Hello and welcome to a new blog post. In today's post we discuss some potential materials for replacing established power tool housing materials. Among the established materials for power tool applications are mainly polyamides, in particular polyamide 6 (PA 6) with 30 wt% glass fiber reinforcement and also polyamide 6 with impact modifications. They have been in use for over 25 years and also the polyamide compounds over time were improved leading to an increased quality of the final parts. There are several motivations for material change and the major driver is material cost, together with good availability of commodity plastics.
In parallel there are potential replacement materials coming up, for example ABS which is used more and more for certain parts of power tools however also polypropylene compounds find more and more their way into engineering applications.
Comparison: PP, PP-GF, PP with chemically coupled GF vs PA 6 –GF30
Polyolefin compounds with chemically coupled class fibers are attractive materials to replace PA-GF 30wt%. Figure 1 compares the tensile strength of an unreinforced polypropylene, a polypropylene with standard class fiber reinforcement and a polypropylene with chemically coupled class fibers (both with a 30 wt% glass fiber loading) at room temperature. On the right side of Figure 1, the tensile strength of PA 6- GF 30 wt% is shown (orange lined bar). It can be shown that by using chemically coupled class fiber PP compounds, an improvement in tensile strength of 180 to 190% compared to the unreinforced PP is achieved as well as a doubling of the tensile strength compared to the standard PP- GF 30 wt%.
Interesting is the comparison of PA 6 - GF 30 wt% (conditioned state) to the chemically coupled GF - PP: PA 6 tensile strength ranges between 100-110 MPa and with chemically coupled GF PP we are slightly below that value, however with adoption in design, similar performance can be achieved.
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| Figure 1: Comparing the tensile strength of PP, PP-GF30, PP-GF30 (chemically bonded GF), and PA 6- GF30 at room temperature. |
Designing parts with Polyolefins compared to engineering plastics: Advantages and critical topics
Designing technical parts with polyolefins such as PP can be challenging. Part design engineers need to balance the integration of functions and need to achieve high technical quality parts however with a reduced property level of the material (PP vs PA). Therefore understanding the advantages and some critical points of PP with chemically coupled glass fibers is crucial.
Table 1 outlines the most important advantages of using PP with chemically coupled glass fibers, together with critical points. On the one hand, PP has excellent flow properties and this enables to have parts with longer flow length or thinner wall thickness. Also, filling more complicated geometries is possible too. PP has good impact properties and important is that PP is not losing these impact properties in the minus temperature range. We have almost the same deformation capability as with a polyamide. Important advantage is the lower cost of the material, together with lower density compared to PA and we have also a good heat distortion temperature (HDT). For certain engineering applications, the HDT of PP is sufficient. Additionally, there is no need of conditioning the final parts compared to PA (dry and conditioned state).
More critical with such materials is the higher shrinkage and warpage level compared to polyamides, resulting in a stronger dependency of the shrinkage in the flow and cross-flow direction. An important topic is surface quality especially with power tool housing and know-how in colouring of such PP compounds is needed. In terms of processing, polyolefins have a longer processing cycle (10 to 15% longer compared to a polyamide). In the part design phase, more engineering is needed, since we want the same quality level of parts however have a material with reduced or other properties (such us other shrinkage/warpage behaviour).
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| Table 1: Comparison of advantages and critical points of PP with chemically coupled GF. |
Other potential materials: Polyketones and recycled PA 6 for carbon footprint reduction
Apart from PP with chemically coupled glass fibers, polyketones with 30 wt% glass fiber reinforcement can be interesting too, especially when the application reaches a temperature level of 90°C.
Figure 2 compares the tensile strength of PK- GF 30 wt% and PP - GF 30 wt% at 23°C and 90°C. Polyketone reaches a tensile strength level at 90°C which is higher than the tensile strength of PP - GF 30 wt% at room temperature.
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| Figure 2: Comparison tensile strength of PP-GF30 with PK-GF30 at 23°C and 90°C[2]. |
Reducing the carbon footprint of PA 6 - GF 30 wt% (and potentially also costs) can be achieved by using a mechanically recycled PA 6 (Figure 3; up to 85% reduction - check out the calculator here) or switching to another polymer. Polyketones can lower the CO2 footprint as much as 28 % CO2 eq/part compared to PA 6.6 - GF 30 wt%.
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| Figure 3: Potential CO2 reduction by switching from PA6-GF30 to a mechanically recycled PA6-GF30. |
Allover, replacing engineering plastics by cheaper commodity plastics is in full swing and if you have interest in a material switch, I invite you to reach out to me for support.
Check out the YouTube video on this topic here or below too:
Thanks for reading/watching and #findoutaboutplastics
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Literature:
[1] https://www.borealisgroup.com/products/polyolefins/brands/fibremod
[2] https://akro-plastic.com/en/compounds/akrotek-pk
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