Improvement of additive manufactured parts by nanofibers

Technologies

• Nanofibers
• Polyetherimide
• Additive manufacturing
• Nozzle design
• Conductivity

Background

Miralon nanofibers under the microscope

Additive Manufacturing is highly used for prototyping and pre-serial manufacturing.

Huntsman's portfolio includes the novel entangled nanofibers Miralon, which exhibit a high aspect ratio. In combination with thermoplastics, Huntsman, FHNW and KATZ have developed injection moulding and filament materials for the Fused Filament Fabrication (FFF) process with improved properties.

The transverse strength of FFF parts is lower compared to the longitudinal one. By incorporating such nanofibers, this strength can be increased. Another advantage of the fibers is the high electrical conductivity.

Goals

Printing a bracket in PEI with Miralon nanofibers

The main goal of this project was to improve the transverse strength of additive manufactured parts by high aspect ratio nanofibers. For that reason, different compounds with Miralon, compatibilizers and thermoplastic polymers had to be produced and characterised. One of the main challenges was the dispersion and distribution of Miralon within the thermoplastic polymer. For optimization various compounding methods had to be compared: internal mixer, twin-screw-extruder, multi-spindle-extruder and co-kneader.

A filament extrusion line had to be developed, built, and installed.

Mechanical analysis of injection moulded and printed tensile test specimens had to be performed.

Results

The project team clearly proved that adding Miralon nanotubes into technical and high-performance polymers such as PET-G, PA12 or PEI increase significantly the mechanical performance by roughly 10-30% and the conductivity by several orders of magnitude in injection moulded and of 3D-printed parts.

The printing process, respectively the resulting flow mechanism in the nozzle during extrusion, was simulated and investigated. Based on the resulted findings, a new nozzle geometry was elaborated and manufactured using the SLM printing process. This new nozzle geometry aims to change the direction of the Miralon nanofibers in the molten polymer while printing. In this way, the Miralon nanofibers should not align only in flow direction but also transversely to it.

The team could show with semi-crystalline and an amorphous material with and without nanofibers that a special nozzle geometry can have a positive effect on the mechanical performance in general and on the transversal strength. Additionally, the mechanical performance of printed parts with 1% Miralon nanofibers was better compared to a commercial reference with 20% carbon fibres, especially when using the specific nozzle geometry.

As a demonstrator a 3D printed bracket was shown at the JEC 2022 in Paris

Filament and brackets made from PEI + Miralon presented at the JEC fair 2022