Hello and welcome to the Part 2B of our High Performance Thermoplastics selection blog series. Today we discuss imide-based polymers and Polybenzimidazoles, their chemistry and production processes, their main properties, processing methods, and applications.
We will discuss six major high performance thermoplastics families (“the magnificent six”) which are outlined in the following enumeration
1. Introduction to High Performance Polymers
2. Short profile of the "magnificent six" families:
-Part 2B: Imide-Based Polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK)
-Part 2C: Polyether (PPE, PAEK, PEEK, PEKK)
-Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate - PCT)
-Part 2E: Semi- and Fully Aromatic Polyamides (PARA, PPA, Aramid)
-Part 2F: Polyhalogenolefins (PTFE, PCTFE, FEP, PVDF, ECTFE)
Imide-Based Polymers (PEI, PAI, PESI, TPI, PI)
Polyetherimide (PEI)
In the 1980s, Joseph G. Wirth developed PEI at General Electric’s Plastics Division and it found its way into the market as Ultem. When Saudi Basic Industries Corporation (SABIC) bought the GE Plastics business in 2007, it took over the PEI patents and continued its marketing and development.
Chemistry and Production Process
Polyetherimide (PEI) is an amorphous high-performance polymer known for its excellent thermal stability, mechanical strength, and electrical properties. Its chemical structure consists of aromatic rings linked by ether and imide groups. This unique structure contributes to its exceptional properties.
The production of PEI typically involves a multi-step process. One common method is the reaction between bisphenol A and trimellitic anhydride. This reaction forms a precursor, which is then subjected to thermal imidization to yield the final PEI polymer.
Main Properties
- Excellent Thermal Stability: PEI exhibits outstanding resistance to high temperatures, making it suitable for applications in harsh environments. The glass transition temperature (Tg) is at 217°C and the Relative Thermal Index (RTI) of PEI is 180°C.
- High Mechanical Strength: It possesses excellent tensile strength, flexural strength, and impact resistance.
- Good Electrical Properties: PEI offers good dielectric strength, arc resistance, and low moisture absorption, making it ideal for electrical and electronic applications.
- Chemical Resistance: It is resistant to a wide range of chemicals, including acids, bases, and solvents. PEI is able to retain its strength and resist stress corrosion cracking when exposed to aliphatic hydrocarbons, alcohols, automotive and aircraft fluids, acids, weak aqueous solutions , and acids.
- Flame Retardancy: PEI is inherently flame-retardant, reducing the risk of fire hazards.
- Transparent: PEI can be colored, both transparent and opaque.
- Biocompatibility: For example Ultem 1010 is biocompatible and it holds NSF 51 certification for food contact. Additionally, it is capable of withstanding steam sterilization.
- Alternative to Sulfones: PEI is an alternative to replace Polysulfones in certain applications. PEI has a higher UV resistance compared to PSU, PESU, and PPSU. Also, PEI has good mechanical properties, together with low moisture uptake and higher dimensional stability. Figure 1 compares the properties of PEI and Polysulfones (PSU, PESU, and PPSU).
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| Figure 1: Property comparison of PEI vs Polysulfones (PSU, PESU, PPSU). |
- Low smoke generation: in case of burning, PEI generates low amounts of smoke, making it an ideal interior material for railway, aeroplanes, and aerospace applications. Additionally, it shows low toxicity making it a material which performs excellent in Flame, Smoke, Toxicity (FST) tests.
- Flexible: PEI is flexible and can be used in simple spring applications as well as for frame in eyewear.
Processing Methods
PEI can be processed using various methods, including:
- Injection Moulding: This method is commonly used to produce complex parts with high precision.
- Extrusion: PEI can be extruded into films, sheets, and profiles.
- Thermoforming: This process allows for the shaping of PEI sheets into various forms.
- Additive manufacturing: apart from the costly materials such as PEEK and PEKK for 3D printing, the amorphous PEI is a more economic alternative. It is used as a filament for FDM 3D printers, and it is compatible with high-performance FDM/FFF printers (incl. Stratasys printers).
Applications
PEI's exceptional properties make it suitable for a wide range of applications:
- Electronics: It is used in printed circuit boards, connectors, and other electronic components due to its excellent electrical properties and thermal stability.
- Aerospace: PEI is employed in aircraft components, such as engine parts and structural elements, owing to its high temperature resistance and mechanical strength.
- Automotive: It is used in automotive components, including under-the-hood parts, due to its resistance to heat, chemicals, and mechanical stress.
- Medical Devices: PEI's biocompatibility and sterilisation resistance make it suitable for medical devices like surgical instruments and medical device housings.
- Food Processing Equipment: Its chemical resistance and high temperature tolerance make it ideal for food processing equipment.
Main manufacturer and trade names
SABIC: Ultem™ PEI, Siltem™ polyetherimide(PEI)-siloxane copolymer, Extem™ amorphous PI
Economic Aspects
PEI is a high-performance polymer, and its cost is generally higher than that of more common plastics. However, its exceptional properties often justify the higher cost, especially in demanding applications where performance is critical.
In conclusion, Polyetherimide (PEI) is a versatile high-performance polymer with excellent thermal, mechanical, and electrical properties. Its wide range of applications, coupled with its superior performance, makes it a valuable material in various industries.
Polyamide-Imide (PAI): An amorphous high-performance polymer which can be still melt processed
Polyamide-Imide (PAI) is an extremely strong, rigid and wear-resistant high performance polymer with use temperature form -200°C till up to 260°C. Additionally, PAI can keep its mechanical properties over the whole use temperature range and is not melting when reaching the glass transition temperatures. Reason is a post curing process after processing turning the material into a thermoset-like structure. In 1973, chemical company Amoco introduced PAI as Torlon® to the market. Nowadays, the newly formed chemical company Syensqo, which routes back to Ernest Solvay and the Solvay company, produces and market this high performance polymer.
Chemistry and Production Process
Polyamide-imide (PAI) is a high-performance polymer that combines the properties of polyamides (nylons) and polyimides. It is synthesized through a multi-step process involving the reaction of diamines with dianhydrides. The resulting polymer chains have alternating amide and imide groups, providing a unique combination of properties.
Main Properties
PAI exhibits a remarkable set of properties:
- High Temperature Resistance: With a glass-transition temperature (Tg) of 275°C, PAI can withstand continuous use at temperatures up to 260°C and short-term exposure to even higher temperatures.
- Excellent Mechanical Properties: It offers high tensile strength, flexural modulus, and impact resistance.
- Chemical Resistance: PAI is resistant to a wide range of chemicals, including acids, bases, and solvents.
- Good Electrical Properties: It has low dielectric constant and dissipation factor, making it suitable for electronic applications.
- High compressive strength: PAI has a compressive strength which is double that of PEEK when unfiled. Compared to PEI it is about 40% higher.
- Extreme low wear and friction: PAI has a dynamic friction coefficient around 0.4; by adding additives such as graphite, it can be lowered to 0.3.
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| Figure 2: Wear during dry running of PAI vs PI and PTFE. |
- Flame Retardancy: PAI is inherently flame-retardant, reducing the risk of fire.
- Dimensional Stability: It exhibits excellent dimensional stability, maintaining its shape even at high temperatures. It has a low thermal expansion, even with reinforcements (low CLTE values).
- Moisture uptake: PAI absorbs water up to 3.5%, however with a controlled curing process, water can be removed and extreme dimension stable parts in injection moulding with only 1% shrinkage.
Processing Methods
Due to its high melting temperature, PAI is typically processed using specialized techniques:
- Injection Moulding: High-temperature injection moulding machines are required to process PAI.
- Extrusion: PAI can be extruded into films, sheets, and profiles.
- Compression Moulding: This technique is suitable for complex shapes and parts with a diameter larger than 25 mm.
- Machining: PAI can be machined for creating prototype parts or precision finished parts.
Applications
PAI's exceptional properties make it suitable for a wide range of applications:
- Aerospace: Components like engine parts, hydraulic systems, and structural elements.
- Automotive: High-temperature components such as engine covers, turbocharger housings, and under-hood components.
- Electronics: Printed circuit boards, connectors, and electronic packaging.
- Industrial Machinery: Bearings, gears, and other high-performance components.
- Medical Devices: Sterilizable components and peristaltic pump rollers and bushings for prosthetics (long life due to low wear).
Trade Names and Economic Aspects
- Syensqo (former Solvay): Torlon PAI
The cost of PAI is higher than that of many other engineering plastics due to its complex manufacturing process and high-performance properties. However, its long-term durability and reliability often offset the initial cost.
Polyamide-imide (PAI) is a versatile high-performance polymer that offers a unique combination of properties. Its excellent thermal, mechanical, and chemical resistance make it a valuable material for demanding applications across various industries.
Polyimides (PI): A Versatile Polymer
Introduction
Polyimides (PIs) are a class of high-performance polymers renowned for their exceptional thermal and chemical resistance, mechanical strength, and electrical insulation properties. PIs show a wide range of use temperatures, from cryogenic up to 400°C and the mechanical properties remain the same in this range. PIs combine low thermal expansion, high wear resistance, and low creeping with high purity and low off-gassing. Their unique combination of properties makes them indispensable in a wide range of applications, from aerospace and electronics to automotive and medical industries.
Chemistry and Production Process
- Chemistry: PIs are synthesized through a two-step process involving the reaction of a dianhydride with a diamine. This reaction, known as polycondensation, results in the formation of a polyamic acid, an intermediate product. The polyamic acid is then subjected to thermal or chemical imidization to form the final polyimide.
- Production Process:
1. Monomer Synthesis: High-purity dianhydrides and diamines are synthesized through various chemical processes.
2. Polymerization: The monomers are reacted in a suitable solvent to form a polyamic acid solution.
3. Imidization: The polyamic acid solution is converted into polyimide through thermal curing or chemical imidization. Thermal curing involves heating the solution to drive off water and form the imide rings. Chemical imidization uses a dehydrating agent to accelerate the process.
4. Processing: The polyimide can be processed into various forms, such as films, fibers, coatings, and composites, depending on the desired application.
Main Properties
- Excellent Thermal Stability: PIs exhibit outstanding thermal stability, with heat deflection temperatures above 300°C and decomposition temperatures above 400°C. No softening and glass transition temperature can be noticed. SHort term use temperatures are up to 500°C. PI behaves like a thermoset with a linear property profile over the whole temperature range.
- Chemical Resistance: They are resistant to a wide range of chemicals, however they can be attacked by strong acids, and bases. PIs are hygroscopic and are not resistant towards hydrolysis.
- Mechanical Strength: PIs possess high tensile strength, flexural strength, and impact resistance.
- Electrical Insulation: They are excellent electrical insulators with low dielectric constants and high dielectric strength.
- Flame Retardancy: Many PIs are inherently flame-retardant.
Processing Methods
- Solution Processing: Polyimide solutions can be cast into films, coated onto substrates, or spun into fibers.
- Press-sintering: is used for making higher amounts of parts; otherwise cutting the part out of semi-finished shapes is done.
- Melt processing: thermoplastic Polyimides (TPIs) are injection moldable and extrusion prossable PIs. The major two commercially available are Ultem PEI (PI based on bisphenol A bisether-4-diphthalic anhy-dride [BEPA]) and Aurum TPI (PI based on Pyromellitic dianhydride [PMDA]). Aurum TPI has a Tg of 245°C.
- Copper enamel coating: Polyesterimides (PEsI) are used for wire enamel with excellent thermal properties. These kinds of wires are widely used for compressors, washing machine motors, explosion-proof motors, dry transformers, and electric tools.
- Additive Manufacturing: PIs are being explored for 3D printing applications, enabling the fabrication of intricate components.
Applications
- Electronics: PIs are used in flexible printed circuit boards, high-temperature wire insulation, and semiconductor packaging (combination of high dielectric strength with low dissipation factors at various frequencies makes it a excellent insulation material)
- Aerospace: They are employed in aircraft components, such as engine seals, heat shields, and structural reinforcements.
- Automotive: PIs are used in engine components, electrical connectors, and thermal insulation.
- Medical Devices: They are used in medical devices, catheters, and drug delivery systems.
- Other Applications: PIs find applications in various industries, including energy storage, filtration, and protective coatings.
Trade Names and Economic Aspects
- DuPont: Vespel® S, SP, SCP, and Kapton®
- Mitsui: Aurum® TPI
The global polyimide market is growing steadily, driven by increasing demand from electronics, aerospace, and automotive industries. However, the high cost of raw materials and complex manufacturing processes can limit the widespread adoption of PIs.
In conclusion, polyimides are a versatile class of high-performance polymers with a wide range of applications. Their unique combination of properties, including exceptional thermal and chemical resistance, mechanical strength, and electrical insulation, makes them indispensable in many industries.
Polybenzimidazole (PBI) - the ultra high performance plastic which was developed in cooperation with NASA
Polybenzimidazole (PBI) is a high-performance polymer known for its exceptional thermal stability, chemical resistance, and mechanical properties. Its unique structure, consisting of a repeating benzimidazole unit, imparts these remarkable characteristics. It was developed in cooperation with NASA to have a lightweight, high heat, low friction, high chemical and radiation resistant polymer which can be used in space and aircraft applications. Nowadays the application field of PBI is much broader and it is used in electric & electronic appliances too. Its unique structure, consisting of a repeating benzimidazole unit, imparts these remarkable characteristics. PBI has a glass transition point of 427°C and its high purity makes it ideal for cable insulation powder coatings, friction parts and housings.
Chemistry and Production
PBI is synthesized through a condensation polymerization reaction between a diamine, typically 3,3′-diaminobenzidine, and a dicarboxylic acid, such as terephthalic acid or isophthalic acid. The reaction involves the formation of amide bonds between the amine and carboxylic acid groups, leading to the formation of the PBI polymer chain.
The production process of PBI typically involves the following steps:
1. Monomer Preparation: The diamine and dicarboxylic acid monomers are purified to remove impurities that could affect the polymerization reaction.
2. Polymerization: The purified monomers are combined under controlled conditions, such as temperature, pressure, and solvent, to initiate the polymerization reaction.
3. Polymer Isolation: The resulting PBI polymer is isolated from the reaction mixture through techniques like filtration or precipitation.
4. Purification: The polymer is further purified to remove any residual monomers or byproducts.
5. Processing: The PBI polymer is processed into various forms, such as fibers, films, or composites, depending on the desired application.
Properties of PBI
PBI exhibits a range of properties that make it suitable for demanding applications:
- Thermal Stability: PBI possesses excellent thermal stability with a glass transition temperature of 427°C, capable of withstanding temperatures up to 500°C without significant degradation. This property is attributed to the aromatic nature of the benzimidazole unit and the strong intermolecular forces between polymer chains. Figure 3 shows an overview of the PBI and PBI blends as well as PBI compounds with their glass transition temperature.
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| Figure 3: Overview Tg of PBI, PBI blends, and PBI compounds [2]. |
- Chemical Resistance: PBI is highly resistant to a variety of chemicals, including acids, bases, and solvents. This makes it ideal for applications in corrosive environments and applications where high temperatures and aggressive chemicals are combined present.
- Mechanical Properties: PBI offers good mechanical properties, such as tensile strength, modulus, and toughness. Its mechanical performance can be further enhanced through reinforcement with fibers or other materials.
- Wear resistance: PBI has low friction properties with a coefficient of friction of 0.4. The wear of PBI is low too. The PBI grade Celazole TL-60 is a very good wear grade material, reaching a PV of 225,000 psi-ft/min at 200 fpm.
- Flame Resistance: PBI is inherently flame-resistant and can be used in applications where fire safety is a critical concern.
- Barrier Properties: PBI can serve as an effective barrier to gases and vapors, making it useful in applications such as filtration and gas separation.
Processing Methods
PBI can be processed using various methods, depending on the desired form and properties:
- Solution Processing: PBI can be dissolved in suitable solvents and processed into films, coatings, or fibers through techniques like casting, spinning, or printing.
- Melt Processing: Although PBI has a high melting point, it can be processed using melt-spinning or melt-extrusion techniques under specific conditions. Also blending PBI with PEEK and PEKK enables processing in injection moulding and extrusion.
- Composite Processing: PBI can be combined with other materials to form composites, such as carbon fiber-reinforced PBI, which offer enhanced mechanical properties and thermal stability.
- Compression moulding: can be used to make semi-finished shapes such as rods, films, sheets, and tubes.
Applications of PBI
PBI's unique combination of properties makes it suitable for a wide range of applications, including:
- High-Temperature Applications: PBI is used in components for aerospace isolations, aircraft engines, industrial furnaces, and heat exchangers due to its exceptional thermal stability.
- Chemical Processing: PBI is used in chemical processing equipment, such as filters, gaskets, and valves, due to its chemical resistance.
- Protective Clothing: PBI is used in protective clothing for firefighters, industrial workers, and military personnel due to its flame resistance and thermal protection.
- Gas Separation: PBI membranes are used in gas separation processes to selectively separate different gases.
- Fuel Cells: PBI is used as a polymer electrolyte membrane in fuel cells, enabling efficient energy conversion.
Trade Names and Economic Aspects
There is only one major company producing the polymer PBI and offering it under various trade names, including:
- PBI Polymer: Celazole(R)
- PBI Advanced Materials (PBi-am; SATO Group): 7000 series
The market for PBI is relatively small compared to other polymers, but it is expected to grow due to increasing demand in niche applications. The economic aspects of PBI production and processing are influenced by factors such as the cost of raw materials, energy consumption, and market demand.
Conclusion
PBI is a high-performance polymer with exceptional properties that make it suitable for demanding applications. Its thermal stability, chemical resistance, and mechanical properties have led to its use in various industries, including aerospace, chemical processing, and protective equipment. As the demand for high-performance materials continues to grow, PBI is expected to play an increasingly important role in various technological advancements.
In the upcoming Part 2C we will discuss the Polyether high performance polymers such as PPE, PAEK, PEEK, and PEKK.
Thanks for reading & #findoutaboutplastics
Greetings,
Herwig Juster
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Literature:
[1] https://pbipolymer.com/wp-content/uploads/2016/05/Polymer-Protects-Firefighters-Military-Civilians.pdf
[2] https://www.pbi-am.com/en/base-polymers/pbi
[3] Dynamic Mechanical Analysis of High Temperature Polymers, Ning Tian, Aixi Zhou, The University of North Carolina
[4] https://pbipolymer.com/wp-content/uploads/2021/07/Dynamic-Mechanical-Analysis-High-Temperature-Polymers.pdf
[5] https://pbipolymer.com/wp-content/uploads/2016/05/High_PV_Wear_Study_of_Six_High_Performance_Polymers.pdf
[6] https://www.pbi-am.com/en/base-polymers/pbi
[7] https://www.sabic.com/en/products/specialties/ultem-resin-family-of-high-heat-solutions/ultem-resin
[8] https://www.3dnatives.com/en/ultem-030820204/#!
[9] https://www.ensingerplastics.com/en/thermoplastic-materials/torlon-pai-polyamid-imide
[10] https://www.researchgate.net/publication/329955339_Thermoplastic_Polyimide_TPI
[11] https://pmc.ncbi.nlm.nih.gov/articles/PMC7240679/
[12] https://www.sciencedirect.com/science/article/abs/pii/S001191642400211X#:~:text=Nanofiltration%20(OSN).-,Abstract,temperatures%2C%20and%20low%20fuel%20crossover.
