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Optimal filament storage conditions and drying methods.


In: Knowledge On: Hit: 71

Hygroscopicity, i.e. the tendency of a solid to absorb moisture, is the great enemy of 3D printing as it is a characteristic feature of almost all thermoplastic materials.

BCN3D comparison of fiber drying methods

Optimal filament storage conditions and comparison of fiber drying methods.

Hygroscopicity, i.e. the tendency of a solid to absorb moisture, is the great enemy of 3D printing as it is a characteristic feature of almost all thermoplastic materials. Even a small percentage of moisture can adversely affect most fibers and therefore the final result of your print job. This article discusses the harmful effects of moisture on polymers and compares traditional 3D printing filament drying methods with the effectiveness of the BCN3D smart cabinet.

Optimal filament storage conditions

Water is one of the most important components of the atmosphere, and depending on geographic factors and weather, it can account for up to 2% of the air we breathe. Most polymeric materials interact with water to absorb it, regardless of its physical form. Therefore, raw thermoplastic materials are usually subjected to a so-called dehydration phase when treated at high temperature before use to ensure that no water remains in the form of bubbles. These water bubbles would remain trapped in the polymer matrix and would generate local imperfections which are detrimental to the aesthetic and mechanical properties of the plastic object made therefrom.

Depending on the nature of the polymer and its behavior in a water-rich environment, it can be characterized as either hygroscopic or non-hygroscopic. Non-hygroscopic materials tend to absorb water only on their surface, which makes them easier to remove by simply heating. On the other hand, hygroscopic materials are able to absorb large amounts of moisture from the air and store it deep in their matrix. Heating the hygroscopic material helps to remove the water absorbed on the surface, but not the water accumulated deep in the matrix. For this reason, hygroscopic polymers require more careful care and storage before processing and storage in a dry and sealed environment.

The most popular 3D printing filaments are formulated from hygroscopic materials such as PA, TPU, PVA, PET-G or ABS.

Research conducted on wet filaments for 3D printing by a team of BCN3D engineers

The BCN3D Engineering team conducted research on the effect of moisture on filaments for 3D printing with the aim of obtaining basic knowledge about how various materials absorb moisture, how it affects their performance and what are the best methods for drying them. First, they investigated the water absorption characteristics of PA, PVA and TPU filaments and their ability to produce reliable end results when subjected to certain levels of relative humidity as they are the most hygroscopic materials in our filament portfolio and therefore the most sensitive to abnormal storage conditions.

Weight variation of different 3D printing materials

Table 1: Weight variation of different 3D printing materials at different relative humidity levels

The results in Table 1 above show the amount of water absorbed by these filament spools in relation to the water content of the environment. There was no significant increase in weight when the spools were kept in a dry atmosphere (item 1, table 1), however, when exposed to higher humidity coefficients, they absorbed proportionally more water.

As the table shows, each material had a unique absorption profile: PVA is the most hygroscopic of the materials tested, and when stored at 70% RH for 4 days it absorbed the equivalent of 1.22% of its original weight in water. Meanwhile, PA and TPU appeared to behave similarly when exposed to low levels of ambient humidity (items 1-4, table 1, 10-40% RH), consuming equal amounts of water. However, while the absorption capacity of TPU flattened above 40% RH, PA showed a more hygroscopic behavior in a high humidity environment (item 5, table 1).

The team then started printing a few simple geometric shapes with these pre-prepared fibers to see if exposure to moisture had negatively impacted the printability of the materials. The test prints consisted of a thin-walled cylinder and a cuboid, ideal for checking the presence of bubbles, voids and threads.

In the control experiment, the humidity was kept below 10%, all spools gave excellent prints as shown in the figure below, the printed samples show no imperfections.

At 12% moisture, while PA and PVA were still printed as well as in the control experiment, TPU already showed significant threading, meaning that the melt viscosity was reduced by the presence of water acting as a plasticizer.

PA began producing cloudy surfaces and showed flossing at 30% RH, while PVA, although the most hygroscopic of the three materials tested, withstood high humidity levels, maintaining printability at only 40% RH.

3D test prints printed by BCN3D

Image shows 3D test prints printed by BCN3D engineering team at RH <10%, RH 12% and RH 70%. From left to right: PVA, TPU and PA.

This experiment sheds light on important information on the behavior of PA, PVA, and TPU fibers when stored in an environment with different levels of relative humidity. By measuring the amount of water absorbed, the BCN3D engineering team was able to identify PVA as the most hygroscopic material, followed by PA and finally TPU. However, it turned out that TPU, which is the least hygroscopic of the three materials, is also the most sensitive to improper storage.

Limits of printability for tested materials

Table 2: Limits of printability for tested materials

The second experiment that the team conducted was to investigate the effect of time on how quickly different materials absorb water.

The BCN3D engineering team was also able to calculate a theoretical shelf life at 60% RH in a well-ventilated room by crossing the data from the first and second experiments. From these calculations, the team was able to determine that PVA takes 12 hours to reach the critical water content of 0.47%, leading to unsuccessful prints (Table 3). In the case of PA, this time is reduced to 4 hours in order to reach the critical water content of 0.10%. According to these calculations, the TPU only needs 1.5 hours at 60% RH and no longer passes the printing test (Table 3). These numbers are quite alarming and show how easily humidity and incorrect storage can affect the outcome and consistency of the FFF 3D printing process.

Calculation of the theoretical lifetime of various 3D printing materials

Table 3: Calculation of the theoretical lifetime of various 3D printing materials based on experiments by the BCN3D engineering team

They also investigated the behavior of the materials inside the BCN3D Smart Cabinet, an environment designed to protect against moisture, as explained later in this document. The graph below shows the environmental parameters of the smart cabinet in operation with an external relative humidity of 55%.

BCN3D Smart Cabinet

Graph 1: BCN3D Smart Cabinet maintains an internal humidity level between 15% and 20%, even with an external relative humidity of 55%

The BCN3D smart cabinet keeps the fibers in a low humidity environment, greatly reducing the risk of printing failure due to excessive water content. As shown in Figure 6, even with an external humidity of 55%, the Smart Cabinet provides an internal humidity between 15 ° and -20% to maintain the printability of the fibers, extend their shelf life and reduce aesthetic defects in the final result.

Efficiency of traditional filament drying methods compared to Smart Cabinet BCN3D

There are several methods of drying filament that are well known in the 3D printing industry. However, these methods have various disadvantages that can even damage the polymer.

Traditional methods of drying filament

Baking in the oven

Oven dried fibers can cause high energy costs while reducing tensile strength and even melting them if they are too hot. It is also a very time consuming process.

Air conditioner or dryer

Using an air conditioner or dehumidifier to dry a filament can also be quite expensive, as it cannot dry the filament below 40% RH. It is also ineffective when the ambient temperature is low.

Desiccants

The RH cannot be controlled and this method requires constant replacement and maintenance.

Other traditional methods of drying filament

Constantly heating the filaments to dry them can also have high energy costs while drying only a few spools of filament at a time.

Professional methods of drying filament

Adsorption dehumidifiers

Adsorption dryers are a common method of drying solids and polymers that tend to absorb moisture. Their action is based on the combination of adsorbents with water; they effectively capture water particles from the air, which significantly reduces air humidity. These adsorbents are usually in the form of granules or spheres and are made of silica, alumina or special clays which have the ability to absorb large amounts of water from the air and can be regenerated. The drying process sequentially increases the rate of water evaporation from the surrounding solid surfaces, thus reducing the total water content. After taking a certain amount of water from the air, the adsorption material becomes saturated and its effectiveness drops quickly. By isolating the absorbent material from the heating chamber and increasing its temperature, we can release all absorbed moisture to the environment and regenerate the material.

The BCN3D Smart Cabinet also works based on this method, alternating between drying and regenerating cycles, thus maintaining a constant dry environment around the stored reels and protecting them from sudden external changes.

Hot air drying process

This simple process circulates hot, dry air through a layer of plastic granules. Pellets are usually moved mechanically, and their final water content depends on the air temperature and the residence time in the hopper (Fig. 2). This process is most effective for non-hygroscopic and high-melting materials as materials such as PLA would be affected by heat treatment.

Hot air drying process

Figure 1: Hot air drying process. Source: www.process-heating.com

Vacuum process

Vacuum drying is based on the fact that the vapor pressure and the boiling point of the liquid depend on the ambient pressure. By lowering the atmospheric pressure, the boiling point of water can be lowered. For example, if the pressure were to drop to one tenth of normal atmospheric pressure (from 1.0 to 0.1 atm), the boiling point of water would change from 100 ° C to 33 ° C. In this way, it is possible to remove liquids from solids without actual heating. For this reason, vacuum drying is considered to be a very gentle and effective way to reduce the water content of solids. However, the great disadvantage of vacuum drying is the cost of the equipment and the constant maintenance needed to ensure safe and long-term operation.

BCN3D Smart Cabinet

BCN3D Smart Cabinet

Compared to all the previously mentioned methods, Smart Cabinet BCN3D has a low power consumption (12W average / 100W max) while it can keep the filament below 40% RH, which is optimal for most 3D printing materials.

It can dry up to 8 small spools of filament (750 g to 1 kg) or 4 large spools (up to 2.7 kg per spool) without heat, thus maintaining the tensile strength of the materials.

BCND Smart Cabinet protects the filaments for a long time and significantly reduces printing errors caused by moisture. The silica gel inside, open to the drying environment, absorbs moisture from the air in the chamber. Once saturated, the gel is isolated from the materials and heated until it releases the moisture, removing it from the system. After cleaning, the silica gel has been refreshed and ready to store more moisture. This process effectively keeps the filament dry and optimal for use.

As the above results from all experiments carried out by the BCN3D engineering team show, moisture-rich filaments can spoil the end result of the print job as well as seriously damage the 3D printer itself.

Therefore, it is extremely important to always store 3D printing materials in a sealed place where the level of relative air humidity can be controlled. This is where the BCN3D Smart Cabinet comes in handy, which effectively extends the life of materials by storing them in optimal conditions, keeping them even during the printing process, ensuring a flawless 3D printing experience.

Order Smart Cabinet now.

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