Technical Datasheet Walkthrough (3/3)

Note

It is highly recommended, to read the Technical Datasheet Walkthrough (1/3) & (2/3), before you move on with this article.

Introduction

This article explains what portion of the information should be extracted from a Technical Datasheet (TDS) prior to an extrusion test. A first extrusion experiment on a new material can only be successful (e.g. the produced filament will be of good quality) if:

  • The material has been pre-processed correctly
  • The extrusion test is launched with appropriate starting settings
  • The right adjustments to these starting settings are made to improve the quality

In this article, we will examine the TDS of the grade of Polylactic Acid PLA we use at 3devo to perform endurance tests: IngeoTM Biopolymer 4043D, provided by NatureWorks (link). This TDS will be referred to as “TDS PLA”, it is going to be commented and should therefore be read alongside this tutorial.

1 – Pre-processing

For a successful extrusion, the material must be pre-processed correctly. The pre-processing of a plastic consists in the drying of said plastic, using the recommended drying conditions (duration and temperature). These parameters are sometimes given for a specific type of dryer or drying technique, which is why they must also be considered indications, not exact values. Measuring the moisture content of the material at the end of the drying process, or at different points during the drying process, allows the user to verify that the means of drying available to him or her give similar results to those found in the datasheet. A target moisture content threshold or acceptable range is sometimes given in the datasheet in addition to the drying conditions. If not, a moisture content inferior to 0.05% or even 0.025% in weight is often recommended.

In TDS PLA, it can be found in the “Drying” section (page 1) that typical drying conditions consist of 4h at 80°C, the target moisture content being 0.025%. A conventional kitchen oven can be used with these parameters but a measurement of the moisture content is recommended to validate the drying step.

2 – Setting up the extruder

To perform an extrusion test, one must find a starting point to process the material and then adjust the extrusion settings. In TDS PLA, a processing temperature profile is suggested, as shown in Figure 1.
When such an extrusion thermal profile is provided, it is recommended to start extruding at the given temperatures or slightly above (by about 10°C). The goal is to achieve sufficient melting first, without degrading the material. The rotation speed by default should be set on 3.5RPM. Fan cooling does not affect the melting process, it is therefore not a priority at this stage, but the filament fan speed can be set on 50% as a starting point for further improvement of the product quality. In the case of TDS PLA, correct starting settings would be as in Table 1:

Figure 1 (extract from TDS PLA, page 1)



Table 1

In other cases, when processing temperatures are not indicated, all four heaters may be set on 50°C above the melting temperature, which is often given as a range of temperatures.

WARNING

The melt temperature given in Figure 1 refers to the processing temperature at which the flow of polymer should be inside the extruder. The melting temperature, referred to as “Peak Melt Temperature” in Figure 2, but sometimes also as “Melt Temperature”, refers to the temperature at which the crystalline fraction of the polymer reaches a liquid-like state.

Taking TDS PLA as an example, if the processing thermal profile had not been provided, a possible approach could have been to set all four heaters on [145-160]+50=200°C approximately.

Figure 2 (extract from TDS PLA, page 1)