Fused Deposition Modeling of Polyolefins: Challenges and Opportunities

Polyolefins are the largest class of commercially available synthetic polymers that are extensively used in a variety of applications from commodities to engineering owing to their low cost of production, good physico-mechanical properties, light weight, good processability, and recyclability. Compared to conventional molding techniques, fused deposition modeling (FDM)-based 3D printing is a smart manufacturing technology for thermoplastics due to its low cost, ease of production of complex geometrical parts, rapid prototyping, and scalable customization. FDM 3D printing can be an ideal manufacturing technology for polyolefins to manufacture various complex parts. However, FDM 3D-printing of polyolefins is challenged bycritical printing problems like high warpage, dimensional inaccuracies, poor bed adhesion, and poor layer-to-layer adhesion. In this review, a fundamental understanding of polyolefins and their FDM 3D-printing process is established, and the recent progress of FDM 3D printing of polyolefins is summarized. Furthermore, strategies to overcome warpage and to improve mechanical strength of the 3D-printed polyolefins are provided. Finally, future prospectives of FDM 3D-printing of polyolefins are critically discussed to inspire prospective research in this field. It is believed that this review article can be tremendously useful for research work related to FDM of polyolefin-based materials.     

熔融沉积成型3D打印技术应用进展及展望

介绍熔融沉积制造(FDM)3D打印技术的产生和特点。着重介绍了FDM 3D打印技术在汽车工业、航空航天、医疗卫生、教育教学、食品加工等领域的实际应用情况。并对FDM 3D打印技术的应用前景进行展望。     

3D-printing of polymer‐derived SiCN ceramic matrix composites by digital light processing

In this study, we present a DLP 3D-printing strategy for the fabrication of SiCN ceramic matrix composites (CMCs). The polysilazane-based preceramic polymer containing inert fillers was UV-cured into a green body and then converted to SiCN CMCs after pyrolysis. The introduced fillers (Si₃N₄ particles and Si₃N₄ whiskers) as reinforcements are well dispersed in the matrix, which can not only effectively reduce the linear shrinkage and weight loss, but also greatly improve the mechanical properties of the SiCN CMCs. The bending strength of the SiCN CMCs reinforced with 10 wt% Si₃N₄ whiskers (without surface polished) reached 180.7 ± 15.6 MPa. Furthermore, the effect of fillers content on microstructure and porosity of the SiCN CMCs are discussed, and it was found that the excessive fillers led to increased pore defects and decreased continuity of the matrix, thereby reducing the mechanical properties of the SiCN CMCs. This strategy provides a promising ceramic manufacturing technique to fabricate polymer‐derived CMCs with complex-shaped and high-performance for potential demanding applications.     

Compatibility of Kraft Lignin,Organosolv Lignin and Lignosulfonate With PLA in 3D Printing

The compatibility of three different types of lignin, such as Kraft lignin, Organosolv lignin, and lignosulfonate, with PLA, in particular without the addition of any further reagents or compatibilizers, is investigated. The unmodified lignins were thoroughly characterized to establish their interaction potential in lignin-PLA composite formation. The obtained double-extruded binary systems containing 5, 10, and 15?wt % lignin in PLA were characterized in terms of chemical conversion (^31?P NMR), thermal behavior (TGA, DSC), and cellular morphology (SEM). Additionally, the flexural and impact properties as well as the melt volume rate (MVR) of the extruded materials, in the form of 3D-printed bars, were analyzed, and the effect of lignin addition to PLA studied. The results revealed poor mechanical properties for the Kraft lignin-PLA blends, but higher compatibility of Organosolv lignin-PLA blends. Lignosulfonate-PLA blends showed a promising behavior for 3D-printing. A special nucleation effect, potentially useful in foaming applications, was observed in this study.     

Complex geometry macroporous SiC ceramics obtained by 3D-printing,polymer impregnation and pyrolysis (PIP) and chemical vapor deposition (CVD)

We present here an original route for the manufacturing of SiC ceramics based on 3D printing, polymer impregnation and pyrolysis and chemical vapor deposition (CVD). The green porous elastomer structures were first prepared by fused deposition modeling (FDM) 3D-printing with a composite polyvinyl alcohol/elastomer wire and soaking in water, then impregnated with an allylhydridopolycarbosilane preceramic polymer. After crosslinking and pyrolysis, the polymer-derived ceramics were reinforced by CVD of SiC using CH₃SiCl₃/H₂ as precursor. The multiscale structure of the SiC porous specimens was examined by X-ray tomography and scanning electron microscopy analyses. Their oxidation resistance was also studied. The pure and dense CVD-SiC coating considerably improves the oxidation resistance.     

Field-dependent nonlinear piezoelectricity: a focused review

ABSTRACT

This contribution presents a multidisciplinary review of the so-called field-dependent nonlinear piezoelectricity. It starts with an introduction that poses the literature analysis framework, through defining this operational (that is often met in practice) piezoelectric field-dependent nonlinearity. Indeed, the latter is a less known phenomenon although it is inherent to stress-free actuation responses of corresponding smart materials, actuators and structures. Then, related experimental observations from piezoelectric materials, actuator devices and smart structures tests are multidisciplinary surveyed for understanding the underlying mechanisms of the encountered field-dependent nonlinearity. Next, empirical material and numerical structural modelling and simulation approaches are critically reviewed from, respectively, the constitutive and finite element analysis points of view. Summary conclusions and few future directions for research are finally provided as a closure. It is worth mentioning that, although it is concise (retains only experiments and experimentally-correlated models and simulations), this critical review covers the last three decades period which is almost the whole age of the piezoelectric materials, actuators and smart structures research field.     

Morphological evolution,growth mechanism,and magneto-transport properties of silver telluride one-dimensional nanostructures

Single crystalline one-dimensional (1D) nanostructures of silver telluride (Ag₂Te) with well-controlled shapes and sizes were synthesized via the hydrothermal reduction of sodium tellurite (Na₂TeO₃) in a mixed solution. The morphological evolution of various 1D nanostructures was mainly determined by properly controlling the nucleation and growth process of Ag₂Te in different reaction times. Based on the transmission electron microscopy and scanning electron microscopy studies, the formation mechanism for these 1D nanostructures was rationally interpreted. In addition, the current–voltage (I-V) characteristics as a function of magnetic field of the highly single crystal Ag₂Te nanowires were systematically measured. From the investigation of I-V characteristics, we have observed a rapid change of the current in low magnetic field, which can be used as the magnetic field sensor. The magneto-resistance behavior of the Ag₂Te nanowires with monoclinic structure was also investigated. Comparing to the bulk and thin film materials, we found that there is generally a larger change in R (T) as the sample size is reduced, which indicates that the size of the sample has a certain impact on magneto-transport properties. Simultaneously, some possible reasons resulting in the observed large positive magneto-resistance behavior are discussed.     

“2D or not 2D”: Shape-programming polymer sheets

This review summarizes progress toward programming two-dimensional (2D) polymer sheets which respond to a variety of external stimuli to form three-dimensional (3D) shapes or topographical features on macroscopically planar sheets. Shape programming strategically adds value or function to 2D sheets, films, or coatings that can be created inexpensively. 2D substrates are common form factors that are compatible with ordinary 2D patterning techniques (i.e., inkjet, photolithography, roll-to-roll printing) and may be stored, packed, and shipped efficiently. Polymer materials are attractive due to their flexibility, light weight, low price, and compatibility with high throughput processing. This review highlights strategies for triggering shape change in planar polymeric materials. The strategies are divided into four broad categories: (1) 2D substrates with latent topography “programmed” using conventional microfabrication, (2) 2D substrates that form topography due to imposed or self-generated stress, (3) 2D substrates that form 3D shapes by out-of-plane bending, and (4) 2D substrates that use “hinges” to achieve out-of-plane folding. The review highlights all strategies while focusing primarily on last two approaches.     

Light and Shape-Memory Polymers: Characterization,Preparation, Stimulation,and Application

Shape-memory polymers (SMPs) are smart materials that change shape when exposed to stimuli and have various applications in different fields due to their unique properties. Light, as a kind of electromagnetic radiation, plays an important role in understanding the structure-property relations of SMPs, preparing original shapes, using them as non-contact stimuli sources, and tuning the optical properties of SMPs. This review provides a comprehensive review of the involvement of light in structure-preparation-stimuli-application of SMPs. The review is divided into four sections. First, applications of optical/spectroscopic approaches that provide information for understanding structure-property relations in SMPs, especially during programming and recovery. Second, describes how to build SMPs with light, including different photochemical reactions and 3D photocuring technologies. Third, discusses how light is used to trigger the shape change of SMPs through both photochemical and photothermal mechanisms. Last, focuses on how to take advantage of the shape-memory effect to tune the optical characteristics of polymers, including various structures of SMP color-changing materials and their synthetic strategies. Future research could focus on developing efficient photothermal fillers, new 3D printing techniques for SMPs, exploring their use in biomedical and wearable devices, and optimizing SMPs for industrial applications.     

Helikauranoside A, a New Bioactive Diterpene

A new ent-kaurane glucoside, named helikauranoside A (4), was isolated from the aerial parts of Helianthus annuus L. together with three known ent-kaurane-type diterpenoids: (−)-kaur-16-en-19-oic acid (1), grandifloric acid (2), and paniculoside IV (3). The structure of 4 was determined by using a combination of 1D (¹H-NMR and ¹³C-NMR) and 2D (COSY, HSQC, and HMBC) NMR techniques. Bioactivity spectra of isolated compounds were tested by using the etiolated wheat coleoptile bioassay in aqueous solutions at concentrations ranging from 10⁻³ to 10⁻⁶M. Helikauranoside A (4) was the most active (−84%, 10⁻³M; −56%, 10⁻⁴M). These results suggest that this new compound may be involved in defense mechanisms of H. annuus.     

Controlling Crystallization: A Key Factor during 3D Printing with the Advanced Semicrystalline Polymeric Materials PEEK,PEKK 6002, and PEKK 7002

Controlling the crystallization of advanced, high-performance polymeric materials during 3D printing is critical to ensure that the resulting structures have appropriate mechanical properties. In this work, two grades of polyetherketoneketone (PEKK 6002 and PEKK 7002) are used to print 3D specimens via a fused filament fabrication process. The samples are compared with polyetheretherketone printed under the same conditions. Two approaches for controlling the crystallization process are undertaken. The first involves adjustment of the chamber temperature between room temperature and 190 °C to create two regions where crystallization is governed by the slow diffusion process and elevated by limiting the nucleation process. The second approach involves selection of PEKK materials with varying crystallization kinetics, namely. Application of this method into 3D-printing process allows for printing semicrystalline materials with tailored mechanical, thermal, and chemical properties as either amorphous or in situ crystallized products. The studies undertaken here provide the basis to eliminate expensive and time-consuming post-processing of 3D fabricated parts. In particular, solutions for the avoidance of poor adhesion to the building plate and weak interlayer adhesion that can lead to warping are described. The materials are divided into three groups, slow, moderate, and too fast crystallization kinetics.     

3D printing of bone substitute implants using calcium phosphate and bioactive glasses

Customized implants for bone replacement are a great help for a surgeon to remodel maxillofacial or craniofacial defects in an esthetical way, and to significantly reduce operation times. The hypothesis of this study was that a composite of β-tricalcium phosphate (β-TCP) and a bioactive glass similar to the 45S5 Henchglass^® is suitable to manufacture customized implants via 3D-printing process. The composite was chosen because of the bioresorption properties of the β-TCP, its capability to react as bone cement, and because of the adjustability of the bioactive glass from inert to bioresorbable. Customized implants were manufactured using the 3D-printing technique. The four point bending strength of the printed specimens was 14.9 MPa after sintering. XRD analysis revealed the occurrence of two other phases, CaNaPO₄ and CaSiO₃, both biocompatible and with the potential of biodegradation. We conclude that it is possible to print tailored bone substitute implants using a bioactive TCP/glass composite. The glass is not involved as reactive substance in the printing process. This offers the opportunity to alter the glass composition and therefore to vary the composition of the implant.     

2D Cationic Metal-Organic Frameworks of Ag+ with Mixed Ligands (Semi-Rigid Dipyridyl, 3-pmpmd, and Diphosphine, dppe)

Abstract  

With the complex 1 or 2 ([Ag(3-pmpmd)]_n·n(X) (X⁻ = BF₄ ⁻, 1; X = PF₆ ⁻, 2) from the semi-rigid 3-pmpmd (N,N′-bis(3-pyridylmethyl)-pyromellitic diimide) ligand and AgBF₄ or AgPF₆ as the precursor, two new coordination polymers [Ag₂(3-pmpmd)₂(dppe)(BF₄)₂]_n·4nDMF (3) and [Ag₂(3-pmpmd)₂(dppe)(PF₆)₂]_n·4nDMF (4) with the 2D cationic MOFs (metal-organic frameworks), have been obtained in the presence of the second dppe (Ph₂P(CH₂)₂PPh₂) ligand. In the 2D layer network, the 3-pmpmd ligands show the Z _T -mode and the Z _C -mode conformations, and the bridged dppe ligands have the same anti conformation. In the meantime, the functions of the two selected ligands, together with the supramolecular interactions from counter ions and solvates molecules within, should play a key role in the construction of the 2D noninterpenetrated network.     

Rapid preparation of novel MgNH4PO4·H2O porous scaffolds via 3D-printing combined with a hydrothermal-process-assisted post treatment

Novel dittmarite (MgNH₄PO₄·H₂O) 3D porous scaffolds were firstly fabricated via 3D-printing combined with a hydrothermal-process-assisted post treatment. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the phases, morphologies, and element compositions of the 3D porous structures. The hydrothermal process played the key role in the formation of dittmarite phase. The porosity, compressive strength, and in vitro degradation of the dittmarite scaffolds were studied in detail. In addition, the cytotoxicity on MC3T3-E1 osteoblast cells and cell adhesion were evaluated and the results showed that the dittmarite porous scaffold possessed superior cytocompatibility and could support MC3T3-E1 cellular attachment. The research indicated that dittmarite porous scaffolds had a wide application prospect in bone tissue repair fields.     

Algorithm for solving problems related to the natural vibrations of electro-viscoelastic structures with shunt circuits using ANSYS data

ABSTRACT

An algorithm for numerical realisation of a mathematical statement of the natural vibrations problem for electro-viscoelastic bodies with passive external electric circuits (i.e. shunting circuits) with an arbitrary configuration using the finite element method is proposed in the present paper. The proposed algorithm allows considering the viscoelastic properties of materials using the model of linear hereditary viscoelasticity with complex dynamic moduli and is used to solve 3D solid structure problems that are compatible for ANSYS package element types. This technique implies the usage of the global assembled matrices of stiffness and mass, formed in the ANSYS package. The basis of the algorithm is a novel approach that allows performing decomposition of the global assembled stiffness matrix formed in the ANSYS software package into constituents that are needed for calculation of the natural vibration frequencies of the objects under study. These matrix components are used in the program that was written in FORTRAN (Formula Translation) language. This problem could be efficiently applied for analysis of the dynamic processes in smart systems based on piezoelectric materials and could also form a basis for the development of numerical finite element algorithms for optimization of the dissipative characteristics of electromechanical systems with shunted piezoelectric elements.     

Aligned three-dimensional microstructures of conducting polymer composites

The composites of polypyrrole (PPy) and poly(vinyl alcohol) (PVA) with aligned 3-dimensional (3D) microstructures have been fabricated via vapor deposition polymerization (VDP) of pyrrole onto the microstructured composites of PVA and FeCl₃ (PVA-FeCl₃) formed by directional freezing. In these composites, the microstructures of PVA act as the frameworks and the conducting polymer components provide the materials with conductive function. The composites are foam-like with low weight density. However, they have good mechanical properties, and can be easily mechanically processed into various desired shapes. The apparent conductivity of the composite containing 20 wt% PPy was measured to be approximately 0.1 S cm⁻¹. The ammonia gas sensor based on this 3D composite exhibited high sensitivity. The strategy developed here can be extended to fabricate the 3D microstructured conductive composites by using other conducting polymers or water-soluble polymers.     

Using X-ray tomography,PALS and Raman spectroscopy for characterization of inhibitors in epoxy coatings

Model paint materials were generated by adding a range of inorganic materials into an epoxy. The inorganic materials included inhibitors (Zn₃(PO₄)₂ and SrCrO₄) and a filler (rutile TiO₂).The SrCrO₄ system was characterized using SEM, TEM, PALS and Raman spectroscopy and found to have an even distribution of inhibitor in the polymer matrix. X-ray tomography was performed on the mixed SrCrO₄/TiO₂ and Zn₃(PO₄)₂/TiO₂ systems. A new technique called data constrained modelling was combined with the tomographic technique to produce a 3D distribution of the inorganic phases within the polymer matrix.     

Generation of Internally Mixed Insoluble and Soluble Aerosol Particles to Investigate the Impact of Atmospheric Aging and Heterogeneous Processing on the CCN Activity of Mineral Dust Aerosol

Heterogeneous reactions of trace gases with mineral dust aerosol not only impact the chemical balance of the atmosphere but also the physicochemical properties of the dust particle and the ability of the particle to act as a cloud condensation nuclei (CCN). Recent field studies have shown that carbonate minerals are preferentially associated with nitrates whereas aluminum silicates (i.e., clay minerals) are preferentially associated with sulfates. To better understand how this association can impact the climate effects of mineral dust particles, we have measured the CCN activity of a number of pure and internal mixtures of aerosols relevant to these recent field studies. The CCN activity of CaCO ₃ -Ca(NO ₃ ) ₂ aerosol, simulating the activity of mineral dust aerosol that has been partially processed by nitrogen oxides in the atmosphere, is significantly enhanced relative to CaCO₃ aerosol of the same diameter. Similar results are obtained for a clay mineral, kaolinite, internally mixed with (NH ₄ ) ₂ SO ₄ . For example, at 0.3% supersaturation, a 200 nm particle containing a soluble nitrate or sulfate component is 2 to 4 times more active than an unreacted particle. The results presented here show that when determining the contribution of mineral dust aerosol to the overall impact of the aerosol indirect effect on radiative forcing, changes in chemical composition due to atmospheric processing cannot be ignored.     

Characterization of unsteady flow in a 3D-printed Schwarz Diamond monolith using magnetic resonance velocimetry

Process engineering applications such as heat transfer, reactions, and separations involve passing fluid through a porous medium. Historically, random-channel porous media have been used for these operations. Such systems do not represent optimal configurations for process performance because of poor flow distribution and high-pressure drop. It is now possible to fabricate porous monoliths with tailored morphology and regular channel structure using 3D-printing. In this work, we use magnetic resonance imaging to study flow through a Schwarz Diamond triply periodic minimal surface (TPMS) monolith for Reynolds numbers up to 350. A transition to unsteady flow was observed experimentally for the first time. The channel structure diverts flow such that free shear layers form in the channel centers that contribute to flow instability. These measurements serve to inform the design of novel transport processes with enhanced performance.