Solid‐state shear milling method to prepare PA12/boron nitride thermal conductive composite powders and their selective laser sintering 3D‐printing

Characterization of PA12/HA composite scaffolds based on selective laser sintering

Composite scaffolds have been extensively studied in bone tissue engineering, which can achieve excellent properties that cannot be obtained by a single material. In this study, the effect of hydroxyapatite (HA) on the reliability of polyamide 12 (PA12) scaffold for bone graft was explored in terms of mechanical and biological properties. Thermal properties testing showed that no physical or chemical reaction occurs in the prepared PA12/HA composite powders. Further, compression experiments showed that adding a small amount of HA promoted the mechanical properties of the scaffold, while excessive HA results in agglomeration and impairs the PA12/HA scaffold. For the scaffolds with the porosity of 65%, the 96% PA12/4% HA scaffold has a 7.3% higher yield strength and a 13.5% higher compressive modulus than the pure PA12 scaffold while the strength of the 88% PA12/12% HA scaffold decreases by 35.6%. Furthermore, contact angle and CCK-8 tests confirmed that 96% PA12/4% HA scaffold effectively improved the hydrophilicity and biocompatibility of the scaffold. Its OD value on the 7th day is 0.949, which is significantly higher than that of other groups. In summary, PA12/HA composites have good mechanical properties and biocompatibility, which can be used as an effective strategy in bone tissue engineering.

Thermal Conductivity and Mechanical Properties of Polymer Composites with Hexagonal Boron Nitride-A Comparison of Three Processing Methods: Injection Moulding, Powder Bed Fusion and Casting

Materials providing heat dissipation and electrical insulation are required for many electronic and medical devices. Polymer composites with hexagonal boron nitride (hBN) may fulfil such requirements. The focus of this study is to compare composites with hBN fabricated by injection moulding (IM), powder bed fusion (PBF) and casting. The specimens were characterised by measuring thermal conductivity, tensile properties, hardness and hBN particle orientation. A thermoplastic polyurethane (TPU) was selected as the matrix for IM and PBF, and an epoxy was the matrix for casting. The maximum filler weight fractions were 65%, 55% and 40% for IM, casting and PBF, respectively. The highest thermal conductivity (2.1 W/m∙K) was measured for an IM specimen with 65 wt% hBN. However, cast specimens had the highest thermal conductivity for a given hBN fraction. The orientation of hBN platelets in the specimens was characterised by X-ray diffraction and compared with numerical simulations. The measured thermal conductivities were discussed by comparing them with four models from the literature (the effective medium approximation model, the Ordóñez-Miranda model, the Sun model, and the Lewis-Nielsen model). These models predicted quite different thermal conductivities vs. filler fraction. Adding hBN increased the hardness and tensile modulus, and the tensile strength at high hBN fractions. The strength had a minimum as the function of filler fraction, while the strain at break decreased. These trends can be explained by two mechanisms which occur when adding hBN: reinforcement and embrittlement.

Mild air oxidation of boron nitride nanotubes. Application as nanofillers for thermally conductive polycarbonate nanocomposites

Boron nitride nanotubes (BNNTs) have experienced considerable growth in recent years due to their unique intrinsic properties, in particular for the fabrication of polymer nanocomposites. Dispersion of pure BNNTs in nanocomposites is often difficult due to their poor compatibility with most polymer matrices. An approach involving the creation of hydroxyl groups on their surface could improve their dispersion. While some harsh oxidation processes have been reported so far, a mild oxidation of BNNTs using air as the oxidant is reported here. This new catalytic reaction leads to slightly oxidized BNNTs, which were characterized by scanning electron microscope, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Polycarbonate nanocomposites were then fabricated using pristine and oxidized BNNTs as nanofillers. The measured thermal conductivity increased linearly with the mildly oxidized BNNTs content. It reached a five-fold increase up to 1.19 W m.K^-1at 15% vol. content which is significantly improved over nanocomposites fabricated with severely oxidized BNNTs, while the electrically insulating character remained unchanged.

A Review on Mechanochemistry: Approaching Advanced Energy Materials with Greener Force

Mechanochemistry with solvent-free and environmentally friendly characteristics is one of the most promising alternatives to traditional liquid-phase-based reactions, demonstrating epoch-making significance in the realization of different types of chemistry. Mechanochemistry utilizes mechanical energy to promote physical and chemical transformations to design complex molecules and nanostructured materials, encourage dispersion and recombination of multiphase components, and accelerate reaction rates and efficiencies via highly reactive surfaces. In particular, mechanochemistry deserves special attention because it is capable of endowing energy materials with unique characteristics and properties. Herein, the latest advances and progress in mechanochemistry for the preparation and modification of energy materials are reviewed. An outline of the basic knowledge, methods, and characteristics of different mechanochemical strategies is presented, distinguishing this review from most mechanochemistry reviews that only focus on ball-milling. Next, this outline is followed by a detailed and insightful discussion of mechanochemistry-involved energy conversion and storage applications. The discussion comprehensively covers aspects of energy transformations from mechanical/optical/chemical energy to electrical energy. Finally, next-generation advanced energy materials are proposed. This review is intended to bring mechanochemistry to the frontline and guide this burgeoning field of interdisciplinary research for developing advanced energy materials with greener mechanical force.

Dust Particle Counter for Powder Bed Fusion Process

The paper presents a novel dust detector based on an innovative laser system that can be successfully used in applications where continuous dust monitoring is necessary. The measurements obtained with FeNi18Co9Mo5 (maraging MS1 steel) particles are compared with the particle fall times calculated using the Navier-Stokes equation. The measurement powder was subjected to sieve analysis and laser system detection. Based on the results obtained, a formula was developed to determine the dust concentration depending on the number and size of particles. With filtration applied, the detector measurement range was from 16 to 100 µm. The developed solution can be the basis for the development of a dedicated sensor for powder bed fusion processes.

A Facile Fabrication of PA12/CNTs Nanocomposites with Enhanced Three-Dimensional Segregated Conductive Networks and Electromagnetic Interference Shielding Property through Selective Laser Sintering

The material design could be very critical in the preparation of conductive polymer composites for electromagnetic interference (EMI) shielding applications. In this work, two methods were proposed to prepare PA12 composite powders coated with CNTs, including ball-milling (BM) and ultrasonic dispersion-liquid phase deposition strategies. Then, by applying selective laser sintering printing (SLS) 3D printing, the segregated network structures were successfully constructed. Various characterization techniques were employed to validate the presence of the formed segregated network structure in the SLS 3D printed parts. The BM SLS 3D printed part at a loading of 5.66 wt % CNTs exhibited an optimum electrical conductivity of 3.0 S/m and an electromagnetic interference shielding (EMI SE) of 23.9 dB (2.0 mm thickness), while its electrical percolation threshold was found to be at 0.347 wt %. However, the EMI SE values of homogenous PA12/CNTs composites prepared by the melt compounding-cryogenic pulverization (MP) method and melt compounding-compression molding were only 9.8 and 15.6 dB, respectively. In addition, the incorporation of CNTs decreased the mechanical performance of the PA12/CNTs printed part due to their negative effect on the sintering. However, such a decrease could be inhibited by increasing the laser energy density. The related investigation could offer a solution to the preparation of the conductive polymer composite and the EMI shielded material through SLS 3D printing processing.

Boosted Mechanical Piezoelectric Energy Harvesting of Polyvinylidene Fluoride/Barium Titanate Composite Porous Foam Based on Three-Dimensional Printing and Foaming Technology

The popularity of intelligent and green electronic devices means that the use of renewable mechanical energy has gradually become an inevitable choice for social development. However, it is difficult for the existing energy harvesters to meet the requirement for efficient collection of discrete mechanical energy due to the limitation of traditional two-dimensional (2D) film deformation. In this research, a green and convenient supercritical carbon dioxide foaming (Sc-CO2)-assisted selective laser sintering method was developed, and piezoelectric energy harvesters with a 3D porous structure of polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) were successfully constructed. The 3D structure combined with the porous structure made full use of the normal space, amplified the stress-strain effect, and improved the piezoelectric output capability. Under the synergistic effect of BaTiO3, the foams exhibited high output with an output voltage of 20.9 V and a current density of 0.371 nA/mm2, which exceeded most of the known PVDF/BaTiO3 energy harvesters, and the prepared piezoelectric energy harvester could directly light up 11 green light-emitting diodes and charge a 1 μF commercial capacitor to 4.98 V within 180 s. This work emphasizes the key role of 3D printing and Sc-CO2 foaming in fabricating 3D piezoelectric energy harvesters.

Thermomechanical Multifunctionality in 3D-Printed Polystyrene-Boron Nitride Nanotubes (BNNT) Composites

In this work, polystyrene (PS) and boron nitrides nanotubes (BNNT) composites were fabricated, prepared, and characterized using modified direct mixing and sonication processes. The polymer composites were extruded into filaments (BNNTs at 10 wt. %) for 3D printing, utilizing the fused deposition modeling (FDM) technique to fabricate parts for mechanical and thermal applications. Using a direct mixing process, we found that the thermal conductivity and the mechanical strength of the PS-BNNT composite were respectively four times and two times higher compared to the sonication method. The thermal stability and glass transition temperatures were positively affected. A 2D microstructural mechanical entanglement model captured the exact geometry of the nanotubes using the MultiMechanics software, and the performance of the additive manufactured (AM) PS-BNNT composites part for thermomechanical application was simulated in COMSOL. The modified direct mixing process for PS-BNNT, which affects morphology, proved to be effective in achieving better interfacial bonding, indicating that BNNTs are promising fillers for improving thermal and mechanical properties, and are applicable for thermal management and electronic packaging.

The combination of Al2O3 and BN for enhancing the thermal conductivity of PA12 composites prepared by selective laser sintering

A powder-based 3D printing technology, selective laser sintering (SLS), is a novel strategy of manufacturing complex components with specially tailored properties, including mechanical properties, as well as thermal and electrical conductivity. In this study, the effect of incorporating Al₂O₃ particles and BN plates on the thermal conductivity of PA12 composites was investigated. PA12 composite powders, which can be well applied to SLS, were prepared via a two-step approach to mixing. Morphology characteristics demonstrated that the fillers dispersed uniformly in the PA12 matrix, as expected. With 35 wt% Al₂O₃ and 15 wt% BN hybrid fillers, the tensile strength had the potential to reach 25.7 MPa, while the thermal conductivity could reach 1.05 W m⁻¹ K⁻¹, 275% higher than that of pure PA12. In addition, the study investigated the effects of filler content on the thermal stability and mechanical properties whilst analysing the melting and crystallisation behaviours of SLS components. The results demonstrate that these composites have favourable thermal stability and exhibit no severe deterioration in mechanical properties. The PA12 composites prepared in this work therefore illustrated vast potential in thermal management materials.

The introduction of hybrid fillers in SLS technology is an effective method for the manufacture of thermally conductive polymer composites with high thermal conductivity, complex structures and good mechanical properties.