The Sticky Truth About Gluing Plastics: Why Surface Energy Matters (Plastics Processing Rule of Thumb)

Hello and welcome to todays post focusing on gluing plastics.  Ever tried to glue two pieces of plastic together, only for the bond to fail miserably? You're not alone! Gluing plastics can be surprisingly tricky, and a key factor often overlooked is something called surface energy. Think of surface energy as how "eager" a material's surface is to bond with something else. And when it comes to adhesives, eagerness is a good thing!

The Rule of Thumb: High Surface Energy = Stronger Bonds

Here's the golden rule for gluing: the higher the surface energy of a material, the greater the strength of the adhesion you can achieve.

Imagine a tiny water droplet on a surface. On a highly energetic surface, the water spreads out, trying to maximize its contact. On a low energy surface, it beads up, shrinking away. Adhesives behave similarly. They want to spread out and "wet" the surface completely to form a strong bond.

Diving Deeper: High vs. Low Surface Energy Plastics

Plastics are generally categorized into two main groups when it comes to surface energy:

• High Surface Energy (HSE) Plastics: These plastics are generally easier to bond. Their surfaces are more receptive to adhesives, allowing for better "wetting" and stronger molecular interactions.
• Low Surface Energy (LSE) Plastics: These are the notorious "difficult-to-glue" plastics. Their surfaces are less receptive, causing many common adhesives to bead up and struggle to form a lasting bond.

A Quick Look at Surface Energy Values (mJ/m²)

To give you a better idea, below is a small table (Table 1) with approximate surface energy values for some common plastics and other materials. Remember, these values are guides, and specific formulations can impact them.

Table 1: Overview of surface energy values of plastics [1].

As you can see, materials like PTFE (often known as Teflon) have very low surface energy, making them incredibly challenging to bond without specialized adhesives or surface treatments. Another example is the high performance polymer PPS. The surface energy of untreated polyphenylene sulfide (PPS) is typically around 38 mJ/m2. This relatively low surface energy makes PPS challenging to bond to other materials without surface treatment. However, PPS can be treated to increase its surface energy, such as through plasma treatments, which can raise the surface energy to 38 mJ/m2 or higher, depending on the treatment method. In contrast, materials like Polyimide are much more accommodating.

What Does This Mean for Your Next Plastics Gluing Project?

When you're facing a plastic gluing challenge, keep this rule of thumb in mind:

1. Material selection: list gluing as a post-processing operation during part requirement analysis.
2. Identify the Plastic: If you know the type of plastic, you can often infer its surface energy.
3. Opt for HSE Plastics When Possible: If you have a choice of materials, pick higher surface energy plastics for easier and more reliable bonds.
4. Specialized Adhesives for LSE Plastics: For low surface energy plastics, don't reach for your all-purpose super glue. You'll likely need specialized adhesives designed for LSE materials, or consider surface preparation techniques (like primers or plasma treatment) to temporarily increase the surface energy.

Conclusiones

Understanding surface energy is a game-changer for anyone working with adhesives and plastics. By keeping this simple principle in mind, you'll significantly improve your chances of achieving strong, long-lasting bonds and avoid those frustrating gluing failures. Happy gluing!

More Rule of Thumbs can be found in the section "Start here".

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

📚My Polymer Material Selection Book - Available Here

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Literature: 

[1]https://www.3m.com/3M/en_US/bonding-and-assembly-us/applications/material-bonding/engineered-plastics/

[2] https://www.findoutaboutplastics.com/2025/04/nature-is-built-on-5-polymers-modern.html

Design Data for Engineers: Thermal Aging of PPS Compounds

Hello and welcome to today’s blog post on thermal aging of PPS compounds. During material selection, focus on gathering and understanding all the requirements of the application is essential. Key questions to answer are: What is the service environment of your part? And also: What types of load at which service temperature and time need to be fulfilled?

Thermal aging of Polyphenylene sulfide (PPS) compounds (glass; glass/mineral filled)

High performance polymers such as Polyphenylene sulfide (PPS) offer excellent performance during high heat exposure. PPS mouldings, both filled and unfilled, maintain inherent flame resistance and excellent chemical resistance due to the base resin.

Long-term heat aging results align with the polymer's thermal stability. PPS has a UL 746B continuous use temperature (CUT) of 220°C. It is in a similar range with PPSU which has a CUT of 210°C and PTFE is even above 230°C. 

Figure 1 highlights the good retention of tensile properties in glass and glass/mineral-filled compounds over long-term exposure. An aging test was performed at two temperatures (175°C and 230°C) for a maximum duration of 10,000 hours [2]. 

Figure 1: Thermal aging of PPS compounds (175°C and 230°C; 10,000 hours).

Due to the curing characteristics of cross-linked PPS, aging at temperatures above those in Figure 1 can enhance property retention, attributed to a "case hardening" effect from high-temperature air exposure.

At elevated temperatures, PPS compounds show classical deterioration beyond their glass transition temperature (Tg). Despite crystallinity effects, strength loss is gradual, with significant integrity retained even at 200°C. PPS compounds filled with glass and mineral can retain the tensile properties at both temperatures at a higher level (80% retention rate) compared to glass fiber reinforced PPS compounds (60% retention rate).

Generally, 40% glass-filled mouldings retain about 80% of their original strength at 100°C, 60% at 160°C, and 40% at 200°C.

Conclusion

In conclusion, Polyphenylene sulfide (PPS) compounds demonstrate exceptional performance under high heat exposure, making them a reliable choice for applications requiring thermal stability. Both filled and unfilled PPS moldings exhibit inherent flame resistance and chemical resistance, aligning with the polymer's robust thermal properties. The long-term heat aging results confirm PPS's ability to retain tensile properties, even at elevated temperatures. With a continuous use temperature of 220°C, PPS stands out among high-performance polymers, maintaining significant strength and integrity over time. This makes PPS an excellent candidate for applications demanding durability and reliability in challenging thermal environments. When selecting materials, it is crucial to thoroughly understand the application's requirements, including service environment, load types, and service temperatures, to ensure optimal performance and longevity.

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

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Literature: 

[1] https://www.findoutaboutplastics.com/2024/09/high-performance-thermoplastic.html

[2] Don Brady: Polyphenylene sulfide (PPS), Phillips Petroleum Company

Injection Moulding of Polyphenylene sulfide (PPS) - The Key to High Crystallinity and Performance

Hello and welcome to a new post in which we discuss the importance of mould temperature for achieving optimal crystallinity and performance in polyphenylene sulfide (PPS) moulded parts.  

Why is mould surface temperature critical with PPS?

The high-performance polymer PPS is a semi-crystalline polymer and its backbone consists of aromatic rings (phenylene groups) linked by sulfide bridges. It has a glass transition temperature of 88°C, melting temperature of 282°C and a processing temperature of 320°C. It combines high heat resistance (UL 746B exceeding 200°C), with high chemical resistance and mechanical strength at an economical price range.  As a high temperature plastics, also attention to proper processing, especially injection moulding needs to be given. Achieving the optimal level of crystallinity of PPS parts is important. 

Crystallinity significantly impacts the part's performance and stability, and even cooling is essential for high-quality mouldings. Mould surface temperature for PPS should be between 135° and 150°C in order to obtain high levels of crystallinity (maximum crystallinity levels of PPS: 55%).

Injection mould temperature settings for PPS

There is the "hot mould" and "cold mould" approach.  "Hot mould" temperatures (above 135°C) are preferred for precision parts as they promote crystallization, resulting in the best overall appearance, thermal stability, and dimensional stability.  "Cold mould" temperatures (below 88°C), on the other hand, produce amorphous parts with a mottled/grainy surface appearance. While cold moulds offer some advantages in physical properties and less shrinkage directly out of the mould, hot moulds are generally favored for achieving the best balance of properties, especially in precision applications.

Important are suitable cooling methods, and it is recommended to use circulation-type systems using hot oil or pressurized water.  If heater cartridges are used, they should have a minimum capacity of 1 kW per cartridge. 

Differential Scanning Calorimetry (DSC) can assess crystallinity in an effective way.

After moulding the PPS part, we can use the DSC to check if the part was fully crystallized and as a consequence, all important properties such as thermal and chemical stability, as well as dimension stability are fully developed. Figure 1 shows the results of two DSC curves. The upper curve shows a not fully crystallized PPS, having a so-called cold crystallisation peak at 114°C (exothermal) and a melting peak at 282°C. The lower curve shows a fully crystallised PPS part having only a melting peak at 282°C. 

Figure 1: Example comparison DSC curve of a not fully and fully crystallized Polyphenylene sulfide (PPS) moulded part. 

Conclusion

In essence, the careful control and selection of mould temperature (135-150°C), along with appropriate cooling methods, are crucial for optimizing the crystallinity and ultimately the performance of PPS moulded parts.

If you need support in moulding high-performance polymers such as PPS and PEEK, you can reach out to me here .

Learn more about high performance polymers such as PPS in my series “High Performance Thermoplastics Selection” .

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

New to my Find Out About Plastics Blog - check out the start here section

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Literature: 

[1] https://www.syensqo.com/en/brands/ryton-pps

[2] https://analyzing-testing.netzsch.com/de/produkte/dynamische-differenzkalorimetrie-dsc-differenz-thermoanalyse-dta

[3] https://www.solvay.com/sites/g/files/srpend221/files/2018-08/Ryton-PPS-Mold-Temperature_EN-v1.0_0.pdf

Design Properties for Polymer Engineering: Comparative Tracking Index (CTI) after heat aging and moisture treatment (PA 6.6, PBT, and PPS)

Hello and welcome to this post on design properties for plastics engineering. In this post we deep dive into the Comparative Tracking Index (CTI) of aliphatic Polyamides, Polybutylene terephthalate (PBT) as well as Polyphenylene sulfide (PPS) used for electronic components made out of plastic. 

In previous posts we discussed the CTI of high performance polymers such as PPS and how we can improve it. The values shown in past posts were estimated according to the standard IEC-60112.

What is the Comparative tracking index (CTI) and why the CTI is important?

In general, when the plastic surface, which is the insulation material, carbonizes due to voltage exposure,  a conducting path is formed and tracking occurs. Over time, the surface erodes and a conduction of electricity takes place continuously. The resistance to the occurrence of tracking and erosion is represented by the Comparative tracking index (CTI).

How is the CTI value changing if flame retardant additives and glass-fiber reinforced are added to PA and PBT?

Figure 1 compares the CTI values of Polyamide 6 (PA 6), Polyamide 6.6 (PA 6.6) and Polybutylene terephthalate (PBT) with and without reinforcements, as well as with and without halogen free flame retardants. For Polyamides and PBT, adding reinforcement is not leading to a decline in CTI performance. PBT shows a decline in CTI performance in case flame retardants are added. 

Figure 1: CTI of PA 6, PA 6.6 and PBT with and without reinforcements, as well as with and without HFFR [1].

How is the CTI of PA, PBT, and PPS changing after heat aging and moisture influence?

Figure 2 [2] shows the results of the CTI measurements on untreated and treated PA 6.6, PBT, and Polyphenylene sulfide (PPS) samples (all with glass or glass/mineral reinforcement). For heat aging and moisture influence, the samples were exposed to 85°C at 85% relative humidity for 1,000 hours (in line with the international standards e.g. IEC 60068) .  PA 6.6- GF33 wt% (Zytel® 70G33L) and PBT-GF30 wt% (DURANEX® CG7030) reached in the untreated test scenario the maximum achievable value of 600 V. PPS-(GF+MF) 65 wt% (TEDUR® HTR PPS 2465) reached 500 V in the untreated test scenario. After the heat aging and moisture treatment, PA 6.6 and PPS did not show a decline in CTI performance. The advantage of Polyamides is their molecular structure which enables an inherent resistance to tracking and erosion. Achieving a 500 V level with PPS needs for example a special additive modification which we discussed here. PPS has a CTI in the range of 250 V.  In hot and humid environments, PBT showed a decline in CTI; however, it can still keep the CTI above 500 V. 

Figure 2: CTI of PA 6.6, PBT, and PPS before and after heat aging and moisture treatment (85°C/85%RH/1000h) [2]. 

Additional influences on CTI performance - part surface structure

Apart from moisture and temperature influence, part surface influences the CTI performance of your plastic part too (Figure 3). In case of PPS (Tedur HTR), a highly polished surface can increase the CTI from 500 V to 550 V [3]. On the other hand, rough surface structures such as the K29 and K30 (Knauf Industries), decrease the CTI value from 500 to 450 V [3]. 

Figure 3: CTI of PPS and influence of different surface finishes onto the CTI value [3].

Conclusions

CTI plays an important role when designing electronic components such as busbars for traction motors and power electronics. Selecting the optimal polymer material which can withstand temperature, humidity, time and mechanical impacts is key in order to make your design compact and safe without having short-circuits in the long run. 

Thanks for reading & #findoutaboutplastics

Herwig Juster 

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

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Literature:

[1] https://en.kunststoffe.de/a/specialistarticle/against-the-current-2586918

[2] https://www.polyplastics.com/en/product/lines/pbt_pa66/index.html

[3] https://www.plastverarbeiter.de/markt/elektroniktauglich-polyphenylensulfid-compound-mit-hoher-kriechstromfestigkeit.html

Global Warming Potential (GWP) Reduction of Engineering and High Heat Plastics - Example PPS and PBT

 Hello and welcome to this blog post. Today we discuss how we can reduce the global warming potential (GWP) of engineering thermoplastics with the focus on Polybutylene terephthalate (PBT). Also we discuss how to reduce the GWP of Polyphenylene sulfide (PPS) by applying a replacement strategy. In another post we discussed the PPS GWP reduction in more detail. 

Effective ways to reduce the global warming potential (GWP) of thermoplastics

One way is to replace a high GWP polymer by a lower GWP one, and have at the same time a cost benefit as well as no reduction in performance. An example of this is the suggestion of material manufacturer Polyplastics to replace PPS components in the EV battery cooling system by low-cost long-glass fiber PP or POM [5]. PP has a GWP of 1.63 kg CO2 eq and POM has a GWP of 3.2 kg CO2 eq. Those are much lower compared to PPS with 5.46 kg CO2 eq or even higher in some cases. Reason which makes this change possible is that long-life coolants (LLC) for cooling batteries in EVs is maxim 100°C and for most time between 60 to 80°C, allowing PP and POM to take over this job. In this example we have a cost, and lower GWP advantage and keeping the needed performance. In addition, if one would like to keep the PPS and still lower the Carbon footprint, an effective way is to use recycled glass fibers. In detail we discussed this approach here. 

Another way to reduce the GWP of an existing polymer is to use recycling methods. This approach we discuss next. 

Using PET-bottles to reduce GWP of PBT 

It is possible to exchange fossil based raw material by post-consumer (PCR) PET bottle waste as feedstock in order to reduce the GWP of PBT. In our example, 60 wt% PCR PET bottles were up-cycled to a higher engineering PET which shows almost the same properties as a PBT resin based on 100% fossil feedstock. The carbon footprint could be reduced by 49% compared to the fossil based PBT.  Table 1 compares the properties of the standard PBT and low GWP PBT and Figure 1 shows the GWP reduction achieved with this up-cycled product. 

Figure 1: comparing the cradle-to-gate CO2 footprint of PBT and low-GWP PBT [1].

Table 1: Overview properties of PBT and low-GWP PBT [1].

Properties	PBT (Valox)	PBT low GWP (Valox iQ)
Tensile strength at yield (MPa)	54	50
Flexural stress at 5% strain (MPa)	85	82
Flexural modulus (MPa)	2500	2460
Notched Izod, 23°C (J/m)	35	35
Specific gravity	1.31	1.31
Tc (°C)	164	170
Tm (°C)	225	220
HDT, 0.45 MPa (°C)	155	150

Conclusions

Considering the GWP during your material selection journey is becoming more and more easier since material manufacturers start to up-cycle and recycle their products. Also, based on requirements, new low GWP and low cost materials can be used for traditional engineering and high performance polymer applications. 

Thanks and #findoutaboutplastics

Greetings, 

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

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Literature:

[1] https://www.researchgate.net/figure/58_tbl2_298399814

[2] https://www.researchgate.net/publication/298399814_Environmental_Benefits_of_post-consumer_recycled_PET_based_Valox_iQ_resin_vs_Valox_resin_using_Life_Cycle_Assessment_Approach

[3] https://www.findoutaboutplastics.com/2022/01/global-warming-potential-gwp-vs-thermal.html

[4] https://www.findoutaboutplastics.com/2021/12/eco-profiles-of-polymer-resins-global.html

[5] https://www.plasticstoday.com/automotive-and-mobility/ev-cooling-components-can-be-molded-less-heat-resistant-plastics

6+ Inputs for Reducing Flash Formation of Polyphenylene sulfide (PPS) During Injection Molding

Hello and welcome to this post on injection molding tips with the focus on flash reduction of PPS and obtaining low flash PPS parts.

Background

Having worked in the field of high-performance polymers and specifically with PPS for the past ten years, I have often received the same question: How can flash formation be minimized and reduced during PPS molding? In this text, I will share more than six practical tips to address this issue, based on my extensive experience in the industry.

Let us get started. We will first discuss the possible causes of flash and then show possible solutions. 

What is flash formation in injection moulding?

In general, flash occurs when molten plastic flows out of the mould during injection and solidifies, causing a visible effect (Figure 1). 

Figure 1: Visible flash formation on an injection moulded part. 

Why flash can be an issue with PPS?

Since PPS is a high flow polymer, it is an excellent choice for thin walled injection moulded parts. Also, the good flow properties allow for high filling loads. The good flowability allows the PPS to flow during filling out of the cavities without too much effort. Figure 2 compares the spiral flow length of different PPS types to Polyamide 6 with 50 wt% glass fiber [based on 1,2]. The highly filled PPS (GF/MD 65 wt%) reaches 40% more in flow length compared to the PA 6 (GF 50 wt%).

Figure 2: comparison of spiral flow length (1 mm thickness) of different PPS compounds (incl. unfilled) vs. PA 6- GF 50 wt% [based on 1,2].

Reducing flash with PPS: possible causes vs solutions 

How to start: Check the Mold, Clamping Force, Packing Pressure

The first step to enable flash-free injection molding with PPS is to control the mold, specifically by cleaning and inspecting the venting and parting line. 

Next, the required clamping force should be verified. Short shots should then be produced to determine the switch-over point, followed by the application of the appropriate packing/holding pressure (height and time).

Optimize Molding Parameters

1) Low packing phase from 0.0 to 0.5 s and then start with regular packing phase. The 0.5 seconds in delay allow the melt to freeze the parting line (seal it off) and flash is reduced.  

2) Too high injection pressure -> decrease cutoff position, injection packing pressure, and injection time forward

3) Too high injection rate -> decrease injection rate

4) Too high polymer melt temperature -> decrease barrel temperature and lower backing pressure

5) Too high mould temperature -> decrease mould temperature (min. 135-140 °C)

6) Too low mould clamping force -> increase clamping force; alternatively check the possibly to move mould to larger injection moulding machine (higher possible clamping forces)

During molding operations

Mold Wear and Misalignment During Production: At the start of production, parts typically exhibit no flash; however, flash may develop as the production run progresses. It is important to verify that the mold steel has adequate hardness and that cavity edges are not experiencing excessive wear. Additionally, ensure correct mold alignment and keep parting lines clean and free from material buildup in the parting area.

Check PPS Drying Procedures

Mineral-filled PPS compounds can be hygroscopic, they should be dried at 135–163 °C (275–325 °F) for 2 to 3 hours to prevent moisture-driven "drool," which can cause flash.

Bonus Tip: Select Low-Flash Grades: 

Utilize specific PPS compounds designed to minimize flash, such as Ryton R-4-230BL (40% glass fiber reinforced), which provide improved processability.

Furthermore, there are PPS alloy compounds which have low flash properties and fast cycle times (f.e. Ryton PPS XK2340 or XK3340). 

Check out my YouTube training video on this topic too: 

Now I am curious, let me know - what are your tips to reduce flash when moulding polymers such as PPS?

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature: 

[1] http://mold-technology4all.blogspot.com/2011/07/wall-thickness.html

[2] https://www.plastics.toray/technical/torelina/tec_017.html

[3] https://www.solvay.com/sites/g/files/srpend221/files/2018-10/Ryton-PPS-Processing-Guide_EN-v2.1_0.pdf

[4] https://youtube.com/shorts/ci88l0FtSUM

[5] https://www.syensqo.com/en/brands/ryton-pps

[6] https://www.linkedin.com/pulse/6-inputs-reducing-flash-formation-polyphenylene-sulfide-herwig-juster-fzjhf

Virgin vs. recycled glass-fiber PPS: How much can the carbon footprint be lowered?

Hello and welcome to a new post. Today’s post deals with the question of how much the carbon footprint of 40 wt% glass-fiber reinforced PPS can be lowered. Using a low carbon footprint polymer may be on your requirement list for material selection and thus we have a brief look at this topic. 

Several options to decrease Global Warming Potential of thermoplastics

There are more than one way to lower the carbon footprint of a polymer. For instance, one can use a base resin which has a lower carbon footprint by its manufacturing process. As an example, Polyketone is mentioned, which has a Global Warming Potential (GWP) of 3.08  kg CO2 eq, whereas Polyamide 6 has a GWP of 6.70 kg CO2 eq. Another way is to use recycled fillers such as recycled glass- and carbon fibres. Also, using natural feedstock for monomers and applying a mass balance approach is another great option and widely used already among engineering and more and more with high performance polymers too. 

Example standard 40 wt% glass-fibre reinforced PPS

Speaking of high performance polymers, Polyphenylene sulfide (PPS) is often used for applications in high temperature, stringent chemical environments and often I receive the question how much the carbon footprint can be lowered of a standard 40 wt% glass-fiber reinforced PPS? 

I have already some experience with recycled PPS usage (my regrind Rule of Thumb post) and I searched for some data on this interesting question. Starting from 5.43 kg CO2 eq of a standard PPS-GF40 grade, carbon footprint could be lowered to 3.01 Kg CO2 eq, reducing the greenhouse emissions by about 2.42 kg CO2 eq (Table 1). The calculation are based on the ISO 14067 standard. The low carbon footprint PPS uses 50 wt-% post industrial recyclates to achieve such a reduction. 

Table 1: Reduction of the carbon footprint of PPS by using recycled material [1]. 

Update: recently I came across a 40 wt% glass-fiber reinforced PPS which has 0.619 kg CO2 eq which uses recycled PPS to lower the carbon footprint [3].

More on the topic can be found here (eco-profiles of polymers)

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature: 

[1] https://plasticker.de/news/shownews.php?nr=43176&nlid=64581.d.h.2023-06-01

[2] https://plas.tv/?p=33837

[3] https://www.convena-polymers.de/News-63?news_id=33

Material Selection Considerations for Electric Vehicles (EV’s) - Thermal Management Systems

In this post, we will have a closer look at the key considerations for thermal management systems used in electric and hybrid cars. This can support an optimal selection of plastic materials.

Traditionally, in internal combustion engine cars a powertrain thermal management and a passenger cabin thermal management system are present. Here, it well understood which type of plastic materials can be used depending on the application requirements.

In EV’s, thermal management systems support additional systems such as:

• Lithium battery: Thermal management systems need to ensure operating temperatures of 40-45°C to maximize battery service life. Composing parts need to retain material properties after 6.000-10.000 hours to ensure safe handling. Thus, precise control of temperature deltas is crucial.

• Traction motor: Thermal management systems need to ensure operating temperature of coils up to 190°C to allow high torque at small size.

• Power electronics: For high power electronic controllers, liquid cooled systems are favored and plastic materials used in housing need to have a thermal conductive role.

• Hybrid EVs: Downsizing of the combustion engine leads to local hot spots, which thermal management systems need to be able to handle.

What are the market trends and emerging needs?

For internal combustion engines increased temperatures due to downsizing of engines are expected. Simultaneously, more and more turbocharging systems need to be used to compensate the missing engine performance. EV’s have a system temperature ranging from 70°C to 80°C. The latter makes polyolefins accessible for thermal management applications.

Furthermore, in battery EV’s an increased aging exposure to water glycol coolant from 3.000 up to 6.000 till 10.000 hours is expected. Thermal management systems need to be active during charging time as well as when the surrounding temperatures are extremely low. Also, when the EV is not operating, temperature is monitored and in case extreme temperatures are reached, thermal management systems have to be activated too.

All this leads to ongoing discussions at the OEM and Tier-1 level on the requirements, which can be summarized as follows:

1) Coolant fluid temperature: ranging from 80°C to 110°C

2) System pressures: can reach up to 3 bar

3) Increased lifetime: up to 10.000 hours

4) Use of dielectric conductive coolant fluids

New design challenges

As mentioned in the beginning, having additional systems such as the battery, traction motor and power electronics for monitoring tasks require higher complexity thermostat valves which need to fulfill a more precise control. Temperature deltas between one battery module and the next module can be as stringent as 1°C.

Since available space for battery module placement is limited, the design of thermal management systems must be compact. Long operation times (during driving, charging and parking) and chemical resistance of water glycol coolant fluids represent another design challenge. One of the most critical challenges is the material strength which includes the weldline strength, especially after long term aging exposure.

Weldlines represent always the weak point of the plastic application, since the connection is weakened due to random orientation of glass fibers in the connection area. In addition, weldline strength is further weakened by water glycol aging. Since we will be dealing with more complex parts, weldlines are unavoidable and need to be taken care of.

Can all this be handled by plastics? - Yes, but only with the proper material selection

Let us summarize the key considerations for our material selection and give suitable polymer examples:

1. Aging temperature: 120-150°C: Polyphenylene sulfide (PPS); 120-135°C: Polyphthalamide (PPA)

2. Aging time: 1.000 – 3.000 hours: PPS and PPA; > 6.000 hours: PPS or PPA based on required temperature.

3. Increased chemical degradation due to different coolants: PPS has best in class chemical resistance.

4. Dimensional stability for sealing tasks: PPS and PPA.

5. Secondary operations such as laser welding: PPA has good laser welding capabilities.

PPS and PPA show promising mechanical behavior even when exposed to high temperatures, water-glycol coolant and long aging time.

Figure 1 shows mechanical data of PPS after exposure to water-glycol coolant (Ryton® R-4-220BL, Solvay). Figure 2 shows the mechanical data of a suitable PPA for water-glycol applications (Amodel® A-1933 HSL, Solvay).



Figure 1: Mechanical data of PPS after exposure to water-glycol coolant (Ryton® R-4-220BL, Solvay).

Figure 2: Mechanical data of a suitable PPA for water-glycol applications (Amodel® A-1933 HSL, Solvay).

PPS and PPA: not all grades are equal

PPS has unbeatable chemical performance due to the benzene sulfide group in the backbone. When exposed to water-glycol coolant, the PPS polymer matrix can withstand long aging times. However, attention needs to be payed to the glass fiber sizing. The same applies to PPA grades as well.

Interfacial adhesion of the polymer to the glass fiber is achieved over the sizing which is coated onto the glass fiber. Standard glass fiber sizings are cleaved when exposed to glycol and thus the mechanical values drop. Therefore, special sizings are used when the final compound is exposed to glycol. When your application is exposed to coolants, using of glycol resistant glass fillers is a must. The compounds shown in Figure 1 and 2 use such glycol resistant glass fiber fillers.

Material recommendations

Table 1 shows a recommendation concerning material selection for EV’s thermal management system based on existing data.

Table 1: Comparison of PPS and PPA for EV thermal management systems

Comparison PPA and PPS for thermal management systems

Overarching, high performance and engineering plastics will find more and more applications in EV thermal management systems.

If you would like support in the material selection of thermal management systems (from polymer to supplier) for ICE and/or EV feel free to get in contact with me. We can discuss your project.

Thanks for reading & till next time!

Greetings,

Herwig Juster

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Literature
[1] https://www.solvay.com/en/brands/ryton-pps#Design-Guidelines
[2] https://www.solvay.com/en/brands/amodel-ppa#Grades

Polyphenylene sulfide (PPS) – The Conquering of Electric Car Parts



In this blog post I explain why polyphenylene sulfide (PPS) is conquering more and more key parts in higher voltage electric cars. In my electrification series, I have discussed the requirements of certain parts already in detail as well as which advanced polymers can be used. A major one is PPS.

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). This is a huge increase. Let’s find out why it is so heavily in use.

Reason number 1: Elevated temperatures during usage over a long lifetime (over 6000 hours)

Applications such as capacitor cases, invertor cores, motor cores and housings have to withstand elevated temperatures during use and need to have excellent heat cycle performance. PPS can fulfill these set of requirements in an economic manner.

Reason number 2: Thermal management systems

Cooling of the battery and the electric motor requires water pumps. The latter need to perform when constant exposed to the water-glycol mixture. The outstanding thermal and chemical performance of PPS makes it a very suitable candidate for any application inside the water pump, e.g. impellers. Cooling of the battery is necessary when the car is charging as well. As such the lifetime expectation of (plastic) parts is also higher.

Reason number 3: Good metal overmolding capabilities

Busbars are usually thick copper lines which need to be overmoulded. Here again, processing of PPS due to good flow properties is an advantage together with its good electrical insulation properties.

Reason number 4: Dimensional stability at ambient conditions

Exterior positioning sensors in electrical vehicles need to be dimensional stable at various ambient temperatures and humidity. This ensures accurate positioning detection. In this context, PPS exhibit negligible water uptake which makes them suitable for external positioning sensors. For instances, Nylons would be less of suitable candidates here due to their inherent higher hydrophilicity.

Reason number 5: Price level suitable for automotive market

With PPS you will get a lot of value for a reasonable price, i.e. continuous use temperature of 200-240°C, UL94 V0 rating, chemically resistance up to 200°C and dimensional stability at ambient conditions. Price is a major advantage in comparison to other high performance polymers.

A short word on linear vs cross-linked PPS:

There are three major routes to obtain PPS. First one is called flash process with curing. The curing step is needed to increase molecular weight [2]. This process results in branched PPS. The second route encompasses the flash process and metal carboxylates and results in linear PPS [3]. The third route is over the quench process and results in linear PPS as well [3]. Leaders in the industrialization of the PPS polymerizations were Chevron Philips and Kureha back in the 1980s. For electric vehicles, linear types of PPS are optimal. These show superior toughness and improved weldline strength. In general, linear PPS does not process as well as cross-linked PPS. However, less moulding flash is generated by linear PPS types.

What are the potential downsides of using PPS for e-mobility applications?

One aspect to consider is the comparative tracking index of PPS which is between 250 and 275 Volts. This is low compared to PPA which can easily reach 600 Volts. Another point is its low thermal conductivity, 0.3 -0.5 W/mK and finally its brittleness.

Besides PPS, what are next best candidate materials?

In the table below, I have listed polymers which can be in competition for applications using PPS: syndiotactic polystyrene (sPS), polybutylene terephthalate (PBT), and polyphthalamide (PPA).

Conclusion:

PPS, branched or linear, are in the lead for e-mobility applications, especially for high temperature electronics. Automotive, regardless of ICE or EV, will be the main driver for using PPS. This was a wrap up on PPS used in electrification applications.

I hope you have enjoyed it!

Till next time!

best regards,

Herwig Juster

If you liked this post, share and like!

Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section.
Check out also my personal webpage.


Literature:
[1] https://www.plasticstoday.com/automotive-and-mobility/chinaplas-pps-recording-explosive-growth-evs/50108596960874
[2] Nexant Chemical Systems
[3] Solvay Specialty Polymers – Ryton PPS https://www.solvay.com/en/brands/ryton-pps