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 surfaces an 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 

Interested in having a second opinion on your material selection and high performance polymers or  discuss with me about your current sustainability, and part design needs - here you can contact me 

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

Interested in our material solutions - check out our product page here

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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

Chlorine Based Plastics: PVC vs PVDC (Specialty Materials Know-How)

Hello and welcome to this blog post in which I discuss the differences and similarities of PVC and PVDC, as well as the unique barrier properties of PVDC. 

Re-cap: what is PVC? 

Poly(vinyl chloride) is an amorphous  thermoplastic polymer consisting of carbon (C), hydrogen (H) and chlorine (Cl) and PVC is, after polyolefins, the second largest plastics material group. Since the molar weight of this polymer contains 56.7% of chlorine [1], it uses  less petroleum and gas feedstock  for its production in comparison to other polyolefins. This elevated content of chlorine also provides PVC with flame-retarding properties. As a result, PVC holds the lead in civil- and construction  engineering applications, such as isolations and floorings. Apart from the construction sector, PVC plays an important role in medical device applications, where it ranks right after the Polyolefins in overall usage. A blog post on detailed applications using PVC in medical device applications can be found here. 

What Is Polyvinylidene Chloride (PVDC)?

PVDC fulfils not the classic definition of high heat/performance polymers (UL 746B - polymers need to withstand a continuous use temperature of 150°C for 100,000 hours), however we can classify it as a special polymer, based on its unique set of properties. 

PVDC, chemically defined as 1,1-Dichloroethene, has a temperature usage range from -20°C up to +100°C (from 160°C on chemical-thermal degradation starts, resulting in hydrogen chloride). The additional Chlorine results in a semi-crystalline morphology, whereas PVC is an amorphous polymer.

What is the difference between PVDC and PVC?

Figure 1 shows the chemical structure of PVC and PVDC. It can be seen that PVDC contains double the amount of chlorine compared to PVC. The combination of symmetric Chlorine leads to a high barrier towards oxygen and water vapor as well as superior flame retardancy performance. Figure 1 also contains the oxygen permeability of PVOH, EVOH, PVDC, and R-PVC. PVOH and EVOH perform slightly better than PVDC, however if you combine it with the water vapor chart, things look differently. PVDC has a low water vapor permeability compared to PVOH and EVOH. This allows you to have a material which has excellent oxygen and water vapor resistance which can be used for several interesting applications.

Figure 1: Chemical structure of PVC and PVDC, together with oxygen and water vapor permeability [5].

PVDC applications

PVDC is mainly used as film for packaging applications and as waterborne high-barrier resin dispersion which allows coating of textiles, paper, and plastics. 

For packaging, the combination of oxygen and water vapor barrier play a role for fresh and processed meat packaging, together with dry fruit, seafood and vegetable packaging. 

In the field of medical packaging, PVDC is used for pouching systems.

Also wine bottle caps use PVDC as a barrier layer. The well known Stelvin wine caps use a Saranex™ liner based on a PVDC [7]. 

Conclusions

To summarise, PVDC is a high barrier polymer with outstanding gas barrier and water vapor properties. This unique combination of properties makes it an optimal material choice during your material selection journey for advanced packaging and medical film solutions. Apart from PVDC, PARA (MXD6) has also interesting barrier properties which we discuss in the post here. 

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig Juster

Interested in our material solutions - check out our product page here

Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me 

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

My YouTube channel

My personal website

Literature: 

[1] W. Kaiser: Kunststoffchemie für Ingenieure: Von der Synthese bis zur Anwendung, Carl Hanser (2011)

[2] https://www.findoutaboutplastics.com/2015/02/pvc-not-always-in-best-spot-but-still.html

[3] https://www.findoutaboutplastics.com/2017/03/my-top-5-commodity-plastics-for-medical_23.html 

[4] https://us.metoree.com/categories/5347/

[5] https://www.syensqo.com/en/brands/ixan-pvdc/faq

[6] https://www.amcor.com/stelvin

Design Properties for Engineers: Superior Gas Barrier Properties of PolyArylAmide (PARA; MXD6)

Hello and welcome to this new blog post. We discussed several outstanding properties of PolyArylAmide (PARA; MXD6) in detail here. 

However, another impressive property is the superior gas barrier against oxygen and carbon dioxide in film applications. PARA is able to outperformance other commercial available Polyamides, and can compete with well established materials such as ethylene-vinylalcohol copolymers (EVOH)，acrylonitrile copolymers (PAN) and vinylidenchloride copolymers (PVDC). 

Film extrusion and crystallization speed of PARA (MXD6)

PARA crystallizes similarly to PET allowing PARA to stay in an amorphous state easily if it is cooled immediately after the extrusion or injection moulding process. 150°C to 170°C is the temperature range where PARA crystallizes the fastest.  The moderate crystallization speed opens up a wider operation window compared to other Polyamides in the thermoforming or the orientation process for film making.

Gas barrier properties 

Figure 1 shows the oxygen permeation rate of PARA (MXD6) films (stretch ratio 4x4) and other barrier polymers. The data indicates that the oxygen barrier property of PARA is much less moisture sensitive than that of EVOH. PARA with its high heat stability and wide processing window can be co-extruded and co-injection moulded with PET, PP, and PE in order to make multilayer containers or films.  Also, the gasoline barrier properties are outstanding and therefore it is used in the fuel system of Internal Combustion Engines (ICE) cars. In case the Polyamide will be coated with PVDC, moisture influence can be kept on a stable level. In another post we will discuss the oxygen and water barrier properties of Polyvinylidene chloride (PVDC). 

Figure 1: oxygen permeation rate of PARA-MXD6 films compared to EVOH and PA 6 (PVDC coated) [1].

In case you want to read more on PolyArylAmide - check out "The ABCs of Polyarylamide (PARA; MXD6)".

Thank you for reading this post and #findoutaboutplastics.

Greetings,

Herwig Juster

Interested in our material solutions - check out our product page here

Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me 

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

My YouTube channel

My personal website

Literature:

[1] https://www.fostercomp.com/wp-content/uploads/2018/11/MX-Nylon_properties.pdf

[2] https://www.syensqo.com/en/brands/ixan-pvdc/properties

[3] https://us.metoree.com/categories/5347/

Plastic Part Marking Codes of Aliphatic and Semi-Aromatic Polyamides (ISO 16396-1:2022 -prev. ISO 1874)

Plastic Part Marking Codes of Polyamides 

Hello and welcome to the first post of the new year 2024! I hope you had a great Christmas break and I welcome you all back to a new exciting year of polymer engineering topics. 

Let us start with a community question which is about the part marking codes for Polyamides, in particular the ISO 16396 (previously ISO 1874). 

In my previous posts I discussed mainly the ISO 1043 for part marking since it covers all polymers. However, apart from the ISO 1043, the ISO 16396 was established to deal with the wide range of Polyamides. 

What is the ISO 16396 (previously ISO 1874) exactly?

The ISO 16396-1:2022 (prev. ISO 1874) [1]: Polyamide moulding and extrusion materials 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 (TPA) / hexamethylenediamine together Polyamide 66 which is based on hexamethylenediamine and adipic acid. 

M: injection moulding; H: heat ageing stabilized

14-190: viscosity number (in ml/g) > 130 but below 150; 190: tensile modulus of elasticity between 17000 MPa and 20000 MPa

High heat Polyamides - plastic part marking examples

In Table 1 I summarized commonly used high heat Polyamides which allows you to quickly identify the plastic used for a certain part or to use it for your next project where in the end the part marking question may come up.

Table 1: High heat Polyamides - plastic part marking examples.

Data block 1	Data block 2	Data block 3	Data block 4	Description
PA6T/6I	MH	12-110	GF30	PA based on TPA (6T) and IPA (Isophthalic acid; 6I) with 30 wt% glass fiber; injection moulding; heat stabilized;viscosity number >110-130; Elastic modulus >10.5 -11.5 GPa
PA6T/66	MH	14-250	CF30	PA based on TPA (6T) and PA 6.6 with 30 wt% carbon fiber; injection moulding; heat stabilized; viscosity number >130-150; Elastic modulus >23 GPa
PA 10T/X	MH	14-100	GF30	PA based on 1,10-decamethylene diamine (10) and terephthalic acid (T) with 30 wt% glass fiber; injection moulding; heat stabilized; viscosity number >130-150; Elastic modulus >9.5-10.5 GPa

 

More examples of part marking codes for different plastics compounds can be found here and for PolyArylAmides here. I wrote a miniguide on this topic too, which can be downloaded here.

Thank you for reading and #findoutaboutplastics

Greetings

Herwig Juster

Interested in our material solutions - check out our product page here

Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me 

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

My YouTube channel

My personal website

Literature:

[1] https://www.iso.org/standard/81940.html