Hello and welcome to a new blog post. I received a question on how to improve the Comparative Tracking Index (CTI) of thermoplastics and in this post we will discuss this question since it can be of value for the whole community.
The basics of CTI and its measurement I discuss in this training video.
In general, there are polymers which more likely form a conducting carbonized path compared to other polymers. Aliphatic and semi-aromatic polymers, polyolefins, fluoropolymers, as well as polyesters show high resistance to form a conductive carbonized path. PPS on the other hand more likely forms a conducting carbonized path, combined with a low tracking resistance. Important in this context are the two standards IEC 60112 and UL 746 which are used in several industries to rank CTI of polymers. Figure 1 shows an overview in which CTI class (IEC and UL) different thermoplastics can be placed.
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| Figure 1: Overview CTI of different thermoplastics |
Ways to improve the CTI value
-Use a mineral flame retardant: By adding 8 weight % of mineral flame retardant to a PBT, CTI could be increased 13%. Example is the ACTILOX® 200SM (Nabaltec).
-Use additives: there are multi-functional polyester modified siloxane additives which can be used to improve the CTI of various engineering compounds. Example is the TEGOMER® H-Si 6441 P (Evonik).
-Blending with a high CTI polymer: in the case of PPS, adding polyamide can improve the CTI value from 175 V (PPS-GF40) to 275 V (PPS-GF40+PA). Example is the Ryton XK2430 (Solvay).
Electrical design properties such as the CTI is important during the material selection of components for e-mobility and electronic applications. Choosing the optimal polymer can lead to a more compact design which is the case for busbars overmoulded with a thermoplastics. A high CTI polymer allows you to shorten the distance between the busbars.
Thanks for reading and #findoutaboutplastics
Greetings,
Herwig Juster
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
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Literature:
[1] https://www.toray.eu/eu/plastics/torelina/technical/tec_021.html
[2] https://www.plastic-additives.com/en/application-areas/cable-electronics
[3] https://nabaltec.de/fileadmin/user_upload/03_produkte/03-3_boehmit/nabaltec_tds_actilox-b30-b60-200sm.pdf
[4] https://www.solvay.com/en/product/ryton-xk2340
[5] https://www.youtube.com/watch?v=LzFyKr-SUZQ
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