Amorphous vs crystalline 3D printing materials

Additive manufacturing (AM) is a rapidly evolving technology that is transforming the manufacturing industry. AM refers to the process of creating 3D objects by layering materials on top of each other, as opposed to subtractive manufacturing processes that remove material from a solid block.

Choosing the right 3D printing material is the first step in finding the best use case for your application. The large format 3D printing solutions of CEAD, primarily use short fiber-reinforced thermoplastics (SFRT). Every SFRT consists of a matrix material and a fibre. The thermoplastic matrix of the material serves as a “glue” that holds the fibers in their position and has the biggest influence on the eventual mechanical and thermal properties and the chemical resistance of the material. Therefore, it is important to know the difference between the 2 types of thermoplastic polymers used; Amorphous and Semi-Crystalline.

In amorphous materials, the molecular structure is disordered and lacks a regular repeating pattern. The molecules are arranged randomly, without long-range order or periodicity. This lack of order at the molecular level leads to the characteristic properties of amorphous materials, such as transparency, lower melting points, and a glassy appearance. The absence of a regular repeating structure prevents the formation of crystalline sections.

Advantages:

1. Ease of Processing: Amorphous polymers generally have lower melting points, making them easier to work with in large-format 3D printers.

2. Smooth Surface Finish: They can produce 3D-printed parts with smoother surface finishes and finer details, which is important for some applications.

3. Transparency: Useful for large format 3D printing applications where optical clarity is required, such as in medical devices or clear enclosures.

Disadvantages:

1. Limited Mechanical Strength: Amorphous polymers tend to have lower mechanical strength compared to semi-crystalline counterparts, making them less suitable for load-bearing applications.

Crystalline materials have a highly ordered and repeating molecular structure. The atoms or molecules in a crystalline material are arranged in a specific, repeating pattern, which extends throughout the material over long distances. This ordered arrangement is responsible for the characteristic properties of crystalline materials, including higher mechanical strength and distinct melting points. Semi-crystalline polymers, as the name suggests, have an amorphous structure with crystalline sections, and thus in a combination of the 2 types.

Advantages:

1. High Mechanical Strength: Semi-crystalline polymers generally offer better mechanical properties, including higher stiffness and strength.

2. Chemical Resistance: Many semi-crystalline polymers are highly resistant to chemicals and environmental factors.

Disadvantages:

1. Higher Processing Temperatures: These polymers require higher processing temperatures, which can be challenging for large-format 3D printer equipment.

2. Smaller optimal temperature range: An important factor in producing parts with large format 3D printing is the quality of the bond between the layers (interlayer strength). For this bond strength to be optimal, the previous layer has to be at an optimal temperature, so the molecules can still rearrange themselves with the molecules of the new layer, but still provide enough strength to support the weight of the new layer without deforming. This window is smaller due to the crystalline sections than that of amorphous materials and thus makes quality control and processing harder.

3. Surface Finish: They may produce 3D printed parts with a rougher surface finish and may require post-processing for improved aesthetics.

4. Limited Transparency: Semi-crystalline polymers are generally opaque, which limits their use in applications requiring optical clarity.

5. Lower Dimensional Stability: Due to the crystalline regions, the polymer material tends to shrink in a non-isotropic way thus leading to less dimensional stability while printing.

In conclusion, the choice between amorphous and semi-crystalline thermoplastics should be based on the specific requirements of the application. Understanding the distinct advantages and disadvantages of these materials is crucial for achieving the desired performance and quality in large format 3D printed parts.