3D printing and residual moisture
The residual moisture in the filament during Fused Deposition Modeling (FDM / 3D printing) should not be neglected. This has recently been confirmed by tests conducted by Brabender GmbH & Co. KG. Not only optical defects but also unpredictable changes in material properties, such as reduced mechanical properties, were detected.
Residual moisture in filaments
Due to the corona pandemic, the call for shortened development cycles, series production and prototype construction is particularly loud. Many 3D printing companies, research institutions, and the maker scene are following this call, participating in many ways and offering solutions. However, with regard to medical apparatus engineering and many other critical applications, the demand for the resilience of components (filaments) manufactured using the Fused Deposition Modeling (FDM) process is increasing.
It has been known for decades in the injection molding sector that increased residual moisture plays a significant role in the processing of polymers. This is therefore usually controlled during production by regular measurements and often recorded due to documentation requirements. Brabender GmbH & C KG, based in Duisburg, Germany, manufactures devices specifically for measuring residual moisture in plastics and has now specifically addressed this 3D printing issue. In a series of tests with the common polymers PLA and ASA, residual moisture and tensile strength measurements have again proven that the moisture level in the filament can be a critical quality issue with FDM.
Sample figures
Figure 1: Sample OOTB1ASA
Figure 2: Sample OOTB2ASA
Many filament producers point out this problem and provide appropriate storage advice. The measurements carried out clearly show that these requirements are more than justified. Residual moisture measurement is not only recommended for sensitive product areas as part of the production process. For this reason, residual moisture determination – even beyond sensitive product areas – can be recommended as part of the production process.
Makers and home users should also follow the recommendations of the respective filament manufacturers in order to avoid rejects and unforeseeable material properties. Poor print quality, bubbles on the surface, or noises during printing due to sudden evaporation of water at the print head can be used at home as indications of excessive water content, even without knowing the exact amount. A remedy for this, as in the industrial sector, is to pre-dry the filament according to the manufacturer’s specifications.
Measuring procedure in detail
Preparation – Two test bars were made of ASA and two of PLA by FDM. One each of the test rods made of ASA (sample name OOTB1ASA) and PLA (sample name OOTB1PLA) was produced with a filament from a new, unopened package.
The filaments for the other two test rods from ASA (sample name OOW2ASA) and PLA (sample name OOW2PLA) were enriched with a defined amount of water. Prior to this, the residual moisture of all four filaments was determined with a Brabender AQUATRAC Station:
Observations – Already at the FDM with the wet filaments differences to the dry material are noticeable. Sometimes you can hear how the water in the melted filament suddenly evaporates. This leads to a slightly foaming effect which is visible in direct comparison, especially with the ASA test rods, see figure 2.
Measurement results – comparing the two tensile tests of the test bars made of ASA (red and green curve), the significantly lower tensile strength as well as the reduced modulus of elasticity of the wet material is noticeable. In contrast, the test bars made of PLA show only slight changes in tensile strength and modulus of elasticity. Here it is noticeable that the increased residual moisture appears to be a plasticizer.
