Stereolithography-based additive manufacturing of polymer-derived SiOC/SiC ceramic composites

In order to overcome challenges typically encountered during additive manufacturing of ceramics via the polymer precursor route, a novel polymer-derived SiOC/SiC composite system suitable for advanced geometric designs achievable by lithography-based ceramic manufacturing was established. The photoreactive resin system filled with 20 wt% SiC exhibits suitable viscosity characteristics, adequate stability against sedimentation, and a fast photocuring behavior. After printing and pyrolytic conversion, SiC particulates were well-dispersed within the polymer-derived SiOC matrix. A direct comparison with the unfilled polysiloxane-based resin system showed that the addition of particulate SiC increases handleability, reduces shrinkage, and significantly increases critical wall thicknesses up to 5 mm. The biaxial Ball-on-Three-Balls testing methodology yielded a characteristic strength of 325 MPa for SiOC/SiC composites. The results highlight the high potential of particle-filled preceramic polymer systems toward the fabrication of high-performance SiC-based materials by lithography-based additive manufacturing.     

Cellular,Mineralized, and Programmable Cellulose Composites Fabricated by 3D Printing of Aqueous Pastes Derived from Paper Wastes and Microfibrillated Cellulose

Combining recycling of paper wastes (WPs) with extrusion‐based additive manufacturing represents a sustainable route to cellular cellulose composites tailored for lightweight construction. Particularly, shear mixing of shredded WPs with an aqueous solution of a polymer binder like polyvinyl alcohol (PVA) yields aqueous pastes suitable for 3D printing. As a shear thinning additive, both WP and microfibrillated cellulose account for enhanced shear thinning and dimensional stability. Opposite to the formation of dense WP/PVA composites by melt extrusion, 3D printing of aqueous pastes produces cellular cellulose/PVA composites exhibiting hierarchical pore architectures. In spite of low densities around 0.8 g cm^?3, high Young's modulus (2.0 GPa) and tensile strength (53 MPa) are achieved. Mechanical stability, water resistance, and even flame retardancy simultaneously improve by crosslinking with glyoxal and especially by mineralization. Multimaterial 3D printing combines the 3D dispensing of cellulose/PVA pastes with the simultaneous, staged, or subsequent spraying of aqueous water glass to enable mineralization of composite surface, bulk, and interlayers. Furthermore, the glyoxal‐mediated crosslinking affords thermo‐ and moisture‐responsive cellulose/PVA composites with programmable shape change induced either by heating at 100 °C or by exposure to moisture at 37 °C.     

Fabrication of co‐continuous poly(ε‐caprolactone)/polyglycolide blend scaffolds for tissue engineering

The apparent inability of a single biomaterial to meet all the requirements for tissue engineering scaffolds has led to continual research in novel engineered biomaterials. One method to provide new materials and fine‐tune their properties is via mixing materials. In this study, a biodegradable powder blend of poly(ε‐caprolactone) (PCL), polyglycolide (PGA), and poly(ethylene oxide) (PEO) was prepared and three‐dimensional interconnected porous PCL/PGA scaffolds were fabricated by combining cryomilling and compression molding/polymer leaching techniques. The resultant porous scaffolds exhibited co‐continuous morphologies with ～50% porosity. Mean pore sizes of 24 and 56 μm were achieved by varying milling time. The scaffolds displayed high mechanical properties and water uptake, in addition to a remarkably fast degradation rate. The results demonstrate the potential of this fabrication approach to obtain PCL/PGA blend scaffolds with interconnected porosity. In general, these results provide significant insight into an approach that will lead to the development of new composites and blends in scaffold manufacturing. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42471.     

High density carbon fiber/boron nitride matrix composites: Fabrication of composites with exceptional wear resistance

This paper describes the fabrication of high density (ρ ∼ 1.75 g/cc) composites containing a hybrid (carbon and boron nitride), or complete boron nitride matrix. The composites were reinforced with either chopped or 3D needled carbon fibers. The boron nitride was introduced via liquid infiltration of a borazine oligomer that can exhibit liquid crystallinity. The processing scheme was developed for the chopped carbon fiber/boron nitride matrix composites (C/BN) and later applied to the 3D carbon fiber reinforced/boron nitride matrix composites (3D C/BN). The hybrid matrix composites were produced by infiltrating the borazine oligomer into a low density 3D needled C/C composite to yield 3D C/C-BN. In addition to achieving high densities, the processing scheme yielded d₀₀₂ spacings of 3.35 Å, which afforded boron nitride with excellent hydrolytic stability. The friction and wear properties of the composites were explored over the entire energy spectrum for aircraft braking using an inertial brake dynamometer. The C/BN composites outperformed both the previously reported C/C-BN and chopped fiber reinforced C/C. The high density 3D C/BN performed as well as both the 3D C/C and the C/BN. The 3D C/C-BN provided outstanding wear resistance, incurring nearly zero wear across the entire testing spectrum. The coefficient of friction was relatively stable with respect to energy level, varying from 0.2 to 0.3.     

Morphological,mechanical, and thermal characterization of biopolymer composites based on polylactide and nanographite platelets

This work focuses on development and optimization of polylactide (PLA) and nanographite platelets (NGP) based composites to display possible superior mechanical and improved thermal stability. Melt blending and dry mixing methods of fabrication were employed at temperature of 180°C. Different Loading fractions of NGP were incorporated into polymer matrix. Morphological evaluation techniques such as XRD and TEM were applied to determine the degree of dispersion of NGPs into PLA matrix. Mechanical properties were evaluated and correlated to structural morphologies of PLA/NGP composites. Thermal properties of composites were studied to examine possible changes in T_g, T_c, T_m, and percentage crystallinity of these composites. The effect of mixing was also explored through double extrusion of some samples. It was concluded that composites containing 3 wt% NGP showed optimum mechanical performance without any significant changes in the thermal characteristics. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Additive manufacturing of polymer-derived ceramic matrix composites

This study presents a fabrication method and identifies processing bounds for additively manufacturing (AM) ceramic matrix composites (CMCs), comprising a silicon oxycarbide (SiOC) ceramic matrix. A digital light projection printer was used to photopolymerize a siloxane-based preceramic resin containing inert ceramic reinforcement. A subsequent pyrolysis converted the preceramic polymer to SiOC. Particle reinforcements of 0 to 40% by volume in the green state were uniformly dispersed in the printed samples to study their effects on pyrolysis mass loss and shrinkage, and CMC notch sensitivity and strength. Both particle and whisker reinforcements toughened the glassy SiOC matrix (1 MPa m^1/2), reaching values >3 MPa m^1/2. Bending strengths of >300 MPa (>150 MPa (g cm⁻³)⁻¹) and a Weibull modulus of 10 were measured on AM samples without surface finish. We identified two pore formation mechanisms that placed processing bounds on sample size and reinforcement volume fraction. Methods for increasing these bounds are discussed. With properties commensurate to traditionally processed technical ceramics, the presented process allows for free-form fabrication of high-performance AM CMC components.     

选择性激光烧结用聚合物基材料制备研究进展

选择性激光烧结（selective laser sintering, SLS）是一种重要的3D打印加工技术,可制备传统加工无法制备的任意复杂形状的制件,广泛应用于航空航天、国防装备、医疗器械以及汽车等高新技术领域。本文介绍了SLS技术的加工原理和优势,综述了SLS技术加工成形用材料种类及聚合物基粉体材料的制备方法,主要包括相分离法、机械粉碎法、溶液法和喷雾干燥法。重点对SLS技术制备聚合物基压电复合材料及制品的国内外研究现状进行总结。虽然SLS打印制造技术面临聚合物原料种类少、功能缺乏、粉体生产成本高以及难以批量制备等瓶颈问题,但经过不断地创新与发展,SLS打印技术将成为高性能多功能高分子复合材料及其大型复杂制件的极佳制造方法。     

Fabrication of artificial defects and their effect on the mechanical properties of C/C-SiC

Determining the effect of defects in fiber-reinforced materials, such as polymer matrix composites (PMCs), can be studied by creating artificial flaws in these materials, for example by introducing artificial PTFE foil to induce material delaminations. For fiber-reinforced ceramics (CMCs), this approach is more difficult due to the more complicated production routes of CMCs, which involve several processing steps at elevated temperatures. This work deals with the fabrication and introduction of defined defects in carbon fiber reinforced silicon carbide (C/C-SiC) composites in a way, which allows their detection by non-destructive material testing methods during and after each production step of the composite. It was shown that the defects produced using boron nitride (BN) and alumina fiber roving were stable over the entire manufacturing process and could be detected by ultrasound and x-ray tomography techniques. To determine any possible effects, an initial sampling of bending samples with artificial defects was manufactured, tested and compared with defect-free reference materials. These tests showed a lower bending strength and failure strain for the defect samples compared to samples without defects.     

Fabrication of bimetallic nanoparticles/multi-walled carbon nanotubes composites for microelectronic circuits

A method for the fabrication of electrically-conducting polymer composites has been developed by mixing modified multi-walled carbon nanotubes (MWCNTs) functionalized by bimetallic nanoparticles (Ag/Ni/MWCNTs) into a UV curable resin. MWCNTs were treated by a concentrated H₂SO₄/HNO₃ mixture followed by ultrasonication with AgNO₃ and NiSO₄ in an ethylene glycol solution, producing MWCNTs decorated with Ag and Ni nanoparticles. The microstructure and surface morphology of the Ag/Ni/MWCNTs were investigated by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was found that the addition sequences of NiSO₄ and AgNO₃ influence the morphology of the Ag/Ni/MWCNTs. The electrically-conducting polymer composites were obtained by dispersing the prefabricated Ag/Ni/MWCNTs in UV curable resin, the curing process of which was tracked by Fourier transform infrared spectroscopy, and the electrical resistance was measured using the four-probe method. The fabrication of microelectronic patterns made by screen printing on different substrates was described.     

Functional polymer from high molecular weight linear polyols and polyurethane‐based crosslinking units: Synthesis,characterization, and boron retention properties

The objective of this work was to synthesize functional polymers, with boron removal properties, from high molecular weight linear polyols based on N‐methyl‐d ‐glucamine (NMDG) and polyurethane units as crosslinking reagent. For that, (4‐vinylbenzyl)‐N‐methyl‐d ‐glucamine monomer (VbNMDG) was synthesized from vinylbenzyl chloride and NMDG, and subsequently, high molecular weight linear poly(VbNMDG) was obtained by radical free polymerization. Later, polymer dots were obtained from poly(VbNMDG) and urethanization reactions using methylene diphenyl diisocyanate at room temperature. Monomers and polymers were characterized by different techniques (FTIR, DLS, elemental analysis, H¹‐NMR). In addition, boron retention properties were studied by diafiltration technique using the azomethine‐H method. It was concluded that synthesis of polymer dots, with high boron retention capacity, can be easily synthesized by procedure described. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43895.     

Processing of Piezocomposites by Fused Deposition Technique

Piezoelectric ceramic/polymer composites were made by a fused deposition (FD) technique, which is a solid-freeform fabrication (or layered manufacturing) technique where three-dimensional (3-D) objects are built layer by layer from a computer-aided design (CAD) file on a computer-controlled fixtureless platform. Indirect and direct FD methods were used to fabricate lead zirconate titanate (PZT)/polymer composites. For the indirect method, a CAD file for the negative image of the final part was created. A polymer mold was made via FD using a thermoplastic filament, and composite formation was completed via a lost mold technique. In the direct FD method, a thermoplastic polymeric filament that was filled with 50–55 vol% of PZT powder was used to form a positive image of the desired structure. Three-dimensional honeycomb ("3-D honeycomb") composites and "ladder" composites with 3-3 connectivity, which were formed via the FD technique, showed excellent electromechanical properties for transducer applications. In addition, the FD technique showed the ability to form composites with controlled phase periodicity, various volume fractions, and a variety of microstructures and macrostructures that are not possible with traditional composite-forming techniques.     

Developing a novel technique for the fabrication of PLA-graphite composite filaments using FDM 3D printing process

Developing a uniform polymer-based composite filament is a critical factor for a successful 3D printing process. In this regard, a novel technique for the fabrication of PLA-graphite filament with the potential to be applied to other PLA-based composite filaments was proposed and compared to the solvent casting method. This modified mixing technique involves partial dissolution of the PLA pellets surface by dichloromethane (DCM), which creates a sticky surface for the strong adhesion of reinforcement powders. The manufactured composite filament by this method exhibited excellent structural features, while the solvent casting method yielded a heterogeneous filament with a non-uniform diameter and numerous voids. In addition, graphite, as a cost-effective carbon-based filler for polymer matrix composites, could effectively act as a reinforcement phase, leading to noticeable mechanical strength enhancement of PLA. Furthermore, significantly enhanced printability and mechanical properties of 3D-printed PLA-graphite composite specimens indicate the efficiency of the modified mixing method as a practical and time-saving technique for developing uniform PLA-based composite filaments for the extrusion-based additive manufacturing techniques such as FDM.     

Potentials with small‐angle neutron scattering technique for understanding structure–property relation of 3D‐printed materials

Carbon fiber (CF)‐embedded acrylonitrile butadiene styrene polymer composites printed on the large‐scale printer at Oak Ridge National Laboratory were investigated by small‐angle neutron scattering to correlate the microstructure of the composites with their mechanical strength. The microstructure of the polymer domains and the alignment of CF were characterized across the interfaces between layers of the hot‐melt extruded material and were compared with CF‐free ABS. The small‐angle neutron scattering data show that the CF‐containing material displays strong anisotropic scatterings suggesting molecular alignment along the printing direction that is not present in the CF‐free ABS. Scattering data analysis across the interfacial layer revealed enhanced molecular alignment along the printing direction near the boundaries and inhomogeneous size distribution of polymer domains upon the addition of CF. We attribute the compromised strength across interfacial layers from CF‐containing material to this inhomogeneous size distribution which prevents effective lateral interaction between layers. POLYM. ENG. SCI., 59:E65–E70, 2019. © 2018 Society of Plastics Engineers     

The synergistic effects on enhancing thermal conductivity and mechanical strength of hBN/CF/PE composite

In this work, a simple and novel method was applied to prepare polymer composites by taking the advantage of melt flow shear force driving orientation of the fillers. By using this method, hexagonal boron nitride/polyethylene (hBN/PE) and hexagonal boron nitride/carbon fibers/polyethylene (hBN/CF/PE) composites were fabricated to be possessed of high thermal conductivity and mechanical properties. A high thermal conductivity of 3.11 W/mK was realized in the composite containing 35 wt% hBN and 5 wt% CF, which was over 1,200% higher than that of unfilled PE matrix. Under this component, the compressive strength and modulus of hBN/CF/PE composite were determined to be 30.1 and 870.9 MPa, respectively, which were far higher than that of unfilled PE accordingly. The bending performance was also somewhat enhanced. Meanwhile, the bulk resistivity of the composite material reached 2.55 × 10¹¹ Ω·cm, which was basically the same as that of pure PE. The novel composites with high thermal conductivity, excellent mechanical properties, and controllable electrical insulation could be a potential thermal management material for electrical and electronics industries.     

Recent Developments in Additive Manufacturing of Conductive Polymer Composites

Additive manufacturing, also named 3D printing, can be used to create objects from diverse polymers, metals, and other materials in diverse shapes and dimensions. If special physical or chemical properties are necessitated, using corresponding feedstock enables varying such properties in a broad range. Besides choosing a suitable base material, often composite materials are used for specific applications. Here, an overview of recent developments in 3D printing of polymer composites with conductive properties is given. After a definition of conductivity ranges and the respective potential applications, additive manufacturing methods applicable for these polymer composites as well as potential resistivity or resistance measurement methods are reported. An overview of the most recent reports of 3D printing polymer composites with different conductive fillers is followed by a summary of the applications found in the recent literature.     

Additive manufacturing of B4C-W-based composites via fused deposition molding using highly filled granular feedstocks

The miniaturization and mobility of nuclear reactors have become an important trend in the development of nuclear energy. In order to simplify the design of shielding materials with improved complexity and reduced weight, 3D B₄C-W-based composites were fabricated via fused deposition molding using highly-filled granular feedstocks containing 62 vol% B₄C-W powders (boron carbide accounted for 30 wt% and tungsten for 70 wt%) and 38 vol% polymer binders (60 wt% Carnauba wax, 22 wt% polypropylene, 13 wt% polystyrene, and 5 wt% stearic acid). The rheological properties and microstructure of the feedstock and extruded filaments were clarified. Roles of the printing parameters including extrusion temperature, platform temperature and deposited-layer height in the morphology of 3D composites were investigated in detail. Extruded filaments with good shape retention, dense fracture surface, and uniformly dispersed B₄C-W grains were achieved, benefiting from the smooth printing and shear thinning behaviour of the feedstock. Defects including warping, small pores or stacking pores could be formed under improper printing parameters, owing to the poor bonding strength between deposited layers induced by thermal internal stress or decomposition of wax. 3D composites with large size of 130 × 130 × 5 mm were fabricated, which showed a satisfactory compressive strength of 34.8 MPa. This work showed a facile route to fabricate 3D radiation shielding materials based on highly-filled polymers.     

Epoxy/oil fly ash composites prepared through in situ polymerization: Enhancement of thermal and mechanical properties

The utilization of oil fly ash (OFA) as a filler in polymer composites to enhance their strength and flow properties and reduce the cost of fabrication is a promising technique. OFA filled epoxy composites, based on bisphenol‐A liquid epoxy, were prepared via in situ co‐polymerization with isophorone diamine as a curing agent. In the present work, the possibility of using residual OFA (<30 μm) as filler in epoxy composites was studied using thermal, mechanical, and morphological characterization techniques. The results showed a significant improvement in the performance of epoxy composites containing OFA. In addition, OFA filled epoxy exhibited a higher resistance to degradation in acidic and basic environments when compared to unfilled epoxy. Statistical analysis tools were used to determine the significance of the improvements. It is proposed that up to 4 wt% of OFA can be used in epoxy industrial pipes to improve their corrosive chemical resistance properties without affecting their bulk physical properties. POLYM. COMPOS., 37:512–522, 2016. © 2014 Society of Plastics Engineers     

A Review on Polymeric Nanocomposites of Nanodiamond,Carbon Nanotube,and Nanobifiller: Structure,Preparation and Properties

In this review, an overview of various types of nanofillers is presented with special emphasis on structure, synthesis and properties of carbon nanotube, nanodiamond, and nanobifiller of carbon nanotube/nanodiamond, carbon nanotube/graphene oxide and carbon nanotube/graphene. In addition, polymer/carbon nanotube, polymer/nanodiamond, and polymer/nanobifiller composites have been discussed. The efficacy of different fabrication techniques for nanocomposites (solution casting, in-situ, and melt blending method) and their properties were also discussed in detail. Finally, we have summarized the challenges and future prospects of polymer nanocomposites reinforced with carbon nanofillers hoping to facilitate progress in the emerging area of nanobifiller technology.     

Mechanical,morphological, and thermal properties of chemically treated pine needles reinforced thermosetting composites

Natural fibers are widely used as reinforcement in composites. Pine needles are one of the major biowaste generated by Pinus roxburgii plant. This species is found abundantly in the forests of Himachal Pradesh. In this work, composites of urea–resorcinol–formaldehyde resin‐reinforced with Pine needles fibers were prepared. Fibers were chemically modified to improve their compatibility with matrix. These fibers were mercerized with NaOH solution and acetylated to increase their hydrophobic character. The chemically modified fibers were characterized with Fourier transform infrared spectra, ¹³C‐nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy. The composites were prepared with treated and untreated fibers containing 30% fibers by weight using compression molding technique. The morphology of the materials thus obtained was evaluated by scanning electron microscopy. The chemical modifications of fibers improve fiber–matrix adhesion and also have markedly effect on mechanical properties of composites. Moreover, the thermal resistance of these composites was improved on chemical modification. These results indicate that chemically modified fibers exhibit better compatibility with the polymer matrix than that of untreated fiber. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci, 2013     

High Thermal Conductivity Polymer Composites Fabrication through Conventional and 3D Printing Processes: State-of-the-Art and Future Trends

The lifespan and the performance of flexible electronic devices and components are affected by the large accumulation of heat, and this problem must be addressed by thermally conductive polymer composite films. Therefore, the need for the development of high thermal conductivity nanocomposites has a strong role in various applications. In this article, the effect of different particle reinforcements such as single and hybrid form, coated and uncoated particles, and chemically treated particles on the thermal conductivity of various polymers are reviewed and the mechanism behind the improvement of the required properties are discussed. Furthermore, the role of manufacturing processes such as injection molding, compression molding, and 3D printing techniques in the production of high thermal conductivity polymer composites is detailed. Finally, the potential for future research is discussed, which can help researchers to work on the thermal properties enhancement for polymeric materials.