High-performance plastics

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A comparison of standard plastics, engineering plastics, and high-performance plastics

High-performance plastics are plastics that meet higher requirements than standard or engineering plastics. They are more expensive and used in smaller amounts.[1]

Definition

See also: Plastic § Special purpose plastics

High performance plastics differ from standard plastics and engineering plastics primarily by their

mechanical properties, production quantity, and price
.

There are many synonyms for the term high-performance plastics, such as: high temperature plastics, high-performance polymers, high performance thermoplastics or high-tech plastics. The name high temperature plastics is in use due to their continuous service temperature (CST), which is always higher than 150 °C by definition (although this is not their only feature, as it can be seen above).

The term "

polymers" is often used instead of "plastics" because both terms are used as synonyms in the field of engineering
.

However, the differentiation from less powerful plastics has varied over time; while nylon and poly(ethylene terephthalate) were initially considered powerful plastics, they are now ordinary.[2]

History

The improvement of mechanical properties and thermal stability is and has always been an important goal in the

aggressive reactants, the product could hold only a short time on the market. For this reason, the majority of high-performance plastics is nowadays produced by polycondensation processes.[2]

In manufacturing processes by polycondensation a high purity of the starting materials is important. In addition, the stereochemistry plays a role in achieving the desired properties in general. The development of new high-performance plastics is therefore closely linked to the development and economic production of the constituent monomers.[2]

Characteristics

High performance plastics meet higher requirements than standard and engineering plastics because of their more desirable mechanical properties, higher chemical and/or a higher heat stability. Especially the latter makes processing difficult, often requiring specialized machinery. Most high-performance plastics are exploited for a single property (e.g. heat stability), in contrast to engineering plastics which provide moderate performance over a wider range of properties.[1] Some of their diverse applications include: fluid flow tubing, electrical wire insulators, architecture, and fiber optics.[4]

High performance plastics are relatively expensive: The price per kilogram may be between $5 (PA 46) and $100 (PEEK). The average value is slightly less than 15 US-Dollar/kg.[5] High-performance plastics are thus about 3 to 20 times as expensive as engineering plastics.[2] Also in future there cannot be expected a significant price decline, since the investment costs for production equipment, the time-consuming development and the high distribution costs are going to remain constant.[5]

Since production volumes are very limited with 20.000 t/year the high-performance plastics are holding a market share of just about 1%.[1][3]

Among the high-performance polymers, fluoropolymers have 45% market share (main representatives: PTFE), sulfur- containing aromatic polymers 20% market share (mainly PPS), aromatic polyarylether and Polyketones 10% market share (mainly PEEK) and

liquid crystal polymers (LCP) 6%.[5][6] The two largest consumers of high-performance plastics are the electrical and electronics industries (41%) and the automotive industry (24%). All remaining industries (including chemical industry) have a share of 23%.[5]

Thermal stability

Thermal stability is a key feature of high-performance plastics. Also mechanical properties are closely linked to the thermal stability.

Based on the properties of the standard plastics some improvements of mechanical and thermal features can already be accomplished by addition of stabilizers or reinforcing materials (

phenyl) with oxygen (as diphenyl ether group e. g. PEEK), sulfur (as diphenyl sulfone groups in PES or diphenyl group, for example in PPS) or nitrogen (imide group in PEI or PAI). Resulting operating temperatures might be between 200 °C in the case of PES to 260 °C in case of PEI or PAI.[7]

The increase in temperature stability by incorporating aromatic units is due to the fact, that the temperature stability of a polymer is determined by its resistance against

statistical chain scission; depolymerization
and removal of low molecular weight compounds are playing only a minor role.

The thermal-oxidative degradation of a polymer starts at lower temperatures than the merely thermal degradation. Both types of degradation proceed via a radical mechanism.

CO). By mixing these different elements the diversity of high-performance plastics is created with their different characteristics.[2]

In practice a maximum temperature resistance (about 260 °C) can be obtained with

construction material due to poor mechanical properties (low strength and stiffness, strong creep under load).[7]

Crystallinity

High-performance plastics can be divided in amorphous and semi-crystalline polymers, just like all polymers. Polysulfone (PSU), poly(ethersulfone) (PES) and polyetherimide (PEI) for example are

semi-crystalline
.

Crystalline polymers (especially those reinforced with fillers) can be used even above their glass transition temperature. This is because semi-crystalline polymers have, in addition to a glass temperature Tg, a crystallite melting point Tm, which is usually much higher. For example PEEK possesses a Tg of 143 °C but remains usable up to 250 °C (continuous service temperature = 250 °C). Another advantage of semi-crystalline polymers is their high resistance against chemical substances: PEEK possesses a high resistance against aqueous acids, alkalies and organic solvents.[2]

See also

References

  1. ^
    ISBN 978-3-5272-9962-1. Makromoleküle, p. 298, at Google Books
  2. ^
    ISBN 978-3-527-30673-2
    .
  3. ^
    ISBN 978-3-446-43047-1. Kunststoffchemie, p. 439, at Google Books
  4. ^ "The Different Applications and Variations of Fluoropolymer Tubing". Fluorotherm. October 15, 2015.
  5. ^ a b c d "KIweb.de Kunststoff Information". Retrieved 2014-01-24.
  6. ^
    ISBN 3-5273-1582-9. Kunststoffchemie, p. 214, at Google Books
  7. ^
    ISBN 978-3-446-42436-4. Werkstoff-Führer, p. 1, at Google Books
  8. ISBN 978-3-446-21851-2. Beständigkeit von Kunststoffen, p. 38-47, at Google Books
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