Functionally Modified Composites for FDM 3D Printing

Abstract

Fused Deposition Modeling (FDM) 3D printing is an additive manufacturing technique used to fabricate solid thermoplastic polymer objects directly from computer-modeled designs. The current uses for this technology are restricted due to a limited choice of materials, which offer minimal functionality to the printed 3D parts. To expand the application space for FDM-based 3D printing, this chapter is aimed to add functional attributes to printable polymers through the creation of thermoplastic composites. The work focuses on a simple fabrication method to create composite for FDM printing and analytical techniques to characterize dispersion, thermal, and mechanical properties of the nanocomposite. Lastly, the functional characteristics of the FDM printed nanocomposite including their conductivity, ferromagnetism, and radiation shielding properties were studied.

1. Introduction

Fused deposition modeling (FDM) 3D printing is an additive manufacturing technology used to construct solid objects directly from computer-modeled designs. In an FDM process, a solid thermoplastic polymer (as the feedstock) is extruded from a nozzle to build the 3D object. When the thermoplastic polymer is heated above its melting temperature, it flows as a viscous liquid, and can be patterned into thin layers. The layers cool quickly after leaving the nozzle, enabling successive layers to be deposited on top of each other, and thus forming a final 3D object. This technology offers an inexpensive and efficient method to produce customized parts with intricate geometries using a simple printing process. Despite the wide range of potential applications from consumer products and medical to industrial, automotive, and aerospace, FDM has been mostly limited to fabrication of prototype items with no inherent functionality. This limitation has restricted FDM technology within the 3D printing and manufacturing industries, as it prevents fabrication of end products and functional systems [1, 2]. The goal of this chapter is to describe a simple and optimized method for improving the functionality of FDM printing through creation of printable composite materials and to demonstrate a broad application space for functional FDM 3D printing.

The principal reason for the constraint in FDM technology is the limited choice of materials available for FDM printing. Thermoplastic polymers, namely polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), Nylon, thermoplastic polyurethane (TPU), and polycarbonate (PC), are primarily used for their thermal processability, which is necessitated by the FDM extrusion process [3]. Very few commercial thermoplastic polymers provide functional characteristics beyond just printability and prototypes. For FDM 3D printing to progress to the next level and compete with traditional manufacturing, direct production of useful and functional products is necessary. Therefore, future research must focus on imparting functionality into materials used in the FDM 3D printing process.

One method that can be used to achieve this goal is the creation of thermoplastic composites, where thermoplastic polymers are mixed with additives with one or more functionality such as improved electrical conductivity, enhanced ferromagnetism, electrochemical or radiation shielding capabilities. The resulting combination will continue to work as a printable material while simultaneously providing the desired functional attribute. This technique has gained popularity recently as researchers work toward developing new materials to broaden the application space for FDM 3D printing. Functional additives studied in the past include fibers of carbon [4, 5, 6] or glass [7], and particles, such as iron [8], graphene [9], or silicon carbide [10]. Most of the above studies used compound mixing to distribute the additive within the thermoplastic matrix, while a few have used a fiber encapsulation technique. Several factors must be considered and evaluated to achieve true thermoplastic polymer composites, including composite processability, printability with optimal thermal and mechanical characteristics, dispersion, and uniformity, and finally, improvement in the functional properties. Functional properties include electrical conductivity [11, 12, 13, 14], magnetism [15, 16], and bacterial/biofilm resistance [17, 18, 19] and have been demonstrated in FDM composite materials. One of the least studied functional attributes in relation to FDM printing is the radiation shielding capabilities [20]. Radiation shielding is important attribute for component manufacturers with stringent radiation protection requirements such as aerospace, unmanned aerial vehicle (UAV), and satellite manufacturers. Among the many ionizing radiations, neutrons are considered to be extremely severe as they can degrade not only material and electrical components but can also cause damage to biological tissues [21, 22]. By infusing functional attributes such as radiation shielding in FDM composites, the radiation-sensitive component manufacturers can directly create complete functional FDM components, rather than just form prototypes.

Here in this chapter, we report on (a) novel protocol for fabricating FDM composite filaments using a thermoplastic polymer as the matrix material and functional additives as the filler; (b) analytical characterization of resulting functional FDM composite to assess particle dispersion, material uniformity, thermal behavior, and mechanical stability; and (c) assessment of functional properties of fabricated filaments and printed 3D parts. In this work, different functional additives, namely carbon black, nickel, boron nitride, and gadolinium particles, were added to an acrylonitrile butadiene styrene (ABS) polymer matrix to form functional composites that could be directly FDM 3D printed. In the rest of the chapter, these functional additives will be independently evaluated (using analytical and functional techniques) to assess improvements in their functional properties. The significance of this work is that by using simple solution mixing and desktop filament extruder approaches, functional characteristics including electrical conductivity, ferromagnetism, and unique radiation shielding properties were tested in FDM printed ABS composite samples.

2. Methodology

2.1 Materials

Thermoplastic Polymer Matrix: Acrylonitrile butadiene styrene (ABS) is one of the widely used thermoplastic polymers in FDM 3D printing [23]. The reasons being its low cost, printability, and reasonable material strength. Therefore, in this work, ABS was chosen as composite matrix for FDM printing. ABS was purchased in the pellet form from IC3D Printers.

Functional Additive: As the functional additive, various micro/nanoparticles and powders were selected based on the intended functional property such as electrical conductivity, ferromagnetism, and radiation shielding capability. For electrical conductivity functionality, Timical Super C65 (EQ-Lib-Super65) carbon black in fine powder form was purchased. For ferromagnetic functionality, nickel nanopowder (of size <100 nm and > 99% purity) was purchased from Sigma-Aldrich (#577995). For radiation shielding capability, boron nitride nanoparticles (purity >99.8% in hexagonal structure) and gadolinium particles (of size <149 μm and purity >99.9%) were purchased from US Research Nanomaterials, Inc. (#US2019) and Sky Spring Nanomaterials, Inc. (#3580DX), respectively. Boron nitride and gadolinium particles have been demonstrated to be effective in blocking neutron radiation [24, 25]. This is a result of the high neutron capture cross section, an indicator of the ability of an element to block and absorb incident neutrons. For example, boron has a value of approximately 760 barn, the 10th highest of all elements, and gadolinium at 490,000 barn is the highest of all elements [26].

2.2 Fabrication of functional nanocomposite filament for FDM printing

Nanocomposite mixing: After several unsuccessful attempts involving solid mixing of ABS (in either powder or pellet form) and functional additives, followed by thermal compounding, a solution processing method was finally optimized for the fabrication of functional composite filaments.

In this method, first ABS pellets (Figure 1) were dissolved in acetone. Hundred grams of ABS pellets were added to 400 mL of acetone, left to react for 24 hours, and then mixed mechanically (using paddle mixer and ultrasonication) to form a homogeneous polymer solution. One of the functional additives, namely carbon black, nickel, boron nitride and gadolinium particles, was added to the solution, mixed, and sonicated to evenly disperse the particles. It was determined that the composite material properties (including mechanical and thermal) degrade significantly for greater than 20% by weight of the functional additive (irrespective of the additive). Therefore, three percentages (corresponding to their equivalent masses), namely 5%, 10%, and 20%, by weight were used in this study. For example, in the case of boron nitride (BN) nanoparticles, 5%, 10%, and 20% by weight correspond to 5.27, 11.11, and 25.0 grams of BN, respectively. First, the solution mixture was solvent evaporated on a glass plate. Next, the dried mixture was sliced into approximately 5 mm x 5 mm pieces and dried at 80°C. Next, to obtain in the composite powder, the pieces were grinded in a hammer mill. Lastly, the composite powder was stored at 60°C with periodic agitation daily for 7 days to ensure no residual solvent was left in the composite powder.

Figure 1.

Optical image of as obtained ABS pellets.

Nanocomposite filament extraction: Next, for use in standard FDM printer, the composite powder was extruded into a filament form. To accomplish this task, a Filastruder filament extruder was used. First, 1.75 mm nozzle and 190°C were set in the extrude. This was followed by feeding of the powder into the hopper as the screw pushed it toward the nozzle. In this process, the powder was heated to its molten state, pressurized, and filament was extruded at a slow extrusion rate of around 22–25 cm/min. Next, the extruded filament was wound onto a spool using an automated guide after it was air cooled. Finally, 1.75 mm pure ABS and composite filaments (ABS with functional additives) that can be used in any standard FDM 3D printer were obtained. The accuracy of the extruded filament (cross-sectional diameter) was measured (discussed in Section 3). In general, the different composite filaments were found to be 1.75 ± 0.13 mm.

2.3 Analytical, thermal, mechanical, and functional characterization

Analytical characterization: Pure ABS and functional composite filaments were set in EpoThin2 epoxy resin and polished for cross-sectional imaging. EpoThin2 epoxy is a low-viscosity, low-shrinkage resin that is ideal for mounting samples for optical and electron microscopy imaging. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements were performed on a Zeiss Auriga Field Emission Scanning Electron Microscope (FESEM) (Carl Zeiss AG, Germany) to analyze the dispersion or aggregation of particles and its elemental composition. Horiba XploRA Raman system was used to obtain Raman spectrum of selected nanocomposite filaments (particularly boron nitride filaments). The collected Raman spectra were plotted using Horiba LabSpec 6 Spectroscopy suite. Pure boron nitride particles were also characterized, and the obtained spectra were compared with literature values.

Thermal characterization: Two techniques were used to assess thermal properties: thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Thermal degradation onset points and residual mass percentages were calculated on a TA Q500 Thermogravimetric Analyzer. Titanium hang-down pans were loaded with 10 mg of the samples. Heat rate was ramped at 10°C/min from 30–600°C under a nitrogen environment at a 60 mL/min flow rate. This analysis is typically done under nitrogen (or inert) environment to prevent other gases from interfering with the sample during the thermal treatment (i.e., oxidation). Using differential scanning calorimetry (DSC) measurements, the glass transition temperatures (T_g) were analyzed on a TA Q200. Here, 5 mg of each composite was ramped from 35–180°C at 10°C/min. Then, using half heat flow extrapolation, T_g was calculated from the temperature versus heat flow curves.

Mechanical characterization: Mechanical properties, namely strength and modulus of elasticity of both pure ABS and functional composites, were measured. An Instron 5900R material test frame with 5 kN load cell was used to perform mechanical testing. Four-inch filament sections were cut during the extrusion process. These sections were epoxied to plastic tabs as attachment points for the instrument grips, leaving a 2-inch gauge length for tensile testing. Tensile stress was measured using a load cell and plotted as a function of percent strain. Slope of the stress–strain curve in the elastic zone was calculated to determine modulus of elasticity.

Next, ASTM D638 test specimens were cut using a water jet from the printed 3D sample for further mechanical testing. The specimen dimensions adhered to guidelines for type V samples. Dynamic mechanical analysis (DMA) was performed on a Perkin Elmer DMA 8000. This analysis was used to study composite’s mechanical properties at different temperatures. Here, the 3D printed samples were cut into rectangular sections of dimensions 50.5 x 12.6 x 3.6 mm. Dual cantilever testing was performed at a frequency of 0.05 Hz with a temperature ramp from 30 to 150 C. The storage modulus values were studied.

Functional characterization: Lastly, functional properties of different nanocomposites and different functional 3D printed samples were measured. 3D printing of both pure ABS filaments and the functional composite filaments was done on a Fusion3 F306 3D printer. The sample dimensions were 65.3 x 65.3 x 3.4 mm at 100% infill and + 45°/−45° raster pattern. The print head temperature was maintained at 245°C printing on a heated bed set at 110°C.

To test the electrical functionality, electrochemical impedance spectroscopy (EIS) was used to assess electrical impedance of the carbon black infused filaments (Figure 2). EIS was performed on a VersaSTAT 4 potentiostat in a frequency range of 0.1–10 KHz with an amplitude of 5 mV RMS. Next, to test ferromagnetic functionality of ABS/nickel nanocomposites, a Quantum Design physical property measurement system (PPMS) was used to study magnetization of the nanocomposite 3D prints. The magnetic moment was plotted as a function of applied magnetic field. Finally, in order to evaluate neutron attenuation characteristic, the 3D printed composite samples were exposed to neutron particle beam at the Breazeale Nuclear Reactor, part of the Radiation Science & Engineering Center at Penn State University. A detector was then used to measure incident neutrons before and after exposure of the 3D printed composite samples. The test methodology is as follows. First, using a carrier system, the 3D printed samples were moved into the collimated neutron beam consisting of thermal neutrons with average energy of 0.025 eV. This beam was in between BF₃ detectors and the reactor. Next, a minimum of 15,000 counts of neutrons (counting time of at least 30 seconds) were allowed to penetrate the 3D printed sample at multiple spots. For control and for data normalization, both “blank” (with 0% shielding capability) and “black” (with 100% effective shielding) were measured.

Figure 2.

Functionally modified composite filaments (ABS/carbon black) for electrical impedance measurements.

3. Results and discussion

Analytical characteristics of different nanocomposite filaments: First, pure ABS extruded filament was studied. Figure 3a and b show optical image of the pure ABS filament (after the extrusion process) and its corresponding Raman spectrum. Caliper measurements confirmed the uniformity of filament diameter during extrusion, with readings of 1.75 ± 0.05 mm. Raman spectra confirmed pure ABS with definitive peaks at 1629, 1696, and 2262 cm⁻¹. The 1629 cm⁻¹ peak corresponds to C − C and C=C vibrations in the styrene aromatic ring, the 1696 cm⁻¹ peak demonstrates C=C bonds in the butadiene monomer, and the 2262 cm⁻¹ peak shows the presence of C ≡ N bond in acrylonitrile. The 654 and 1031 cm⁻¹ peaks are related to aromatic C-H bending.

Figure 3.

a) Optical image of the extruded ABS filament and b) its Raman spectra.

Next, the different extruded composite filaments were studied. As discussed in Section 2.2, all cross-sectional SEM images were obtained after setting the nanocomposite filaments (about 3–5 cm sections) in EpoThin2 epoxy resin and surface polished to expose the “first” layer below the surface. Figure 4a and b shows SEM cross-sectional and optical images of the carbon black in composite filament after 20% ABS/carbon black solution processing. Carbon black is in fine powder form, with submicron primary and agglomerates averaging around 20 μm. The measured diameter of the fabricated filament was 1.60 ± 0.15 mm. Arrows in all the optical images indicate a general area (around the middle of the nanocomposite filament) where the SEM cross-sectional images were taken.

Figure 4.

a) SEM cross-sectional image of 20% ABS/carbon black composite filament and b) optical image of the 20% ABS/carbon black composite filament.

Figure 5a and b show SEM cross-sectional and optical images of ABS/nickel composite filament after 20% ABS/nickel solution processing. A broad nickel particle dispersion profile was observed, with some agglomerates larger than 100 μm in size. The measured diameter of the fabricated filament was 1.68 ± 0.12 mm.

Figure 5.

a) SEM cross-sectional image of 20% ABS/nickel composite filament and b) optical image of 20% ABS/nickel composite filament.

Figure 6a and b show SEM images of boron nitride and gadolinium particles. In the case of boron nitride particles, primary particles were observed in the nano range (70–80 nm), and large secondary particles in the range of 10–50 μm were apparent. In the case of gadolinium particles, a broad size range was apparent with large particles in the range of 10–100 μm.

Figure 6.

SEM images of a) boron nitride particles and b) gadolinium particles.

Figure 7a,b, and c show the ABS/boron nitride composite filaments of 5%, 10%, and 20% by weight, respectively. The particles in the composite appeared to be evenly distributed with 5% and 10% concentrations exhibiting smooth surface finish (Ra ~20–30 μm), while surface of the 20% concentration appeared to be rougher (Ra ~80–100 μm). With the respect to the composite filament diameters 5%, 10% and 20% composite filaments were in the range of 1.79 ± 0.06 mm, 1.77 ± 0.04 mm, and 1.76 ± 0.08 mm, respectively. These results were consistent and were within necessary tolerance for FDM printing. Figure 7d,e, and f show the ABS/gadolinium composite filaments of 5%, 10%, and 20% weight, respectively. The material appeared to be consistent and showed a smooth surface finish at 5% concentration (Ra ~40–60 μm), slight surface roughness at 10% (Ra ~80–120 μm), and significant irregularity at 20% (Ra >250 μm). The diameter measurements for the 5% composite were in range of 1.83 ± 0.08 mm, 1.79 ± 0.12 mm for the 10% composite, and 1.69 ± 0.21 mm for the 20% composite. The severe roughness of the 20% sample resulted in a very inconsistent diameter. The combination of severe surface roughness and inconsistency resulted in this composite being unsuitable for F306 FDM printing.

Figure 7.

ABS/boron nitride composite filaments, a) 5%, b) 10%, c) 20% and ABS/gadolinium composite filament, a) 5%, b) 10%, c) 20%.

Raman spectroscopy was used to verify the presence of boron nitride within the nanocomposite filament. Figure 8 shows the Raman spectra of pure BN particles, pure ABS, and 5%, 10%, and 20% BN composites, respectively. In the case of pure boron nitride (BN), a distinct peak at 1364 cm⁻¹, as reported in literature [27], is clearly visible. 1364 cm⁻¹ Raman peak is the result of vibrational bond between boron and nitride in their native hexagonal lattice. The Raman spectra of pure ABS spectra also agree with the reported values in literature [28]. This indicates that boron nitride as an additive is present in the composite and does not interfere with any bonding between monomers, as all vibrational modes are also present in the spectra. As expected, at higher additive percentages (10% and 20%), the Raman peak becomes more pronounced because of higher particle concentration.

Figure 8.

Raman spectra of boron nitride (BN), pure ABS, and 5%, 10%, and 20% ABS/BN nanocomposite filaments.

Thermal characteristics of ABS/BN nanocomposite filaments: Using TGA plots, the dispersion uniformity was studied for pure ABS and the different composite filaments. ABS achieves an average residual mass of approximately 1% at 533°C, while the 5%, 10%, and 20% boron nitride composite samples reach an average residual mass percentage of 6.02 ± 0.07%, 10.23 ± 0.05%, and 20.12 ± 0.13% residual mass, respectively. It is clearly evident that the residual mass is primarily attributed to the boron nitride additive (remaining) added to the ABS matrix, as it is known that ABS will thermally degrade before boron nitride. In addition, the measurements also confirm that the residual mass percentage closely matches the intended 5%, 10%, or 20% by weight of boron nitride. Lastly, when the above measurements were conducted at different time points during the filament extrusion process, it resulted in small standard error (<1%). These results suggest that the boron nitride as an additive in ABS is evenly dispersed in the filament. Similarly, even dispersion results were obtained for other functional additives, namely carbon black, nickel, and gadolinium particles.

Figure 9.

TGA plot of ABS and ABS/boron nitride nanocomposites.

From the TGA plots, the thermal onset points were also determined for the different composites. The onset point, which is the temperature at which thermal degradation begins, is also used to assess a material’s thermal stability at high temperatures. It is calculated by extrapolation of the slopes of predegradation and postdegradation points. The onset point for ABS was measured to be 384.66 ± 1.13°C. The addition of boron nitride did not significantly change the degradation point of ABS/BN composites compared with pure ABS. ABS/BN composite onset point for 5%, 10, and 20% of BN were 385.55 ± 0.48°C, 384.25 ± 1.15°C, and 390.90 ± 2.01°C, respectively (Figure 9). Onset point for 5% and 10% ABS/BN composites closely matched that of pure ABS, while 20% ABS/BN composite showed even a slightly larger thermal onset point. This may indicate that higher concentration of additives may be preventing early thermal degradation. Next, to further understand the thermal properties of ABS/BN composites, differential scanning calorimetry (DSC) measurements were performed to study their glass transition temperature (T_g). This value related to the temperature at which a polymer begins to experience chain movement due to an increase in thermal energy and is an important consideration for 3D printability. The detailed DSC results are reported elsewhere [20].

Mechanical characteristics of ABS/BN nanocomposite filaments: The mechanical characteristics of ABS and ABS/BN composite samples were studied. This was done to determine the effect of BN additive on ABS polymer strength. Following ASTM D638 tensile tests, the stress–strain curve of ABS and ABS/BN composites is shown in Figure 10. The variations in stress–strain curves for different additive concentrations were clearly evident. Pure ABS shows the highest tensile stress of 34.01 ± 0.55 MPa, while 5%, 10%, and 20% ABS/BN composite samples have an average tensile stress of 23.85 ± 0.62 MPa, 18.86 ± 0.91 MPa, and 23.16 ± 1.16 MPa, respectively. It is evident from these results that BN addition does degrade the ultimate tensile stress of the ABS polymer. Furthermore, pure ABS showed a superior modulus of elasticity at 1.365 ± 0.05 GPa, while 5%, 10%, and 20% ABS/BN composite samples showed 1.179 ± 0.07 GPa, 0.979 ± 0.06 GPa, and 1.420 ± 0.06 GPa, respectively. It is also evident from these results that a smaller percentage of BN as additive influences the composite’s elasticity as a softer material while at higher concentrations, it may stiffen the 3D printed composite. The samples were tested to evaluate the storage modulus of the 3D composite as a function of temperature using dynamic mechanical analysis. Detailed results are reported elsewhere [20]. In summary, pure ABS and ABS/BN composites show nearly similar mechanical characteristics. Pure ABS is seen to maintain a glassy region modulus of 2.67 GPa from room temperature to around 105°C, which is the glass transition temperature (Tg) for ABS. After Tg and around 140°C, the modulus falls to rubbery region modulus of 2.15 MPa. Similarly, ABS/BN composites’ storage moduli up to 105°C ranges between 2 GPa and 2.54 GPa and at 140°C, it reaches a minimum of 1.31 MPa. It may be concluded that this degradation of ultimate tensile stress may be due to interactions between the additive (BN) and the polymer (ABS) chains, whereby the BN as an additive may be interfering with ABS polymer bonding. Despite the degraded mechanical properties in ABS/BN composites, all composite filaments were printed on a standard FDM printer without any problem. Slight variations in the material strength did not affect the printability of any of the composite filaments, carbon black, nickel, boron nitride, and gadolinium particles.

Figure 10.

Stress–strain curves of pure ABS and ABS/boron nitride nanocomposite filaments.

Functional characteristics of different nanocomposite filaments: Functional assessment was performed to assess conductivity (impedance), magnetism, and radiation shielding characteristics of pure 3D printed ABS and 3D printed functional composites.

First, electrical conductivity of ABS/carbon black functional composites was studied. In this case, the pure ABS and 20% carbon black composite was compared with copper wire. Figure 11 shows the plot of impedance as a function of frequency for samples of each material. The results show high impedance values for pure ABS, as expected with no electrically conductive components. By adding 20% weight of carbon black, the impedance was lowered by 4–7 orders of magnitude, depending on the frequency, to a value of 2.8 k Ω. This indicates that the composite material is far more conductive than pure ABS. Even though, the carbon black/ABS composites were not as conductive as copper, which has an additional 5 orders of magnitude lower impedance value, close to 15.8 mΩ. Nonetheless, the fabricated 3D functional composite showed marked improvement in electrical conductance.

Figure 11.

EIS plot of ABS, 20% carbon black, and copper.

Next, magnetic characterization of pure ABS and ABS/nickel composites was performed on a physical property measurement system (PPMS). A magnetic field was applied to pure ABS and 5%, 10%, and 20% ABS/nickel composites to measure the resulting magnetic moment. The plots of moment as a function of applied field at room temperature are shown in Figure 12, where (a) is pure ABS, and (b) is 20% nickel/ABS composite. Pure ABS showed an inverse relationship between field strength and moment, indicating diamagnetic properties. This is typical of polymeric materials and is a result of absence of any paramagnetic or ferromagnetic response. With increasing nickel additive concentration, hysteresis responses were observed, as well as a magnetic saturation point, indicating the presence of ferromagnetic function. Magnetic saturation point for 20% nickel/ABS composite was 11.5 emu/g.

Figure 12.

Magnetic moment plots of (left) pure ABS and (right) ABS/nickel composites.

Finally, radiation shielding properties of pure 3D printed ABS and 3D printed composites of boron nitride and gadolinium particles were studied. Figure 13 shows the attenuation percentage data for pure ABS, boron nitride/ABS, and gadolinium/ABS composites. Pure ABS showed 50.37% neutron attenuation capability, which means that around half of the neutrons passed through the shielding panel. This was not unexpected. Pure ABS, which contains a large amount of hydrogen atoms, provides some limited shielding capability at high concentrations. 5% and 10% ABS/BN composite samples showed slightly higher neutron attenuation capability, between 55% and 57%. Around 71.76% incident neutron attenuation was exhibited in 20% ABS/BN 3D printed composites. In the case of ABS/gadolinium composites, 5% and 10% of gadolinium showed very significant attenuation for incident neutrons at 81.07% and 90.12%, respectively. The theoretical calculations for attenuation coefficients to further understand radiation shielding of these 3D printed composites are reported elsewhere [20].

Figure 13.

Neutron attenuation for ABS, BN/ABS, and gadolinium/ABS composite 3D prints.

4. Conclusions

In summary, in this work, we have shown that incorporation of functional additives, carbon black, nickel, boron nitride or gadolinium particles, into FDM printable ABS mixture is feasible. Various filament nanocomposite materials for use in FDM printers were successfully created by using simple solution mixing approach and desktop extruder. Even dispersion of additives in the ABS polymer matrix was confirmed using optical, electron microscopic, and thermogravimetric analysis. Furthermore, thermal analysis confirmed that thermal properties were only altered minimally compared with pure ABS. Even though, mechanical measurements revealed some variations in polymer strength in the composite filaments, compared with pure ABS, the printability on regular 3D FDM printers was not significantly affected.

Finally, functional testing of the 3D printed nanocomposite samples for properties such as conductivity, magnetic response, and neutron attenuation showed marked to very significant increase in functional properties, particularly in the case of radiation shielding capability of 3D printed composite with gadolinium particles. The neutron radiation shielding capability was enhanced from 50% with pure ABS samples to up to 90% with 10% ABS/gadolinium particles and around 72% with 20% ABS/boron nitride nanocomposites. This enhancement in radiation shielding capability is extremely valuable to reduce damage from neutron sources for aerospace, UAV, and satellite applications. In conclusion, the ability to manufacture functional FDM components is expected to assist the additive manufacturing community to move beyond just “form-and-fit” prototyping into the production of complete end-use parts with functional attributes.

Acknowledgments

This work was conducted at the Joint School of Nanoscience and Nanoengineering (JSNN), a member of the Southeastern Nanotechnology Infrastructure Corridor (SENIC), and a site for National Nanotechnology Coordinated Infrastructure (NNCI), with partial support from the National Science Foundation (EECS-1542174 and ECCS-2025462).

Conflict of interest

The authors declare no conflict of interest.