Troubleshooting: polymer degradation

Extruding a material with inapropriate settings or an unclean barrel can result in material degradation.

1. Definition

Polymer degradation is the change in the properties of a polymer under the influence of environmental factors such as heat, oxygen, light, or chemicals. At a molecular level, degradation often happens via ‘chain scission’.

2. Main causes

  • in order to degrade, a polymer must spend enough time at a temperature high enough. Degradation kinetics generally involve time and heat (e.g. the longer time a polymer spends at high temperature, the more it degrades).
  • moisture can chemically destroy hygroscopic polymers (=polymers that absorb moisture from the air). Solution = dry the material before extrusion according to the manufacturer’s recommendations

3. Severity levels

  • minor –> the polymer becomes more fluid, making it difficult to control the flow. Solution = decrease temperatures by small steps (typically 5°C every 20min)
  • medium –> the polymer ‘boils’, generating bubbles and making it impossible to produce good filament. Solution = dry the material before extrusion according to the manufacturer’s recommendations. If done, decrease temperatures by small steps.
  • major –> the polymer essentially burns (yellow/brown discoloration, or even black carbonization). There is a risk of clogging the barrel (shown in Figure 1). Solution = immediately purge the extruder. Then restart the extrusion tests with lower temperatures.

Figure 1: Devoclean HighTemp with traces of burnt polymer (left), then clean after 10min of purging (right)

4. Special case: contamination

This typically takes the form of burnt particles that were produced during a previous extrusion session. These particles of burnt polymers got stuck in the barrel, and can suddenly be released and contaminate the new material you are trying to process.

Solution

  • Purge your Filament Maker at the end of each extrusion session, before stopping the flow.
  • When transitioning from one material (A) to another material (B), please always make sure the hopper is completely 100% empty without a ingle particle of A before feeding B.

5. Chart with causes and actions

Figure 2 shows a summary of the possible causes and the corrective actions that should be taken when a polymer is degrading.

Figure 2: Summary of potential causes and corrective actions in the event of material degradation