Guide to use, structure and materials (2023)

What are high temperature thermoplastics?

High temperature thermoplastics are a specialized and fast-growing segment of the plastics market. Today, the market for high-temperature melt-processable thermoplastics encompasses several polymer families, and each family consists of several types of polymers. In the plastics industry, terms such as "alta performance", "technical polymers", E "Standard" or "crazy"Plastics to describe the applications of these materials.

These are processable thermoplastic plastics. They have durable structural capabilities at service temperatures above 150°C and short term service at temperatures above 250°C. These materials require a combination of exceptional properties.

Depending on their application, they must exhibit superior short- and long-term thermal stability, chemical and radiation resistance, flame resistance, and superior mechanical properties, often similar to those of metals.

Another differential of high-temperature thermoplastics is their cost, which is on average ten times higher than that of the most common plastics. It is not just the excellent temperature stability of these polymers that has attracted interest and led to the relatively high growth rate. In many applications, its chemical resistance, wear resistance and other performance properties are valued even more than heat resistance. Sometimes these high temperature thermoplastics are also called "high performance plastics".

What makes them thermally resistant?

High temperature thermoplastics generally get their temperature resistance from theIntroduction of rigid aromatic ringsinstead of aliphatic groups in its molecular structure. This restricts main chain movement and requires two chemical bonds (compared to one in aliphatic structures) to be broken for a chain break, as shown in the figure below:

Degradation of an aromatic and straight-chain polymer by thermal aging

Therefore, the mechanical properties, high temperature capability and chemical resistance are greatly improved, and can often be equal to or even better than cross-linked thermosetting polymers.

How to improve the performance of high temperature plastics?

High temperature thermoplastics are used in special applications that require a combination of exceptional properties. Depending on their application, they must exhibit superior short-term and long-term thermal stability, chemical and radiation resistance, flame resistance, and superior mechanical properties that are often equated with metals.

Guide to use, structure and materials (2)

High temperature thermoplastics are subject to significant improvementaboveComposition and Modifications. By using special reinforcing materials such as glass fibers, heat resistance and stiffness can be further improved compared to the base polymer. Additives such as fluorocarbon or graphite particles significantly improve the sliding friction properties.

Classification of high temperature thermoplastics

These versatile high temperature thermoplastic resins are used in numerous applications across multiple industries. A pictorial classification of high temperature thermoplastic resins is shown below.

High temperature thermoplastic resins are generally classified by acontinuous use temperature(CUT) orrelative thermal index(RTI) superior a 150°C.

These temperatures are considered the maximum usable service temperature for materials where a critical property is not unacceptably affected by 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 begin to thermally decompose.

A plastic that softens at a high temperature but begins to decompose at a lower temperature is only used below the temperature at which it begins to decompose.

The actual maximum continuous use temperature depends on how you define "continuous use". Time and load affect the response, as does the exact structure of the polymer and which additives, modifiers or boosters can be used.

Each high temperature thermoplastic resin has its own advantages and disadvantages in terms of processing characteristics and performance characteristics. Selection of a high temperature thermoplastic resin comes down primarily to balancing these application benefits and limitations and the associated costs.

Despite the high average price compared to other engineering plastics and the current turbulent situation in world markets, high temperature thermoplastic resins are still considered one of the fastest growing segments of the plastics industry. Today, the high temperature thermoplastic resin market includes a variety of polymers, which mainly include melt-processable polyimides, sulfone polymers, polyaryletherketones, polyphenylene sulfide, etc.

Thermoplastic structures for high temperatures

High temperature thermoplastics (like all polymers) comprise two molecular structures: amorphous (randomly ordered) and crystalline (highly ordered). For practical reasons, thermoplastics are amorphous polymers or semicrystalline polymers that have both amorphous and crystalline regions.

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

Type	thermal characteristics	examples	Characteristics
amorphous	Has a melting range rather than a defined melting point Wide range of glass transition temperature	polysulfona Polyetherimide Polyphenylsulfone	strength, stiffness Isotropic dimensional stability toughness and impact resistance clarity good surface optics
semicristalino	Well-defined melting point and glass transition temperature	Polyphenylensulfeto liquid crystal polymer Polyetheretherketone Poliftalamida	chemical resistance wear resistance Lower ductility and impact resistance Opaque Low stiffness and creep resistance at high temperatures Low dimensional stability

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

Advantages and disadvantages of high temperature plastics

High temperature plastics vs. metals

have high temperature thermoplasticscontinuous operating temperaturesabove 150°C. However, its high temperature resistance properties offer other valuable performance characteristics.

These include wear and chemical resistance. High temperature plastics also offer weight savings in many applications (eg automotive) and are therefore often considered as metal substitutes. Table 2 summarizes the advantages and disadvantages of high temperature thermoplastics over metals.

advantages over metals	Disadvantages compared to metals
low density Good noise and vibration damping Electrical and thermal insulation or adjustable conductivity Good chemical and corrosion resistance Greater design freedom Adaptable to high-volume production processes Adaptable to property changes for specific applications	Greater thermal expansion Low creep resistance Lower thermal resistance Vulnerable to UV, moisture and oxidation Does not count as a vapor barrier inferior mechanical properties Plastic parts often need to be re-engineered relative to metal parts

High temperature thermoplastics vs. thermosets

Heat resistant thermoplastics are also often considered as substitutes for thermosetting polymers such as epoxy, phenolic, polyester, etc. The main advantages and disadvantages of high temperature thermoplastics compared to thermosets are summarized in the table below. They have good thermal stability because they have a high glass transition temperature Tg. They also exhibit excellent toughness and high ductility, which is reflected in high elongation at break and low moisture absorption. In general, the mechanical properties of pure thermoplastic resins are comparable and many times better than those of thermosets.

Property	thermosetting resin	thermoplastic resin
melt viscosity	Low	hoch
machining cycle time	Lang	Kurz
processing temperature and pressure	low to moderate	hoch
mechanical properties	fair to good	fair to good
toughness	Low	medium high
Moisture resistance	Relatively bad, depending on the resin	Generally high, depending on the resin
to sneak	intestine	Arm

Comparison between pure thermosetting resins and high temperature thermoplastics
The high Tg of high temperature thermoplastics results in high melt viscosities that can make it difficult to compound and process them into finished parts. High processing temperatures usually close todecomposition temperatureare needed to lower the viscosity of the melt. For example, polyimides exhibit very high Tgs, but their melt processability is considered poor. The development of very fluid, high temperature thermoplastics that have improved performance properties is a matter of continuous development in the industry.