Printable Polymer Research Articles

Early-age strength and failure characteristics of 3D printable polymer concrete

The time-dependent rheological and early-age strength parameters of polymer concrete (PC) were investigated. PC flow decreased, and the static yield stress and thixotropy increased as the specimen aged, while the dynamic yield stress remained unchanged. The study found that the Herschel-Bulkley model can accurately describe the PC’s rheological behavior over time. The change in cohesion strength and internal friction angle over time was observed using uniaxial unconfined compression and direct shear tests of fresh PC. A time-dependent Mohr-Coulomb failure criterion was established. Temperature analysis was used to determine the gel time and explain the evolution of the time-dependent early-age strength of PC.

Designable thermal conductivity and mechanical property of polydimethylsiloxane-based composite prepared by thermoset 3D printing

Three-dimensional (3D) printing is a layered additive manufacturing technology. In common 3D printing methods, direct ink writing (DIW) and fused deposition modeling (FDM) are new extrusion-based technologies. FDM works by melting a hot-melt material and squeezing it out through a tiny nozzle. Conversely, DIW, accurately deposit accurate amount of paste at different distances through the conveying system (extruder). As a unique approach, this technology introduces design freedom, versatility and stability into the printing structure at the same time. In addition, DIW technology is suitable for thermoset 3D printing. The influences of filler orientation in polymer matrix and printing paths on the thermal conductivity (λ) of thermoset 3D printing products are worth studying. Therefore, we built a thermoset 3D printer, and optimized the structure of the nozzle device, effectively improved the printing accuracy. Polydimethylsiloxane (PDMS) and hexagonal boron nitride (hBN) are selected as polymer matrix and thermally conductive filler, respectively. Compared with pure PDMS, the λ value of hBN/PDMS composites increases obviously with increasing hBN content. Meanwhile, the mechanical properties of composites with different printing paths are systematically studied. This designable orientation provides opportunities and challenges for other functional structure design such as hollow structure.

Interfacial Photopolymerization: A Method for Light-Based Printing of Thermoplastics.

Ultraviolet (UV) printing of photopolymers is a widely adopted manufacturing method because of its high resolution and throughput. However, available printable photopolymers are typically thermosets, resulting in challenges in postprocessing and recycling of printed structures. Here, we present a new process called interfacial photopolymerization (IPP) which enables photopolymerization printing of linear chain polymers. In IPP, a polymer film is formed at the interface between two immiscible liquids, one containing a chain-growth monomer and the other containing a photoinitiator. We demonstrate the integration of IPP in a proof-of-concept projection system for printing of polyacrylonitrile (PAN) films and rudimentary multi-layer shapes . IPP shows in-plane and out-of-plane resolutions comparable to conventional photoprinting methods. Cohesive PAN films with number-average molecular weights greater than 15 kg mol-1 are obtained, and to our knowledge this is the first report of photopolymerization printing of PAN. A macrokinetics model of IPP is developed to elucidate the transport and reaction rates involved and evaluate how reaction parameters affect film thickness and print speed. Last, demonstration of IPP in a multilayer scheme suggests its suitabiliy for three-dimensional printing of linear-chain polymers.

Multimaterial 3D printing of self-assembling smart thermo-responsive polymers into 4D printed objects: A review

Multimaterial 3D printing of self-assembling smart thermo-responsive polymers into 4D printed objects: A review

A Study On Mechanical Properties Of 3d Printed Hybrid Polymer Composites

The use of 3D printing has gained significant popularity for producing functional components, ranging from prototypes and membranes to shields and sports wearables. As this method becomes more prevalent, there is a growing need to address challenges related to the limitations of suitable printing materials compared to traditional materials. Innovative methods for simulating failures in 3D-printed cellular structures have been developed to emphasize the impact of various process variables. The scarcity of appropriate printing materials can be attributed to the constraints of 3D printing techniques in accommodating a diverse range of materials. Over the past decade, 3D printing technologies have found extensive application across industries, including the military, serving as a rapid prototyping, and manufacturing method. However, commercially available printing polymers have exhibited inherently lower mechanical properties, such as strength and stiffness, when compared to traditional manufacturing materials. To overcome these limitations, multi-material additive manufacturing (AM) technology has emerged as a promising alternative. This approach allows for the creation of complex structures with a broad spectrum of mechanical characteristics, presenting a significant advancement over traditional assembly methods. In ongoing efforts to enhance material qualities, there is a current focus on fabricating polymer composites using 3D printing techniques. Various reinforcement materials, including carbon fibers and multi-walled carbon nanotubes (MCNTs), are being incorporated into matrix materials like ABS and PETG. This endeavor aims to exploit the capabilities of 3D printers to innovate and create complex items with improved material properties, opening the door to further research and development in fast manufacturing processes.

Fabrication of poly(lactic acid), poly(butylene succinate), and poly(hydroxybutyrate) bio‐based and biodegradable blends for application in fused filament fabrication‐based 3D printing

AbstractThe present study highlights biodegradable and bio‐based polymer blends from poly(lactic acid), poly(butylene succinate) (PBS), and poly(hydroxybutyrate) (PHB) as potential filaments for additive manufacturing. Dog‐bone‐shaped parts were prepared using the fused filament fabrication (FFF) technique. To assess polymer compatibility, interface, and printing performance, vertical and horizontal models were prepared and compared. The ratios of PBS/PLA and PBS/PHB were fixed at 5:5 and 7:3 for this research, respectively. The design concept is based on combining high elastic modulus glassy polymers (PLA and PHB) with soft, ductile PBS. The addition of PBS enhanced thermal processing and rheological properties. Scanning electron microscopy images revealed that the blends produced high‐quality prints while maintaining the original resolution and input parameters. Tensile tests revealed that PBS/PLA blends had significantly higher performance properties than PBS/PHB blends. Vertical prints that coincided with strain direction produced significant plastic deformation in PBS/PLA blends, achieving uniform elongation values of up to 10.4% and elongation at break values exceeding 150%. PBS/PHB blends showed lower compatibility for FFF compared with PBS/PLA blends. Produced bio‐based prints showed an increase in elastic modulus and tensile properties distinct from pure‐polymers; thus, blends have excellent potential for tuning the mechanical properties of the final product.

Radical-Mediated Ring-Opening Photopolymerization for Semicrystalline Thermoplastic Additive Manufacturing

Conventional approaches to stereolithographic additive manufacturing (SLA) employ liquid resin formulations based on multifunctional (meth)acrylates and epoxides that afford cross-linked polymeric networks upon polymerization. Nevertheless, the utilization of resins that yield semicrystalline thermoplastics provides facile access to physical and mechanical properties that are otherwise difficult to attain, such as high toughness and resistance to solvent swelling as well as additional postfabrication processing options that can be used to extend the life cycle of three-dimensional printed polymers. Here, we report the SLA-based additive manufacturing of semicrystalline thermoplastics utilizing the radical-mediated ring-opening photopolymerization of seven- and eight-membered cyclic allylic sulfides. Photopolymerization of resin formulations incorporating seven- and eight-membered cyclic allylic sulfides and crystallization of the resultant (co)polymers were examined using Fourier transform infrared spectroscopy, photorheology, and isothermal photo-differential scanning calorimetry. The formulated resins were found to polymerize and subsequently crystallize rapidly upon irradiation under ambient conditions. The mechanical properties of stereolithographically printed copolymers approached the bulk copolymer mechanical properties, demonstrating unusually strong interlayer adhesion atypical of layerwise, stereolithographic printing of semicrystalline polymers. Finally, high-quality, recyclable, semicrystalline thermoplastic parts were printed and melted down, demonstrating the potential for these semicrystalline materials to provide a path for improved sustainability of polymeric parts produced via SLA.

Printable piezoresistive polymer composites for self-sensing medical catheter device applications

There is a constant demand for new and/or improved health treatments that require flexible sensor devices. This is particularly relevant in relation to neurogenic bladder dysfunction.In this context, polymer composites have been developed based on three different matrices, carboxymethyl cellulose (CMC), styrene-ethylene/butylene-styrene (SEBS) and polyvinyl alcohol (PVA), with different concentrations of multiwalled carbon-nanotubes (CNT) filler contents for catheter medical device application.The mechanical properties of the nanocomposites are critically dependent on the polymeric matrix and also depend on CNT content with maximum strain is about 4%, 100% and 700% for CMC, PVA and SEBS materials, respectively. Electrical conductivity increases near 10 orders of magnitude up to 0.11 S/m for PVA with 5 wt percentage (wt.%) of CNT, one magnitude order than the most filled PVA and CMC composites. The percolation threshold (fc) of the composites are fc = 3 wt% for CMC, fc = 2 wt% for SEBS, and fc = 1 wt% for PVA as polymer matrices. Furthermore, the functional performance of the composites is characterized by the piezoresistive response, with a gauge factor (GF) ranging between 1 and 6 for the different composites. Finally, a self-sending catheter device was developed as a proof-of-concept, based on a PVA composite with a GF∼1.5. demonstrating proper adhesion and excellent sensing behavior at bending up to 7 mm.Thus, it is demonstrated that screen-printable piezoresistive sustainable composites can be developed for medical application with excellent electrical and mechanical properties.

The influence of metallic particulate inclusions on the mechanical and thermal performance of 3D printable acrylonitrile-butadiene-styrene/thermoplastic polyurethane fused polymer blends

Acrylonitrile butadiene styrene (ABS) shows exceptional mechanical behavior, however, the application of ABS for manufacturing thin parts has been limited because of its significantly lower melt fluidity. Thermoplastic polyurethane (TPU), on the other hand, has acceptable melt fluidity, but its mechanical performance is limited when compared to ABS. This paper combines these two polymers and incorporates elongated iron powder particulates as a reinforcing agent to manufacture a cost-effective yet performance-enhanced blended polymer filament for 3D printing. The melt-mixing approach was followed for blended polymer filament manufacturing. The thermal performance of the extruded filaments was evaluated using differential scanning calorimetry (DSC). The glass transition and melting temperatures were found to be slightly higher for the particulate-reinforced samples when compared to the control unreinforced ABS/TPU blend. This is attributable to the fact that the inclusions limit the mobility of the structure therefore it requires more energy to break down the molecular structure. The tensile strength of the filaments was obtained using a uniaxial tension experiment whereas the fracture toughness of the 3D printed parts was determined using the microindentation technique. The tensile strength and fracture toughness was found to be increasing with an increase in iron powder dosage by up to 5 %. The results reflect that appropriate dispersion of iron particulates is required to achieve the desired performance enhancement. Overall, the findings of this paper can potentially lead to various cost-effective and efficient means for performance enhancement in the manufacturing of 3D printable blended polymer composite filaments.

Microwave Devices for Wearable Sensors and IoT.

The Internet of Things (IoT) paradigm is currently highly demanded in multiple scenarios and in particular plays an important role in solving medical-related challenges. RF and microwave technologies, coupled with wireless energy transfer, are interesting candidates because of their inherent contactless spectrometric capabilities and for the wireless transmission of sensing data. This article reviews some recent achievements in the field of wearable sensors, highlighting the benefits that these solutions introduce in operative contexts, such as indoor localization and microwave sensing. Wireless power transfer is an essential requirement to be fulfilled to allow these sensors to be not only wearable but also compact and lightweight while avoiding bulky batteries. Flexible materials and 3D printing polymers, as well as daily garments, are widely exploited within the presented solutions, allowing comfort and wearability without renouncing the robustness and reliability of the built-in wearable sensor.

Printability of Poly(lactic acid) Ink by Embedded 3D Printing via Immersion Precipitation.

Immersion precipitation three-dimensional printing (ip3DP) and freeform polymer precipitation (FPP) are unique and versatile methods of 3D printing to fabricate 3D structures based on nonsolvent-induced phase separation via direct ink writing (DIW). Immersion precipitation involves complex dynamics among solvents, nonsolvents, and dissolved polymers, and the printability of 3D models in these methods requires further understanding. To this end, we characterized these two methods of 3D printing using polylactide (PLA) dissolved in dichloromethane (7.5-30% w/w) as model inks. We analyzed the rheological properties of the solutions and the effect of printing parameters on solvent-nonsolvent diffusion to achieve printability. The PLA inks exhibited shear-thinning properties, and their viscosities varied over three orders of magnitude (10-1∼102 Pa·s). A processing map was presented to understand the ideal ranges of the concentration of PLA in inks and the nozzle diameter to ensure printability, and the fabrication of complex 3D structures was fabricated with adequate applied pressure and nozzle speed. The processing map also highlighted the advantages of embedded 3D printing over solvent-cast 3D printing based on solvent evaporation. Lastly, we demonstrated that the porosity of the interface and inner structure of the printed objects was readily tailored by the concentration of the PLA and the porogen added to the ink. The methods presented here offer new perspectives to fabricate micro-to-centimeter objects of thermoplastics with nanometer-scale inner pores and provide guidelines for successful embedded 3D printing based on immersion precipitation.

Understanding the multilevel phenomena that enables inorganic atomic layer deposition to provide barrier coatings for highly-porous 3-D printed plastic in vacuums

The potential of 3-D printing polymers to achieve low-weight space flight hardware has seen increasing interest. Additionally, robust 3-D printed polymer vacuum equipment would provide highly attractive low-cost alternatives to conventional industrial-scale tools for the scientific community. Inorganic barrier coatings of plastic parts can be used to minimize outgassing and damage to polymers from extreme vacuum environments. Among different coating technologies in this area of research, atomic layer deposition (ALD) has shown the most promise. Nevertheless, the exact formation morphology of ALD coatings on 3-D printed polymers under vacuum are not yet well understood, which hinders use of 3-D printed polymers in vacuum environments. In this study, the film formation mechanisms of ALD alumina on porous 3-D printed polymers are investigated via SEM, EDS, XRD, ATR-FTIR, and XPS. ALD alumina is deposited on 3-D printed pigmented and un-pigmented acrylonitrile butadiene styrene, polycarbonate, commercially available polypropylene, and pure polypropylene. The results reveal that the formation of the ALD barrier layer, its thickness, and diffusion of ALD precursor materials into the polymer substrate is a multi-scale phenomenon, and that substrate porosity and polymer functionality both dominate film formation behavior. Additionally, this study demonstrates that during ALD processes on 3-D printed polymers a vapor phase infiltration (VPI) growth mode also occurs, especially where porosity is present.

Modification of 3D Printable Polymer Filaments for Radiation Shielding Applications

There is a growing need to develop lead-free shielding materials that are safe, low weight, durable, environmentally friendly, chemically and mechanically stable and customizable for specific applications. Fused deposition modeling (FDM), an additive manufacturing technique based on the extrusion of a thermoplastic filament into a 3D printed object one layer at a time, could be employed well in applications involving ionizing radiation due to its relatively low cost, design flexibility and high manufacturing precision. This study aimed at developing 3D printing composites that contain Titanium dioxide as a filler agent for shielding in a medical radiation environment. First, the effect of low-dose ionizing radiation (up to 15 Gy) on the mechanical properties of common 3D printing polymers, ABS, ULTRAT, PLA, NYLON, ASA and PETG, was investigated. Since ABS experienced the lowest variation in its ultimate tensile strength (±5%) and Young's modulus (-5%/+11%), it was chosen as a matrix for a new extruded 3D filament containing TiO2 at 1 wt.%, 3 wt.%, and 5 wt.%. With the incorporation of TiO2 at different filler contents, the UTS of the ABS composites varied between 24.1 MPa and 28.4 MPa, with the highest value recorded for 3 wt.% TiO2. Young's modulus values were dependent on both the TiO2 concentration and on the irradiation dose. In addition, the ABS/TiO2 composites with a higher filler content (3 wt.% and 5 wt.%) maintained their attenuation ability even after exposure to a radiation dose of 100 Gy as opposed to pure ABS, which exhibited a ~2.5% reduction in its mass attenuation coefficient after exposure to the same dose of radiation. The pilot investigation performed demonstrated that the newly developed ABS/TiO2 composite containing 5 wt.% of filler can be successfully employed to shield electronic devices operating in a radiotherapy room.

Sonochemical Degradation of Gelatin Methacryloyl to Control Viscoelasticity for Inkjet Bioprinting.

Inkjet printing enables the mimicry of the microenvironment of natural complex tissues by patterning cells and hydrogels at a high resolution. However, the polymer content of an inkjet-printable bioink is limited as it leads to strong viscoelasticity in the inkjet nozzle. Here it is demonstrated that sonochemical treatment controls the viscoelasticity of a gelatin methacryloyl (GelMA) based bioink by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups. The rheological properties of treated GelMA inks are evaluated by a piezo-axial vibrator over a wide range of frequencies between 10 and 10000Hz. This approach enables to effectively increase the maximum printable polymer concentration from 3% to 10%. Then it is studied how the sonochemical treatment effectively controls the microstructure and mechanical properties of GelMA hydrogel constructs after crosslinking while maintaining its fluid properties within the printable range. The control of mechanical properties of GelMA hydrogels can lead fibroblasts more spreading on the hydrogels. A 3D cell-laden multilayered hydrogel constructs containing layers with different physical properties is fabrictated by using high-resolution inkjet printing. The sonochemical treatment delivers a new path to inkjet bioprinting to build microarchitectures with various physical properties by expanding the range of applicable bioinks.

Avian‐Inspired Perching Mechanism for Jumping Robots

The integration of multiple locomotion strategies and behaviors allows robots to extend the working environment and enhance the performance of each motion. This work integrates perching to a jumping robot to improve the jumping performance. The developed avian‐inspired perching device has a shock‐absorbing mechanism, which consist of a 3D printable flexible polymer material that absorbs the perching impact. This work characterizes the shock‐absorbing performance of the viscoelastic material as a function of hardness and thickness of the material, initial angles of a mechanism, mechanism length, perching speed, and perching angle. This work also characterizes the performance of mechanical interlocking and penetration as the engagement strategies for vertical surfaces. The performance of perching mechanism as a function of hardness of the target surface, contact angle of the claw, and performance of the shock absorption is observed. Finally, demonstrations to evaluate the perching mechanism's performance on the complete system are conducted, and the robot's performance enhancement with an integrated perching motion is shown. This work provides a design methodology to develop and integrate a perching mechanism into jumping robots.

Recent Developments in Additive Manufacturing of Conductive Polymer Composites

AbstractAdditive 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.

Effect of Adhesion Conditions on the Shear Bond Strength of 3D Printing Resins after Thermocycling Used for Definitive Prosthesis.

Three-dimensional (3D) printing polymers such as urethane dimethacrylate (UDMA) and ethoxylated bisphenol A dimethacrylate (Bis-EMA) are typically used in definitive prosthesis and require surface treatments before bonding. However, surface treatment and adhesion conditions often affect long-term use. Herein, polymers were divided into Groups 1 and 2 for the UDMA and Bis-EMA components, respectively. The shear bond strength (SBS) between two types of 3D printing resins and resin cements was measured using Rely X Ultimate Cement and Rely X U200, according to adhesion conditions such as single bond universal (SBU) and airborne-particle abrasion (APA) treatments. Thermocycling was performed to evaluate the long-term stability. Sample surface changes were observed using a scanning electron microscope and surface roughness measuring instrument. The effect of interaction between the resin material and adhesion conditions on the SBS was analyzed via a two-way analysis of variance. The optimal adhesion condition for Group 1 was achieved when U200 was used after APA and SBU, whereas Group 2 was not significantly affected by the adhesion conditions. After thermocycling, the SBS significantly decreased in Group 1 without APA treatment and in the entire Group 2. Additionally, porosity, along with increased roughness, was observed on both material surfaces after APA.

High-performance, printable quasi-solid-state electrolytes toward all 3D direct ink writing of shape-versatile Li-ion batteries

The era of miniaturized and customized electronics requires scalable energy storage devices with versatile shapes. From the perspective of manufacturing, direct ink writing (DIW)-based 3D printing has attracted unprecedented interest, paving the way to demonstrate micro-batteries with design freedom and outstanding performance. Despite demands for all-printed Li-ion batteries with maskless processing, most of the efforts have been dedicated to developing printable active electrodes or building the 3D architecture, remaining challenges in both manufacturing and printable materials toward form-free, all 3D DIW printed Li-ion batteries. Herein, we present all 3D DIW printed, scalable shape versatile Li-ion batteries (ADP-LIBs) with high-performance, printable gel polymer electrolytes (GPEs). The rheological optimization of DIW printable inks for solid-state current collectors, electrodes, electrolytes, and packaging enables us to demonstrate well-defined shape-versatile ADP-LIBs with reliable extrusion. In particular, UV-curable polydimethylsiloxane (PDMS) and ethoxylated trimethylolpropane triacrylate (ETPTA) monomers provide thixotropic fluid behaviors and a mechanical framework in the quasi-solid-state electrolytes, respectively, which results in high-throughput and mechanically robust printed electrolyte layers. Our ADP-LIBs demonstrate a great deal of promise as a realistic solution for powering the target applications on-demand with aesthetic versatility, free-form factors, and competitive electrochemical performance.

Exploring Effects of Graphene and Carbon Nanotubes on Rheology and Flow Instability for Designing Printable Polymer Nanocomposites.

Nowadays, a strong demand exists for printable materials with multifunctionality and proper rheological properties to overcome the limitations to deposit layer-by-layer in additive extrusion. The present study discusses rheological properties related to the microstructure of hybrid poly (lactic) acid (PLA) nanocomposites filled with graphene nanoplatelets (GNP) and multiwall carbon nanotubes (MWCNT) to produce multifunctional filament for 3D printing. The alignment and slip effects of 2D-nanoplatelets in the shear-thinning flow are compared with the strong reinforcement effects of entangled 1D-nanotubes, which govern the printability of nanocomposites at high filler contents. The mechanism of reinforcement is related to the network connectivity of nanofillers and interfacial interactions. The measured shear stress by a plate-plate rheometer of PLA, 1.5% and 9% GNP/PLA and MWCNT/PLA shows an instability for high shear rates, which is expressed as shear banding. A rheological complex model consisting of the Herschel-Bulkley model and banding stress is proposed for all considered materials. On this basis, the flow in the nozzle tube of a 3D printer is studied by a simple analytical model. The flow region is separated into three different regions in the tube, which match their boundaries. The present model gives an insight into the flow structure and better explains the reasons for printing enhancement. Experimental and modeling parameters are explored in designing printable hybrid polymer nanocomposites with added functionality.

A new strategy for the reinforcement of paraffin-based fuels based on cellular structures: The armored grain — Ballistic characterization

Slow regression rate of the solid fuel is the main limitation for the use of hybrid rocket engines in high thrust applications. Paraffin-based fuels tackle this limitation thanks to the entrainment mass transfer. In this study, ballistic behaviors of conventional polymeric fuel (ABS) and paraffin-based blends are studied and compared with those of the armored grains. These latter are a new generation of fuels featuring 3D printed cellular structures embedded in the wax-based grain. The ballistic characterization focuses on the evaluation of the regression rate (rf) and its dependence on the oxidizer mass flux. Relative ballistic grading of the formulations is pursued via thickness over time methods and an optical technique for rf determination. The armored grains are reinforced by gyroid structures that are 3D printed using three different polymers (ABS, PLA, and Nylon 6) and two relative densities (10% and 15%). Despite the slow burning behavior of the printing polymers, the embedded reinforcement enhances the rf of the paraffin-based formulations, with percent increases ranging from +48% to +91%. This result could be explained by the uneven and irregular texture of the burning surface promoting turbulence (and therefore, propellant mixing) and convective heat transfer. For both the armored grains and the paraffin-based formulations, blending the pristine paraffin wax with polymeric additives results in more viscous formulations and in a rf reduction. Armored grain combustion performance makes this novel fuel an interesting candidate for high-thrust hybrid rockets.