Recently, Fused Filament Fabrication (FFF), one of the most encouraging additive manufacturing (AM) techniques, has fascinated great attention. Although FFF is growing into a manufacturing device with considerable technological and material innovations, there still is a challenge to convert FFF-printed prototypes into functional objects for industrial applications. Polymer components manufactured by FFF process possess, in fact, low and anisotropic mechanical properties, compared to the same parts, obtained by using traditional building methods. The poor mechanical properties of the FFF-printed objects could be attributed to the weak interlayer bond interface that develops during the layer deposition process and to the commercial thermoplastic materials used. In order to increase the final properties of the 3D printed models, several polymer-based composites and nanocomposites have been proposed for FFF process. However, even if the mechanical properties greatly increase, these materials are not all biodegradable. Consequently, their waste disposal represents an important issue that needs an urgent solution. Several scientific researchers have therefore moved towards the development of natural or recyclable materials for FFF techniques. This review details current progress on innovative green materials for FFF, referring to all kinds of possible industrial applications, and in particular to the field of Cultural Heritage.

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A Review of Polymer-Based Materials for Fused Filament Fabrication (FFF): Focus on Sustainability and Recycled Materials

Assessment of materials, design parameters and some properties of 3D printing concrete mixtures; a state-of-the-art review

Carbon nanotube (CNT) is a promising nanomaterial with excellent mechanical, electrical, thermal, and chemical stability. It has received extensive attention due to its unique multifunctional properties in engineering materials. Researchers have explored the preparation and characterization of CNT reinforced cement-based materials. Studies have shown that adding CNT will significantly improve the performance of cement-based materials. This article introduces the techniques for the dispersion characterization of CNT and summarizes the advantages and disadvantages of these techniques. The functionalized applications of CNT in cement-based materials are reviewed, including sensing performance, structural health monitoring of concrete, electromagnetic shielding, and other applications. In addition, the application and development prospects of CNT in 3D printing concrete have been prospected. Finally, we discussed the existing problems and challenges in developing and applying CNT in cement-based materials and suggested future research.

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Developments and Applications of Carbon Nanotube Reinforced Cement-Based Composites as Functional Building Materials

Abstract High value utilization of renewable biomass materials is of great significance to the sustainable development of human beings. For example, because biomass contains large amounts of carbon, they are ideal candidates for the preparation of carbon nanotube fibers. However, continuous preparation of such fibers using biomass as carbon source remains a huge challenge due to the complex chemical structure of the precursors. Here, we realize continuous preparation of high-performance carbon nanotube fibers from lignin by solvent dispersion, high-temperature pyrolysis, catalytic synthesis, and assembly. The fibers exhibit a tensile strength of 1.33 GPa and an electrical conductivity of 1.19 × 10 5 S m −1 , superior to that of most biomass-derived carbon materials to date. More importantly, we achieve continuous production rate of 120 m h −1 . Our preparation method is extendable to other biomass materials and will greatly promote the high value application of biomass in a wide range of fields. 

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Continuously processing waste lignin into high-value carbon nanotube fibers

3D printing is a process of hierarchically fabricating three-dimensional microstructures by successively adding materials in a bottom-up manner. The technology has been rapidly advancing, especially in the manufacturing of high-strength, lightweight industrial composite materials. Thus far, many studies have focused on the spontaneous alignment of short reinforcing fibers that are subject to adjustment during the 3D-printing process, along with an inevitable void formation arising due to an intrinsic nature of the additive process. However, systematic examination of the 3D-printed anisotropic microstructures, related with a markedly high degree of fiber alignment and formation of voids in the matrix, has not been sufficiently conducted to analyze its effect on the anisotropic mechanical behaviors of fiber-reinforced composites. Here, we sought to examine in detail the internal morphology of fibers and voids in 3D-printed composites by 3D X-ray microscopy to explore their anisotropic architecture. The position, length, and alignment of fibers and voids were identified, visualized, and quantitatively characterized with a help of computational tomography (CT). Furthermore, the anisotropy approximation of the 3D-printed composites, precisely predicted through CT-assisted simulation, was derived based on the quantitative data obtained from the 3D reconstruction image. These measurements were effective in exploring the process-induced alignment nature of fibers and voids in the local region layers on the microscopic scale, and the corresponding microstructure resulted in a change in the elastic modulus of the composites with the printing direction. The comparative results showed that the experimental results were well supported by the simulation-based estimations, but did not exactly match the rule-of-mixture of the composites in terms of interfacial nature due to the distinctive microstructure with the fiber-to-matrix interface as well as the filament-to-filament interface.

Anisotropic microstructure dependent mechanical behavior of 3D-printed basalt fiber-reinforced thermoplastic composites

Carbon nanotube fibers with high specific electrical conductivity: Synergistic effect of heteroatom doping and densification

Complex anisotropic fracture behaviors of 3D-printed fiber-reinforced composites based on multi-scale hierarchical microstructure

A novel scan matching method based on a spectral technique is proposed to estimate the robot pose by matching 2D range scans without an initial alignment. The proposed method finds consistent correspondence between two range scans, by considering how well their associated pairwise geometric relationships are satisfied.

Spectral scan matching for robot pose estimation

Carbon nanotubes (CNTs) of a sufficiently large diameter and a few layers self-collapse into flat ribbons at atmospheric pressure, forming bundles of stacked CNTs that maximize packing, and thus CNT interaction. Their improved stress transfer by shear makes collapsed CNTs ideal building blocks in macroscopic fibers of CNTs with high-performance longitudinal properties, particularly high tensile properties as reinforcing fibers. This work introduces cross-sectional transmission electron microscopy of focused ion beam-milled samples as a method to univocally identify collapsed CNTs and to determine the full population of different CNTs in macroscopic fibers produced by spinning from floating catalyst chemical vapor deposition. We show that close proximity in bundles is a major driver for collapse and that CNT “stoutness” (the number of layers/diameter), which dominates the collapse onset, is controlled by the growth promotor. Despite differences in the decomposition route, different carbon precursors lead to similar distributions of the ratio layers/diameter. The synthesis conditions in this study give a maximum fraction of collapsed CNTs of 70% when using selenium as the promotor, corresponding to an average of 0.25 layer/nm.

Seunggyu Park

Papers

Anisotropic microstructure dependent mechanical behavior of 3D-printed basalt fiber-reinforced thermoplastic composites

Carbon nanotube fibers with high specific electrical conductivity: Synergistic effect of heteroatom doping and densification

Complex anisotropic fracture behaviors of 3D-printed fiber-reinforced composites based on multi-scale hierarchical microstructure

Spectral scan matching for robot pose estimation

Identification of Collapsed Carbon Nanotubes in High-Strength Fibers Spun from Compositionally Polydisperse Aerogels