PLA Filament Moisture Study: Effect of Moisture on 3D Printing Filament Properties

Moisture influences printability of 3D printing filaments. This PLA filament moisture study shows that even different filament colours influence the printing properties.

PLA (polylactic acid) is a biodegradable 3D printing filament material made usually of starch, potato or sugarcane. It decomposes in a span of several months to few years. Petroleum-based plastics are non-degradable and almost immune to atmospheric conditions, but PLA is not. It absorbs water when exposed to moist or humid environments and expedites its process of decomposition. Let aside the natural degradation, the presence of moisture even influences the quality of parts in 3D printing. We will now discuss the effect of PLA filament moisture for variations in filament colour and manufacturers.

PLA FILAMENT MOISTURE PROJECT

iGo3D, an online shop selling 3D printers and accessories, and Fraunhofer Institute of Wood Research, a research institute, together conducted a project to analyse the influence of moisture on printability of PLA filaments. iGo3D has a track record of being Germany’s first online store for home 3D printing and involves in regular research projects. In this project, they took PLA filaments from three different manufacturers in six different colours: black, white, grey, dark blue, light blue, transparent, and yellow. The names of filament manufacturers were not released due to copyright reasons, but the effects on various coloured filaments were presented.

DIAMETER VARIATIONS

The filaments were first pelletized into uniform pieces and exposed to distilled water vapour for 14 days at 130 degree Celsius. Then they were tested for moisture content. Initially black and white filaments from first manufacturer were tested and it was found that moisture content kept increasing in both filaments up to 140 – 150 hours. After 150 hours, the material attained its saturation. The interesting part of this study was the variation in diameter. After 14 days in damp environment, white filaments had more or less the same initial dimensions. But the diameter of black filaments kept increasing and reached up to 40 micrometres higher than the white counterparts. Diameter variation is one of the major problems in 3D printing. Although our printers’ working environments are not as harsh as these test conditions, we still need to consider the colour variations for PLA filament moisture effects.

MASS FLOW RATE VARIATIONS

The next study was to measure the mass flow rate of PLA filaments. We generally desire high flow rates, but very high flow rates lead to over-extrusion. On the other hand, low flow rates indicate high viscosity of filament and lead to under-extrusion. The flow test is conducted by measuring the amount of material extruded in 10 minutes through a standard-sized nozzle. Black, white and light blue filaments from different manufacturers were tested for mass flow at three different conditions: dry, wet and room temperature. Dry filaments are those that were kept at 100 degree Celsius for 24 hours. Wet filaments are those that were kept in water for 240 hours. Inspection at each condition showed only expectable results: wet filaments had the highest flowability and dry filaments had the lowest.

Now comparing the colours, first black vs white, it was found that white filaments had better flowability than the black ones. But comparing these two with light blue filament showed stark different results. As can be seen in image below, the blue filaments from another manufacturer had very high mass flow rates. This points out that we might have to optimise printing parameters for the same PLA filament purchased from different suppliers in different colours.

PLA IS NOT ALWAYS PLA

The results of the PLA filament moisture study indicate that the mass flow rate is directly correlated with the moisture content. An overall comparison of mass flow rate of filaments of all colours from all manufacturers is shown in the image below. Yellow coloured filament is seen to have the lowest viscosity and highest mass flow rate. Hence it is clear that it is necessary to manage the storage conditions of PLA filaments. Too tropical and humid countries require better supply chain conditions than drier lands. All these tests were carried out with Ultimaker2.0 which has good tolerance against such variations, but we need to take these factors into account for all other printers too. The ultimate result: PLA is not always PLA.