Hello and welcome to a new blog post. In a previous post we discussed the coefficient of linear thermal expansion (CLTE) of high performance polymers such as PPS, PEEK and PVDF already.
In this post we will introduce the CLTE of commodity polymers, mineral fillers and metals with the focus on how to control CLTE in an optimal way.
Optimizing the CLTE of polymer compounds - how to do it?
Comparing the CLTE values of metals, minerals and polymers (Figure 1) we notice that polymers have a factor 3 to 5 times higher CLTE in comparison to metals. Comparing the polymer CLTE with minerals the factor is with 10 even higher [1]. Based on this fact, lowering the CLTE of polymers can be done by mixing them with minerals. Also it is important to use isotopic fillers which result in equal mechanical properties and CLTE in the x,y, and z directions.
Figure 1 compares the CLTE of unfilled and filled plastics as well as minerals and metals.
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| Figure 1: CLTE of polymers, minerals, and metals. |
Example of talc filled Polypropylene
Figure 2 shows the CLTE of PP in comparison with 10 w% and 20 w% talc filled PP. The CLTE could be reduced from 150 to 95 x 10-6 K-1 (36%).
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| Figure 2: CLTE of PP and talc filled PP |
Example comparison CLTE of glass and glass/mineral filled semi-aromatic Polyamide (PPA)
Another example shows the impact of combined filling of glass fiber with mineral filler on the CLTE. A 33 wt% glass-fiber reinforced PPA is compared to a 66 wt% glass-fiber and mineral filler PPA. In the temperature range of 0°C to 100°C, the CLTE could be lowered 30% in flow direction and 28% in transverse direction. In the temperature segment from 100°C to 200°C, the reduction in flow direction is 40% and in transverse direction 40% too (Figure 3).
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| Figure 3: Comparison CLTE of glass and glass/mineral filled semi-aromatic Polyamide (PPA) [4]. |
In conclusion
CLTE can be a critical requirement for enclosed or metal overmoulded parts. Modification of polymers with certain fillers to reduce the CLTE needs to be kept in mind during polymer material selection.
Thank you for reading and #findoutaboutplastics
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[1] https://phantomplastics.com/fillers-for-cte-clte-modification-of-plastics/
[2] https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
[3] https://www.findoutaboutplastics.com/2020/04/design-properties-for-engineers_28.html
[4] Syensqo, Amodel(R) Product Guide
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