Material selection - Choosing the right polymer

Some materials are easier to extrude, print, recycle, than others. Choosing the right polymer can save you a lot of research time.

1. Why does material selection matter? 

The success of your 3D print depends on your 3D printer, finding the correct printing settings and conditions, using quality filament, and of course, choosing the right  material . Even before 3D printing, the success of the Filament Making step depends on your material choice, too.

You should choose your material based on its properties and its processability. Choosing an appropriate material is essential to get the outcomes you want during the extrusion and printing steps.

2. Starting from your application

What is it you want to gain from your project? Before choosing your material, it’s crucial that you define your needs precisely. The material you choose can be a variable in your project. If several materials that tick all the boxes of your needs, it would be wise to choose the one easier to process.

Example 1:  If you need a material with high mechanical and temperature resistances, PEEK is a popular option, but there are others to choose from; PEKK and PEI, for example. Even if you decide to continue with PEEK, you have to be aware of the many different grades of PEEK there are to choose from, some of them easier to extrude than others.

Example 2:  You want to test PP with Copper Powder. If your project goal is to experiment with the additive copper, you might want to start by processing PLA and Copper. PLA is much easier to extrude and print compared to PP.   

3. What is a grade of polymer ?

A grade of polymer corresponds to one specific reference of one polymer type by one manufacturer. Normally, each individual grade is associated to a precise technical datasheet.

For instance, “ABS” is a family of hundreds of grades of ABS.

Or even more precisely : Ingeo Biopolymer 4043D is a grade of PLA by NatureWorks.

4. How to differentiate grades ?

Every grade is unique, but we can classify them into big families of grades.

The main difference between these categories is the flowing behavior of the molten polymer, which can be quantified by one simple viscosity indicator : the Melt Flow Index (or Rate), in g/10min. The MFI test is quite simple : measuring what mass of molten polymer can be pushed through a hole, under standardized conditions. The higher the MFI, the more fluid the plastic is, the lower its viscosity.

5. How to choose the right grade based on the MFI ?

material selection mfi scale

These MFI values are only estimations. This scale is a general indication to help you choose your first material if you have the option to choose, but it does not mean that only extrusion grades can be processed with our Filament Maker. At 3devo, we have successfully processed many injection grades.

Manufactured items typically do not have material technical datasheets. In that case, the MFI is unknown.

6. Certain materials are trickier than others

Not all materials have the same processability or require the same filament extrusion settings. Special processing, transitioning, and purging techniques are required with high-temperature polymers like PEEK, PEKK, and PEI. It is crucial to learn and know about these techniques before starting an experiment to avoid clogging the Filament Maker.

Polymers such as PP and HDPE are challenging to solidify as round filament because of their high crystallinity. While they are very safe to use with our equipment, they take time to master.

7. Recycling

Typically, recycling plastic comes with more challenges than processing virgin plastics. Namely because of the steps involved: collecting and sorting parts, shredding, maintaining the cleanliness of the batch, and there is no datasheet available.

Don’t let this stop you! We successfully extruded recycled plastic multiple times and have learned that it works well when all parameters are controlled.

8. Composites (Additives)

To make a composite, the additive, or filler, must be dispersed throughout the polymer matrix. You have two options:  

  • Pre-compounding the additive and the polymer into homogeneous pellets, typically via twin-screw extrusion, then turning them into filament. This method generally allows you to achieve higher additive proportions. 
  • Feeding the polymer and additive in the hopper of the Filament Maker, to combine the mixing and filament making steps at the same time. The risk of clogging the extruder is higher. 

When experimenting, it is always wise to start with small additive percentages (typically 5%wt) and increase that proportion gradually. The additive particle size is critical. Sizes around 100microns have proven to work very well.

9. Conclusion

Choosing the right material - including the right grade - makes reaching your goal more effortless.

Following a safe procedure will allow you to quickly assess the processability of a given grade, and perhaps choose another one, if needed.

We are constantly learning about new processing tricks. Even though our guidelines may look like limitations and restrictions, they correspond to opportunities and discoveries.