June 2022, researchers from the University of Trento in Italy have developed a new type of 3D printed polymer composite material, which was prepared using a solvent-free process and filled with materials such as graphene. Their research has been published in Nanomaterials under the title "Three Dimensional Printing of Multiscale Carbon Fiber-Reinforced Polymer Composites Containing Graphene or Carbon Nanotubes".
The use of 3D printing to fabricate thermoplastic composites containing different multiscale reinforcements has been a focus of research in the field of materials science. Embedded multiscale filler particles can enhance the properties of 3D printed polymers, such as their mechanical properties, electrical conductivity and thermal stability. This research area has been applied in the field of additive manufacturing, which can improve the product properties of fused filament manufactured FFFs by extending the printable materials. The synthesis of novel polymeric materials for various industries has been intensively studied over the past decade. In the current study, researchers evaluated the potential of several nanoscale and micron-scale particles to enhance polymer properties. For example, carbon-based materials can improve stiffness, corrosion resistance and weight reduction.
In the past few years, researchers have also investigated the performance of micro-fillers like milled carbon fibers and nano-fillers like graphene nanosheets and carbon nanotubes as polymer composite modifiers. The research has shown that nanocomposites containing conductive nanoparticles hold great promise for applications in 3D printed devices such as microbatteries, electronic sensors and microcircuits.
Studies have shown that polymer composites fabricated using fused deposition have enhanced toughness, increased Young's modulus, tensile strength, elastic modulus, and many other excellent properties. For example, multi-walled carbon nanotubes enable a direct correlation between resistance change and concentration, with an enhanced response at reduced loading. Specific concentrations of carbon nanotubes in different polymer composites can increase electrical conductivity. ABS composites containing dispersed graphene nanosheets have high thermal stability and elastic modulus, but reduced strain at break and stress. In addition, graphene nanoparticle-modified polypropylene has high interfacial shear strength.
The researchers used a new solvent-free process to produce multi-scale composite filaments. The properties of different ratios of carbon-based reinforcements incorporated into the ABS polymer matrix were investigated. (milled carbon fibers, carbon nanotubes and graphene nanosheets).
● The results showed that the carbon nanotube and graphene nanosheet fillers increased the modulus and strength of the composites, but the addition of milled carbon fibers decreased their strain at break values. The nanofillers also improved the electrical conductivity of the composites, with carbon nanotubes showing the strongest conductivity enhancement.
● The density and properties of the final samples are strongly influenced by the production process. Due to the voids created by the 3D printing process, samples lose up to 65% of their ductility. This ductility is different in each composite. All composites with carbon nanotubes have low resistivity.
● The authors proposed comparative and selective parameters to evaluate the best composites. The composites are evaluated based on processability and performance to elucidate their suitability for applications such as sensors and thermoelectric devices.
1. the novelty of this study is the proper compounding, processing and characterization of multi-scale carbonaceous ABS composites based on microfibers (MCFs) and nanofillers (CNTs or GNPs) in different ratios by a solvent-free process.
2. The mechanical properties (modulus and strength) of the compression molded ABS composite samples were improved by the addition of microfillers (CNTs and GNPs) and the strain at break values were reduced by the addition of microfillers (MCFs). The electrical conductivity of the nanofillers was improved and the CNT fillers achieved the best performance compared to pure ABS and micro composites.
3. The multi-scale ABS/MCF/GNP composites showed good mechanical properties for the compression molded samples. Conversely, ABS/CNTs showed a significant improvement in electrical conductivity. The production process can greatly affect the density of the samples, which in turn affects their mechanical, electrical and thermal properties. In particular, if compared to CM specimens, the 3D printed samples show a sharp loss of ductility (in the range of 33-65%) due to the presence of voids, even if for some components the electrical conductivity can be maintained.
Overall, the paper demonstrates a potentially advantageous production process for multiscale polymer composites, proving that it will benefit several industries, such as sensors and thermoelectric devices.