Plastics can be classified into general plastics, engineering plastics and high-temperature engineering plastics according to their long-term use temperature. High-temperature plastics are also called heat-resistant plastics, high-performance plastics, special engineering plastics, etc.

 

General plastics have a long-term use temperature below 100℃. Usually including PE, PP, PS, PVC, ABS. General plastics are the largest type of plastics used in our daily life, usually used for packaging, daily necessities, toys, etc.
Long-term use temperature of engineering plastics is around 100℃ to 150℃. Five major engineering plastics include PA, POM, PBT, PC and PPO. They are usually used in mechanical parts, automobiles, electrical appliances and electronics, etc.
Use temperature of high-temperature engineering plastics is above 150℃. In addition to high heat resistance and flame retardancy, these materials usually have excellent mechanical processing performance, aging resistance, dimensional stability and excellent electrical properties. It can be used to replace metal materials and is widely used in electronics, aerospace, medical equipment, automobiles, and military fields. It is material at the top of plastic pyramid.
Common high-temperature engineering plastics are divided into following 8 categories:

Fluoroplastics (Fluoroplastie) refers to plastics made of fluorine resin. Common main varieties include polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer (ETFE), polyperfluoroethylene propylene (FEP), polyvinylidene fluoride (PVDF), etc. Operating temperature is between 150℃-260℃.

 

For example, so-called king of plastics, polytetrafluoroethylene (Teflon), has following characteristics:
(1) High chemical stability: It has good chemical inertness, and strong acids, strong alkalis or strong oxidants and organic solvents have no effect on it.
(2) Good thermal stability: Cracking temperature is above 400℃, so it can work normally in temperature range of -200℃ to 300℃.
(3) Good anti-friction property: Friction coefficient between PTFE materials is 0.1-0.2, dry friction coefficient between PTFE materials and metal is 0.2-0.3, and dry friction coefficient with liquid lubrication is 0.02-0.04. Its dynamic and static friction coefficients are relatively small, and its initial friction coefficient is almost same as dynamic friction coefficient.
(4) Excellent self-lubrication: Surface of PTFE materials has outstanding surface self-lubrication, and almost all sticky substances cannot adhere to its surface.

Polyaryletherketone (PAEK) is a polymer whose main chain is composed of phenylene rings connected by ether bonds and ketone bonds. According to number and order of ether groups and ketone groups, it can be divided into polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), etc.

PEEK is a special engineering plastic with excellent comprehensive performance. It has excellent heat resistance, water resistance, solvent resistance, and electrical insulation; high fatigue strength; the best radioactivity resistance among all plastics; high oxygen index, less smoke and non-toxicity when burning.
PEEK, top product in engineering plastics industry
Polyetheretherketone (PEEK) is an ultra-high performance special engineering plastic developed by British Imperial Chemical Industries (ICI) in 1978. Since PEEK is an aromatic crystalline thermoplastic polymer material with a melting point of 334℃, it has high mechanical strength, high temperature resistance, impact resistance, flame retardancy, acid and alkali resistance, hydrolysis resistance, wear resistance, fatigue resistance, radiation resistance and excellent electrical properties. In most cases, it can replace metals, alloys, ceramics and other materials. Although it is a compound material, it does not produce non-toxic gases when burning, so today, when green and environmentally friendly design is advocated, its application field has been rapidly expanded.
01 Molecular structure of PEEK

 

02 Characteristics of PEEK
(1) High temperature resistance: PEEK has a high glass transition temperature (Tg=143℃) and melting point (Tm=343℃). Its load heat deformation temperature is as high as 316℃, long-term use temperature is 260℃, and instantaneous use temperature can reach 300℃.
(2) Self-lubricating property: PEEK has good sliding properties and is suitable for occasions with strict requirements for low friction coefficient and wear resistance. In particular, PEEK modified with carbon fiber, graphite, and PTFE has excellent wear resistance.
(3) Corrosion resistance: PEEK is insoluble in any solvent except concentrated sulfuric acid and has high chemical stability.
(4) Flame retardancy: PEEK is self-extinguishing and can reach UL standard 94V-0 level even without any flame retardant.
(5) Processability: Due to its good high-temperature fluidity and high thermal decomposition temperature, PEEK can be processed in a variety of ways, such as injection molding, extrusion molding, compression molding and melt spinning.
(6) Mechanical properties: PEEK has good toughness and rigidity, and it has excellent fatigue resistance comparable to alloy materials.
(7) Electrical properties: PEEK has high volume resistivity and surface resistivity, can withstand AC potential field strengths of various frequencies under a wide temperature range and environmental changes, maintaining good insulation properties.
(8) Hydrolysis resistance: Resins and their composite materials are not chemically affected by water and high-pressure steam, can be used continuously under high temperature and high-pressure steam or water environments while maintaining good mechanical properties.
(9) Weather resistance: With excellent weather resistance, polymers can be used to manufacture components with strict working environment requirements or that require frequent sterilization treatment.

Comparison of PEEK and several typical high-temperature resistant plastics
Application of PEEK
PEEK materials have been developed abroad for decades and are widely used in automotive, military, medical, aviation, electrical and other industries. However, its relatively high price has long limited its penetration into general civilian market. It is currently mainly used in aerospace, high-end industry and medical fields.
Aerospace
PEEK can replace aluminum and other metal materials to manufacture aircraft parts, reducing weight by up to 70% compared to metal and improving fuel efficiency. Currently, Boeing, Airbus and other companies have adopted PEEK materials on a large scale.
Medical
PEEK has advantages of being non-toxic, lightweight, corrosion-resistant, and has excellent biocompatibility. It is a highly promising bioprosthetic material. It is used for intervertebral fusion devices, medical catheters, bones, etc.
Energy
PEEK is specially used in high-temperature, high-pressure and chemically corrosive environments, which can expand the scope of oil and gas exploration. It can be used to manufacture annular and mesh valve plates for hydrogen compressors and LPG compressors on large petrochemical production lines. In addition, PEEK can also be used for nuclear power components.
Automobile
PEEK has excellent mechanical properties and excellent chemical corrosion resistance to automotive working fluids, good wear resistance, etc. It is widely used in automotive gears, vacuum pumps, clutches, valve cones, etc., to improve fuel efficiency and increase durability.
Food and Beverage Industry
PEEK can be used for food processing, storage, cooking equipment parts and water, beverage transmission, storage equipment, such as pipes, valves, containers, etc.
Electronic and Electrical
PEEK has excellent electrical properties and is an ideal electrical insulator. It can still maintain good electrical insulation under harsh environments such as high temperature, high pressure and high humidity. It is used to manufacture chip carriers, insulating diaphragms, printed circuit boards, high-temperature connectors and various electrical connectors. PEEK film can be used for micro speaker diaphragms, 5G RF antenna substrates, etc.

Because proportion of ether bonds and ketone groups in its molecular structure is lower than that of PEEK, its melting point and glass transition temperature are higher than PEEK, and its heat resistance is better than PEEK, with a continuous use temperature of 250℃.

PEKK, whose Chinese name is polyether ketone ketone, is a high-performance material. This material has a high melting point of about 300℃ to 600℃, has strong chemical resistance and wear resistance. In recent years, application of PEKK in the field of 3D printing has made rapid progress, and it has better performance than traditional 3D printing materials.

 

PEKK is used in 3D printing

High temperature nylon is divided into three categories:

PA46 is an aliphatic polyamide formed by polycondensation of diaminobutane and adipic acid. Compared with PA6 and PA66, PA46 has more amides on each given length of chain and a more symmetrical chain structure, which makes its crystallinity as high as 70% and gives it a very fast crystallization speed.
Melting point of PA46 is 295℃, and HDT (heat deformation temperature) of unreinforced PA46 is 160℃. After being reinforced with glass fiber, its HDT can be as high as 290℃, and long-term use temperature is also 163℃. Unique structure of PA46 gives it unique properties that other materials cannot achieve.
PA46 is mainly used in electronics, aerospace, and automobiles.

 

PPA is formed by polycondensation of dibasic acid containing benzene ring and aliphatic diamine. Its melting point is between 310-325℃ and its heat deformation temperature is between 280-290℃. Main varieties are PA4T, PA6T, PA9T, PA10T, etc.
Compared with ordinary PA66, PPA has a very low water absorption rate. Even if it is soaked in cold water for several years, its tensile strength can be maintained at more than 80%. PPA has good oil resistance and has extremely high resistance to lubricating oil and fuel even at high temperatures. PPA also has excellent dimensional stability and weather resistance.
Commonly used in automobiles, electrical and electronic, mechanical industry, and daily necessities.

 

Connector

PARA was invented by DuPont, the most famous of which are Nomex (polyisophthalamide, also known as aramid 1313) and Kevlar (full para-polyaramid, also known as aramid 1414).
This type of material is mainly used to prepare high-performance fibers and sheets. Fibers made have characteristics of high strength, high rigidity, high modulus, high heat resistance and high dielectric strength.
It can be applied to super-strong fibers and reinforcement materials, used in military, aviation and aerospace structural parts. Aramid 1414 can be used in bulletproof vests, and Solvay PARA is used in disposable surgical instruments.

Polyphenylene sulfide (PPS) is the fastest-growing and most widely used special engineering plastic in recent years. It has excellent high temperature resistance, chemical resistance, weather resistance, flame retardancy, electrical properties, good dimensional stability and other advantages. It is widely used in automobiles, electronics and electrical, machinery, petrochemicals, pharmaceuticals, light industry, military, aerospace, 5G communications and other fields. It is the most widely used special engineering plastic.

 

PPS is also the most domestically produced special engineering plastic in China, with a self-sufficiency rate of more than 80%.
According to incomplete statistics, production capacity of major global polyphenylene sulfide (PPS) companies exceeds 200,000 tons. From perspective of capacity distribution, current global polyphenylene sulfide (PPS) industry capacity is mainly concentrated in Japan and China.
Summary of capacity of major PPS companies as of 2021

Traditional PPS giants such as DIC, Toray, Solvay, and Kureha are still relatively advanced in PPS production and technology. Capacity of these four companies accounts for more than 56% of global capacity. However, Chinese companies are showing a rapid rise. Domestic companies such as Zhejiang Xinhecheng and Chongqing Jushi have formed large-scale production, and many other companies have already mass-produced or are planning to layout.

Polyimide (PI) is an aromatic heterocyclic polymer compound with an imide chain link in its molecular structure. It is one of the most heat-resistant varieties of engineering plastics at present. It can withstand extreme temperatures, with a thermal decomposition temperature of up to 600℃, and will not brittle in liquid helium at -269℃. In addition, it also has excellent mechanical properties, acid and alkali resistance, biocompatibility and electrical properties.

 

Polyimide is used for high-performance parts
Polyimide engineering plastics can be divided into both thermosetting and thermoplastic types, such as polymellitic imide (PMMI), polyetherimide (PEI), polyamide-imide (PAI), etc., and have their own uses in different fields.
PMMI has a heat deformation temperature of 360℃ under a load of 1.8MPa, and has excellent electrical properties. It can be used for precision parts under special conditions, high-temperature resistant self-lubricating bearings, seals, blower impellers, etc. It can also be used for valve parts in contact with liquid ammonia, and jet engine fuel supply system parts.
PEI has excellent mechanical properties, electrical insulation properties, radiation resistance, high temperature resistance and wear resistance, good melt fluidity, and a molding shrinkage rate of 0.5% to 0.7%. It can be molded by injection and extrusion, and is easy to post-process. It can also be combined with other materials by welding. It is widely used in industries such as electronics, aviation, automobiles, and medical devices.
PAI has the highest strength among current non-reinforced plastics, with a tensile strength of 190MPa, a flexural strength of 250MPa, and a heat deformation temperature of up to 274℃ under a load of 1.8MPa. PAI has good ablation resistance and electromagnetic properties at high temperature and high frequency, has good bonding properties to metals and other materials. It is mainly used for gears, bearings, and copier separation claws, etc. It can also be used for ablative materials, magnetically permeable materials, and structural materials for aircraft.

PSU is a slightly amber, amorphous, transparent or translucent polymer with excellent mechanical properties, high rigidity, wear resistance, and high strength. Its outstanding advantage is that it maintains excellent mechanical properties even at high temperatures; its range is -100~150℃, long-term use temperature is 160℃, and short-term use temperature is 190℃.
Polysulfone includes ordinary bisphenol A type PSU (commonly known as PSU), polyphenylsulfone, and polyethersulfone.
1. Molecular formula of ordinary bisphenol A type PSU:

 

Conjugation effect of sulfone group provides antioxidant and thermal stability; ether chain improves toughness, benzene ring ensures its mechanical strength and modulus.
2. Molecular formula of polyphenylsulfone PPSU:
Benzene ring on main chain of polyphenylsulfone provides high heat resistance and mechanical properties; ether bond provides excellent fluidity and processing performance.
3. Molecular formula of polyethersulfone PESU:
Ether group provides flexibility and high fluidity, sulfone group provides heat resistance, and phenylene group provides rigidity.
Comparison of performance of bisphenol A type polysulfone, polyarylsulfone, and polyethersulfone

 

Polyarylate (PAR) is a thermoplastic resin containing benzene ring and ester bond on main chain. PAR has good light transmittance (nearly 90%), toughness, heat resistance, elastic recovery, weather resistance and flame retardancy, and continuous use temperature can reach up to 170℃. It is mainly used in precision devices, automobiles, medical treatment, food and daily necessities.
PAR is used for car lamp parts
PAR has a similar structure to PC, and its performance is roughly same. It can be molded using same mold, but high density of aromatic rings on main chain of PAR makes PAR better in heat resistance than PC. Its heat deformation temperature is 20~40℃ higher than PC, it has excellent UV resistance and creep resistance. However, its elongation at break and impact resistance are not as good as polycarbonate.

 

Performance comparison of PAR and PC

 

LCP is called liquid crystal compound in Chinese. So-called "liquid crystal" has both fluidity of liquid and orderly arrangement of crystal molecules in molten state.
Chinese name of LCP is liquid crystal compound. So-called "liquid crystal" is a substance that has both fluidity of liquid and orderly arrangement of crystal molecules in molten state.

 

LCP has excellent mechanical properties. The biggest feature is that as wall thickness becomes thinner, relative strength increases. LCP has good thermal properties and continuous use temperature can reach 200℃-300℃.
LDS-LCP material for mobile phone antennas
LCP has very small dielectric constant and dielectric loss, so it is used in electronic devices such as connectors, slots, switches, brackets and sensors. The most widely studied application is application of mobile phone 5G antennas.