Wednesday 6 November 2024

Design Properties for Engineers: Dynamic Mechanical Analysis (DMA) of Ultra Performance Polymers (PBI and PBI blends)

Hello and welcome to a new post on design properties for engineers. In today’s post we discuss the storage modulus E’ measured by DMA of the ultra performance polymer Polybenzimidazole (PBI). Check out here my other post on DMA of high performance polymers here. DMA is an essential tool for polymer material selection, allowing you to immediately capture the mechanical behaviour over a wide temperature range. 

What is Polybenzimidazole (PBI)?

PBI is the ultra high performance plastic which 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. 

Storage Modulus E’ of PBI and PBI-blends

Figure 1 shows the storage modulus vs. temperature behaviour of the PBI, PBI-PEEK blend, PAI, and PEI. They all show a significant drop in modulus in the glass transition region. Before reaching the Tg, The neat PBI polymer still has a storage modulus of 3 GPa, whereles the other presented polymers have already reached the zero level at this temperature. Blending PBI with PEEK makes it easier for melt processing and still up to 200°C a high level of modulus can be achieved. Among the amorphous high performance polymers, PAI has with 275 °C the highest glass transition temperature. A continuous use temperature of 260°C is feasible. PAI is melt processable in an injection moulding machine and needs an annealing step after moulding. 

Figure 1: Storage modulus E' of PBI and PBI blends [1]

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster
Literature:

Sunday 27 October 2024

My Guest-Contribution in "Sustainable medical technology: Rethinking plastics in medical technology" by BIOPRO Baden-Württemberg GmbH

Hello and welcome to a new blog post. Today I show you an article written by Dr. Ruth Menßen-Franz from the BIOPRO Baden-Württemberg GmbH to which I have contributed to as a guest. 

Plastics play a vital role in medical technology and medical device applications. In this article we discuss how to create more environmentally friendly plastic products in the future, using new bioplastics, best-practices in part design, and new ways of recycling. 

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 







Friday 25 October 2024

Rule of Thumb in Polymer Injection Moulding: Fast Estimation of Cooling Time

Hello and welcome to another Rule of Thumb post. Today we discuss how to fast estimate the cooling time in injection moulding. 

Main influencing factor of the cooling time is the wall thickness, since it the wall thickness is included squarely in the cooling time calculation. Another factor is the tool temperature. For example, a 10°C increase of tool temperature will lead to a 30% elongation in cooling time. Increasing the melt temperature will lead only to a 3% increase in cooling time. 

Equation 1 shows the simplified cooling time calculation which can be used for a fast assessment (it is still recommend to calculate the cooling time with a more detailed equation whenever possible). We need to have the maximum wall thickness of your part and a multiplication factor between 1.5 and 2 (sometimes also higher e.g. 2.5 for PARA). 

Equation 1: Estimating the cooling time in injection moulding [1].

Check out the video on this topic on my YouTube channel too: 


More polymer engineering Rule of Thumb posts can be found under "start here".

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster
Literature:
[1] https://www.emsgrivory.com/fileadmin/user_upload/EMS-GRIVORY/documents/Brochures/English/5017_en_Long-fibre-reinforced-polyamides.pdf
[2] https://www.findoutaboutplastics.com/2018/04/plastics-part-design-10-holy-design.html

Sunday 6 October 2024

Rule of Thumb in Polymer Engineering: How Economy of Scale Can Lower Costs

 Hello and welcome to this new Rule of Thumb post. More Rule of Thumbs can be found in my section "Start here"

Economy of Scale: A Brief Explanation

Economy of scale refers to the cost advantage that arises when a company increases its production level. In simpler terms, the more a company produces, the lower the cost per unit becomes. This is because fixed costs (like rent, machinery, and salaries) are spread out over a larger number of units.

How Economy of Scale Can Lower Costs

  • Increased Production Efficiency: Larger production runs often lead to more efficient processes, reducing waste and improving productivity (each time the cumulative production of a given product gets doubled, costs can be reduced in range of 15%).
  • Bargaining Power with Suppliers: Larger companies can negotiate better deals with suppliers due to their increased purchasing volume.
  • Specialized Equipment: Investing in specialized equipment can significantly reduce production costs for large-scale operations.
  • Risk Diversification: Larger companies can better absorb market fluctuations and other risks.
Example: Plastic Injection Moulding

In plastic injection molding, economy of scale is a significant factor in determining production costs. A company that produces a large number of plastic parts can benefit from:

  • Specialized Moulding Machines: High-volume production justifies the investment in advanced, efficient moulding machines that can produce parts faster and with less waste.
  • Optimized Production Processes: With experience and scale, companies can fine-tune their production processes to minimize setup time, reduce cycle times, and improve quality. Using a Lang-factor of 0.75 we can reach a cost reduction of 30% when doubling the production amount (Figure 1).  
  • Bulk Material Purchasing: Larger quantities of plastic resin can often be purchased at a discounted rate, reducing material costs.
  • Efficient Manufacturing Layout: A well-designed manufacturing layout can streamline production flow, minimizing material handling and reducing overhead costs.
Figure 1: xample economy of scale in plastic injection moulding - doubling the production amount leads to a 30% cost reduction. 


By leveraging economy of scale, plastic injection moulding companies can significantly lower their production costs, making their products more competitive in the marketplace. 

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster
Literature:
[1] https://www.stratxsimulations.com/latest_materials_circular_markstrat/NetHelp/enu/Handbook-SM-B2C-DG/DocToHelpOutput/NetHelp/index.html#!Documents/productivitygains.htm
[2] https://www.voestalpine.com/highperformancemetals/en/blogposts/how-to-increase-efficiency-and-productivity-in-plastic-injection-molding/#


Friday 4 October 2024

Polymer Selection Funnel Example - Smartphone Front Bezel (Consumer Electronics Material Selection)

Hello and welcome to another polymer material selection example for which we use the POMS-Funnel Method (in detail explained here and in this video). Today’s mission is to select the optimal polymer for Liquid Crystal Display (LCD) bezel used in smartphones. 

Figure 1 presents the four different stages of the material selection funnel as well as the tools we can use to facilitate the selection. We can use this as a guideline throughout the selection journey. 

Figure 1: Polymer Selection Funnel - overview of the four different funnel stages and tools.

POMS-Funnel Method: 

Funnel stage 1: Material selection factors

In the first Funnel stage we focus on gathering and understanding all the requirements of the LCD bezel for smartphones (Figure 2).  
Figure 2: Overview of a LCD front bezel used in the iPhone 14 Plus. Aim of the first funnel step is to lay out the requirements.


Covering effectively the product requirements, a combination of functionality questions and selection factor questions can support you to achieve this. First we have to ask some questions on the functionality of the part. 

Following questions can help us with this assessment:
-What are the performance requirements (structural, etc.)?
-Do you want to combine multiple parts or functions?
-What will be the structural load of the part (static, dynamic, cycling, impact, etc.)?
-What will be the environmental impact on the part (chemical, temperature, time)?
-What is the expected lifetime of the product?

After answering the functionality questions, we continue with the, in my point of view,  six essential questions on material selection factors (6 What's).

A more detailed list can be found here (incl. download): Material Selection Requirements Checklist

1. What is the service environment of your part?
2. What are the regulatory requirements?
3. What types of load at which service temperature and time need to be fulfilled?
4. What other things such as wear and friction, electrical properties such as CTI, electrical breakdown strength, aesthetics and colour (relevant for application with food contact, and toys), and more, need to be considered?
5. What is the processing and fabrication method?
6. What are the economic and commercial considerations?

In general, LCD bezels, the outer frame that surrounds the LCD screen in smartphones, play a crucial role in both aesthetics and functionality. The materials used for these bezels must meet specific requirements to ensure optimal performance and durability.

Key Requirements for LCD Bezel Materials:

Aesthetics:
-Color: The bezel's color should complement the overall design of the smartphone and align with current trends.
-Finish: The finish can range from matte to glossy, depending on the desired aesthetic.
Texture: The texture can be smooth, textured, or even embossed to create a unique feel.

Durability:
-Scratch Resistance: The material should be resistant to scratches, as smartphones are often carried in pockets or bags and may come into contact with other objects.
-Impact Resistance: The bezel should be able to withstand minor impacts without cracking or shattering.
-Strength: Thin wall frame need to have high strength levels too, together with dimensional stability.
-Wear and Tear: The material should be durable enough to resist wear and tear over time.

Functionality:
-Signal Transmission: The bezel material should not interfere with wireless signal transmission, such as Wi-Fi or cellular data. The material should have a dielectric constant of 3.5.
-Display Visibility: The bezel should not obstruct the viewing angle of the LCD screen.
-Thermal Conductivity: The material should have good thermal conductivity to help dissipate heat generated by the smartphone's internal components.
-Processability: High flow material enabling to fill thin wall thickness; possibility for  IML/IMD “In-Mold Labelling/Decoration”,

Cost:
-Affordability: The material should be cost-effective to ensure that the smartphone remains competitive in the market.

Capturing all requirements and project details can be done by using the requirement worksheet and Table 1 shows the outcome. 
Table 1: Overview of requirements for the LCD front bezel using the requirement worksheet. 

Funnel stage 2: Decision on thermoplastic or thermoset

With the LCD bezel requirements, together with the understanding of the differences of thermoplastics (amorphous and semi-crystalline) and thermosets we can screen the databases and material suppliers for suitable material candidates.  

There are reliable database such as Campus and Omnexus and I created dashboards to support this step too: 



All dashboards can be found also here.

Deciding between the thermoplastic or thermoset route is the first step. In our case, thermoplastics offer many advantages for this application, especially impact performance at low and high temperatures and injection moulding in the range of million parts per year in an economical way. Reviewing the bezel requirements, both amorphous and semi-crystalline materials are feasible. 

After the material screening, I pre-selected the following materials (Table 2): 
  • Lexan® HFD4472 (PC-CoPo-GF20)
  • Kalix 2545 (PA 6.10-GF45; bio-sourced)
  • TORAYCON™ 7151G-F03 (PBT+SAN-GF30)
  • Zytel® HTN52G35HSL (PPA-GF35; PA6T/66-GF35)
Table 2: Overview preselected grades and their commercial suppliers.

Funnel stage 3: Selection discussion with worksheet (qualitative matrix analysis)

The third funnel stage represents a core element in the whole material selection funnel. It is a detailed selection discussion with a worksheet. I call it the decision matrix analysis and it ranks all of the pre-selected polymers. The decision matrix analysis consists of five steps. The base calculation principle is a scoring of each of the pre-selected materials for each of the material selection factors. In the end we add up all weighted scores for each material. The materials with the highest score are most suitable for selection and further investigation in the fourth stage.

How to start the qualitative matrix analysis?
I developed an online tool in order to facilitate this step here (Polymer Material Selector V1.1). As an alternative, you can reach out to me and I will provide you with an excel version of it. I only considered the must-have requirements.

In Table 3 the outcome of the qualitative matrix analysis is shown. PA 6.10-GF45 scored the highest number of points (score: 132 points), followed by PC-CoPo-GF20 (score: 98 points) and PBT+SAN-GF30 (score: 97 points) and PPA-GF35 (score: 93). All four materials should be validated in the Funnel stage 4 since there are important tests such as the antenna performance tests, falling and rolling test, and anti-stain test. 

Table 3: Results of the qualitative matrix analysis.

Funnel stage 4: Testing, selection of material and vendor

In the final step of the POMS-method we perform the antenna performance tests, falling and rolling test, and anti-stain test, as well as build first prototypes (with the support of CAE - filling simulation). Once all the test results are available, the final material decision can be done. 

For the premium consumer segment of smartphones, PA6.10-GF45 and PC-CoPo-GF20 are a good choice and if surface aspects are not the most important criteria, the remaining two materials (PPA and PBT+SAN) can be considered too. 

Conclusions
In this example we applied the POMS-method  for selecting the optimal thermoplastic grade for a LCD bezel used in smartphones. It is a systematic approach with a resin-agnostic view allowing to consider different material choices and document them for a later review and optimization. 

More polymer material selection examples using the funnel approach can be found here:

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster
Literature:
1] https://www.sunsky-online.com/de/p/EDA006095301/For-iPhone-15-Plus-Front-LCD-Screen-Bezel-Frame.htm
[2] https://www.polymerio.com/tds-pds/pbt-compound-toray-toraycon-7151g-f03-b--tds-pds
[3] https://materials.celanese.com/de/products/datasheet/SI/Zytel%20HTN52G35HSL%20BK083
[4] https://www.syensqo.com/en/brands/kalix-hppa
[5] https://www.sabic.com/en/products/specialties/lnp-compounds-and-pc-copolymer-resins/lexan-copolymer
[6] https://www.plastics.toray/de/products/toraycon/pbt_003.html











Wednesday 11 September 2024

Plastic Part Marking Codes: ISO 11469 vs. ISO 16396

Hello and welcome to a new blog post. Today we discuss the differences between ISO 11469 and ISO 16396 used for plastics identification as well as for part marking and how each of them is used in the plastics industry.

Check out this post which provides you with an overview on the major part marking codes  and standards (incl. miniguide for downloading).

Download the miniguide here.

Why Plastic Part Marking Codes?

Identification of plastics products is easier with a part marking system. This allows for better decision making for:

  • handling plastic products,
  • better waste recovery
  • more efficient disposal.

Plastic identification and part marking with ISO 11469

ISO 11469:2016 defines a system of uniform marking of products which were made from plastics materials and it references the following standards since they are indispensable for its application: 

  • ISO 472, Plastics — Vocabulary
  • ISO 1043-1, Plastics — Symbols and abbreviated terms — Part 1: Basic polymers and their special characteristics
  • ISO 1043-2, Plastics — Symbols and abbreviated terms — Part 2: Fillers and reinforcing materials
  • ISO 1043-3, Plastics — Symbols and abbreviated terms — Part 3: Plasticizers
  • ISO 1043-4, Plastics — Symbols and abbreviated terms — Part 4: Flame retardants

Example for marking according ISO 11469: acrylonitrile-butadiene-styrene polymer “>ABS<”

ISO 16396-1:2022: Polyamide moulding and extrusion materials

On the other hand we have the ISO 16396 which was introduced particularly for Polyamides used in injection moulding and extrusion (PA 6, PA 66, PA 69, PA 610, PA 612, PA 11, PA 12, PA MXD6, PA 46, PA 1212, PA 4T, PA 6T and PA 9T and copolyamides of various compositions for moulding and extrusion).

The designation consists out of five data blocks:

-Data block 1: identification of the plastic by its abbreviated term (PA), and information about the chemical structure and composition

-Data block 2: position 1: Intended application and/or method of processing; positions 2 to 8: Important properties, additives and supplementary information

-Data block 3: designatory properties

-Data block 4: fillers or reinforcing materials and their nominal content

-Data block 5: contains additional information which may be added if needed

Example: PA6T/66 MH, 14-190, GF50

  • PA6T/66: Polyamide 6T which is a homopolymer based on terephthalic acid and Polyamide 66 which is based on hexamethylenediamine and adipic acid. 
  • M: injection moulding; 
  • H: heat ageing stabilized
  • 14: viscosity number (in ml/g) > 130 but below 150; 
  • 190: tensile modulus of elasticity between 17000 MPa and 20000 MPa
  • GF50: wt% 50 glass fiber reinforcement

Below you find a YouTube shorts on this topic too. 

Thanks for reading/watching and #findoutaboutplastics

Greetings

Herwig Juster

[1] https://www.iso.org/obp/ui/en/#iso:std:iso:11469:ed-3:v1:en

[2] https://www.findoutaboutplastics.com/2020/12/plastic-part-marking-overview-codes-and.html


Sunday 8 September 2024

High Performance Thermoplastic Selection - Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR) [Part 2A]

Hello and welcome to the second part of our High Performance Thermoplastics selection blog series. The second part will focus on the introduction of high performance polymers, their chemistry and production processes, their main properties, their processing methods, and last but not least, applications.

Here you can jump to Part 1.

There are six major high performance thermoplastics families (“the magnificent six”) which we will discuss: 

-Part 2A: Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

-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)

-Part 2E: Semi- and Fully Aromatic Polyamides (PARA, PPA, Aramid)

-Part 2F: Polyhalogenolefins (PTFE, PCTFE, FEP, PVDF, ECTFE)

All thermoplastics can be visualized by using the performance pyramid, as shown in Figure 1. Based on production volumes, performance, and price, thermoplastics can be categorized as commodity plastics such as Polyolefins, engineering plastics such as Polyamide, and high performance polymers. Polysulfides (PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR) are highlighted since they will be discussed in this post.

Figure 1: Plastics Performance Pyramid highlighting PPS, Polysulfones, and PAR. 

Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

The first major family we discuss is the Polysulfide family which contains Polyphenylene sulfide (PPS), followed by Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR). Polyphenylene ether (PPE) can be added to this family too, however I placed it in the family of Polyethers together with Polyetheretherketone (PEEK). 

Polyphenylene sulfide (PPS) - The polymer that thinks it’s metal…

Everyone who had already a part made out of PPS in his hand and let it drop will immediately recognize its metal-like sound. Thus, sometimes PPS is referred to as the “polymer that thinks it’s metal”. 

Chemistry and Production

PPS is a semi-crystalline polymer and its backbone consists of aromatic rings (phenylene groups) linked by sulfide bridges. This unique structure grants PPS its remarkable properties. The production process typically involves step-growth polymerization, where para-dichlorobenzene reacts with sodium sulfide under specific conditions in a solvent like N-methylpyrrolidone (NMP). However, numerous modifications and post-treatments can be employed to create specific PPS grades with tailored properties. There are two main routes making PPS and depending which route was taken, a so-called cured PPS (“flash PPS”, referring to the flash evaporation of water and solvent at the end of the two-step process; first step: sodium hydroxide reacts with solvent N-Methyl-2-pyrrolidone (NMP); step two: hydrogen sulfide gas introduced and a suspension is the result; curing by air is needed to increase the molecular weight; it leads to chain elongation and branching; typical MW before curing: 18,000 – 22,000 and after: 45,000) or linear PPS (“quench PPS”, where the reaction takes place in a solvent and it is continuous without having to remove water; "quench" or "quenching" = process of rapidly heating and mixing the slurry from the reactor with a quench medium, usually water and/or steam, leading to polymerization determination). The flash process has a higher yield efficiency (>92 %), good operational stability with better quality control. The quench process results in higher MW directly ( MW ~50,000) and lower yield efficiency (~88%).

Cured (“branched”) PPS has a dark brown color and in the beginning, linear PPS grades showed superior toughness, less off-gasing, lower flash appearance, and improved weldline strength. Parts ade out of cured PPS show an improved dimensional stability and creep performance. However, over time and with production improvements, differences were minimized.  

Well-known trade names for PPS include Ryton® (Syensqo), Torelina® (Toray), Fortron® (Celanese), Durafide® (Polyplastics), Xytron® (Envalior) and DIC PPS (DIC).

Properties of PPS

  • High-temperature performance: PPS boasts a melting point around 280°C (536°F) and can withstand continuous use (UL 746B) at temperatures exceeding 200°C (424°F). This makes it ideal for applications that encounter extreme heat.
  • Chemical resistance: PPS exhibits exceptional resistance to a wide range of chemicals, including strong acids, bases, and solvents. This allows it to function in harsh chemical environments. Concentrated nitric acid is one of the few chemicals which can dissolve PPS, apart from that there are no other chemicals which can dissolve PPS at a temperature below 200°C. 
  • Dimensional stability: PPS maintains its shape remarkably well at elevated temperatures, minimizing warping or shrinkage. For medium sized parts, 0.1% of its given dimension can be held and for large parts, 0.2% of the set dimension can be held.
  • Flame retardant: PPS is inherently flame retardant and self-extinguishing, making it a safe choice for applications requiring fire resistance. It can achieve the UL94 V0 at 0.75 mm and has a limiting oxygen index (LOI) which is estimated according to ISO 4589, of 45%.
  • Electrical insulator: The non-polar structure of PPS makes it a good electrical insulator. 
  • Excellent flow properties: allowing to fill thin wall thicknesses. Amount of crystallization is around 50%. 

Table 1 summarizes selected mechanical properties of non reinforced PPS, cured PPS, and linear PPS moulding compounds. Often questions around the part marking code for highly filled PPS compounds arise. According to ISO 11469, the 65 wt% PPS compound R-7-120NA has following part marking code, which is in line with the VDA 260 too: >PPS-(GF+MD)65<.

Table 1: Selected mechanical properties of non reinforced PPS, cured PPS, and linear PPS moulding compounds [1].

Processing Methods

PPS can be processed using various techniques:

  • Injection Moulding: This is the most common method for shaping PPS into complex parts. Mould temperatures of minimum 135°C are needed to have a proper crystallization of the polymer. 
  • Extrusion: PPS can be extruded into sheets, rods, tubes, and pipes for diverse applications.
  • Machining:  PPS exhibits good machinability, allowing for the creation of precise components.
  • Coating: PPS powders can be used to coat metal sureafce such as kitchen pans. 

Applications of PPS

Due to its exceptional properties, PPS finds applications in a variety of industries:

  • Automotive:  PPS is used for pump components, engine parts close to the combustion engine, and electrical connectors due to its heat and chemical resistance. Also for e-mobility, PPS plays a key role, especially for high temperature electronics. Currently, a typical internal combustion engine (ICE) has around 700 grams of PPS polymer on board. New numbers form Asia reveal that there will be 3 to 4 kg of PPS in electric vehicles (EVs) and hybrid electric vehicles (HEVs).
  • Chemical Processing: PPS is ideal for pipes, valves, and pump housings due to its excellent chemical resistance.
  • Electrical & Electronics: PPS is a valuable material for connectors, circuit boards, and other electrical components because of its electrical insulating properties.
  • Aerospace: PPS finds use in aircraft components due to its lightweight nature and high-temperature performance.

Economic Aspects

PPS is a high-performance polymer, and its production costs are typically higher than those of some commodity plastics. However, PPS prices are still much lower compared to other high performance polymers such as PEEK. PPS and its exceptional properties often translate into longer lifespans, reduced maintenance needs, and improved performance, justifying the initial investment.

PPS stands out as a versatile and high-performance thermoplastic. Its unique combination of properties makes it a valuable material for demanding applications across various industries. As polymer engineering continues to evolve, PPS is certain to remain a key player for years to come.


Polysulfones (PSU, PESU, PPSU) - Take me to the moon

Polysulfones (PSFs) are an amorphous class of high-performance thermoplastics renowned for their exceptional properties, including heat resistance, chemical resistance, and dimensional stability. These attributes make them ideal for applications requiring materials that can withstand harsh conditions and maintain their integrity over time. Polysulfone was used as an external sun protection helmet visor for the Apollo 11 crew which landed on the moon on  July 20th 1969. 

Chemistry and Production

The chemical structure of polysulfones is characterized by a repeating ether sulfone unit (-O-SO2-). This unique structure contributes to the material's excellent properties.

Polysulfones are typically produced through a nucleophilic aromatic substitution reaction between bisphenol A and a dichlorosulfone. The reaction is carried out in a polar aprotic solvent, such as dimethyl sulfoxide (DMSO), in the presence of a base.

Main Properties

  • Heat resistance: Polysulfones have a glass transition between 190°C (374 °F) for PSU and 220°C (428 °F) for PESU and PPSU, leading to a  high heat deflection temperature, making them suitable for applications in hot environments.
  • Chemical resistance: They are resistant to a wide range of chemicals, including acids, bases, and solvents.
  • Dimensional stability: Polysulfones exhibit excellent dimensional stability, maintaining their shape and size even under varying conditions.
  • Flame retardancy: Many polysulfone grades are inherently flame-retardant and fulfil the UL94 V0.
  • Hydrolytic stability: They are resistant to hydrolysis, making them suitable for applications in contact with water. PSU and PPSU polymers exhibit excellent resistance to hydrolysis, remaining stable under high-temperature steam and water exposure. This characteristic makes them suitable for medical instruments requiring repeated autoclaving. For example, PSU performs well even after 100 autoclave cycles at 134°C. PPSU on the other hand, maintains its original physical properties like rigidity and ductility up to 1000 cycles at the same temperature.
  • Biocompatibility: There are polysulfone (PSU) and polyphenylene sulfone (PPSU) grades which have been developed for usage in medical devices that require long-term biocompatibility. For example, there are PSU and PPSU grades such as Syensqo's Eviva PSU and Veriva PPSU grades which are biocompatible polymers developed for long-term medical implants. They meet regulatory standards for devices in contact with bodily tissue/fluids for 30+ days and are manufactured following ISO 13485 and cGMP guidelines. In addition, standard grades of polysulfone and PPSU are used in medical devices that are in contact with bodily fluids and tissue short-term, or less than 24 hours.

Differences between polysulfone (PSU), polyethersulfone (PESU) and polyphenylene sulfone (PPSU)

While all three materials - polysulfone (PSU), polyethersulfone (PESU), and polyphenylene sulfone (PPSU) - are high-performance thermoplastics with similar properties, there are some key differences between them.

  • Polysulfone (PSU): The repeating unit in PSU is a bisphenol A sulfone. PSU offers good heat resistance, chemical resistance, and dimensional stability.
  • Polyethersulfone (PESU): PESU has a repeating unit of bisphenol S ether sulfone. It exhibits excellent heat resistance, hydrolytic stability, and chemical resistance, making it suitable for applications in harsh environments.
  • Polyphenylene Sulfone (PPSU): PPSU has a repeating unit of biphenyl sulfone. It offers exceptional heat resistance, mechanical strength, and flame retardancy. It has the highest stress crack resistance and notched impact strength of all three types of Polysulfones. 

Table 2 compares the different properties of PSU, PESU, and PPSU to each other. 

Table 2: Comparison of the the different properties of PSU, PESU, and PPSU.

Processing Methods
Polysulfones can be processed using various methods, including:
  • Injection molding: This is the most common method for producing polysulfone parts.
  • Extrusion: Polysulfones can be extruded into sheets, films, and profiles.
  • Blow molding: This process is used to produce hollow objects from polysulfone.
  • Thermoforming: Polysulfones can be thermoformed into complex shapes.

Applications
  • PSU: Automotive components, electronics, medical devices, and food processing equipment.
  • PESU: Medical devices, electronics, water filtration, and chemical processing.
  • PPSU: Aerospace components, electronics, medical devices, and high-temperature applications.
Trade Names and Economic Aspects
There are a hand full of  major chemical companies which produce polysulfones, including:
  • BASF: Ultrason® E PESU; Ultrason® P PSU; Ultrason® S PPSU;
  • Syensqo: Udel® (PSU), Veradel® (PESU), Radel® (PPSU)
  • Sumitomo Chemical: Sumikaexcel® PESU
The market for polysulfones is expected to continue to grow due to their versatility and performance advantages. However, the high cost of polysulfones compared to other engineering thermoplastics can limit their use in some applications. For lower end applications it is competing against Polycarbonate (PC) and in the high-performance segment with Polyetherimide (PEI). 

Polysulfones are a valuable class of high performance thermoplastics with a wide range of applications. Their exceptional properties, including heat resistance, chemical resistance, and dimensional stability, make them ideal for demanding environments. As the demand for high-performance materials continues to grow, the use of polysulfones is expected to increase in the coming years.


Polyarylates (PARs) - UV protection with excellent retention of optical properties, combined with high temperature resistance

Polyarylates (PARs) is an aromatic polyester derived from aromatic dicarboxylic acids and bisphenols. They possess a combination of excellent properties, including high heat resistance, chemical resistance, and mechanical strength, making them suitable for a wide range of applications.

Chemistry and Production
The synthesis of polyarylates typically involves a condensation polymerization reaction between aromatic dicarboxylic acids and bisphenols. The most common monomers used are terephthalic acid (TPA) and bisphenol A (BPA) or bisphenol S (BPS). However, other monomers can be used to tailor the properties of the resulting polymer.

The reaction is typically carried out in a melt polymerization process, where the monomers are heated in the presence of a catalyst. The reaction proceeds by forming ester linkages between the carboxylic acid and phenolic groups. Based on the used monomers we can distingish between Type 1 and Type 2 PAR. 

Type 1 vs. Type 2 Polyarylates: A Key Distinction
Polyarylates can be broadly categorized into two types based on their chemical structure and properties: Type 1 and Type 2 (Table 3).

Type 1 Polyarylates
  • Structure: Typically composed of only aromatic hydroxycarboxylic acid. Most common Type 1 PAR is the Poly-4-hydroxybenzoate (PHB) which consists of aromatic rings linked by ester groups.
  • Properties: Known for their excellent heat resistance, dimensional stability, and chemical resistance. They often exhibit a balance of properties, making them suitable for a wide range of applications.

Type 2 Polyarylates
  • Structure: Typically composed of terephthalic acid (TPA) and bisphenol A (BPA) or other aromatic dicarboxylic acids or bisphenols, such as isophthalic acid or bisphenol S. Most common Type 2 is the Polybisphenol-A terephthalate (PBAT).
  • Properties: May exhibit enhanced properties in specific areas, such as higher toughness, lower water absorption, or improved flame retardancy. The choice of monomers can be tailored to meet specific application requirements.
Table 3: Structure and property comparison of Type 1 and Type 2 PAR. 


Main Properties
Polyarylates exhibit a number of desirable properties, including:
  • High heat resistance: They have excellent thermal stability, allowing them to be used in high-temperature applications. BPAT has a Tg of 196°C (384.8 F), allowing for a short term usage up to 170°C. The heat deflection temperature (1.8 MPa) of BPAT is 174°C (345.2 F) and 40°C higher compared to PC (Tg=148°C; HDT = 135°C). 
  • Chemical resistance: They are resistant to a wide range of chemicals, including acids, bases, and solvents. They are especially resistant towards oils and alcohols when blended with PET, still keeping their transparency. Resistance towards alkali, ketones, and aromatic hydrocarbons is slow.   Also, neat PAR resins are more sensitive to stress cracking. 
  • UV stability: The UV-stability of PARs is high, since UV radiation causes the formation of a protective layer which in turn serves as UV protection. PARs are able to prevent the passage of ultraviolet light at and below 350 nm and transmit almost 90% light at a wavelength of 400 nm or more. It could be shown in various 8,000-hour long-term tests that PAR, in contrast to PS and PC, retains its almost untarnished shine even under the influence of UV. 
    • Why is there such a high ultraviolet absorption capacity and high weathering durability? PAR absorbs UV energy and causes a so-called Fries rearrangement reaction. This reaction produces a benzophenone structure on the resin surface. As a consequence, PAR is able to block light of 400 nm or less. The tone of color (yellowing) changes of PAR too due to the Fries rearrangement.
  • Mechanical strength: They have good mechanical properties, including high tensile strength, flexural strength, and impact resistance. In general, they can be placed between Polycarbonate and Polysulfones. Strength and stiffness are better compared to PC. Impact strength is high at lower temperatures (-40°C), however not as high as with PC. Additionally, the elongation at break is not as good as that of PC.
  • Dimensional stability: They exhibit low shrinkage and excellent dimensional stability. PARs have excellent elastic recovery which makes them a suitable material for spring applications. 
  • Electrical properties: They have good electrical properties, such as high dielectric strength and low water absorption.
  • Optical properties: almost as transparent as Polycarbonate and PMMA. PARs have a slight yellow color and transmit almost 90% light.
  • Good for blending with other polymers: 
    • with PET and PETG, to decrease shrinkage and warpage of PET; 
    • with PC and PBT, in order to increase the thermal heat resistance.
    • with PC, PET and PETG, to integrate a permanent UV protection. 

Processing Methods
Polyarylates can be processed using various methods, including:
  • Injection moulding: This is the most common method for processing polyarylates, allowing for the production of complex parts. PARs have a high melt viscosity and processing is harder. As a result, flow enabler such as adding special groups or atoms, mineral filler/glass fiber reinforcement, and alloying with other polymers, resulting PAR/PET, PAR/PA, PAR/ PC is done. Since the structure of PAR is similar to PC, it can be processed by the same injection moulds. 
  • Extrusion: Polyarylates can be extruded into sheets, films, and profiles.
  • Thermoforming: This process involves heating a sheet of polyarylate and forming it into a desired shape.
  • Compression moulding: This method is suitable for producing large, thick-walled parts.

Applications
Polyarylates are used in a wide range of applications, including:
  • Automotive industry: Components such as engine covers, under-hood parts, and interior trim.
  • Electrical and electronics: Connectors, circuit boards, and housings.
  • Medical devices: Surgical instruments, implants, and diagnostic equipment.
  • Aerospace: Structural components and protective coatings.
  • Industrial equipment: Pump housings, valves, and pipes.
Trade Names and Economic Aspects
Following major chemical companies produce polyarylates under various trade names, including:
  • Unitika: U-Polymer®
  • Westlake Plastics: Ardel® (only semi-finished products)
The market for polyarylates is growing at an average of 3% p.a., driven by increasing demand in various industries. The high performance and versatility of polyarylates make them attractive to manufacturers seeking materials with superior properties.

Outlook to Part 2B
In Part 2B we continue with the detailed discussion of Imide-based polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK).


Thank you for reading!
Greetings and #findoutaboutplastics
Herwig Juster

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