The Secret of High Performance Polymers: Why They Can Handle High Heat and Harsh Chemicals?

In this blog post, we explore the reasons why high performance polymers can handle high heat and harsh environmental conditions over a long period of time. 

Definition of high performance polymers 

There are several definitions for high performance polymers. One good way to define high performance polymers is over the Underwriters Laboratory (UL) Relative Thermal Index (RTI). According to the UL 746B, high heat polymers need to withstand a continuous use temperature of 150°C for 100,000 hours (approx. 11 years), while retaining at least half of the initial properties afterwards. 

Polymers such as PPS and PEEK inherently fulfill this requirement. Conversely, PPA’s need to be mechanically reinforced and thermal stabilized so that their continuous use temperature can rise from 130°C to 150°C. Most PPA’s have a continuous use temperature of 130°C. 

Fundamental structure- property relationships 

For better understanding the high heat resistance, we go back to the basic structure of a polymer such as a Polyethylene (PE). The main backbone consists out of carbon-carbon bonds and on the carbons, hydrogens are also bonded. This linear macromolecule has a maximum temperature resistance of ca. 80°C and continuous use temperature of 50°C.

If we replace now the carbon in the main chain with a phenyl group, which is an aromatic cyclic group of atoms with the formula C6H5 we obtain the Polyparaphenylene (PPP).

PPP has a temperature resistance of 500°C and is a linear macromolecule made out of benzene building blocks. Aromatic structures result in high macromolecule stiffness. Aromatics in the backbone are a main driver to obtain high heat and chemical resistance. The detailed look at the structure of benzene reveals that the double bonds are not statically localized, i.e. electrons move along the carbon cyclic structure, which is expressed by the ring in the structural formula. This together with inherent molecular stiffness supports stability at high temperatures and in contact with chemicals. If we alternate benzene rings and amide groups, we will get a polymer called poly para-phenyleneterephthalamide (PPTA) or more common known as Aramid and has a heat resistance of 250°C (decomposition temperature between 430-480°C; peak temperature use up to 400°C). It can be processed to fibers and makes it a perfect material for personal protective equipment for firefighters and armed forces [2; 3].

7 basic building blocks of high performance polymers

The high thermal resistance of PPP has one major downside, i.e. it makes it unsuitable for all melt-based processing techniques such as injection moulding and extrusion.

However, the integration of heteroatoms such as Oxygen, Nitrogen, and Sulfur in a polymeric aromatic-based structure can change this. Following, common chemical groups which are used to make melt-processable high performance polymers are described.

1. Diphenyl ether group: In this case, oxygen is the linkage of two phenyls. Diphenyl ether groups are used for example in Polyaryletherketones (PAEK’s).

2. Diphenylsulfone group: Here, sulfur is double-bonded to oxygen as well as bonded to phenyls. Diphenylsulfone groups are the main building block for Polysulfone (PSU), Polyethersulfone (PESU) and Polyphenylsulfone (PPSU).

3. Diphenylketone group: Oxygen is bonded over a double bond to carbon resulting in a carbonyl group. Together with the diphenyl, it forms the ketone group. The ketone group is the second crucial element for obtaining Polyetheretherketones (PEEKs).

4. Diphenylsulfide group: Here, sulfur is linked to phenyls and forming the sulfide group. It forms the basis of Polyphenylensulfide (PPS).

5. Imide group: It consists out of two acyl groups (R-C=O) bounded to nitrogen. It is the base element of Polyimides (PIs), Polyamideimides (PAIs), and Polyetherimides (PEIs).

6. Terephthalic acid (TPA) and Isophthalic acid (IPA): It is used as precursor for making Polyethylene terephthalate (PET). It also forms the monomer for Polyphthalamides (PPAs). Two carboxyl groups are attached to a benzene in a 1,4 or 1,3 configuration.

7. Fluor-carbon group: the fluor-carbon bond is the most stable single bond with 485 kJ/mol bonding energy (in comparison, carbon-carbon bond has 350 kJ/mol). Additionally, the fluor atom is much larger compared to the carbon forming a protecting layer around the carbon-carbon main chain. This explains to the same extent the high chemical and thermal stability of fluoropolymers such as PTFE and PVDF.

Chemical resistance of high performance polymers 

As a rule of thumb, the chemical resistance of polymers decreases with increasing temperature, i.e. increasing molecular mobility. In this case, high performance polymers have inherent advantages compared to commodity or engineering polymers. I made a table comparing all major high performance polymers with chemical resistance.

Conclusions

A key element to achieving high temperature and chemical resistance is the inclusion of aromatic structures. The combination of the latter with various heteroatoms such as carbon, oxygen and sulfur impart flexibility to the resulting polymer macromolecule, which enables melt processing. The use of melt processing techniques enable high performance polymers to be economically used in several high-end applications such as airplanes, automotive, oil and gas, and chemical processing industries.

If you want to use high performance polymers for your application and you need support to choose the optimal grade, I am glad to help. Reach to out to me here.

A further blog post on high performance polymers on my blog you can read here.

Thank you for reading! 

Till next time! 

Greetings 

Herwig 

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Literature:

[1] Johannes Fink - High Performance Polymers, Plastics Design Library

[2] https://www.teijinaramid.com/en/expertise/what-is-aramid#:~:text=Aramids%20are%20man%2Dmade%20fibers,from%20long%2Dchain%20synthetic%20polyamides.

[3] https://www.dupont.com/content/dam/dupont/amer/us/en/safety/public/documents/en/Kevlar_Technical_Guide_0319.pdf

Fluoropolymers As Enabler For Megatrends: From Resource Efficiency To Digitalization

The world of fluoropolymers is versatile and fluoropolymers can be seen as an enabler to support the realization of the so-called megatrends. This is the main topic of this blog post.

The base of fluoropolymers are monomers such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF) which can be synthesized from the raw material fluorspar. Using the monomers, polymerization to polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), and fluorinated ethylene-propylene (FEP) can be done.

In 2015, 270,000 metric tons of fluoropolymers were consumed worldwide. Altogether, the world of fluoropolymers can be divided into three major pillars: PTFE, fluorothermoplastics, and fluoroelastomers. PTFE represents with 140,000 metric tons the largest part (52%), followed by PVDF with 41,000 metric tons (15%) and on third place is FEP with 22,500 metric tons (8%). Smaller positions are occupied by ethylene-tetrafluoroethylene copolymer (ETFE), 8,400 metric tons (3%), and fluoroelastomers (FKM), which account for 31,000 metric tons (12%).

There are several megatrends which result in economic, social, and environmental shifts. Understanding megatrends and how to incorporate fluoropolymers as a material enabler will result in better allover results in the long run. Following, are some examples on how fluoropolymers can support to solve challenges ahead of us.

Resource limitation: a major topic in chemical industry is the extension of a plant’s lifetime. Using fluoropolymers for corrosion protection, especially in reactor-, mounting-, and pipelining can be seen as positive step to battle this challenge. Going further, you can design even an all-fluoropolymer reactor to increase the productivity of your reaction. Plastics industry is also investigating ways of up-cycling end-of-life products, including but not limited to fluoropolymers.

Digitalization: data transfer and data storage are major topics in the internet of things (IoT). We want to have smaller overall designs and improved performance of high frequency components. Using fully fluorinated polymers, better insulation with thinner insulation layers at higher frequencies is possible. Furthermore, non-flammable indoor high frequency (LAN) cables are needed and those cables take advantage of the flame retardant property of fluorine chemistry.

Transport changes: in automotive, we have more stringent CO2 reduction needs (Euro Six Norm) combined with reduced consumption of gasoline. Therefore, more sensors are placed on several positions in the exhaust gas flow. Using fluoroelastomers as sealing materials allows us to have a compression set at temperatures up to 280°C, which guarantees proper sealing of the sensor housings. In the field of car electrification, PVDF is a key enabler in battery technology. PVDF is used as cathode binder, separator coating, and anode binder. PFA and FKM can be used as cell gasket sealing materials as well.

Aging population: there will be increasing demand for medical devices and fluoropolymers can provide chemical stable components for dialysis devices. Also, endoscopic surgery equipment is made from fluoropolymers. This ensures proper resistance to the sterilization process. Furthermore, in emerging regions such as BRIC states, cooking devices such as rice cookers, frying pans and bakeware use non-stick coatings, driving demand for fluoropolymers in this area too.

In conclusion, fluoropolymers have established themselves in many applications and will be a major material enabler for the megatrend challenges ahead of us.

I published also are more general fluoropolymer post which you can check out here.

Thanks for reading & till next time!

Greetings,
Herwig Juster

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Literature:
[1] Kunststoffe International 10/2016
[2] https://www.solvay.com/en/brands/solef-pvdf/solef-pvdf-li-ion-batteries

10 Fluoropolymer Facts for Designers & Engineers

Fluoropolymers are used nowadays in several industries and applications like flexible tubing, packaging, cooking equipment, wear and friction parts.

In the table below you can find an overview of the thermoplastic fluoropolymer family.

What is their secret and why are they used in high-end applications?

In this blog post I made a fact list which will answer those questions:

1. Fluoropolymers contain a carbon-fluorine bond which is very polar with a very high bond strength leading to very low intermolecular attractions.
2. Based on this, fluoropolymers have very low surface energy, a low coefficient of friction and are lipid, water and stain repellant.
3. Fluoropolymers have both: low and high temperature resistance; furthermore they have excellent dielectric properties and are chemically inert.
4. When blended with other polymers, fluoropolymers will bloom to the surface due to the very low surface free energy (lubricous behavior).
5. Latest market studies implicate that the global fluoropolymer market will be worth over $8.8 billion by 2019 and thought to be between 80,000 and 90,000 tons.
6. Roy J. Plunkett accidently discovered one of the most famous fluoropolymers (Teflon by DuPont) in 1938.
7. PTFE, PVDF, FEP and ETFE are the most common used fluoropolymers.
8. Among the fluoropolymers, PTFE has with 0.1 the lowest coefficient of friction.
9. Most fluoropolymers are fully fluorinated olefinic (aliphatic based) materials and homopolymers contain over 99% fluorine by weight which makes them most resistant to chemicals.
10. Fluoropolymers are melt processable except of PTFE and PVF.

Here some more honorable mentions:

1. For the semiconductor industry fluoropolymers are vital. Without them, you would not read this blog post on your computer, tablet or smartphone.
2. ETFE can be used as a glass replacement: The Allianz Arena in Germany uses ETFE panels.
3. Coatings out of PTFE are used in high temperature applications up to 290°C e.g. for coating of bakery equipment.
4. The world’s largest manufacturers of fluoropolymers include DuPont, Daikin, Solvay, Dyneon, and Asahi Glass.

5. 

   Infographic - 10 Fluoropolymer Facts for Designers and Engineers

   
   
   

I hope you enjoyed this fact list.

Thanks for reading and till next time!

Greetings,

Herwig Juster


New to my Findoutaboutplastics Blog – check out the starthere section.

Literature:

[1] https://www.fluorotec.com/blog/21-fluoropolymer-facts-for-engineers/

[2] https://www.solvay.com/en/markets-and-products/featured-products/fluoropolymers-faq.html