POLYETHER IMIDE (PEI): General Electric (US) introduced PEI under the name of Ultem in early 1982. This thermoplastic fills the gap between the polyethersulfones and the considerably more expensive polyamide imides and polyfluorocarbons.
PEI is a high performance, amorphous thermoplastic based upon regular repeating ether and imide linkages. The aromatic imide units provide stiffness while the ether linkages allow for good melt-flow characteristics and processability.
Polyetherimide is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. Relative to PEEK, PEI is cheaper, but is lower in impact strength and usable temperature.
The glass transition temperature of PEI is 217 °C. Its amorphous density at 25 °C is 1.27 g/cm3. It is prone to stress cracking in chlorinated solvents. Polyetherimide is able to resist high temperatures with stable electrical properties over a wide range of frequencies. This high strength material offers excellent chemical resistance and ductile properties suitable for various applications, even those including steam exposure.
General Description
PEl is characterized by the following properties:
- Very high strength (even when unreinforced),
- high stiffness and hardness,
- high heat distortion temperature (> 200 °C),
- high continuous service temperature (170 °C),
- high dielectric strength,
- dielectric properties remain almost constant over a wide range of temperature & frequency
- transparent amber color,
- low coefficient of thermal expansion,
- high resistance to chemicals and hydrolysis,
- high weathering resistance,
- high resistance to g-radiation,
low flammability (V-0 at 0.76 mm thickness) &
low smoke emission,
- good, economic processability.
Processing
1. PEI is easily processed on conventional injection molding/ extrusion/blow molding m/c
2. Resin viscosity vs. shear rate profile comparable to PC or PSF (rather than conventional polyimides), although the processing temperature is much higher.
3. Due to its thermal stability, PEI exhibits a much higher processing window than most other engineering plastics.
4. PEI absorbs so much water when stored in air that predrying is required. Molding compounds should not contain >0.05% water for processing.
5. Melt temperature is 375 to 425°C,
6. Mold temperatures 100 to 150°C.
7. Shrinkage is between 0.2 to 0.7%
8. Readily converted into film sheet & profiles via melt extrusion because of its high melt strength.
9. Owing to its melt integrity PEI is easily thermoformed or blow molded using injection or extrusion techniques.
Structure and Properties
PEI consist of imide groups O=C-N-C=O linked by ether groups and thus they have good mechanical and thermal properties.
The ether groups are also responsible for a certain flexibility of the polymer chain and hence good processability.
Structure and Properties
1. PEI consist of imide groups O=C-N-C=O linked by ether groups and thus they have good mechanical and thermal properties.
2. The ether groups are also responsible for a certain flexibility of the polymer chain and hence good processability.
Additives
The main additive is glass fiber reinforcement.
Availability
1. Commercially available granules from General Electric Co. under the trade name of Ultem®.
2. Standard grade (Ultem 1000)
3. Grades reinforced with 10 - 40% w/w glass fiber,
4. Grades reinforced with 15% Carbon fiber
5. The development range (D 6000) distinguished mainly by increased HDT
6. Special purpose grades for moldings subjected to wear and for manufacturing printed circuit boards.
Machining
1. Laser beams are used when high drilling and cutting speeds are required.
2. Close tolerances, the absence of swarf, burrs, etc and low internal stresses are the advantages of this technique.
3. Holes as small as 0.15 mm diameter can be bored in positions inaccessible to conventional drills.
Joining-1
Molded-in threads or self cutting screws can be used for screw connections.
Inserts are molded in or inserted by vibration.
Snap joints use the elastic recovery of PEI.
Joining -2
Diffusion bonding (using methylene chloride) is a suitable method for PEI to PEI glued joints. Adhesion bonding can be used to join PEI to PEI or other materials. Adhesion bonding agents are based on silicone, nonamine epoxide resins & hot melt polyamide adhesives.
Typical Applications
1. High voltage circuit breaker housings, connectors, microwave oven components, flow solder resistant terminal strips,
2. Transmission components, pistons and brake cylinder parts, carburetor housings, headlamps,
Aircraft seat shells, safety belt clips,
Cables,
Bearings, gears,
Vanes for pumps.
PROPERTIES
1. Very high mechanical properties
2. Resistance to most chemicals
3. Excellent resistance to UV radiations
4. Can be stabilised by ethylene oxide and gamma radiation
5. Excellent flame resistance
6. Exhibits the highest LOI 47%
7. Very good thermal stability and warp resistance at elevated temperature.
Transition Temperatures
The high stiffness and good dimensional stability at elevated temperatures are not surprising in view of the high Tg of the original grades (217 °C) and of the development grades (230 °C).
Density: 1.27 g/cm³
Formula: (C37H24O6N2)n
Classification: Thermoplastic
Appearance: Amber-to-transparent solid
Molar mass: Variable
Molecular weight: 592.61 g/mol.
APPLICATIONS
Industrial
Corrosion resistant fluid and gas handling parts, strong mechanical couplers and threaded fasteners, bearing sleeves.
Medical
Nerve simulators, surgical lamp housings, manifold valves for ventilators, endodontic cases
Electrical/Electronics
Precision fibre optic components PCB and IC chip carriers, bobbins, protective clothing for fire fighters, insulating tapes and wire insulators.
Mechanical Properties
1. The structure of PEI results in very high strength and stiffness.
2. The tensile strength of the unreinforced material is greater than 100 N mm-2.
3. The flexural modulus is 3300 N mm-2.
4. Both values are far above the levels of other thermoplastics.
Notch sensitivity
The unreinforced material possesses adequate impact strength although it is notch sensitive.
Stress concentrations in moldings, on sharp edges, for example, should therefore be avoided.
Wear Properties
The special purpose grade PEI is particularly suitable for applications which require high wear resistance, e.g. bearings and vane pumps.
Thermal Properties
One of the most outstanding properties of PEI is its ability to withstand exposure at elevated temperatures. PEI exhibits a Tg at 419℃.
The HDT (at 1.82 N mm-2) of PEI is 200°C, the same as that of PES while those of PSF and PC are 170 and 135 °C, respectively. This accounts for its excellent retention of physical properties at elevated temperatures.
Electrical Properties
1. The unmodified and 30% glass-reinforced PEI resin exhibits an excellent balance of electrical properties which remain stable over a wide range of environmental conditions.
2. The favorable dielectric properties and high volume resistivity of PEIs are constant over a wide range of temperature and are hardly affected by environmental influences.
3. The dissipation factor remains low over a wide range of frequency particularly in the kHz (103 Hz) and GHz (109 Hz) region.
4. This property is significant for logic components in electronics applications or components for microwave applications where the material should absorb as little electrical energy in the form of heat as possible.
Water Absorption
1. The unreinforced PEIs absorb 0.3% water at 60% atmospheric humidity.
2. The maximum permitted content is, however, 0.05%.
Resistance to Chemicals PEI is very resistant to:
1. mineral acids
2. salt solutions,
3. aqueous alkaline solutions (pH < 9),
4. antifreeze, automotive and aviation lubricants,
5. fuels and cleaning agents, alcohols,
6. carbon tetrachloride, ether.
7. hydrolysis.
It has limited resistance to ketones.
It is not resistant to ethyl acetate, MEK
and chlorine containing solvents.
Resistance to Stress Cracking
PEI has only limited resistance to stress cracking. The glass fiber reinforced grades are superior to unreinforced grades.
Weathering Resistance
PEI is resistant to UV radiation without the addition of stabilizers.
Resistance to High Energy Radiation
The resistance to high energy radiation (g-radiation from a Co60 source) is remarkably high.
Even a radiation dosage of 5000 kJ kg-l causes a loss of only 6% in the tensile strength.
Flammability
PEI is flame resistant without the incorporation of additives.
In fire incidents, PEI gives off only very small amounts of smoke.
No comments:
Post a Comment