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Influence of Moisture on Filaments for FFF 3D PrintingFilament moisture on Ultrafuse® PET CF15: Aesthetics, Mechanical Properties, and Best Practices

Internal1.0 Abstract2.0 Introduction3.0 Impact of Filament Moisture on Printability4.0 Impact of Filament Moisture on Dimensional Accuracy and Part Properties5.0 Reducing Filament Moisture5.1 Airtight Boxes5.2 Actively Heated Dry Cabinet5.3 Actively Heated Dry Storage Box5.4 Hot Air Dryer5.5 Vacuum Oven6.0 Conclusion7.0 Appendix7.1 Printer Information & Settings7.2 ReferenesContents225710101112121315161618

InternalIn Additive Manufacturing (AM), the increasing demand for thermoplastic filamentsthat meet industrial needs has led to a continuous improvement and higher materialstandards. Considering plastic filaments, the criteria include color, diameter, ovality,filament moisture level, etc. The moisture level of a filament is a result of thehygroscopic behavior of the material. The water molecules in the filament maycause issues in both the printer and printed part, aside from the filament itself. Oneof the most undervalued problems in the whole process is the filament moistureuptake while printing. The following white paper provides an overview of theimportance of moisture in thermoplastic filaments, specifically in Ultrafuse® PETCF15. Additionally, the paper documents the negative impact on aesthetics, theinfluence of moisture on dimensional accuracy and the decrease of mechanicalproperties. State-of-the-art solutions are proposed to maintain a controlled (high)temperature and low moisture surrounding environment for the spools andrespective filaments.1.0 Abstract2forward-am.com +49 6221 67417 900 sales@basf-3dps.comMoisture is the presence of water in small amounts in the form of vapor within asolid. Moisture absorption is the ability of a material to absorb the vapor from thesurrounding environment. In the context of Fused Filament Fabrication (FFF), thematerial is plastic filament. Common to many other extrusion techniques such asinjection molding, the quality and properties of a raw material such as pellets mayaffect the final material filament [1]. Moisture absorption may be due to free waterliquid/vapor which collects in pores and voids or is absorbed and connects tohydrogen bonds within the material structure resulting in swelling [3]. The diffusionof water particles into the polymeric material may change material properties suchas glass transition and viscoelastic behavior [3].Although the drying process is common in other traditional manufacturingtechniques, there is still little research done on the impact of moisture in AdditiveManufacturing throughout the various material categories.2.0 IntroductionInfluence of Moisture on Filaments for FFF 3D Printing

InternalThe filament moisture level a customer receives when opening a spool of plasticfilament is the result of the moisture absorbed during production, packaging,shipping, storage, and environmental conditions. From the pellet to the final printingprocess, the material goes through several environments and changes which maylead to a decrease in quality. Non-conditioned rooms from the production site to theprinting location increase the odds of irregularities in the filament moisture contentwithin a spool resulting in inconsistencies in the print process.Different levels of moisture may result in different mechanics, questioning therepeatability of the manufacturing process itself. Repeatability and high mechanicalproperties for 3D printing are becoming not only a desire but also a requirement formaterial manufacturers. Users are demanding better filament quality with highmechanical properties to bridge the usage of Additive Manufacturing fromprototyping to final parts. Engineering grade polymers are specially designed tofulfill these engineering and design constraints.BASF Forward AM offers a wide array of filaments, from standard materialsincluding Polylactic Acid (PLA), Acrylonitrile butadiene styrene (ABS), andPolypropylene (PP) to advanced engineering materials such as Carbon FiberPolyethylene Terephthalate (PET CF15), High temperature Polyamide (PAHT),Thermoplastic Polyurethane (TPU), Polyamide (PA), Polyphenylsulfone (PPSU).While many plastics have an overall tendency to pick up moisture, the moisturedoes not have the same impact on every material. In AM, certain filaments have ahigher tendency to absorb water than others, making them more susceptible to adecrease in not only physical characteristics but also in mechanical properties dueto the presence of water molecules. Within Forward AM’s portfolio specifically, it isestimated that the material classes of butene-diol vinyl alcohol copolymer (BVOH),polyamides, thermoplastic polyurethanes and polyethylene terephthalates have ahigher hygroscopic behavior.3forward-am.com +49 6221 67417 900 sales@basf-3dps.comInfluence of Moisture on Filaments for FFF 3D Printing

InternalPET CF15 is polyethylene terephthalate filled with 15% of carbon fibers. Thematerial is used in frames, prototyping, drones, facemasks, etc. The fibers in thematrix allow for more strength and stiffness while still maintaining low weight.Although the material is filled with 15% carbon fibers, PET CF15 offers a mattefinish, avoiding the need for postprocessing when taking aesthetics intoconsideration. PET in its natural form is already susceptible to moisture uptake thatmay be increased with the reinforcement of fibers [5]. Although carbon fibers aremore hygroscopic than glass fibers, it is also important to consider the compatibilitybetween the matrix and the fiber chosen [5]. Figure 1 presents the filamentmoisture level of Ultrafuse® PET CF15 in a conditioned room with ~23°C °C andaverage relative humidity of ~33%.4forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 1: Absorption behavior of PET CF15 at ~23 °C and average relative humidity of 33 %The trend is dependent on both environment moisture and temperature. Underdifferent circumstances (humid environmental conditions), the equilibrium point willbe higher as will the rate of filament moisture uptake. A reliable repeatability printprocess is dependent on the filament moisture content of both filament and theenvironment where it is used.Influence of Moisture on Filaments for FFF 3D Printing

InternalThe increase of moisture in the filament can have various effects on the overallprintability of the material. Some of the issues seen in moist parts are bubblesformed due to the increase in vapor pressure in the hot end. An increase of oozingand stringing may be resultant from the decrease in viscosity due to the watermolecules. The filament moisture once evaporated will also create voidsdecreasing the overall weight of the part along with increasing the dimensions. Thechange in viscosity will also affect the extrusion flow and print quality. Figure 2illustrates a printed part utilizing Ultrafuse® PET CF 15 with a filament moisturecontent of 0.17 w%.3.0 Impact of Filament Moisture on Printability5forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 2. Printed part with filament moisture content of ≥ 0.17 CV w% [7].Influence of Moisture on Filaments for FFF 3D Printing

InternalThe variation in flow due to filament moisture creates an extrusion surplus that isdeposited while printing once the nozzle can no longer hold the material. Thenozzle can also pick up the over extruded material when moving within the partresulting in poor aesthetics, both in flat surfaces and small ones. Intricate detailsand parts that require high retractions also show poor quality due to the oozing andstringing. Although the results can be improved, the parameters will only hold withina certain range of filament moisture content as the material continues to change inrelation to the increase in filament moisture. The excess material may be removedby hand, but with high filament moisture content parts may only be taken with tools.In a continuous and repetitive process, reprinting the same part with the same G-code using a moist spool followed by a new spool that may be dryer will likely resultin under extrusion.Figure 3 presents the same part with a lower filament moisture content of ≥0.007w% and respective optimization.6forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 3. Printed object where the used filament had a moisture content of ≥0.07 w%.An overall decrease in aesthetics may be seen in filament moisture content above0.07 w%. These effects are further visible in lighter colours and more moisture-sensitive filament materials.Influence of Moisture on Filaments for FFF 3D Printing

InternalThe impact of filament moisture is further seen in changes in weight anddimensions when considering the physical properties of an object. The evaporationof trapped water from the filament material during extrusion results in an overalldecrease in weight due to foaming and bubbles. Figure 4 presents the change inweight of Ultrafuse® PET CF15 over 8-10 days when printed in differentsurrounding environments. Bars (4mmx10mmx80mm) were printed under standardenvironment conditions of 22.4 – 23.2 °C and a mean relative humidity of 33.1 –33.4 % or humid conditions of ~23 °C and a mean relative humidity of ~70%.4.0 Impact of Filament Moisture on Dimensional Accuracy and Part Properties7forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 4: Part weight changes per average over storage time of Ultrafuse® PET CF15 filamentInfluence of Moisture on Filaments for FFF 3D Printing

InternalOverall, the weight tends to decrease over time with a higher impact on humidconditions.Regarding dimensions, the neck width of tensile bars type 1A were measured withdifferent filament moisture levels to assess the impact of filament moisture indimensional accuracy as shown in Figure 5. The filament spool was initially dried ina vacuum oven at 60 °C for at least 60 hours8forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 5: Effects of filament moisture on printed tensile bars’ edge widthAccording to the graph, the dimensions of the parts have a tendency to increasewith moisture content in the filament. In addition, the discrepancy between themaximum and minimum value increases suggest that the surface becomes rougherand more irregular with the increase of filament moisture.The difference in aesthetics and dimensions will also impact the mechanicalproperties. To assess the impact of filament moisture in mechanical propertiesseveral tensile bars type 1A were printed in the XY direction with different filamentmoisture levels. The tensile bars were tested according to ISO 527. The printsettings are available in Appendix A. Figure 6 presents the tensile curves underdifferent filament moisture contents.Influence of Moisture on Filaments for FFF 3D Printing

Internal9forward-am.com +49 6221 67417 900 sales@basf-3dps.comFigure 6: Stress-strain curves of the printed PET CF tensile bars when printed with a different filament moisture content, labels indicate moisture content in weight percentage (w%).Overall, the increase of filament moisture content tends to decrease the tensileproperties. With a filament moisture content between 0.15-0.2 w%, the mechanicalproperties tend to decrease by 10 - 15% when printing Ultrafuse® PET CF 15.Additionally, when printing objects with a filament moisture content of 0.4 - 0.5 w%the decrease in tensile strength tends to be approximately 24%. The presence ofvoids decreases layer adhesion which suggests that there will also be a decreasein strength in any printed direction.Influence of Moisture on Filaments for FFF 3D Printing

InternalSeveral stakeholders within the 3D Printing ecosystem have tackled the filamentmoisture impact from different angles. Engineers and industrial users see filamentmoisture as a concern in particular for engineering applications where dimensionalaccuracy or high mechanical properties are essential for a smoother shift frominjection molding to additive manufacturing. To successfully print parts withaccuracy and consistency, a primary concern should be environmental conditions.By keeping the surrounding moisture level low and constant, the filament in turnmay also maintain a low moisture content for a longer period of time. This isimperative, especially for small series production where repeatability is needed tomeet standards and consistency. State of the art drying equipment includes:5.0 Reducing Filament Moisture10forward-am.com +49 6221 67417 900 sales@basf-3dps.comAirtight boxes allow for a consistent moisture environment when fully sealed. It isalso advised to add desiccant to keep the environmental moisture content low. Thesealing is the most important step, given that there is no heat to continuously drythe material. This solution is not permanent, but increases the reliable printabilitytime window. Any air opening will have an impact on the rate of absorptancespecially in highly humid environments. Figure 7 presents the results regardingUltrafuse® PET CF15 when keeping the box fully enclosed and when keeping anopen tube through it which is usually necessary during 3d printing.5.1 Airtight BoxesInfluence of Moisture on Filaments for FFF 3D Printing

Internal11forward-am.com +49 6221 67417 900 sales@basf-3dps.comAn Actively Heated Dry Cabinet offers the right conditions for storage and evendrying over a longer amount of time (days). This solution is usually not connected tothe printer. Continuous storage in a dry cabinet with low moisture will also maintaincertain materials at low moisture levels. Active drying is preferred over an enclosedbox as the air will be above room temperature. Figure 8 presents the resultsregarding Ultrafuse® PET CF15 while kept at 30 °C and 0% environment moisture.5.2 Actively Heated Dry CabinetFigure 7. Filament moisture content (w%) of Ultrafuse® PET CF while stored in a dry boxInfluence of Moisture on Filaments for FFF 3D Printing

Internal12forward-am.com +49 6221 67417 900 sales@basf-3dps.comAn Actively Heated Dry Storage Box (such as Daywise) have been able to providea solution independent of spool size to dry the material while printing. Thecontinuous drying process while printing allows for longer successful printsconnecting the moist filament to a dry and consistent filament extrusion thereforeincreasing print process repeatability.5.3 Actively Heated Dry Storage BoxFigure 8. Filament moisture content (w%) of PET CF while stored in the dry cabinet at 30 °C and 0% relative humidity;A Hot Air Dryer is able to remove moisture from hygroscopic filaments by blowinghot air and dissipating the moisture into the surrounding air [6]. Materials such asPET or TPU present good results when used with a hot air drying oven. Figure 9shows the results when drying Ultrafuse® PET CF15 at 60 °C during 32 h.5.4 Hot Air DryerInfluence of Moisture on Filaments for FFF 3D Printing

Internal13forward-am.com +49 6221 67417 900 sales@basf-3dps.comThe low pressure in a vacuum oven not only allows for a faster decrease in airmoisture with the removal of free moisture, but also reduces bound moisture withinthe solid [4]. The vacuum significantly decreases the boiling point of water [6]. If theproduct is heat sensitive, the vacuum oven temperature may also be reducedresulting in lower energy consumption and less degradation of the material [4]. Avacuum oven is specifically recommended when drying PA and PPSU filaments.Figure 10 shows the results when drying Ultrafuse® PET CF15 at 60 °C during 40-48 h.5.5 Vacuum OvenFigure 9: Filament moisture content of PET CF filament in the Hot Air dryer at 60 °CInfluence of Moisture on Filaments for FFF 3D Printing

Internal14forward-am.com +49 6221 67417 900 sales@basf-3dps.comThe choice between all the available solutions provided will depend on theapplication and material performance needed. Their success depends on:• Being fully sealed• Having some active heating• Having extremely low relative humidity/low moisture (as low as 1% if possible)Features with limited capabilities are not suitable for the final solution and thecontinued reliability of the filament in a continuous production setup. Suppliers thatmay offer active drying or AM machine manufacturers with integrated low humiditychambers should always be checked for the three key points mentioned above.Checking the humidity within the chamber is also important in order to store thematerial for a longer amount of time. Storage options with limited humidity controlor storing the filament in any non-sealed environment, such as a holder inside oroutside the printer or a separate non-sealed filament storage, will not provide anairtight seal and will pick up moisture.Figure 10: Moisture content of PET CF filament during drying study dried in the vacuum oven at 60 °C and 15 mBar pressureInfluence of Moisture on Filaments for FFF 3D Printing

InternalAdditionally, reinforced and flexible materials present the biggest challenge when asetup has an extended distance between the extruder and the spool. Flexiblematerials will tend to stretch and change diameter which may impact the extrusionflow. Reinforced materials also have a tendency to break due to their brittleness.Long and curvy paths may be too difficult for the filament to go through leading tothe ideal case scenario of a tube from the material storage unit feeding directly intothe extruder.15forward-am.com +49 6221 67417 900 sales@basf-3dps.comFilament moisture has a vast impact in the overall success of additivemanufacturing. The absorbance and retention of water from the environment cangreatly influence the aesthetics, dimensional accuracy and mechanical properties ofhygroscopic materials. The presence of moisture can be evaluated quantitatively formore accuracy, nonetheless it can also be assessed qualitatively at high filamentmoisture contents. For the continuous success and reliability, it is always advised tomaintain polymer filaments at constant low moisture levels. Ultrafuse® PET CF15is not advisable to print above 0.7 w% when aiming for top level aesthetics andmechanical properties. State of the art solutions including ovens and airtight boxesmay increase successful printing processes for a smoother adoption of 3D Printingin production facilities.6.0 ConclusionInfluence of Moisture on Filaments for FFF 3D Printing

Internal7.0 Appendix16forward-am.com +49 6221 67417 900 sales@basf-3dps.com• Model: 216931 Ultimaker® S3 (EU)• Serial No: BPP-021557-068456• Ultimaker® Cura software version: 4.11.0• Build plate made of glass and sprayed twice with 3DLAC™ Adhesive spraybefore every print. Test specimens were all printed in XY direction ond by one.Slicer Setting ValueMaterialBASF Forward AM Generic Ultrafuse® PET CF15Print core CC 0.6Quality Layer Height 0.2 mmInitial Layer Height 0.4 mmLine Width 0.6 mmInitial Layer Line Width 100.0 %Walls Wall Line Count 2Z Seam Alignment User SpecifiedZ Seam X 0.0 mmZ Seam Y 0.0 mmTop/Bottom Top Layers 0 (automatic)Bottom Layers 999999 (automatic)Top/Bottom Pattern Zig ZagExtra Skin Wall Count 0InfillInfill Density 100.0%Table 15. Slicer settings used for printing test specimensInfluence of Moisture on Filaments for FFF 3D Printing7.1 Printer Information & Settings

InternalSlicer Setting ValueInfill Pattern Zig ZagMaterial (Initial/Final) Printing Temperature 260.0 °CBuild Plate Temperature (Initial Layer) 75.0 °CFlow 117.0 %Initial Layer Flow 100.0 %SpeedPrint Speed (All parameters) 40 mm/sInitial Layer Speed 16.0 mm/sTravel Retraction Distance 6.5 mmRetraction Speed 25.0 mm/sCombing Mode Within InfillLayer Start X 0.0 mmLayer Start Y 0.0 mmCooling (Maximum) Fan Speed 0.0 %Support Generate Support DisabledBuild Plate AdhesionBuild Plate Adhesion Type SkirtSkirt Line Count 2Skirt Distance 5.0 mm17forward-am.com +49 6221 67417 900 sales@basf-3dps.comInfluence of Moisture on Filaments for FFF 3D Printing

Internal18forward-am.com +49 6221 67417 900 sales@basf-3dps.com[1] Chen, S., Su, H., Mathew, J., Gunawan, H., Huang, C., & Feng, C. (2022). AnInvestigation to Reduce the Effect of Moisture on Injection-Molded Parts throughOptimization of Plasticization Parameters. Applied Sciences, 12(3), 1410. doi:10.3390/app12031410[2] Zaldivar, R. J., Mclouth, T. D., Ferrelli, G. L., Patel, D. N., Hopkins, A. R., &Witkin, D. (2018). Effect of initial filament moisture content on the microstructureand mechanical performance of ULTEM® 9085 3D printed parts. AdditiveManufacturing, 24, 457–466. https://doi.org/10.1016/j.addma.2018.10.022[3] Xuejun Fan. (2008). Mechanics of moisture for polymers: Fundamental conceptsand model study. EuroSimE 2008 - International Conference on Thermal,Mechanical and Multi-Physics Simulation and Experiments in Microelectronics andMicro-Systems. https://doi.org/10.1109/esime.2008.4525043[4] Parikh, Dilip. (2015). Vacuum Drying: Basics and Application. ChemicalEngineering. 122.[5] Costa, M. L., Rezende, M. C., & de Almeida, S. F. (2006). Effect of voidcontent on the moisture absorption in polymeric composites. Polymer-PlasticsTechnology and Engineering, 45(6), 691–698.https://doi.org/10.1080/03602550600609549[6] British Plastics Federation. (n.d.). Drying of polymer (including dehumidifyingdryers, rotary wheel dryers, low pressure dryers, vacuum dryers). British PlasticsFederation. Retrieved August 22, 2022, fromhttps://www.bpf.co.uk/plastipedia/processes/Drying_of_Polymer.aspx#Hot[7] vd print. (n.d.). Digital designs for physical objects. Thingiverse. RetrievedOctober 3, 2022, from https://www.thingiverse.com/vandragon_de/designsInfluence of Moisture on Filaments for FFF 3D Printing7.2 ReferencesContributors:BASF 3D Printing Solutions B.VEerste Bokslootweg 17, 7821 AT Emmen, The NetherlandsDelfina Rodrigues Da SilvaJowie MiddelDr.-Ing. Matthias Fischer

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