CORPORATE TRAINING AND PLANNING SPECIALTY PLASTICS Polyphenylenesulfone (PSU)

CORPORATE TRAINING AND PLANNING

SPECIALTY PLASTICSPolyphenylenesulfone

(PSU)


PSU

Sn

O

O


Polysulfones

Some thermoplastic polycondensates developed in the last thirty years contain sulfur atoms in the form of sulfide (S) or sulfone (SO2) in the building block of their main chain. The sulfur atom is linked to the aromatics in the main chain in the form of diphenyl sulfone or sulfide groups.

PSU


Diphenyl sulfide

Besides sulfur, all polysulfones contain a second characteristic link, the oxygen atom. They can thus be termed polyether sulfones.

The terms polysulfone, polyarylsulfone or polyphenylsulfone used for some polymers of this product family is not justified by the chemical structure as all the products contain SO2 ether and phenyl groups.

Union Carbide Co. introduced ‘Udel’ polysulfone in 1965.


Introduction-1

Commercial Polysulfones are, like polycarboxylics and linear polyesters, monovalent polyaromatics.

Polysulfone excels in many fluid-handling applications.


Introduction -2

Transparent, opaque and glass-fiber reinforced grades of Polysulfone resin are available for injection molding into complex parts or extrusion into forms such as rod, film, sheet, profile and tubing.

Shapes can be machined for prototype evaluations; film and sheet can be thermoformed on conventional equipment. Polysulfone resin can also be blow molded.


Manufacture

Polysulfone is manufactured from bisphenol A and 4, 4-dichlorosulfonyl sulfone by a multi step condensation reaction.

Polyphenylsulfone


General Description

high strength, stiffness and hardness between - 100 and + 150 °C, short

term to 180°C.

high thermal stability & heat distortion temperature,

crystal clear (slightly yellowish) transparency,

high processing temperatures,

high melt viscosity,


General Description

• high chemical resistance,

• susceptibility to stress cracking with certain solvents,

• high resistance to -, X- and IR-radiation,

• high transmittance for microwaves,

• high flame resistance and low smoke development.


Structure and General Properties

• In order to utilize fully the valuable properties of the dimethyl sulfone group,

it must be bonded with thermally and hydrolytically stable links.

• High flexibility is provided by the ether linkage, the oxygen atom which improves thermal stability and processability.

• The aliphatic (isopropylidene) group contributes limited flexibility but does not improve thermal stability.


Additives

• Polysulfones are degraded only by UV radiation of wavelength less than 320

nm.

• Photooxidation is caused mainly by the sulfone group (SO2) rather than by

impurities. Because mainly hydroxyl groups are formed, the most suitable UV

absorbers are hydroperoxide decomposers and radical interceptors (sterically hindered

amines, HALS).

• PSU is inherently flame retardant.

• Properties can be improved by mineral fillers, glass fiber and C-fiber.


Availability

The PSU range includes crystal clear and colored transparent and opaque grades as well as mineral-filled and glass fiber

reinforced grades.

PTFE- and graphite-filled grades are supplied by compounders.

Tube, sheet and film are available.


Mechanical Properties

Transition Temperatures Commercial polysulfone has an amorphous structure and is thus crystal clear.

The benzene rings in the molecule chain result in a glass transition temperature of 190°C. A secondary maximum is found at -100°C.

Over this wide temperature range of almost 300°C, PSU is hard, stiff and tough like PC. The rigid structure results in high heat resistance and the high processing temperature of 300 to 400 °C.


The impact strength of PSU is, as for all thermoplastics, dependent on the notch radius, temperature of the surroundings and moisture absorbed.


Thermal Properties -1

The specific volume of PSU increases linearly between 20 and 170 °C from 0.8038 to 0.8253 cm-3g-1 and between 170 to 400°C more steeply to 0.94 cm-3g-1.

PSU is suitable for applications involving temperatures up to 150°C (continuous) & 170°C (short-term) in air.


Thermal Properties -2

The temperature index (to UL) is 160°C for electrical and mechanical applications in which the impact strength is not of prime importance.

It is lower than that of polyethersulfone (180°C) but higher than that of PBT (140 °C), PC (130°C) and PA (120 °C).


Electrical Properties

Although PSU is a polar plastic, the polarity loses much of its effect because of the high glass transition temperature and associated immobility of the chain segments.

At temperatures above 150 °C, the dissipation factor increases rapidly from 0.001 to 0.01 at all usual frequencies.


Chemical PropertiesResistance to Chemicals

PSU is resistant to aqueous inorganic acids, alkalis, salt solutions, aliphatic hydrocarbons, cleaners and paraffin oil; resistance to fuels is limited.

It is not resistant to ketones, aromatics, chlorinated hydrocarbons, polar organic solvents, water at high temperatures (stress cracking).


Resistance to Stress Cracking

PSU is susceptible to stress cracking in certain solvents. The critical level of stress (internal stress plus external tensile stress) differs according to solvent. Ethylacetate, acetone, trichloroethane, 2-ethoxyethanol, CCl4

It is therefore important that internal stresses in moldings are low. Where moldings are likely to come into contact with cleaning agents, they should be conditioned in a glycerine bath at 166°C or in air at 165°C.


Weathering Resistance

Because of the aromatic bonds, weathering causes chemical degradation of PSU.

Stabilization with active carbon black, lacquering or metallizing (electroplating or in high vacuum) are required for long-term protection.


Resistance to High Energy Radiation

The high resistance to and IR -radiation contrasts with damage caused by UV in sunlight. PSU is very resistant to microwave (2.45 GHz) range radiation even at high temperatures and is thus suitable for cooking utensils for use in microwave ovens, a major use in the USA and Great Britain.


Flammability

• PSU is of low flammability. • It burns with a luminous, sooty flame

without dripping and extinguishes after the ignition source is removed.

• The smell is choking. • Classification varies depending on grade from V-2 to V-0(from 1.02 mm). • The self-ignition temperature is 621 °C. • Only small amounts of smoke are given off.


Toxicological Assessment

PSU has FDA approval for repeated contact with foodstuffs as well as for pipe fittings and other accessories for drinking water supplies.

PSU is certificated for applications in dairy equipment, particularly for pipes for transporting milk.

Sterilization

PSU is an ideal material for manufacturing medical equipment because of its transparency, sterilizability and freedom from taste and smell. The elongation at break, tensile strength and tensile modulus of elasticity remain almost unchanged after 10,000 cycles.


PROCESSING -1

PSU can be processed by all the usual processes for thermoplastics.

Process Processing temperatures Injection molding

350 to 400°C , mold temperature up to 150°C

Extrusion of blown film

410 °C

Extrusion blow molding

275 to 300 °C

Thermoforming

200 to 220 °C, for film thicknesses greater than 375 m, predrying at 375°C, mold temperature 150 to 165°C


PSU

PROCESSING -2• Polysulfone is hygroscopic and must

therefore be dried prior to processing at 120 °C for at least 5 hours.

• The high melt viscosity can easily cause orientation and mold temperatures must therefore be high (see the section on resistance to stress cracking).

• Molding shrinkage is 0.7%; it is independent of direction in the case of unreinforced material.


Surface Finishing

• Conditioned moldings can be electroplated or vacuum metallized.

• The coatings are cured at 163 °C.

• Printing does not require pretreatment.

• A formulation developed for printing on PVC can be used for flexographic printing on film.


Joining -2• Welding PSU moldings and semi-finished products

can be welded by the heated tool, hot gas, ultrasonic or induction methods.

Temperature of the hot plate in the heated tool method is 370°C, contact time 10 secs.

Increasing contact pressure between the surfaces to be joined should be used.

Molded PSU usually contains some moisture and should therefore be dried for 3 to 6 hours at 130 °C in a circulating air oven.

PSU


Joining-2Bonding PSU can be bonded with, for example, a 5% solution of PSU in methylene chloride. The parts are pressed together for 5 minutes using a pressure of 35 N/mm2.

Elastomeric contact adhesives are suitable for joining PSU with rubber, textiles and felt.

Two-pack Epoxide adhesives and Polyurethane adhesives are best for high strength joins.

PSU


Typical Applications

• PSU resin can be injection molded, vacuum formed or machined. Current applications include a wide assortment of medical trays and containers as well as surgical instruments, a binocular ophthalmoscope and bellow housing for anesthetics.

• For severe applications requiring repeated sterilization or uncompromising toughness, PSU stands out. With its high heat deflection temperature of 207°C, it can withstand continuous exposure to heat and still absorb tremendous impact without deflecting or breaking. Plus its chemical resistance surpasses that of most amorphous polymers.



• In electrical engineering and electronics, PSU is used for connector track, coil cores, instrument cases, insulators, condensers, brush holders, components for alkaline batteries, printed circuits and light fittings.

• Many consumer products contain PSU parts, e.g., Food service components, coffee machines, air humidifiers, opera glasses, cookers, cameras, projectors, hair driers, egg boilers, microwave utensils, beverage vending machines, sterilizable medical equipment. In the dairy industry it is used in parts for milking machines, Plumbing fixtures, faucet components, pipes and fittings.



• PSU resins offers unique properties - such as the ability to easily create porous filaments or flat sheet from stable solutions - that allow it to be used in micro and ultra filtration and reverse osmosis membranes. These membranes can be used in applications ranging from artificial kidneys for blood purification to wastewater recovery as well as food and beverage processing.

• Plus, PSU resins are used to create water purification membranes that can filter harmful bacteria spores such as cryptosporidium from municipal drinking water.



PSU

Water PurifierManifoldMedical



• In the automotive and aerospace industries PSU is used for switch and relay components, brush holders, coil cores for suppressors, insulating fittings, seals, fuses, aircraft interiors, visors for astronauts.

PSU


Trade Names

Stabar (ICI, UK)Sumilik FST (Sumitomo Chern. Co., lP) Udel (Solvay, US) Ultrason S (BASF, DE)Radel (Solvay)


Further Reading

1. BRYDSON J.A, Plastics Material, Butterworth Heinemann, oxford, New Delhi (2005)

2. DOMININGHAUS H., Plastics for Engineering, Hanser publishers, Munich, New York (1998)

3. CHARLESS A . HARPER, Modern Plastics Hand Book McGraw –Hill, New York (1999)

4. MARGOLIS J. M., Engineering Thermoplastics, Marcel-Dekker, New York (1985)


TABLE – Guide values of properties of PSUProperties Units PSU PSU (Glass Filled)

Density g/cm3 1.24 1.45

Water absorption (23°C, 24h) % 0.3 0.2

Yield stress N/mm2 70

Elongation at yield % 6

Tensile strength N/mm2 108

Elongation at break % 50-100 2

Tensile modulus of elasticity N/mm2 356000 7400

Impact strength (Izod) J/m No break 96

Notched impact strength J/m 69 75

Rockwell hardness scale M69 M 92

Service temperature in air without mechanical loading

short-term °C 170 180

long-term °C 160 160

Glass transition temperature °C 190 190


TABLE – Guide values of properties of PSUProperties Units PSU PSU (Glass Filled)

Vicat, Method B °C 188

HDT (ISO Method A) °C 174 185

Coefficient of linear expansion between 0 & 50 °C mm/mm/°C 56x10-6 19x10-6

Thermal conductivity W/mK 0.26 0.32

Volume resistivity cm 5x1016 >106

Surface resistance 3x1016

Dielectric constant 3.15 3.5

Dissipation factor, tan 50 Hz 0.001 0.001

0.1 MHz 0.005 0.004

Dielectric strength kV/mm 20 475/25

Tracking resistance class C 150

Fire performance to UL 94 class V-2 V-0

CORPORATE TRAINING AND PLANNING SPECIALTY PLASTICS Polyphenylenesulfone (PSU)

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