Polyether Sulphone (PES)

POLYETHER SULPHONE (PES):

PES with methyl-containing linkages, was introduced by Union Carbide Company under the name of Udel in 1965 was followed in 1967 by Astrel, a wholly aromatic copolymer developed by 3M and later manufactured by Carborundum. 

Astrel contains diphenyl units in place of the aliphatic (isopropylidene) group; this results in increased dimensional stability at high temperatures though at the cost of difficult and expensive manufacturing.

ICI commercialized its Victrex polyethersulfone in 1972 followed in 1976 by Union Carbide with Radel, a product with the same structure as Astrel.

Polyethersulfone (PES) is an amorphous, transparent, and pale amber high-performance thermoplastic and is the most temperature resistant transparent commercially available thermoplastic resin. It has relatively high water absorption. Stable solutions can be made if solvents are correctly chosen. Chemical structure repeating units of several of the commercial polymers.

Polyethersulfone (PES) is an amorphous polymer and a high-temperature engineering thermoplastic. Even though PES has high-temperature performance, it can be processed on conventional plastics processing equipment. PES has an outstanding ability to withstand exposure to elevated temperatures in air and water for prolonged periods.

Because PES is amorphous, mold shrinkage is low and is suitable for applications requiring close tolerances and little dimensional change over a wide temperature range. Its properties include:

1. excellent thermal resistance—T_g 224°C

2. outstanding mechanical, electrical, flame and chemical resistance

3. very good hydrolytic and sterilization resistance

4. good optical clarity

5. processed by all conventional techniques.

Polysulfones are a family of thermoplastic polymers. These polymers are known for their toughness and stability at high temperatures. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for polycarbonates.

PES (Polyethersulfone) Membranes. These hydrophilic, low protein binding, PES membrane filters are ideal for tissue culture media sterilization, life science and microbiology fluid applications, clinical, and general filtration.

PROPERTIES

1. Amorphous in nature

2. Transparent with 60-80 % light transmittance

3. Good thermal stability

4. Excellent creep resistance and load bearing properties upto 100 ºC

5. Good dimensional stability upto 200 ºC

6. Good electrical properties

7. Good flame resistance

8. Good resistance to gamma radiation

9. Low mould shrinkage

10. Can be electroplatable.

11. High strength between - 100 and + 200 °C, short-term to + 260 °C,

12. High stiffness and hardness,

high thermal stability and heat distortion temperature

13. High heat resistance,

14. Good slip and wear properties which can be improved by adding PTFE and graphite, 

15. Electrical and dielectric properties,

16. Transparency,

17. High resistance to chemicals (including hydrolysis)

18. High energy radiation,

19. Good resistance to stress cracking,

20. Low flammability and smoke emission,

Structure and General Properties

1. PES are typical examples of 

2. Thermally stable polymers obtained by selecting

3. Heat resistant monomers which are linked by heat resistant bonds.

4. The bond energy of aliphatic C - C bonds is 335 kJ mol-1, that of aromatic bonds, 520 kJ mol-1. 

5. The presence of the ether linkage (O-atom in the main chain) results in thermoplastic character and high toughness. 

6. The O = S = O group provides high resistance to oxidative degradation. 

7. The bulky structure results in the transparency of PES.

Additives

1. Polysulfones are degraded only by UV radiation of wavelength less than 320 nm. 

2. Photooxidation is caused mainly by the sulfone group (SO2) rather than by impurities. 

3. Because mainly hydroxyl groups are formed, the most suitable UV absorbers are:

hydroperoxide decomposers and 

radical interceptors (HALS)

Availability

1. Low and high viscosity injection molding and extrusion grades with and without glass fiber reinforcement are available.

2. Usually supplied as pellets although some (Victrex) grades are supplied as powders for solvent coating. 

3. Packaged in sacks, it can absorb up to 1.4% moisture and must therefore be dried before processing.

Mechanical Properties

1. Transition Temperatures:

Tg of PES made by ICI (Victrex) is 230°C compared with 288 °C and 290 °C for Astrel and Radel, respectively.

2. This is due to the two benzene rings linked together without an intermediate link. This results in higher service temperatures. 

3. The secondary damping maximum of PES at - 100 °C is responsible for the high toughness over a wide temperature range.

4. The creep characteristics of PES is superior to those of the well known engineering thermoplastics and polysulfones. 

5. PES exhibits high strength, stiffness, toughness and energy-absorbing capacity and these properties are maintained over a wide range of temperature. 

6. Addition of glass fiber improves these properties further (while extensibility decreases).

Thermal Properties

1. The tensile strength increases by about 20% during ageing at 150 °C in air for one year and

- in water at 23 °C it falls by about 10% and

- in boiling water it remains almost constant. 

2. The notched impact strength increases on immersion

- in water at 23 °C from 140 to 172 kJ/m2 and 

- in water at 100 °C it falls to 45 kJ/m2 

(the notch radius of the test piece was 2 mm).

Electrical Properties

1. The dielectric constant of dry PES at 20 °C remains constant at 3.7 over a frequency range of 50 Hz to 1 MHz. 

2. The dissipation factor is relatively constant up to 150 °C in contrast to the other plastics shown with the exception of polyimide. 

3. PES is not damaged by the temperatures which occur briefly during ordinary soldering.

Optical Properties

1. PES is transparent. 

2. The refractive index n20D is 1.65, 

3. The light transmission for wall thicknesses of 1.5 mm and 3 mm is 80% and 69%, respectively.

Water Absorption

1. Molded PES absorbs moisture. 

2. The consequences are relatively small. 

3. A 3 mm thick test specimen reaches its equilibrium weight (an increase of 2.3%) after immersion in water at 100 °C for a week. 

4. At 23 °C equilibrium is reached after two weeks with a 2.1 % increase in weight. 

5. The dimensions of a freshly molded specimen at equilibrium after four months ageing in air at 20 °C & 56% RH show an increase of only 0.15%.

Resistance to Chemicals

1. Resistant to dilute acids, alkaline solutions, alcohols and other aliphatics, oils, cleaning agents. 

2. Not resistant to ketones, esters, chlorinated hydrocarbons, hot water, aromatics, highly polar solvents. 

3. Soluble in highly polar solvents such as dimethyl sulfoxide, pyridine, quinoline, aniline and in methylene chloride and CHCl3.

Resistance to Stress Cracking

1. PES is susceptible to stress cracking on contact with solvents such as ketones, esters and chlorinated hydrocarbons. 

2. As long as the moldings are not subjected to high stresses, they can be cleaned with most of these solvents. 

3. The resistance of glass fiber reinforced moldings is higher than that of unreinforced moldings. 

4. The internal stresses detected with MEK can be removed by conditioning at 190 to 200°C for 2 hrs.

Weathering Resistance

1. As in PSU, the SO2 group in PES acts as a UV absorber thus providing limited weathering resistance. 

2. Natural moldings yellow outdoors, losing strength and becoming brittle. Active carbon black protects effectively against solar UV radiation.

Flammability

1. PES is of low flammability and self extinguishing without the addition of flame retardants as shown by the V-0 classification to UL 94 for wall thicknesses of only 0.5 mm. 

2. The LOI is between 41 and 45 depending on the grade and dimensions of the specimen.

Sterilization

1. PES moldings can be sterilized by all the normal methods 

Resistance to High Energy Radiation

1. Over the entire useful temperature range, PES is very resistant to b-, g- and X-rays. 

2. Only at radiation doses greater than 2x106 J/kg is there a noticeable drop in the yield and elongation at break of the unreinforced grades. 

3. Only small amounts of gas are given off.

Processing

PES can be processed by all the usual methods for thermoplastics. The recommended processing conditions are:

- Pre-drying at 150°C for 3 hours

- Injection molding 340-390°C

- Mold temperature 150°C

- Extrusion 340-390°C

- Thermoforming 300°C

Joining

1. The preferred method of joining is ultrasonic welding

2. Solvents used for bonding- N-methyl-2-pyrrolidone (NMP) or dichloromethane. 3 to 15% PES is dissolved in NMP. Prior to joining, the moldings should be conditioned for 2 hours at 200°C. 

3. One- and two-pack EP resins provide high strength bonding. 

4. One-pack adhesives are permanently flexible between -60 and + 225 °C.

Typical Applications

1. Coil cores, bushes, frames, housings, carbon brush holders, printed and integrated circuits, contacts, condenser foils, 

2. Bearing cages, spark plug suppressors, carburetor components, 

3. Optical and precision engineering components such as reflectors, lamp holders, spotlights, lenses. 

4. Medical equipment, 

5. Chemical engineering, 

6. Hot water installations,

7. Ultrafiltration media, 

8. Domestic appliances, 

9. Instrument cases, 

10. Fittings, connectors.

11. Aircraft nose cones, radomes, air ducts, 

12. Pan coatings, protective finishes for metals.