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. 2020 Aug 26;5(35):22536-22550.
doi: 10.1021/acsomega.0c03174. eCollection 2020 Sep 8.

Three-Dimensional Printed Lightweight Composite Foams

Bharath H S  1 , Dileep Bonthu  1 , Pavana Prabhakar  2 , Mrityunjay Doddamani  1
Affiliations

Three-Dimensional Printed Lightweight Composite Foams

Bharath H S et al. ACS Omega. .

Abstract

The goal of this paper is to enable three-dimensional (3D) printed lightweight composite foams by blending hollow glass microballoons (GMBs) with high density polyethylene (HDPE). To that end, lightweight feedstock for printing syntactic foam composites is developed. The blend for this is prepared by varying the GMB content (20, 40, and 60 volume %) in HDPE for filament extrusion, which is subsequently used for 3D printing. The rheological properties and the melt flow index (MFI) of blends are investigated for identifying suitable printing parameters. It is observed that the storage and loss modulus, as well as complex viscosity, increase with increasing GMB content, whereas MFI decreases. Further, the coefficient of thermal expansion of HDPE and foam filaments decreases with increasing GMB content, thereby lowering the thermal stresses in prints, which promotes the reduction in warpage. The mechanical properties of filaments are determined by subjecting them to tensile tests, whereas 3D printed samples are tested under tensile and flexure tests. The tensile modulus of the filament increases with increasing GMB content (8-47%) as compared to HDPE and exhibit comparable filament strength. 3D printed foams show a higher specific tensile and flexural modulus as compared to neat HDPE, making them suitable candidate materials for weight-sensitive applications. HDPE having 60% by volume GMB exhibited the highest modulus and is 48.02% higher than the printed HDPE. Finally, the property map reveals a higher modulus and comparable strength against injection- and compression-molded foams. Printed foam registered 1.8 times higher modulus than the molded samples. Hence, 3D printed foams have the potential for replacing components processed through conventional manufacturing processes that have limitations on geometrically complex designs, lead time, and associated costs.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Micrographs of as-received (a) GMB and (b) HDPE.
Figure 2
Figure 2
Representative (a) blend of GMB/HDPE and (b) extruded H60 feedstock filament.
Figure 3
Figure 3
(a) Complex viscosity, (b) storage, and (c) loss modulus vs frequency for blends.
Figure 4
Figure 4
Extruded filament micrograph of (a) cross-sectional view for representative H20. H60 at (b) lower and (c) higher magnifications.
Figure 5
Figure 5
DSC for crystallization peaks: cooling cycle in (a) filaments and (c) prints. Melting peaks from the heating cycle (2nd) in (b) filaments and (d) prints.
Figure 6
Figure 6
Representative filament stress–strain plot of (a) H and (b) H20–H60. SEM of (c) H20 and (d) H60 filament post tensile tests.
Figure 7
Figure 7
Challenges in 3DP of HDPE (Table 4). (a) Improper layer deposition, (b) interlayer defects, (c) excessive diffusion, (d) defect-free print, and (e) highest warpage.
Figure 8
Figure 8
Micrograph of printed (a) H in thickness direction and (b) freeze fractured across the thickness (c) H60 and (d) associated raster gaps in H60.
Figure 9
Figure 9
Fractographic analysis of representative 3D printed (a) H and (b) H60 post tensile test. Reprinted Figure 9a (photograph) with permission from [Patil, B.; Bharath Kumar, B. R.; Bontha, S.; Balla, V. K.; Powar, S.; Hemanth Kumar, V.; Suresha, S. N.; Doddamani, M. Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams. Compos. Sci. Technol. 2019,183, 107816]. Copyright [2019] [Elsevier].
Figure 10
Figure 10
(a) Fractured foam samples post-flexural test. Representative (b) stress–strain plots for prints and (c) H60 micrograph post flexure test.
Figure 11
Figure 11
3D printed representative H60 micrograph showing raster gaps.
Figure 12
Figure 12
Tensile (a) modulus and (b) strength of the HDPE composite.,,
Figure 13
Figure 13
Flexural (a) modulus and (b) strength of the HDPE composite.,,
Figure 14
Figure 14
Comparative chart of the 3D printed GMB/HDPE properties.
See this image and copyright information in PMC

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