Light-oriented 3D printing of liquid crystal/photocurable resins and in-situ enhancement of mechanical performance.

Additive manufacturing technology has significantly impacted contemporary industries due to its ability to generate intricate computer-designed geometries. However, 3D-printed polymer parts often possess limited application potential, primarily because of their weak mechanical attributes. To overcome this drawback, this study formulates liquid crystal/photocurable resins suitable for the stereolithography technique by integrating 4'-pentyl-4-cyanobiphenyl with a photosensitive acrylic resin. This study demonstrates that stereolithography facilitates the precise modulation of the existing liquid crystal morphology within the resin. Furthermore, the orientation of the liquid crystal governs the oriented polymerization of monomers or prepolymers bearing acrylate groups. The products of this 3D printing approach manifest anisotropic behavior. Remarkably, when utilizing liquid crystal/photocurable resins, the resulting 3D-printed objects are approximately twice as robust as those created using commercial resins in terms of their tensile, flexural, and impact properties. This pioneering approach holds promise for realizing autonomously designed structures that remain elusive with present additive manufacturing techniques.

3D Printing of High Viscosity UV-Curable Resin for Highly Stretchable and Resilient Elastomer.

Elastomers prepared via vat photopolymerizationus ually exhibit unsatisfied mechanical properties owing to their insufficient growth of molecular weight upon UV exposure. Increasing the weight ratio of oligomer in the resin system is an effective approach to enhance the mechanical properties, yet the viscosity of the UV-curable resin increases dramatically; this hinders its printing. In this study, a linear scan-based vat photopolymerization (LSVP) system which can print high-viscosity resins is implemented to 3D print the oligomer-dominated UV-curable resin via a dual-curing mechanism. A polyurethane methacrylate blocking oligomer is first synthesized and then mixed with a commercialized bifunctional oligomer, photoinitiator, and primary amine as a chain extender to prepare high-viscosity UV-curable resin for the LSVP system. The deblocked isocyanate is further crosslinked with a chain extender via thermal treatment to construct a highly entangled polymer chain network. The optimal thermal treatment parameters are investigated, and the resilience of the 3D-printed elastomer is evaluated through continuous tensile loading and unloading tests. Subsequently, complex structured elastomers are printed, exhibiting favorable mechanical durability without defects. The results obtained from this work will provide a reference for preparing elastomeric devices with excellent physical properties and expand the application scope of vat photopolymerization to new fields.

The Micro-Macro Interlaminar Properties of Continuous Carbon Fiber-Reinforced Polyphenylene Sulfide Laminates Made by Thermocompression to Simulate the Consolidation Process in FDM.

Three-dimensional (3D) printing of continuous fiber-reinforced composites has been developed in recent decades as an alternative means to handle complex structures with excellent design flexibility and without mold forming. Although 3D printing has been increasingly used in the manufacturing industry, there is still room for the development of theories about how the process parameters affect microstructural properties to meet the mechanical requirements of the printed parts. In this paper, we investigated continuous carbon fiber-reinforced polyphenylene sulfide (CCF/PPS) as feedstock for fused deposition modeling (FDM) simulated by thermocompression. This study revealed that the samples manufactured using a layer-by-layer process have a high tensile strength up to 2041.29 MPa, which is improved by 68.8% compared with those prepared by the once-stacked method. Moreover, the mechanical-microstructure characterization relationships indicated that the compactness of the laminates is higher when the stacked CCF/PPS are separated, which can be explained based on both the void formation and the nanoindentation results. These reinforcements confirm the potential of remodeling the layer-up methods for the development of high-performance carbon fiber-reinforced thermoplastics. This study is of great significance to the improvement of the FDM process and opens broad prospects for the aerospace industry and continuous fiber-reinforced polymer matrix materials.

Exceptional Mechanical Properties and Heat Resistance of Photocurable Bismaleimide Ink for 3D Printing.

Photosensitive resins used in three-dimensional (3D) printing are characterized by high forming precision and fast processing speed; however, they often possess poor mechanical properties and heat resistance. In this study, we report a photocurable bismaleimide ink with excellent comprehensive performance for stereolithography (SLA) 3D printing. First, the main chain of bismaleimide with an amino group (BDM) was synthesized, and then, the glycidyl methacrylate was grafted to the amino group to obtain the bismaleimide oligomer with an unsaturated double bond. The oligomers were combined with reaction diluents and photo-initiators to form photocurable inks that can be used for SLA 3D printing. The viscosity and curing behavior of the inks were studied, and the mechanical properties and heat resistance were tested. The tensile strength of 3D-printed samples based on BDM inks could reach 72.6 MPa (166% of that of commercial inks), glass transition temperature could reach 155 °C (205% of that of commercial inks), and energy storage modulus was 3625 MPa at 35 °C (327% of that of commercial inks). The maximum values of T-5%, T-50%, and Tmax of the 3D samples printed by BDM inks reached 351.5, 449.6, and 451.9 °C, respectively. These photocured BDM inks can be used to produce complex structural components and models with excellent mechanical and thermal properties, such as car parts, building models, and pipes.

Synthesis of High-Purity SiC Nanowires via Catalyst-Free Pyrolysis of SiO2/Si and Sponge-Like Graphene Oxide.

The large-scale synthesis of high-purity SiC nanowires is a challenge. In this context, sponge-like graphene oxide (GO) was used as a carbon source as well as a reaction template for directly synthesizing SiC nanowires. GO was completely reacted with SiO to prepare high-purity 3C-SiC nanowires by thermal evaporation and carbothermal reduction without the use of any catalyst, rather than by epitaxy. Characterization was conducted using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction. The SiC nanowires had lengths of several tens of micrometers and a perfect single-crystalline structure with a bamboo-like morphology.

Fabrication of Fullerene Anchored Reduced Graphene Oxide Hybrids and Their Synergistic Reinforcement on the Flame Retardancy of Epoxy Resin.

A C60-PEI-rGO hybrid was prepared by incorporating the fullerene (C60) on the surface of PEI-modified reduced graphene oxide (rGO) and then used to modify the epoxy (EP) resin. Subsequently, the structure of GO and C60-PEI-rGO hybrid were well characterized, showing that the C60 was homogenously anchored on the surface of PEI-rGO. The flame retardancy, mechanical properties, and thermal stability of as-prepared C60-PEI-rGO/EP nanocomposites were systematically investigated. Results show that the C60-PEI-rGO hybrid exhibits high flame retarding efficiency for EP. Specifically, the time to ignition of epoxy increases from 68 to 89 s with the addition of 1.0 wt% C60-PEI-rGO, which are unusual in polymer nanocomposites. In the meantime, the peaks of the heat release rate and total heat release of the modified epoxy reduce by 40.0% and 15.6%, respectively. The synergistic flame retardant mechanism of C60-PEI-rGO to EP is attributed to its unique structure combining both the high efficiency in capturing free radicals by C60, the barrier effect of layered of rGO and increase of crosslinking density of epoxy. It is shown that the thermal stability and mechanical properties of epoxy are simultaneously improved with the addition of C60-PEI-rGO. This work may pioneer a new and efficient method to fabricate fire retardant thermosetting resins with simultaneously other improved properties.

Investigation on the microstructure, mechanical property and corrosion behavior of the selective laser melted CoCrW alloy for dental application.

In this study, an experimental investigation on fabricating Ni-free CoCrW alloys by selective laser melting (SLM) for dental application was conducted in terms of microstructure, hardness, mechanical property, electrochemical behavior, and metal release; and line and island scanning strategy were applied to determine whether these strategies are able to obtain expected CoCrW parts. The XRD revealed that the γ-phase and ε-phase coexisted in the as-SLM CoCrW alloys; The OM and SEM images showed that the microstructure of CoCrW alloys appeared square-like pattern with the fine cellular dendrites at the borders; tensile test suggested that the difference of mechanical properties of line- and island-formed specimens was very small; whilst the outcomes from the electrochemical and metal release tests indicated that the island-formed alloys showed slightly better corrosion resistance than line-formed ones in PBS and Hanks solutions. Considering that the mechanical properties and corrosion resistance of line-formed and island-formed specimens meet the standards of ISO 22674:2006 and EN ISO 10271, CoCrW dental alloys can be successfully fabricated by line and island scanning strategies in the SLM process.