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High Temperature Thermoplastics - Comprehensive Guide

High temperature thermoplastics materials are a specialized and rapidly growing segment of the plastics market. These are used in specialized applications that require a combination of extraordinary properties.

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Get comprehensive information about high heat thermoplastic resins including their key features, comparison with metals & thermosets and major applications.

What are High Temperature Thermoplastics?


TAGS:  High Heat Materials      Metal Replacement 

High Temperature ThermoplasticsHigh temperature thermoplastics are a specialized and rapidly growing segment of the plastics market. Today, the high temperature melt-processable thermoplastics market comprises a number of polymer families and each family consisting of several polymer types within. The plastics industry commonly uses terms such as "high performance", "engineering polymers", and "standard" or "commodity" plastics to describe the applications for these materials.

These are melt processable plastics. They have structural capabilities over the long-term at service temperatures greater than 150°C and short-term use at temperatures of greater than 250°C. These materials require a combination of extraordinary properties.

Depending on their application, they must have superior short- and long-term thermal stability, chemical and radiation resistance, resistance to burning, and superior mechanical properties that are often equal to metals.


Another distinguishing feature of high temperature thermoplastics is their cost, which is on average 10 times higher than more general purpose plastics. It is not only the excellent temperature capabilities of these polymers that has peaked interest and led to the relatively high growth rate. In many applications, their chemical resistance, wear resistance, and other performance properties are even more valued than heat resistance. Sometimes these high temperature thermoplastics are also referred to as "high performance plastics".


What makes them Thermally Resistant?


High temperature thermoplastics generally gain their temperature resistance from the introduction of rigid aromatic rings instead of aliphatic groups in their molecular structure. This restricts the movement of the backbone chain and requires two chemical links to be broken (compared to one in aliphatic structures) for a chain break as shown in the figure below:

Degradation of an aromatic and a straight chain polymer due to thermal aging
Degradation of an aromatic and a straight chain polymer due to thermal aging


Hence mechanical properties, high temperature capability, and chemical resistance are greatly improved and can be often equivalent or even better than crosslinked, thermosetting polymers.


Improving Plastic Performance of High Heat Plastics


Pyramid of plastics performance High temperature thermoplastics are used in specialized applications that require a combination of extraordinary properties. Depending on their application, they must have superior short- and long-term thermal stability, chemical and radiation resistance, resistance to burning, and superior mechanical properties that are often equated to metals.

High temperature thermoplastics are subject to significant improvements via compounding and modifications. By using special reinforcing materials, such as glass fiber, heat distortion resistance and rigidity can be improved even further than that shown by the base polymer. Additives such as fluorocarbon or graphite particles will considerably improve sliding friction characteristics.

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Classification of High Temperature Thermoplastic Resins


These versatile high temperature thermoplastics resins are widely employed in varied applications across industries. A pictorial classification of high temperature thermoplastic resins can be seen below.

High heat thermoplastics


High temperature thermoplastic resins are generally classified by a continuous use temperature (CUT) or relative thermal index (RTI) of greater than 150°C.

These temperatures are considered to be the maximum useful service temperature for materials where a critical property will not be unacceptably compromised through thermal degradation. However, assigning a "maximum service temperature" to any polymeric material must be done with great care. At high temperatures plastics not only soften but can also start to thermally degrade.

A plastic that softens at a high temperature but which starts to degrade at a lower temperature can only be considered for application below the temperature at which it starts to degrade.
The true maximum continuous use temperature depends on how you define "continuous" use. Time and loading will affect the answer as will the exact polymer structure and what additives, modifiers, or reinforcements may be used.

Each high temperature thermoplastic resin has its own advantages and disadvantages relative to processing characteristics and performance properties. Selection of a high temperature thermoplastic resin will most often depend on weighing these benefits and limitations relative to the application as well as the cost involved.

Despite the high average price compared to other engineering plastics and the current turbulent state of the global markets, high temperature thermoplastic resins are still considered to be one of the fastest growing segments of the plastics industry. Today, the high temperature thermoplastic resins market comprises a number of polymers which primarily include melt processable polyimides, sulfone polymers, polyaryletherketones, polyphenylsulfide, etc.
High Temperature Thermoplastic Resin fact


High Temperature Thermoplastics Structures


High temperature thermoplastics (as all polymers) comprise two molecular structures: amorphous(randomly ordered) and crystalline (highly ordered). For practical purposes, thermoplastics are either amorphous polymers or semi-crystalline polymers which have both amorphous and crystalline regions.

One of the major differences between the two types is how they respond to temperature.

Type

Thermal Characteristic

Examples

Properties

Amorphous

  • Has a melt range rather than a defined melt point
  • Broad glass transition temperature range
  • Strength, stiffness
  • Isotropic dimensional stability
  • Toughness and impact resistance
  • Clarity
  • Good surface appearance

Semi-crystalline

  • Sharply defined melting point and glass transition temperature
  • Chemical resistance
  • Wear resistance
  • Lower ductility and impact strength
  • Opaque
  • Low stiffness and creep resistance at high temperatures
  • Poor dimensional stability


Both amorphous and crystalline high temperature thermoplastics are used in the automotive, aerospace, medical, and electrical / electronic industries where demanding properties are required.


Advantages and Disadvantages of High Temperature Plastics over Metals


High temperature thermoplastics have continuous operating temperatures of more than 150°C. However, their high temperature resistant properties provide other performance characteristics that are valuable.

These include wear and chemical resistance. High temperature plastics also provide weight savings in many applications (e.g., automotive) and as a result are often considered for metal replacement. Table 2 summarizes the advantages and disadvantages of high temperature thermoplastics over metals.

These include wear and chemical resistance. High temperature plastics also provide weight savings in many applications (e.g., automotive) and as a result are often considered for metal replacement. Table 2 summarizes the advantages and disadvantages of high temperature thermoplastics over metals.

Advantages Over Metals

Disadvantages Over Metals

  • Low density
  • Good noise and vibration damping
  • Electrical and thermal insulation or adjustable conductivity
  • Good chemical and corrosion resistance
  • Increased design freedom
  • Adaptable to high volume production processes
  • Adaptable to property modification for specific applications
  • Greater thermal expansion
  • Poorer creep resistance
  • Lower thermal resistance
  • Susceptible to UV, moisture, and oxidation
  • Not considered to be a vapor barrier
  • Lower mechanical properties
  • Plastic parts generally must be redesigned over metal parts


High Heat Thermoplastics vs Thermosets


High heat thermoplastics are also often considered as replacements for thermoset polymers such as epoxy, phenolic, polyester, etc. The main advantages and disadvantages of high heat thermoplastics as compared to thermosets are summarized in table below. They exhibit good temperature capability as they possess high glass transition temperature, Tg. They are also characterized by outstanding toughness and high ductility as indicated by high tensile strain to failure and low moisture absorption. In general, mechanical properties of neat thermoplastic resins are comparable and often better than those of thermosets.


Property

Thermoset Resin

Thermoplastic Resin

Melt viscosity

Low

High

Processing cycle time

Long

Short

Processing temperature and pressure

Low to moderate

High

Mechanical properties

Fair to good

Fair to good

Toughness

Low

Moderately high

Moisture resistance

Relatively poor depending on the resin

Generally high depending on the resin

Creep

Good

Poor

Comparison Between Neat Thermoset and High Temperature Thermoplastic Resins


The high Tg of high temperature thermoplastics leads to high melt viscosities which can render them difficult to compound and process into finished parts. High processing temperatures often close to the decomposition temperature are needed to lower the melt viscosity.  Polyimides, for example, exhibit very high Tg's, but their melt processability is considered to be poor. The development of very flowable high temperature thermoplastics that possess enhanced performance properties is a subject of continuous development in the industry.


Market Sectors and Applications


#1. Automotive


High temperature thermoplastics are used to manufacture demanding applications in the automotive industry. The most valued properties are the high heat resistance, dimensional stability, strength, and resistance to a range of chemicals. These properties have led to the replacement of traditional materials such as metal and thermosets. The use of plastics in general has grown in the last decade primarily due to its lightness and resulting greater fuel efficiency. Plastics also offer:

  • Greater design flexibility
  • Reduced development time, and
  • Lower assembly costs

Automotive is the largest market sector for high temperature thermoplastics such as PPS, PEI, and PEEK.

Future trends will continue to be influenced by cost and weight reductions. Environmental considerations will also play an increasingly important role in terms of life cycle cost. There will be an increased need to recycle plastics at the end of the motor vehicle’s life. There will also be increasing demands for higher quality materials and greater use of safety, comfort, and aesthetic features.

For the automotive industry high heat thermoplastics are used to manufacture:
Automotive Application
  • Piston components
  • Seals
  • Washers
  • Bearings
  • Transmission components
  • Transmission thrust washers
  • Braking and air conditioning systems
  • ABS brake systems engineer control systems
  • Truck oil screens
  • Starting disks in gears, etc.


#2. Aerospace


Aerospace ApplicationIn the aerospace market, PEEK polymers are replacing aluminum and other metals in a wide range of applications. The polymer combines outstanding physical and thermal characteristics with light weight and ease of processing. High numbers of large volume components with fine tolerances can be cost-effectively formed and used without assembly or modification. Applications for PEEK in the aerospace industry include:

  • Critical engine parts as the polymer can withstand high temperatures and the tribological interaction of dry and lubricated material contacts.

  • In aircraft exterior parts, PEEK provides excellent resistance to rain erosion, while for aircraft interior components, its inherent flame retardancy and low smoke and toxic gas emission reduce hazard in the event of a fire. In aircraft electrical systems, the polymer is used for manufacture of convoluted tubing to protect wires and fiber optic filaments.

  • PEEK is also used to protect the wire harnesses used in commercial aircraft engines.

  • Polyetherimide (PEI) is also a widely used high temperature thermoplastic in the aircraft industry. Main applications include air and fuel valves, food tray containers, steering wheels, interior cladding parts and semi-structural components. PEI is selected for internal aircraft applications for its inherent flame retardancy and low smoke emissions. It also has excellent chemical resistance to fuels and fluids used in the aircraft industry.

  • PES and PSU are used primarily for aircraft interior and exterior components.

In the aerospace industry, high temperature thermoplastics are used to manufacture:

  • Airbus interior components
  • Bow-shaped luggage compartment retainers
  • Cable conduits
  • Cable clips
  • Ventilation wheels inside aviation fans
  • Suction manifold of aviation pumps
  • Electrical wire harnesses
  • Convoluted turbine
  • Wire insulation
  • Pump casings
  • Impellers, etc.



#3. Electrical and Electronics


Important trends that are driving the electrical / electronic industry, which are influencing plastic selection and performance include:

  • Thin-wall design, as a means of reducing cost.
  • The ability to meet more stringent technical specifications.
  • The desire for higher quality and reliability, driven by expected application lifetimes of 5-20 years.
  • Growing market requirements for flame retardant materials that are either halogen free, or have low halogen content.
  • Low warpage materials.
  • Design flexibility and design for manufacturing and assembly (DFMA).
  • Miniaturization, which increases the temperature and mechanical requirements of plastic materials.

Electrical ApplicationPolymers used for high heat electrical applications are:


These high heat polymers are used in electrical applications like:
  • Wire insulation for high temperature applications
  • Cable couplings and connectors
  • Sub-sea connectors
  • Coaxial connector jacks
  • Sub-sea controlled environment connectors
  • Wafer transport carriers
  • Surface mounted trimming
  • Potentiometers
  • Appliance handles
  • Electrical insulations
  • IC packaging trays, etc.

#4. Industrial Applications


Industrial applications are very demanding for plastics and are often found in hostile operating conditions. In particular, industrial applications require materials that can withstand sliding friction, high temperatures and have good chemical resistance. Machine elements, for example, are subject to sliding friction (slide bearings, rollers, thrust washers, piston rings, seals) for mechanical engineering, textile industry and office equipment.

Industrial machinery and equipment may have to operate at continuous high temperatures, and be required to have a high degree of resistance to chemicals.

High performance plastics are making inroads into industrial applications that were once the domain of metals and thermosets. Engineering and high performance plastics have a number of advantages over traditional materials due to their flexibility in parts design, ease of processing and lightness. They are also tough, abrasion resistant and can withstand high temperature. Continuous product improvement and innovation means that there will be further scope for growth in many areas of industrial applications in future.

Industrial ApplicationIndustrial applications of high heat thermoplastics include:
  • Impeller wheels for regenerative pumps
  • Pump rotors
  • Multi-pin connectors
  • Glue gun bushings
  • Quick coupling systems
  • Laundry system wheels
  • Conductivity sensors & seals
  • Compressor valve plates
  • Heat exchanger parts
  • Bearings


#5. Medical Applications


Medical ApplicationThe future prospects for high temperature thermoplastics growth in the medical devices market are excellent. Plastics will continue to replace traditional materials for medical devices because of their greater design flexibility and excellent cost/performance characteristics. Also, overall spending on medical devices is expected to show continued growth.

The following high temperature thermoplastics are majorly employed in medical applications:

  • Polyphenylsulfone (PPS)- for the development of sterilizable containers.
  • Polyetherimide (PEI)- for both disposable and re-usable medical devices
  • Polysulfones (PS) and Polyethersulfones (PES)- for parts and membranes for dialyzers; instruments; parts for instruments; surgical theater luminaries; sterilizing boxes; infusion equipment; secretion bottles and reusable syringes.
  • Liquid Crystal Polymers (LCP)- for replacing metal in medical devices in techniques of minimally invasive surgery and microsystem technology.
  • Polyetheretherketones (PEEK)- for replacing glass, stainless steel and other metals in a growing range of medical applications like dental instruments, endoscopes, dialyzers, handles on dental syringes and sterile boxes that hold root canal files.


Commercially Available Plastics with High Heat Resistance




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