Composite Feedstock Research Articles

Effect of composite processing technique on tribological properties of 3D printed PLA-graphene composites

The present study investigates the effect of processing method on the tribological behavior of 3D-printed Polylactic acid (PLA)/graphene composite samples. Two different methods, electrochemical (EG) and chemical exfoliation (HG) of graphite, are used to prepare graphene fillers. The PLA/graphene composites are processed using two different solvents, chloroform (CHCl3) and dimethylformamide (DMF). Various PLA/graphene composite combinations are prepared by varying filler type, solvent type, and filler loading. The 3D printable composite feedstock filaments are prepared using a single-screw Desktop extruder. Fused Filament Fabrication (FFF) is employed to print samples for tribological tests. The coefficient of friction (COF) and wear rate are evaluated using the ball-on-flat reciprocating sliding wear tests. It was observed that COF was reduced by 76 % with 0.5 wt% loading of filler. The wear mechanism has changed from predominant abrasive wear in neat PLA to adhesive wear for composites. Further, the interactive effect of process parameters is studied using ANOVA. The results indicate that filler type and filler loading significantly influence weight loss. The solvent type has a minimum effect.

Effect of different exfoliation routes on the properties of chicken feather and elephant grass hybrid biochar

AbstractLiquid‐phase exfoliation, a technique for enhancing the properties of biochar, has been recognized as effective, circumventing the limitations of other methods such as high expenses, scalability, and complexity. This study explored the synergistic effect achieved by combining chicken feathers with elephant grass to create a composite feedstock for biochar production. The biochar was subjected to liquid‐phase exfoliation using acid and acetone. Elemental analysis indicated that the co‐carbonization of the combined biomass produced an enriched hybrid biochar. The oxygen content in both exfoliation routes (acid and acetone) increased, with an increase and decrease in carbon content in acetone and acid exfoliation, respectively. Textural analysis revealed significant enhancement, with surface areas of the acid‐exfoliated biochar more than twice the size of the hybrid biochar. The pore volume of both exfoliated samples was double that of the hybrid biochar. Microscopic surface examination revealed rougher, porous structures in the exfoliated biochars in comparison with the smooth, cohesive surface in hybrid biochar. Functional group analysis showed the presence of aromatic rings, a carbocyclic group, and an alkene, suggesting potential applications in adsorption. This study provides an efficient method for using liquid‐phase exfoliation to enhance biochar properties, benefiting industries reliant on biochar production and biomass utilization by improving product quality, sustainability, and environmental impact.

A novel powder sheet laser additive manufacturing method using irregular morphology feedstock

Irregular (i.e. non-spherical) morphology powder is more cost-efficient to produce than spherical shaped powder. However, its reduced levels of flowability limit the wide application ranges of laser beam powder bed fusion (LPBF). To address this issue, a novel powder sheet additive manufacturing concept (MAPS) is proposed. Herein, a pre-manufactured metal particle-polymer binder composite (i.e. powder sheet) feedstock is employed as a raw material. The printability of irregularly shaped powder particles in sheet (MAPS) format was physically investigated using a range of different process parameters. The manufacturing process was observed by high-speed imaging. Microstructural and chemical element characterisations of the irregularly shaped powder particle print were then compared against those prints which were conducted using sheet-based (MAPS) spherical powder morphologies. The results indicated that the geometric accuracy and density of irregular powder morphology sheet printing improved when using a negative defocus strategy of the laser beam. A negative defocusing strategy allowed for the melting mode of the material to be transformed from keyhole to a more favourable conduction state. High speed imaging revealed that more spatter and vapour plume were observed with the increase in the magnitude of the negative defocus. The multi-morphology 304 L stainless steel (SS304) samples were printed in a single printer using an efficient method for the first time, i.e. printing spherical SS304 material on top of irregular SS304. EDX results indicated an insignificant change of chemical elements between the spherical and irregular prints. EBSD results revealed that columnar grains could grow through the irregular-spherical transition zone and similar grain size can form between spherical and irregular prints. The results of this study provide insights into the optimum printing configurations for powder sheet additive manufacturing using a cost-effective solution of irregular morphology material.

Magnetic polyamide 11 powder for the powder bed fusion process by liquid-liquid phase separation and crystallization

Herein, we demonstrate the preparation of magnetic polyamide 11 feedstock powders for powder bed fusion (PBF) using liquid-liquid phase separation and crystallization. By adding magnetic nanomaterials during the precipitation process, the particulate additive is incorporated into the polymer matrix. This enables the production of filled systems at single particle level, which is advantageous in terms of the adjustable magnetic strength and homogeneity of the powder. Thermogravimetric analysis is used to determine the additive content and onset temperature of decomposition of composite powders, where additive-enhancement of PA11 powders with magnetic iron oxide nanoparticles showed a positive influence on the thermal stability of the feedstock. Successive analysis of particle size distribution, shape, colour, crystal structure, magnetic properties and thermal properties of the composite powders are carried out and their properties are discussed with respect to the PBF process. A decrease in particle size, width of the thermal process window and isothermal crystallization time can be attributed to the nucleating effect of the magnetic additive. The PBF processability of the composite feedstock is demonstrated by the production of magnetic tensile bar specimens from additive-enhanced PA11 powders with 1 wt.-% magnetic iron oxide.

Interrelations between Printing Patterns and Residual Stress in Fused Deposition Modelling for the 4D Printing of Acrylonitrile Butadiene Styrene and Wood–Plastic Composites

Four dimensional printing enables the advanced manufacturing of smart objects that can morph and adapt shape over time in response to stimuli such as heat. This study presents a single-material 4D printing workflow which explores the residual stress and anisotropy arising from the fused deposition modelling (FDM) printing process to create heat-triggered self-morphing objects. In particular, the study first investigates the effect of printing patterns on the residual stress of FDM-printed acrylonitrile butadiene styrene (ABS) products. Through finite element analysis, the raster angle of printing patterns was identified as the key parameter influencing the distribution of residual stresses. Experimental investigations further reveal that the non-uniform distribution of residual stress results in the anisotropic thermal deformation of printed materials. Thus, through the design of printing patterns, FDM-printed materials can be programmed with desired built-in residual stresses and anisotropic behaviours for initiating and controlling the transformation of 4D-printed objects. Using the proposed approach, any desktop FDM printers can be turned into 4D printers to create smart objects that can self-morph into target geometries. A series of 4D printing prototypes manufactured from conventional ABS 3D printing feedstock are tested to illustrate the use and reliability of this new workflow. Additionally, the custom-made wood–plastic composite (WPC) feedstocks are explored in this study to demonstrate the transposability of the 4D printing approach.

Initial Study on Rheological Behaviour of Hydroxyapatites / Polylactic Acid Composite for 3D Printing Filament

The present fused deposition modeling (FDM) printing process has concentrated on combining metal or ceramic filled with polymer because it could provide a strong composite in layered manufacturing technology in comparison to a single polymer material. However, the ability of the composite material to flow into the extruder becomes an obstacle because of the changes in the polymer concentration and dispersion of filler particles in producing the printed part. Hence, the rheological behavior of Hydroxyapatites (HAp) / Polylactic Acid (PLA) composite with different contents of HAp was studied to assess its ability to flow through the extruder during the 3D printing process. Measurements such as pycnometer density, thermal analysis (DSC) and FT-IR were performed on the composite feedstock containing a variation of 10% to 30% HAp powder. The feedstocks behavior then were characterized by rheological tests at three different temperatures (140 oC, 150 oC, and 160 oC). The composition of PLA/20HAp has produced optimum rheological behavior with effective flow behavior index (n) and activation energy (E) of 0.396 and 89.03 kJ/mol, respectively which is suitable for extruding out the HAp/PLA composite to become a 3D printing filament material.

Mixed-Material Feedstocks for Cold Spray Additive Manufacturing of Metal–Polymer Composites

High-performance polymers such as poly(ether ether ketone) (PEEK) are appealing as composite components for a wide variety of industrial and medical applications due to their excellent thermomechanical properties. However, conventional PEEK metallization methods can often lead to poor quality control, low deposition rate, and high cost. Cold spray is a promising potential alternative to produce polymer–metal composites rapidly and inexpensively due to its relatively mild operating conditions and high throughput. In this study, we investigated the deposition characteristics of metal–polymer composite feedstock, composed of PEEK powder and copper flake in varying ratios, onto a PEEK substrate. Copper-PEEK powder blends were prepared by both hand-mixing and cryogenic milling (cryomilling), which predominantly creates composite particles with micron-scale copper domains coating PEEK particle surfaces. This process non-monotonically affects the relative dominance and length scales of the multiple contributing deposition mechanisms present in mixed-material cold spray. In low-pressure cold spray, deposits showed significant changes in deposition efficiency and composition as a result of milling, with improvements in these characteristics most dramatic at lower Cu fractions. Deposits of a cryomilled blend of nominally 30 vol.% copper in PEEK exhibited minimal porosity under scanning electron microscopy, complete retention of powder composition, and the highest deposition efficiency among all samples tested. Notably, neither neat PEEK nor neat Cu meaningfully deposited at the same mild conditions as this 30 vol.% Cu blend, indicating a synergistic departure from linear mixing rules driven by the relative balance of local deposition interactions (e.g., hard–soft, soft–soft, etc.). Intentional powder and process design toward optimizing this balance may facilitate cold spray metallization applications.

Polymeric composites in extrusion‐based additive manufacturing: a systematic review

AbstractSolid composites used in material extrusion additive manufacturing have experienced considerable expansion over the past 5 years, incorporating functional properties into 3D‐printed objects. This paper presents a systematic review that aims to: (I) analyze the current state of development in the field; (II) quantify and categorize the adopted polymeric matrices, reinforcing materials, feedstock shapes, characterization strategies, and extrusion mechanisms; and (III) identify the applications, limitations, and trends for future research. The PRISMA statement was followed and the databases Scopus, Web of Science, and PubMed were consulted. Among the 116 included studies, the use of customized filaments surpassed the commercially available ones, with particulate matter being the most common form of filler when melt‐mixed with the polymer. Polyamide is the most widely adopted matrix (30.3%), followed by PLA (22.0%) and ABS (17.4%). In terms of reinforcements, carbon fiber (32.4%), glass fiber (12.5%), and ceramics (12.5%) compose the podium as the most frequently used, with nanofillers receiving increasing attention. In the conducted analysis, no standardized protocols were identified that clearly encompassed the entire process from feedstock formulation to technical prototype fabrication. At last, recycling, exploration of biodegradable materials, and 4D printing were identified as the main opportunities for future research.Highlights Reinforced polymers enable the enhancement of properties for 3D‐printed parts. Composite feedstock is usually formulated and mixed before printing. 3D printers with filament‐ or screw‐based extrusion mechanisms have been used. Mechanical and morphological analyses are common in material characterization. No identified applications were employed in real‐world scenarios.

Large-scale NiFe2O4-based cermets prepared by composite extrusion modelling: From high-qualified composite feedstock to dense sintered microstructure

Combining with the advantages from mature technologies of fused deposition modelling and powder injection molding, 3D NiFe2O4-based cermet with weight over 1.3 kg and relative density of 95.8 % were fabricated by composite extrusion modelling using polyoxymethylene-based feedstock. Microstructure and rheological properties of the feedstock, roles of printing parameters on the morphology green samples and related catalytic debinding, sintering properties of cermets were investigated in detail. Uniformly dispersed cermet powders in feedstock were confirmed, due to the good wettability between the powders and binders. The feedstock with high solid loading of 58 vol% exhibited shear-thinning behavior and contained high storage modulus for reliable shape retention. With optimized printing parameters, a high compression ratio (layer height/nozzle diameter) over 2.5 tended to shrink the size of stacking pores, resulting in dense green samples. Catalytic debinding was proved to be defect-free and efficient debinding route, which was successfully used to deal with dense cubic samples with thickness of 30 mm. Sintered samples showed uniform microstructure with interconnected FeCuNi and Ni(Fe)Fe2O4 phases. Except for partial stacking pores in the fracture section, polished cermets exhibited mirror-like surfaces, indicating the good controlling of the final microstructure and performance of 3D cermets.

Ternary low-friction coatings on thermoplastics by plasma spraying: Investigations on the process-structure

Thermally sprayed MoS2/graphite/Zn coatings were developed by the atmospheric pressure plasma jet technique to investigate the process-structure-relationship of the low-friction coatings. The fine-tuning of the powder carrier gas flow to the plasma jet was supported by computational fluid dynamics and revealed the impact on the powder particles within the coating process i.e. ideal powder particle temperature for transferring the solid Zn powder into the liquid state as main requirement for a successful embedding process of the dry lubricants. MoS2/graphite/Zn composite coatings were deposited on polyamide 4.6 (PA4.6) substrates to evaluate the adhesion/cohesion properties and tribological performance by tuning the current of the atmospheric pressure plasma jet (APPJ) from 125 A to 150 A. In particular, the plasma spraying distribution of the composite feedstock and the resulting coating architecture are strongly dependent on the plasma process setting, which are investigated by scanning electron microscopy and transmission electron microscopy in combination with an energy-dispersive x-ray spectrometer. Tribological characterisation indicates that coating composition and thickness influence the coating performance significantly. According to the 125 A plasma current setting, the low frictional compounds MoS2 and graphite are embedded in a Zn matrix in contrast to plasma current settings of 150 A, where Zn is embedded in a MoS2 and graphite matrix and demonstrates excellent low frictional properties.

Influence of processing techniques on mechanical and electrical performance of PLA-graphene composite feedstock filaments

The 3D printable PLA-graphene composite feedstock filaments can be used to print components that exhibit multi-functionality. The present work analyzes different processing routes and proposes a standard procedure for making PLA-graphene composite feedstock filaments. We used two routes to process graphene-based fillers: the modified Hummers process (HG) and electrochemical exfoliation (EG). After that, PLA-graphene composites with variable filler loadings were processed by mixing different solvents, DMF and CHCl3. Then, printable feedstock filaments were processed from these composites by using a desktop single-screw extruder. It was observed that solvent type influences mechanical properties, and filler type influences electrical properties. The DMF-based composites showed high ductility compared to CHCl3-based composites. The EG-based filaments showed higher electrical conductivity than HG-based filaments. The printability of processed filaments was investigated by 3D printing test samples using fused filament fabrication (FFF). It was observed that CHCl3 improved printability at low filler loading, and DMF improved printability at high filler loading. The 3D-printed samples showed higher mechanical strength at 0.3 wt% for all filament combinations. The electrical properties of 3D printed samples are highest for EG. It is suggested to use 5 wt% of EG with DMF for enhanced electrical properties of printed samples. Also, 0.3 wt% HG with CHCl3 is suggested for enhanced mechanical properties of printed samples.

Recycling as a Key Enabler for Sustainable Additive Manufacturing of Polymer Composites: A Critical Perspective on Fused Filament Fabrication.

Additive manufacturing (AM, aka 3D printing) is generally acknowledged as a "green" technology. However, its wider uptake in industry largely relies on the development of composite feedstock for imparting superior mechanical properties and bespoke functionality. Composite materials are especially needed in polymer AM, given the otherwise poor performance of most polymer parts in load-bearing applications. As a drawback, the shift from mono-material to composite feedstock may worsen the environmental footprint of polymer AM. This perspective aims to discuss this chasm between the advantage of embedding advanced functionality, and the disadvantage of causing harm to the environment. Fused filament fabrication (FFF, aka fused deposition modelling, FDM) is analysed here as a case study on account of its unparalleled popularity. FFF, which belongs to the material extrusion (MEX) family, is presently the most widespread polymer AM technique for industrial, educational, and recreational applications. On the one hand, the FFF of composite materials has already transitioned "from lab to fab" and finally to community, with far-reaching implications for its sustainability. On the other hand, feedstock materials for FFF are thermoplastic-based, and hence highly amenable to recycling. The literature shows that recycled thermoplastic materials such as poly(lactic acid) (PLA), acrylonitrile-butadiene-styrene (ABS), and polyethylene terephthalate (PET, or its glycol-modified form PETG) can be used for printing by FFF, and FFF printed objects can be recycled when they are at the end of life. Reinforcements/fillers can also be obtained from recycled materials, which may help valorise waste materials and by-products from a wide range of industries (for example, paper, food, furniture) and from agriculture. Increasing attention is being paid to the recovery of carbon fibres (for example, from aviation), and to the reuse of glass fibre-reinforced polymers (for example, from end-of-life wind turbines). Although technical challenges and economical constraints remain, the adoption of recycling strategies appears to be essential for limiting the environmental impact of composite feedstock in FFF by reducing the depletion of natural resources, cutting down the volume of waste materials, and mitigating the dependency on petrochemicals.

Plasma sprayed aluminium nitride (AlN) coating: Microstructural, mechanical, tribological, and corrosion resistance performance

In this work, oxide-free AlN coating was fabricated using single-step, large throughput nitrogen-shrouded plasma spraying. Initially, Al/AlN composite feedstock powder was prepared by a ball-milling at a 70:30 wt% ratio to deposit the AlN coating. Microstructural evaluation revealed the formation of dominant c-AlN phase along with minor h-AlN without presence of any oxides or impurities in the coating. Hardness and elastic modulus (E) were observed to be ∼7.2 GPa and ∼280 GPa respectively. Furthermore, an investigation of tribological performance showed the wear rate ∼0.18 × 10−3 mm3/Nm and coefficient of friction (COF) 0.45 ± 0.02. In addition, the corrosion resistance behaviour of AlN coating in 3.5 wt% NaCl shows as low as 2.95 × 10−9 mm/s indicates the extended life of the coated components. Therefore, the fabricated plasma-sprayed AlN coating can be recommended for high-performing wear and anti-corrosive competitor for industrial applications.

Dry sliding wear behavior of additively manufactured cenosphere-filled PETG syntactic foam composites

PurposeThis study aims to deal with developing composite filaments and investigating the tribological behavior of additively manufactured syntactic foam composites. The primary objective is to examine the suitability of the cenosphere (CS; 0–30 Wt.%) to develop a high-quality lightweight composite structure with improved abrasion strength.Design/methodology/approachCS/polyethylene terephthalate glycol (PETG) composite feedstock filaments under optimized extrusion conditions were developed, and a fused filament fabrication process was used to prepare CS-filled PETG composite structures under optimal printing conditions. Significant parameters such as CS (0–30 Wt.%), sliding speed (200–800 rpm) and typical load (10–40 N) were used to minimize the dry sliding wear rate and coefficient of friction for developed composites.FindingsThe friction coefficient and specific wear rate (SWR) are most affected by the CS weight percentage and applied load, respectively. However, nozzle temperature has the least effect on the friction coefficient and SWR. A mathematical model predicts the composite material’s SWR and coefficient of friction with 87.5% and 95.2% accuracy, respectively.Practical implicationsBecause of their tailorable physical and mechanical properties, CS/PETG lightweight composite structures can be used in low-density and damage-tolerance applications.Social implicationsCS, an industrial waste material, is used to develop lightweight syntactic foam composites for advanced engineering applications.Originality/valueCS-reinforced PETG composite filaments were developed to fabricate ultra-light composite structures through a 3D printing routine.

On fabrication of acrylonitrile butadiene styrene-zirconium oxide composite feedstock for 3D printing-based rapid tooling applications

The 3D-printed rapid tools are being used in finishing operations such as drilling, milling, broaching, roller burnishing, and other finishing operations that need anti-wear plastic composite materials. Zirconium oxide (ZrO2) is one of the ceramic materials which is highly appreciated due to its anti-wear properties. This study aims to develop the ZrO2 ceramic particles reinforced acrylonitrile butadiene styrene (ABS) thermoplastic composite feedstock filaments for 3D printing of rapid tools. In the first stage, the multiple numbers (as per Taguchi L9 orthogonal array (OA)) of ABS-ZrO2 feedstock filaments were developed by varying the loading of ZrO2 in ABS matrix (2 wt.%, 4 wt.%, and 6 wt.%), processing temperature (200, 205 and 210°C), and rotation speed of screw (4, 6 and 8 RPM). The optimum setting obtained for manufacturing ABS-ZrO2 composite feedstock filaments is the combination of 2% ZrO2 loading, 205°C processing temperature, and 6 RPM screw speed. In the next stage, fused filament fabrication (FFF) based 3D printing has been used to prepare the rapid tools. The wear test performed for 3D printed ABS-ZrO2 composites rapid tools shows only .62% weight loss which is lower as compared to virgin ABS (.91% weight loss). The results of the study are supported by fracture analysis, morphology, and mechanical properties.

Extrusion as a tool to enhance the nutritional and bioactive potential of cereal and legume by-products

Cereal and legume by-products obtained from primary food production industries pose an environmental and economic problem. Nevertheless, these residues can potentially yield value-added products due to their elevated content of dietary fiber, phytochemicals, vitamins, minerals, and residual levels of proteins, which makes them a suitable and heightened option for reutilization in human consumption. Several studies identify extrusion as an innovative technology to modify the technofunctionality and nutritional properties of cereal and legume by-products, resulting in the production of improved ingredients. This review focuses on studies that evaluate the effect of extrusion to improve the nutritional and bioactive potential of cereal and legume by-products. A revision of the extrusion process parameters that improve the profile and bioavailability of dietary fiber, proteins, and phenolic compounds, and minimize antinutritional factors associated to cereal and legume by-products was done. The composition of by-products and process parameters such as feed moisture, barrel temperature and screw speed influence the resulting effect of extrusion. Studies suggest that extruding composite feedstock containing cereal or legume by-products may limit the molecular modifications that trigger the nutritional improvements. Therefore, extrusion applied as a pretreatment represents an interesting and economic alternative to improve the profile and bioavailability of the nutrients found in cereal and legume by-products which might lead to the development of functional ingredients useful to produce foods aimed to prevent chronic diseases.

Recycling polymer composite granulate/regrind using big area additive manufacturing

Carbon fiber filled acrylonitrile butadiene styrene (CF-ABS) is an emerging 3-D printable, recyclable thermoplastic composite. A popular application for CF-ABS is printed molds using large scale additive manufacturing (AM) processes produced for a variety of composites end-users. Other applications have not been fully realized as CF-ABS currently has a higher cost than other polymer composite feedstocks. The cost of CF-ABS could be greatly reduced if recycled CF-ABS material was accepted and utilized industrially, which would further expand its application space. The impacts of mechanical recycling on the properties and performance of CF-ABS after AM or other processes are not yet fully understood. As such, most AM CF-ABS is discarded as waste after use. In this work, AM CF-ABS molds used for concrete castings were recycled using an industrial shredder/granulator system. The granulate was then used as feedstock for large area AM to print test specimens. The elastic moduli in the printing direction and transverse to printing direction after mechanical recycling were found to decrease by 25% and 10%, respectively, most likely caused by reductions in the fiber content and polymer molecular weight. It was found that a significant portion of carbon fiber is lost during mechanical recycling through dust generation, while the thermomechanical extrusion during printing caused the polymer degradation. Although the mechanical performance of CF-ABS was reduced after recycling, the recycled feedstock retained properties for reuse as printed molds using large area AM or another suitable application.

Composite Feedstock Filaments for Fused Deposition Modeling (FDM) of Microwave Interconnects

Improved manufacturing methodology of ceramic-thermoplastic composite feedstock filaments using solvent assisted dispersion is presented with one of the highest reported ceramic particle filler volume concentration of 50%. Relative permittivity values up to 12.35 along with a low loss tangent of 0.003 have been achieved for newly developed feedstock filaments. They have been employed for fuse deposition modelling (FDM) of test specimens for characterization of complex permittivity, which exhibited dielectric loss tangent in the range of 0.001-0.007 at frequencies ranging from 4 GHz to 12 GHz. This is on par with that of the best microwave laminates. Also, surfactant-assisted ball milling was used to downsize ceramic fillers, while simultaneously applying a surface treatment by a strategically chosen surfactant to improve the interfaces between organic matrix and inorganic particles. The effect of the surfactant surface treatment on the dielectric and loss properties of the composite feedstock materials has been explored, which is compared with analytical model predictions. Two 40 mm-long dielectric rod waveguides (DWG’s) were 3D printed by using an in-house developed composite filament and a commercial counterpart. The former exhibited a much lower attenuation of 0.012 dB/mm as compared to 0.038 dB/mm shown by the latter. Measurements were compared to 3D EM simulation results to extract effective permittivity of DWG fabricated by FDM printing using in-house developed composite feedstock filament, which agrees very well with measured permittivity values.

Flow induced fiber orientation in short carbon fiber reinforced copper matrix composites

This study investigated the effect of a distinctive design of mold to align short carbon fiber in copper matrix composite produced via metal injection molding. The mold was designed to improve the fiber orientation during flow in the core region of test samples. The composite feedstocks comprising polymeric binder and Cu powder reinforced with 0, 5 and 10 vol. % carbon fiber, prepared in Z-blade mixer, were injection molded to fabricate green samples. Green samples were debound to remove the binder and sintered in sintering furnace at 1050 °C in Argon atmosphere. Dispersion of carbon fibers was examined in composite feedstocks and TGA was used to determine the degradation temperature of binder. Uniform dispersion of carbon fibers was observed in compounded feedstocks, green and sintered samples. Fiber orientation was quantified at various locations of skin and core of the green and sintered samples. Quantification of fiber orientation showed the best value of more than 90% of short fibers aligned in green test samples whereas sintered samples demonstrated just above 70% of fiber alignment in the flow direction in Cu-10%CF at section N. Overall, the results showed fiber alignment within ±22.5° in both green and sintered samples without significant skin-core effect. Moreover, the calculated mechanical properties increased with an increase in alignment of carbon fiber in the Cu matrix. Conclusively, fiber alignment can be improved by controlling flow of molten feedstock during molding with potentially high mechanical properties of composite.

Effect of annealing and carbon nanotube infill on the mechanical and electrical properties of additively manufactured polyether-ether-ketone nanocomposites via fused filament fabrication

The light-weight, high-strength poly-ether-ether-ketone (PEEK) and its composite materials are the ideal candidate for a plethora of engineering applications. However, the inherent high viscosity and melting temperature of PEEK pose great challenges for the extrusion-based 3D printing process, leaving a wide knowledge gap on the properties and functionalities of novel PEEK-based composites. In this work, the PEEK/CNT composite filaments with different CNT content ranging from 1 to 7 wt% are prepared by single-screw extruder and subsequently printed with a custom-made high temperature 3D printer. The effects of CNT content and annealing on the mechanical strength and electrical conductivity of the 3D printed parts are investigated in detail. The tensile test result shows that the presence of CNT significantly enhances the mechanical strength of the composite. With 7 wt% CNT content, the maximum tensile strength and elastic modulus reaches 107.7 MPa and 1908.0 MPa, respectively, which amounts to a rise of 27.4% and 17.0% compared with the neat PEEK sample. The annealing treatment is similarly effective in strengthening the printed composites. The addition of CNT is also found to greatly improve the electrical conductivity to the PEEK, reaching 101 S/m for 7 wt% CNT. With such superior electrical conductivity, the printed PEEK/CNT composite sample exhibits outstanding electromagnetic interference (EMI) shielding performance, reaching 32.4 dB. However, additional annealing treatment decreases the electrical conductivity as wells as EMI shielding performance. Such decrease is mainly attributed to the growth of the crystals during annealing, which expels the CNTs to the grain boundaries and leads to remarkable agglomeration, which disconnects the pervasive conductive networks. The finding in this work can provide insights on the new designs of PEEK composite feedstock materials and cultivate new 3D printing strategies targeted specifically for highly-functional, high-strength novel composites.