to efficiently meet growing demand for drinking water, Arkema has developed a new material to produce a new generation of hydrophilic membranes composed of hollow fibers. Made from specific Kynar® PVDF fluorinated polymer, they allow a better filtration process (suspended solids, bacteria, viruses), an improved output and a much longer membrane lifetime.
PVDF membranes filtration
The production of drinking water and the treatment of waste water are increasingly using membrane filtration technology.
This process is based on the following principle: water is pumped under pressure into hundreds of tubular modules containing a bundle of long hollow fibers, functioning as membranes filters.
These fibers, having a diameter of 1or 2 mm, are semi-permeable and porous: the water entering the module under pressure, has to pass through the pores of the fiber walls before it can flow out, and so is filtered. These micropores (1 to 2 microns in diameter) trap the micro-impurities.
The material which is used, often PVDF, must have several qualities:
- the hollow fibers must be highly porous to allow the water to pass through,
- high selectivity to filter out the micro-particles,
- high mechanical and chemical resistance to remain functional for several years.
This micro-filtration process ensures excellent water quality, but has drawbacks:
- It is is energy intensive (the water is conveyed under pressure),
- It does not filter ultra-fine particles like pesticides or medicine residues.
New Kynar® PVDF for more efficient nanoporous membranes
Arkema's research Group has wide-ranging expertise in the synthesis of nanostructured copolymers. To enhance the performances of Kynar® PVDF fibers, they have developed functionalised copolymers. combined with Kynar® PVDF on a nanometric scale, these functionalised copolymers increase:
- the porosity of the hollow fibers while combining a hydrophilic function,
- the meshing density and regularity of the pores.
Meanwhile, the size of the pores is reduced by 1 to 2 microns, to 10 nanometres, which makes for efficient filtration of ultra-fine particles.
The overall throughput of processed water improves by some 20% for identical energy consumption.
Functional block copolymers
The block copolymers developed by Arkema combine, on the same chain of molecules:
- a "miscible block" of molecules that attaches itself to the Kynar® PVDF,
- and a block of molecules that provides the hydrophilic function.
In every single pore, billions of tiny hydrophilic threads attract the water and help it "glide" more easily, and so increase the overall filtration throughput of the Kynar® PVDF membrane.