Hello and welcome to this blog post. Having worked over one year at a plastic compounding company focusing on highly filled plastics, I would like to share some fruit for thought when formulating thermoplastics compounds. In this post we discuss in my point of view the most important considerations (Figure 1).
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| Figure 1: 5 Key Considerations for Formulating Optimal Thermoplastic Compounds |
Let us get started with the 5 key considerations:
1) Gather product requirements
It is important to gather as much information on the end-use application and industry the part will be used. OEMs and Tier-1 suppliers will provide such information. Industries have different standards which need to be fulfilled and may limit the use of certain additives (f.e. Healthcare industry). Also we need to be aware of mechanical loads, temperature exposure (short- and long term), as well as chemical exposure.
2) Selecting the base polymer
Depending on the requirements and industry the application will be used, selection of the base polymer can start. We can select among a wide range of polymers from commodities such as PP, engineering plastics such as Polyamide, and high performance polymers such as PPS and PEEK. Apart from fulfilling the requirements, it is important to keep the polarity and the pH level of the base polymer in mind since both characteristics influence the filler and additive choice.
3) Selecting additives
In our plastics additives series we already discussed the differences of fillers, reinforces and additives. Check them out here: Part 1, Part 2, Part 3.
Adding additives can improve and protect different areas of the base polymer. UV stabilisers prolong the lifetime of the base polymers, together with UV absorber for additional protection. Also, we can add antioxidants and in some cases such as Polyolefins, without the usage of antioxidants proper processing would be not even possible. Furthermore, we can influence the viscosity, impact strength, friction, thermal conductivity, and provide anti static behaviour.
For formulating it is important to calculate in volume percent. Later when you do compounding we switch to weight percentage since you want to weigh in the different materials.
4) Selecting reinforcements
Property modification of the base polymer is done by using reinforcements such as glass fiber or other types of fibers. Also, fillers are used to lower the overall costs. Mainly calcium carbonate (chalk), magnesium silicate (talc), mica, and glass beads are used to fulfil this. Filler levels above 80 wt% are possible if you want to increase the density of the compound.
Barium sulphate is used to achieve a higher density, calcium carbonate is a well-known cost reducer. Increasing the rigidity and heat deflection temperature, as well as thermal conductivity is done by talc. If sound deadening properties are needed, mica is a good option. Reducing frictional properties is done by glass beads.
5) Compounding your formulation
Now we selected the bases polymers, additive package and filler and/or reinforcements. In the next step we have to combine all components via a twin screw extrusion lab line. Having the material in your hands, first tests such as tensile strength, HDT, density, and impact can be done. This allows you to check where you are standing in terms of desired material requirement achievement. If you are happy with the outcome, it is time to move to a production compounding line which is able to make +1 ton of material per hour. Scaling up a standard material with three to four components may have some challenges in the ramp up, however can be resolved quickly. However, if your lab line compound consists of eight to ten components, scale up on the production line may result in bigger challenges. Furthermore, quality checks need to be done in-line, removing material during the production run, making tensile sample bars and testing them. Then results need to be immediately communicated back and changes applied if needed. On the production line, the optimal processing window including temperature profile along the line needs to be estimated. Heart of the extrusion line is the arrangement of the screws which consists of different elements such as mixing, dispersing and transporting.
Finally you have your plastic compound as it was planned and the formulation as well as production parameters are frozen. Additionally, a quality check via DSC curve can be done, having a footprint for later occasions. Also, the certificate of analysis is done which is needed to supply the customer, together with the material.
If you have any questions or want to create your own plastic compound, pl. reach out here to support you and if you need plastic sample material for testing, you can reach out here.
Thanks and #findoutaboutplastics
Herwig
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://encompolymers.com/blog/5-common-types-of-polymer-additives-and-their-benefits/
[2] https://interplasinsights.com/plastic-industry-insights/technical-101-formulating-plastic-compounds/
[3] Roger F. Jones - Strategic management for the plastics industry
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