Improving Adhesion Issues with ABS/TPU Blends in FDM 3D Printing

In the recently published, ‘Materials with enhanced adhesive properties based onacrylonitrile-butadiene-styrene (ABS)/thermoplastic polyurethane (TPU) blends for fused filament fabrication (FFF),’ authors A.S. de Leon, A. Dominguez-Calvo, and I. Molina outline a recent project where they created new materials with refined properties for 3D printing. In this study, they examine the compatibility of thermoplastics and thermoplastic elastomers on both the macro- and micro-scale.

Designs of a) Monolayers for compositional studies; b) 1BA tensile test specimens and c) monolayers to study influence of platform temperature on first layer adhesion; d) different orientations of the tensile test specimens.

While enhanced materials offer new potential in Fused Deposition Modeling (FDM, also called FFF), the authors are also aware of numerous obstacles to overcome, some of which are in comparison to conventional methods, along with the typical issues regarding mechanical properties such as decreased tensile strength and defects caused by porosity.

“Different strategies have been followed to overcome these problems,” stated the researchers. “Finite element analysis has been made to map the forces distribution when different external loads are applied to be able to predict the fractures modes and locations.”

Adhesion issues are common for users today, and as the authors point out, there is also a ‘lack of consensus’ regarding how to measure such problems, along with testing solutions such as varying position of prints, exploring the influence of build direction and raster orientation, modifying materials, and experimenting with additives. The research team also noted issues in FDM  technology due to constrictions like requirements for a heated platform, with a possible solution in using thermoplastic elastomers (TPE) for better adhesion.

And while ABS and TPU may show good results when blended, for this research, the scientists decided to forego blending, and print the materials separately on a Creality CR10 3D printer, using a series of ABS/TPU blends, comprised of TPU contents from 10 to 30 percent wt%. Five samples were printed using ABS and TPU, and no support structures, using default software parameters.

a) Average Raman spectra of pure ABS (red), ABS:TPU blends containing 10 wt% TPU (blue), 20 wt% TPU (green), 30 wt% TPU (black) and pure TPU (light blue); b–c) Raman micrographs of blends containing 20 wt% TPU. Red area indicates the ABS characteristic peak at 1012 cm−1 while blue area corresponds to characteristic peak of TPU at 1531 cm−1 . These peaks were taken to perform Raman microscopy images shown for b) ABS, c) TPU and d) merged signals from ABS and TPU. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)a) Average Raman spectra of pure ABS (red), ABS:TPU blends containing 10 wt% TPU (blue), 20 wt% TPU (green), 30 wt% TPU (black) and pure TPU (light blue); b–c) Raman micrographs of blends containing 20 wt% TPU. Red area indicates the ABS characteristic peak at 1012 cm−1 while blue area corresponds to characteristic peak of TPU at 1531 cm−1 . These peaks were taken to perform Raman microscopy images shown for b) ABS, c) TPU and d) merged signals from ABS and TPU. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

“It can be observed that TPU characteristic peaks increase proportionally with the TPU content in the blends,” stated the researchers. “This is a first indication of good compatibility between ABS and TPU in the blends, since we cannot identify separated regions of ABS and TPU, at least within the spatial resolution of the Raman laser. To investigate more in detail the chemical composition of the ABS:TPU blends, XY Raman mappings of the blends were performed.”

In examining the compositional distribution of the objects printed, the research team was able to confirm that all the blends did offer a homogeneous distribution of ABS and TPU.

“AFM phase images showed that when TPU content is 10 wt%, it is homogeneously distributed within the ABS matrix, while for blends containing 30 wt% TPU, it tends to form a continuous phase along the ABS matrix,” concluded the researchers. We have correlated this compositional study with the mechanical properties observed in tensile testing specimens printed by FFF. We state that the presence of TPU increases interlayer adhesion (bonding strength) between printed layers while it does not decrease the yield strength value for contents up to 20 wt%.

“For blends containing 30 wt% TPU this adhesion is also enhanced, but yield strength is more like pure TPU than ABS. However, this high content of TPU leads to enhanced adhesion onto the printing platform allowing to keep it at room temperature. Thus, we conclude these blends are promising candidates as materials with enhanced adhesion (between layers and to the platform) to be used in FFF. Due to their commercial availability and simple preparation of the blends, we believe these materials are particular interesting for large-scale, industrial applications as an alternative to pure ABS.”

AFM height images of a) pure ABS, ABS:TPU blends containing b) 10 wt% TPU, c) 20 wt% TPU, d) 30 wt% TPU and e) TPU; AFM phase images of f) pure ABS, ABS:TPU blends containing g) 10 wt% TPU, h) 20 wt% TPU, i) 30 wt% TPU and j) pure TPU. All images have been normalized to the same values to allow direct comparison. Scale bar: 1 μmAFM height images of a) pure ABS, ABS:TPU blends containing b) 10 wt% TPU, c) 20 wt% TPU, d) 30 wt% TPU and e) TPU; AFM phase images of f) pure ABS, ABS:TPU blends containing g) 10 wt% TPU, h) 20 wt% TPU, i) 30 wt% TPU and j) pure TPU. All images have been normalized to the same values to allow direct comparison. Scale bar: 1 μm

Adhesion issues have spurred on many different studies today, from experimenting with a range of different filaments to new heatbed solutions, and improvements for use within industries like construction.

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SEM micrographs of fractures of 1BA test specimens printed in XY using a) pure ABS, ABS:TPU blends containing b) 10 wt% TPU, c) 20 wt% TPU, d) 30 wt% TPU and e) TPU; SEM micrographs of fractures of 1BA test specimens printed in XZ using f) pure ABS, ABS:TPU blends containing g) 10 wt% TPU, h) 20 wt% TPU, i) 30 wt% TPU and j) pure TPU. Scale bar: 500 μm.