Polyetherimides

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General structure of polyetherimides
Ether-imide groups (PEI) .svg
Ether (left) imide groups (right) are marked in blue and are in the main chain of the macromolecules. The hydrocarbon segments are aromatic , the ether groups are formally condensates of phenols (phenol ethers) and the imide groups are arylimides .

Polyetherimides ( abbreviation PEI ) count among the polyimides and are polymers with imide and ether groups in the main chains. They are resistant to high temperatures, transparent and have a golden yellow color. They are among the high-performance plastics with a market share of around 15% in 1996.

Manufacturing

A polyetherimide is produced, for example, from 1,4-bis (4-nitrophthalimido) phenylene and the disodium salt of bisphenol A in a melt condensation:

PEI Synthesis.svg

The prepolymer 1,4-bis (4-nitrophthalimido) -phenylene can be obtained from 4-nitrophthalic anhydride p -phenylenediamine .

This polyetherimide was marketed in 1981 by General Electric Plastics (GE) under the trade name Ultem . In 2007, SABIC bought the plastics division of GE Plastics along with its trademark and continued the activities relating to various high-temperature plastics under SABIC Innovative Plastics . Another trademark is Tecapei from Ensinger .

A classic polyetherimide

As early as the 1960s, polyether imides based on pyromellitic dianhydride and 4,4'-diaminodiphenyl ether were developed and sold under the name Kapton ( DuPont ). However, the polymer is usually not referred to as polyetherimide, but only as polyimide (PI). The polymer is not meltable. In the first step of production, a polyamide that is still soluble in polar solvents is produced. The solution is often used in foils or coatings on wires for the electrical industry via evaporation of the solvent. When the temperature rises, the no longer fusible polyimide is produced through polycondensation with elimination of water:

Kapton Synthesis (PEI) .svg

The service temperature is 260 ° C, short-term temperatures over 400 ° C are possible.

properties

The usage temperature of polyetherimides is briefly above 200 ° C and long-term at 170 ° C. PEI is inherently flame retardant with little smoke development. Even in the unreinforced state, it has a very high strength, which can be increased by adding glass fibers or carbon fibers . PEI has a high dielectric strength, is resistant to hydrolysis and very resistant to UV and gamma rays . Polyetherimide is sold in its pure form and with various additives (glass fibers, carbon fibers).

Infrared spectrum from PEI
Properties (Ultem 1000, Standard PEI)
density 1.27 g / cm 3
Glass transition temperature approx. 217 ° C
hardness 140 MPa ( ball indentation hardness )
Notched impact strength 4 kJ / m 2 (Charpy 23 ° C)
modulus of elasticity 3200 MPa
Water absorption 1.25%
Elongation at break 60%
Chemical resistance Alcohols, gasoline, diesel, sulfuric acid (37%, 90 ° C),
caustic soda (30%, room temperature), acetic acid (20%, 90 ° C)
Heat resistance 190 ° C (HDT / Ae)
Thermal conductivity 0.24 W / (m K)
Thermal expansion coefficient 50 · 10 −6 1 / K

processing

A polyetherimide is mainly processed by injection molding . Depending on the type, the processing temperature is between 320 and 400 ° C, the mold temperature between 120 and 180 ° C. The granulate must be dried to a moisture content of max. 0.05% before processing. Components made of PEI can be welded by induction, vibration or ultrasound or glued with epoxy, polyurethane or silicone adhesive.

use

Polyetherimides are preferably processed into plastic parts for electronics and in the aircraft industry. In aviation , PEI is increasingly being used in aircraft interiors, as it develops a low smoke density in the event of a fire. Its importance is growing in the structural mechanics area of ​​aircraft construction, since PEI in fiber composite structures has a higher impact strength than thermoset matrix systems.

Also membranes of polyetherimide are characterized by their mechanical strength , their good film-forming property and its relatively inexpensive manufacture an inserted in the industrial product. The surface properties of the material can be modified from water-friendly ( hydrophilic ) to water-repellent ( hydrophobic ), so that membranes made of PEI meet various biomedical requirements.

Tweeter membranes are also made from PEI. Another application is the production of picks for stringed instruments.

Individual evidence

  1. ^ Wolfgang Kaiser: Kunststoffchemie für Ingenieure , 3rd edition, Carl Hanser, Munich, 2011, p. 469.
  2. ^ GE Completes Sale of Plastics Business to SABIC. (No longer available online.) General Electric, August 31, 2007, archived from the original on September 12, 2014 ; accessed on February 10, 2020 (English).
  3. ^ Wolfgang Kaiser: Kunststoffchemie für Ingenieure , 3rd edition, Carl Hanser, Munich, 2011, p. 466.
  4. ↑ Bernd Tieke: Makromolekulare Chemie , 3rd edition, Wiley-VCH, Weinheim, 2014, p. 34.
  5. ↑ Hans Domininghaus: The plastics and their properties , 5th edition, VDI-Verlag, 1998, p. 987.
  6. ↑ a b c d e f g h i j www.kern.de , data from Ultem 1000 (standard PEI).

Norms

  • DIN 65498 aerospace; Semi-finished products and molded parts made of polyetherimide (PEI); Technical delivery conditions (1997)
  • ASTM D 5205-1996 Classification System for Polyetherimide (PEI) Materials
  • ASTM D 7293-2006 Standard Test Method for Extruded and Compression-Molded Shapes Made from Polyetherimide (PEI)