Polymer Parts Research Articles

Influence of 3D-printed polymer structures on dynamic splitting and crack propagation behavior of cementitious tailings backfill

Originally developed for polymer materials, 3D printing is an encouraging technique to create versatile geometric shapes and high-precision construction elements from various materials. 3D-printed polymer structures are now employed effectively in various industries, including construction and mining since they significantly improve the ductility properties of cementitious materials like cemented tailings backfill (CTB). Considering the lower tensile strength of CTB (compared to its compressive strength), the study of fill's tensile properties is significant for improving the safety and ensuring the stability of the underground CTB structures. Indeed, this aspect is fairly crucial for the development of green mining which allows sustainable and affordable mining operations. To supremely enhance the tensile strength of CTB, three kinds (OR: ordinary resin) and forms (cross, quarter, and 8 equal parts) of 3D printing polymers (3D-PPL) were employed for this study. A number of experiments including Brazilian splitting tests, digital image correlation (DIC) measurements, and SEM failure/micro-structure analyses were fulfilled for exploring both dynamic splitting and crack propagation behavior of 3D-PPL reinforced CTBs. Results designated that dynamic splitting characteristics of 3D-PPL reinforced CTB samples unveiled a robust strain rate dependence. Besides, the tensile strengths of 3D-PPL reinforced CTB samples are increased under the same conditions and the best results are obtained for cross-shaped reinforced CTB increased by 31.6%. 3D-PPL reinforced CTB samples are characterized with higher strains, and the addition of 3D-PPL effectively inhibits the overall damage process of ordinary CTB and improves the backfill’s strength property. As a result, the results of this study are vital and prominent for realizing the tensile/crack behavior of the backfills placed in underground mined-out openings.

Ni(2,2′:6′,2″-Terpyridine-4′-carboxylate)2 Zwitterions and Carboxylate Polyanions in Mixed-Ligand Uranyl Ion Complexes with a Wide Range of Topologies

The zwitterionic complex formed by NiII and 2,2':6',2″-terpyridine-4'-carboxylate, Ni(tpyc)2, has been used as a coligand with a diverse group of polycarboxylates in uranyl ion complexes synthesized under solvo-hydrothermal conditions, thus giving a series of 14 mixed ligand, heterometallic compounds. Both [(UO2)2(c-1,2-chdc)Ni(tpyc)2(NO3)2]2·4CH3CN (1) and [(UO2)2(tdc)Ni(tpyc)2(NO3)2]2 (2), where c-1,2-chdc2- is cis-1,2-cyclohexanedicarboxylate and tdc2- is 2,5-thiophenedicarboxylate, display discrete U4Ni2 dinickelatetrauranacycles, a motif which is also found as part of a daisychain coordination polymer in [(UO2)4(bdc)3Ni2(tpyc)4(NO3)2]·2CH3CN·2H2O (3), where bdc2- is 1,4-benzenedicarboxylate. Similar U4Ni2 rings associate to form a nanotubular polymer in [(UO2)2(tca)Ni(tpyc)2(NO3)]·2CH3CN·2H2O (4), where tca3- is tricarballylate. [(UO2)2(1,2-pda) (1,2-pdaH)Ni(tpyc)2(NO3)]·CH3CN (5), where 1,2-pda2- is 1,2-phenylenediacetate, crystallizes as a meander-like chain in which each bent section can be seen as an open, semi-U4Ni2 ring. Oxalate (ox2-) gives [(UO2)2(ox)2Ni(tpyc)2] (6), a monoperiodic polymer containing smaller U4Ni rings, while 1,2,3-benzenetricarboxylate (1,2,3-btc3-) and citrate (citH3-) give [Ni(tpycH)(H2O)3][UO2(1,2,3-btc)]2·2H2O (7) and [UO2Ni2(tpyc)4][UO2(citH)]2 (8), two complexes with charge separation, the latter displaying one-periodic + two-periodic semi-interpenetration. [(UO2)2(btcH)Ni(tpyc)2(NO3)] (9) and [(UO2)2(cbtcH)Ni(tpyc)2(NO3)] (10), where btc4- and cbtc4- are 1,2,3,4-butanetetracarboxylate and cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate, respectively, are diperiodic networks with hcb topology, and [(UO2)2(ndc)Ni(tpyc)2(OH)(NO3)] (11), where ndc2- is 2,6-naphthalenedicarboxylate, is a sql network containing dinuclear nodes and involving 100-membered U10Ni4 metallacyclic units. U4Ni2 rings are found in the diperiodic polymer formed in [(UO2)4(t-R-1,2-chdc)4Ni2(tpyc)4] (12), where t-R-1,2-chdc2- is trans-R,R-1,2-cyclohexanedicarboxylate, the heavily puckered sheets being interlocked. 1,3-Phenylenediacetate (1,3-pda2-) gives a very thick diperiodic polymer with KIa topology, [(UO2)4(1,3-pda)4Ni2(tpyc)4]·CH3CN·2H2O (13). A triperiodic framework is formed with nitrilotriacetate (nta3-) in [(UO2)2(nta)2Ni2(tpyc)2] (14), where NiII is found in Ni(tpyc)2 units as well as in Ni(nta)24- moieties which both act as 4-coordinated nodes.

A Set of Novel Procedures for Carbon Fiber Reinforcement on Complex Curved Surfaces Using Multi Axis Additive Manufacturing

There has been considerable research in recent years on the additive manufacturing (AM) of carbon fiber reinforced polymer (CFRP) parts based on the process of fused deposition modeling (FDM). The currently-applied steps within the manufacturing pipeline, such as slicing and path planning, consider only the planar case of filament deposition and mostly make no use of the possibility to place single pre-impregnated (prepreg) filaments. Classical methods such as tape-laying and laminating struggle with highly curved and complex geometries and require the costly production of molds, whereas when using AM, these geometries can be realized more easily and molds can be created using the same process. In this paper, a set of algorithms is presented that aims to resolve these problems. Criteria are formulated which enable the goal oriented development and evaluation of the presented methods and represent metrics for future methods. The developed algorithms enable the use of both continuous and discontinuous fiber patches in a much wider range of applications in designing and manufacturing of CFRPs. This opens up new possibilities in this promising field. The developed metrics and infrastructure further constitute progress in the field of multi-axis non-planar path planning for slicing algorithms in general and the conducted evaluation proves the formal applicability of the developed algorithms.

Self-resistance electric heating of shaped CFRP laminates: temperature distribution optimization and validation

The self-resistance electrical (SRE) heating method to cure the carbon-fiber-reinforced polymer (CFRP) parts possesses the advantages of rapid and volumetric heating, low energy consumption, and low asset investment. But the current SRE heating methods are difficult to uniformly cure the shaped CFRP parts due to the non-uniformly distributed Joule heat power in the parts with a varying cross-sectional area. In this paper, an optimized multi-zone SRE heating method is proposed, in which the uniform heating and curing process of the shaped CFRP part is firstly achieved. By optimizing the orientation of the rectangular zones, the local overheating caused by the voltage gradient and current diffusion between different zones is notably suppressed. Combined with the electro-thermal numerical analysis, the influence of the positional offset of electrodes in two adjacent zones on the temperature uniformity is investigated. Based on this, an automated zone discretization algorithm and the optimal selection method of the zone orientation are established. The proposed method is numerically and experimentally validated with the typical-shaped CFRP parts, and the results are compared with that of the existing SRE heating method. The proposed method realizes that the maximum in-plane temperature difference of shaped CFRP parts is reduced by more than 80%. This method significantly improves the temperature uniformity of shaped CFRP parts during the multi-zone SRE heating process, which provides a potential solution for high-quality and efficient curing of CFRP parts.

3D reactive inkjet printing of bisphenol A-polycarbonate

Additive Manufacturing (AM) techniques have gained extensive attention recently as they are able to directly produce 3D parts utilising a layer-by-layer manner. Inkjet printing is one such technique which can produce micron-scale features but is generally constrained to liquid viscosities of less than 30 mPa·s, therefore available materials are limited. A 3D reactive inkjet printing (3DRIJP) approach to deposit low viscosity monomers and polymerise in-situ to form polymer parts is emerging. In this work, a 3DRIJP approach has been developed to fabricate bisphenol A-polycarbonate (BPA-PC) for the first time by using a low viscosity reactive ink containing monomers, catalyst and solvent. A set of processing parameters were explored and optimised including temperature of droplet formation, substrate temperature and droplet spacing to print films. With a thermal post-curing process, BPA-PC was formed successfully with a molecular weight comparable to those which were manufactured by the conventional melt transesterification process. The thermal properties were evaluated suggesting good thermal resistance characteristics. Finally, a 3D ziggurat structure was printed to demonstrate the capability to fabricate BPA-PC by an AM method, thus broadened the library of AM materials to include engineering grade polymers via 3DRJIP. This approach was innovative in both the BPA-PC material formulation and the 3DRIJP process development from traditional inkjet printing methods, where a single printable formulation of monomers for thermoplastic optical-clear BPA-PC was able to be printed using one printhead to form 3D structures.

Development of Radiator with Thermoplastic Polymer and Insert-Molded Aluminum Alloy Parts for Light-Emitting Diode Headlights

The increasing popularity of electric vehicles has increased the demand for lightweight auto parts. However, the excessive weight of traditional metal heat sinks has remained a concern. Metal has excellent thermal conductivity but low radiation efficiency. Conversely, thermoplastic polymers have excellent heat radiation efficiency but poor thermal conductivity. In this study, we propose a radiator constructed using thermoplastic polymer and insert-molded aluminum alloy parts to maintain the low junction temperature of light-emitting diodes (LEDs); the radiator’s weight is reduced through a combination of aluminum alloy and a thermally conductive polymer designed for automotive headlights. At an LED thermal load of 11.48 W, the measured temperature on the LED pad is 60.8 °C. The weight of the proposed radiator is 23.37% lighter than that of a pure metal radiator. When the lightweight radiator is used in high-power LED headlights, it effectively dissipates heat within a limited space.

Fracture behavior of anisotropic 3D-printed parts: experiments and numerical simulations

The extrusion-based additive manufacturing (AM) is currently the most common there-dimensional (3D) printing for the fabrication of polymer components. In this study, the fracture behavior of 3D-printed polymer parts is investigated. To this aim, polylactic acid material (PLA) was used to print intact and defected specimens based on the fused deposition modeling (FDM) process. The specimens were printed with three different raster directions to determine their effect on the fracture behavior of the parts. Moreover, wood-reinforced PLA material was used to print another group of test coupons. All specimens were subjected to a series of tensile tests and their fracture behaviors are investigated. Based on the comparison of the results, the influence of reinforcement is determined. In addition, parallel to the experiments, a series of finite element analyses were conducted utilizing the anisotropic phase-field fracture model. For an efficient calculation, we treated the whole specimen as a homogenized solid where the anisotropic property of the layered material is considered in the formulation. By calibrating the model based on the experimental measurement, one can predict the anisotropic fracture behavior of the 3D-printed part with high precision. Since applications of 3D-printed composites have been significantly increased, the results of this study can be used for optimization, further numerical analysis, and next development.

Morphology predictions in molded parts: a multiphysics approach

Injection molding of polymer parts at a micro-scale is successfully applied in the fabrication of electronics and biomedical devices where high geometrical accuracy is required. Microinjection molding is more challenging than conventional injection molding due to the necessity to account for the presence of air in the cavity, which slows down the process, and a strong flow field that may induce premature solidification of semi-crystalline polymers. The process modeling and simulation are crucial steps toward predicting all the final parts' properties. For this reason, a multiphysics approach was used to model microinjection molding under different mold cycle temperatures. A well-characterized polypropylene was selected for this purpose. A model for tracking the polymer-air interface during the filling was adopted to account for air's effect in the micro-cavity. Additionally, a model accounting for the effect of crystallization on viscosity was implemented. Models describing the evolution of morphology into fibrils were previously proposed in steady-state conditions. In this work, a model for describing the crystallization into fibrils was proposed and adapted for the first time to the transient conditions of microinjection molding. The aim was the prediction of the final morphology developed during the process. The morphology evolution toward fibrillar structure is consistent with those observed experimentally; in particular, the fibrillar layer thickness decreased with the increase of the mold temperature.

Self-heating evaluation on thermal analysis of polymethyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE)

Thermal analysis has been proven to be an efficiently technique to analyse thermal decomposition reactions of different type of materials. This technique is widely used in different fields. Among them, fire science, where polymeric materials are very common, has a particular issue, being the combustion reactions recurrent on these analyses. Thermal analysis has different particularities depending on the studied material. For instance, polymeric materials could undergo different decomposition reactions that are highly dependent on definition of the thermal analysis boundary conditions. The International Confederation for Thermal Analysis and Calorimetry (ICTAC) (Vyazovkin et al. in Thermochim Acta 590:1–23, 2014) and standards (ISO 11358-1. Plastics—Thermogravimetry (TG) of polymers—Part 1: General principles. ISO. 2014; https://www.iso.org/standard/59710.html. Accessed 31 Jan 2022), (ISO 11357-1. Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles. ISO. 2016; https://www.iso.org/standard/70024.html. Accessed 31 Jan 2022) stablish how to set-up these boundary conditions in the thermogravimetric (TG) and differential scanning calorimetry (DSC) standards. As far as initial amount of sample mass is concern, some discrepancies can be found between the standards. For instance, the standards suggest a sample mass between 10 and 100 mg for TG and between 2 and 40 mg for DSC, whereas the ICTAC recommendations suggests that the sample mass times the heating rate should not exceed 100 mg K·min−1 in thermo-oxidative decomposition analysis, which is equivalent to samples masses lower than 10 mg for heating rates of 10 K·min−1, or lower than 5 mg for heating rates of 20 K·min−1. This discrepancy may lead to obtain different results from the tests. Additionally, according to the thermal and thermo-oxidative decomposition of polymers, the ICTAC remarks the influence on the results of the sample thicknesses, carrier gas and heating rates, but it does not analyse the influence of self-heating as it does for the hazardous materials. This work presents a study of the self-heating influence in the thermal decomposition processes of two widely used polymers as poly methyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE). TG/DSC tests are used to evaluate the thermal decomposition processes. Boundary conditions of the tests definition as sample mass, atmospheres, and heating rate are considered to evaluate its influence on the polymers self-heating effect on the thermal decomposition. It also includes how to check if TG/DSC tests follows the theoretical principles of the thermal analysis, or if the results are affected by the self-heating. In the present study, a series of 32 experimental tests has been performed, analysing 16 boundary conditions. These experimental tests allow evaluating the influence of selected boundary conditions on the mass loss, the heat flux, and the materials decomposition reactions. Additionally, we analyse the effect of the boundary conditions on the temperature of the sample. Results show the impact of each different boundary conditions of the self-heating effect, and its influence in the final thermal decomposition measured and they represent an aid to define the suitable conditions to perform TG/DSC test on PMMA and LLDPE, or similar polymer materials. This is done by the evaluation of the influence of the self-heating in parameters as the sample temperature lags defined in [1], the reactions heat fluxes, and the difference between the sample and the programmed temperature. It is also analysed the influence of the auto-ignition temperature in the thermal analysis. It is remarkable the PMMA auto-ignition temperature effect on the TG/DSC results. Finally, some useful recommendations have been defined.

Infrared Heating for Rapid and Localized Shape Transformations of Additively Manufactured Polymer Parts

Four-dimensional (4D) printing is an advanced application of additive manufacturing which enables additional shape transformations over time in response to external stimuli. For appropriate shape transformation, dedicated materials such as shape memory polymers or 3D printers supporting multi-material printing have been used. Recently, a facile 4D printing method was developed which used a fused filament fabrication type 3D printer and a plain thermoplastic filament. This method used the anisotropic thermal deformation of the FFF-printed part to intentionally impose anisotropy by programming orthogonal printing paths, which resulted in thermoresponsive shape transformation upon a thermal stimulation. While the previous studies used convective heating as the thermal stimulus and thus required a long heating time of more than 10 min, this study uses an infrared (IR) heating to enable rapid thermoresponsive shape transformation. An infrared heating system was developed which included an optical focusing unit, a masking unit and a movable heating stage. To investigate the speed of shape transformation, IR heating was performed on a rectangular strip (60 × 6 × 1.6 mm) and the relevant shape transformation time was compared with the previous convective heating result. The shape transformation proceeded rapidly, and after 70 s formed a fully-closed circular shape, corresponding to the 1/10 reduction compared with the convection type heating (more than 13 min). The IR heating was further applied to 2D-to-3D shape transformations of 2D star-shape and flower-shape specimens. For each specimen, a profiled mask was used to selectively irradiate IR on predefined regions and thus to localize the relevant thermoresponsive shape transformation. The global and local IR irradiations were then compared in terms of heating capability and the variability in shape transformations.

Large-Scale Robot-Based Polymer and Composite Additive Manufacturing: Failure Modes and Thermal Simulation.

Additive manufacturing (AM) of large-scale polymer and composite parts using robotic arms integrated with extruders has received significant attention in recent years. Despite the contributions of great technical progress and material development towards optimizing this manufacturing method, different failure modes observed in the final printed products have hindered its application in producing large engineering structures used in aerospace and automotive industries. We report failure modes in a variety of printed polymer and composite parts, including fuel tanks and car bumpers. Delamination and warpage observed in these parts originate mostly from thermal gradients and residual stresses accumulated during material deposition and cooling. Because printing large structures requires expensive resources, process simulation to recognize the possible failure modes can significantly lower the manufacturing cost. In this regard, accurate prediction of temperature distribution using thermal simulations is the first step. Finite element analysis (FEA) was used for process simulation of large-scale robotic AM. The important steps of the simulation are presented, and the challenges related to the modeling are recognized and discussed in detail. The numerical results showed reasonable agreement with the temperature data measured by an infrared camera. While in small-scale extrusion AM, the cooling time to the glassy state is less than 1 s, in large-scale AM, the cooling time is around two orders of magnitudes longer.

Effects of process conditions on tensile strength and crystallinity of polymeric parts fabricated using ultrasonic vibration‐assisted injection molding

AbstractPolymeric parts have been widely used for various applications and injection molding is one of the most commonly used approaches to fabricate polymeric parts. Both the mechanical properties and microstructures of fabricated parts are severely affected by the process conditions. In this article, polyamide (PA66) was selected as the exemplary polymer to make dogbone‐shaped polymeric specimens. First, the effects of key process parameters including melt temperature, mold temperature, injection pressure, and injection speed on the tensile strength and crystallinity of the specimens were systematically investigated. Then, the effects of external ultrasonic vibration field on the mechanical properties and microstructures were studied using tensile tests, X‐ray diffraction, and polarizing light microscope imaging. After that, the orthogonal experiments were designed to analyze the affecting extent of each process parameter and achieve the optimal combination of the process parameters. Finally, using the optimal process conditions, the polymeric part with the best tensile strength and crystallinity was successfully fabricated. The knowledge from this article can be expanded to the injection molding of polymeric parts from other polymers, unveiling the mechanisms during fabrication and providing guidelines for the selection of optimal process conditions in the future.

Development of Nanocomposite Materials Based on Conductive Polymers for Using in Glucose Biosensor.

Electropolymerized neutral red, thionine, and aniline were used as part of hybrid nanocomposite conductive polymers, to create an amperometric reagent-less biosensor for glucose determination. The structure of the obtained polymers was studied using infrared (IR) spectroscopy and scanning electron microscopy. Electrochemical characteristics were studied by cyclic voltammetry and impedance spectroscopy. It was shown that, from the point of view of both the rate of electron transfer to the electrode, and the rate of interaction with the active center of glucose oxidase (GOx), the most promising is a new nanocomposite based on poly(neutral red) (pNR) and thermally expanded graphite (TEG). The sensor based on the created nanocomposite material is characterized by a sensitivity of 1000 ± 200 nA × dm3/mmol; the lower limit of the determined glucose concentrations is 0.006 mmol/L. The glucose biosensor based on this nanocomposite was characterized by a high correlation (R2 = 0.9828) with the results of determining the glucose content in human blood using the standard method. Statistical analysis did not reveal any deviations of the results obtained using this biosensor and the reference method. Therefore, the developed biosensor can be used as an alternative to the standard analysis method and as a prototype for creating sensitive and accurate glucometers, as well as biosensors to assess other metabolites.

In Vitro Investigation and Characterization of Silicone Matrix IVR Loaded with Levonorgestrel: A Propper Method for Hormon Replacement Therapy

Introduction: Among 3 to 30 percent of women of reproductive age, experience abnormal uterine bleeding (AUB). Vaginal rings are one of the systems of interest for the local delivery of hormones that due to their polymeric structure allow prolonged release of drug. In this study, the design and fabrication of matrix vaginal rings containing levonorgestrel (LNG) were investigated.
 Methods: In this experimental study, at first, two pieces of aluminum mold were designed, then base (A) and cross-linker parts (B) of polymer with LNG were mixed and 48 polymeric rings containing LNG were manufactured by injection molding method. To achieve the desired drug release values in a given time, the effect of temperature, rpm, release environment, different initial loading, cross-linker percentage and a mathematical model to predict release and swelling test were investigated.
 Results: As a result of the experiments, it was revealed that with increasing drug loading, the release rate rises, while increasing the cross-linker percentage reduced the drug release. Finally, the ring A:B=100:9.5 with an initial loading of 0.2 % LNG relative to silicon was selected as an appropriate ring, and release experiments were performed at 37 °C, shaker speed of 80 rpm, and release medium containing 10 % ethanol. Drug release values were measured by spectrophotometer and analyzed by SPSS statistical software version 16.
 Conclusion: Based on the results, it can be deduced that matrix vaginal ring containing LNG is a suitable drug delivery system for prolonged release of LNG for treatment of AUB that depending on the drug initial loading and cross-linker percentage, the required diffusion coefficient, and release rate can be achieved in a certain time.

The Corrosion Control of Temporary Magnesium (AZ31 alloy) Implants Using Electrospinning Polycaprolactone-curcumin Nanofiber Coatings

In this article, polycaprolactone (PCL) polymer nanofibers has been used in the presence of curcumin (Cur) to control the corrosion rate of temporary magnesium (alloy AZ31) implants. PCL, PCL-Cur, and sodium alginate (SA)-polyvinyl alcohol (PVA)/PCL-Cur polymer coating were produced. The mentioned nanofibers were produced using a simple and cost-effective electrospinning technique. We used different techniques to examine the properties of the produced fibers, and it was demonstrated that the hydrophobic produced nanofibers with contact angle of 135.2 degrees have continuous strands and a diameter of 171.57 nm. The presence of Cur inside PCL nanofiber not only did not have any effect on the PCL nanofiber morphology, but also it increased adhesion of the coating, and 74.59% of Cur was released after 7 days. To investigate the effects of different polymeric coatings on the surface of Mg metal in the simulated body fluid (SBF), SEM, weight measurement tests, pH measurement, Polarization, and Electrochemical Impedance Spectroscopy (EIS) has been used. During the study period there was no degradation in any part of the PCL-Cur hydrophobic polymer coating. For this coating, the percentage of weight loss, pH value, corrosion potential (Ecorr) and corrosion rate (CR) were 0.19%, 8.39, -1.388 V and 0.198 mm/y, respectively, where these values indicate the significant decrease of corrosion rate while using PCL-Cur coating.

Effect of carbon nanotubes on mechanical properties of polyamide 12 parts by fused filament fabrication

Polymer parts fabricated by fused filament fabrication (FFF) technique usually exhibit weak and anisotropic mechanical properties, compared with their injection-molded (IM) counterparts. Thus, the evolution of FFF from rapid prototyping into manufacture tool requires three-dimensional enhancement ways for FFF-printed parts. To this end, we develop a series of carbon nanotubes (CNTs)-embedded polyamide 12 (PA12) filaments and investigate the effect of CNTs on the mechanical properties of the FFF-printed PA12 parts. In the direction parallel to the deposited strands, PA12/CNT parts show considerable mechanical reinforcement compared with neat PA12 specimens, including the increase of tensile and impact strength by 18% and 125%, respectively. The marked improvement in impact strength arises from the oriented structures induced by the shear field during FFF process as well as the layer-by-layer microstructure, which provide multiple ways to dissipate impact energy. However, these oriented CNTs and inter-filament voids tend to act as stress concentration points under the tensile stress, thus accounting for a slight increase in tensile strength. In the direction perpendicular to the deposited strands, the FFF-printed PA12/CNT parts also exhibit improved tensile strength, i.e. interfacial weld strength, as CNTs allow the rapid transfer of the thermal energy from the newly-deposited filament to the weld interface and thus provide longer time for molecular interdiffusion. Altogether, the anisotropy in tensile strength of the FFF-printed parts is reduced from 0.36 for neat PA12 parts to 0.28 for PA12/CNT specimens. This work is believed to provide a facile route to overcome mechanical limitations in FFF technique.

Micromechanical characterization of the material response in a PA12-SLS fabricated lattice structure and its correlation with bulk behavior

Selective laser sintering (SLS) of polymers has made possible the introduction of lattice-based cells as building blocks of polymer parts, allowing to obtain optimal specific properties. The actual mechanical performance of an SLS part is strongly dependent on the printing direction and part shape. Nevertheless, macroscopic testing is not usually possible due to size restrictions of the fabricated part, as it happens, for example, in lattice-based materials. In this case, microscopic tests performed directly on the lattice surface become fundamental. In this work, the mechanical behavior of SLS PA12 under a wide range of strain rates from 10−3 to 103 s−1 and different printing directions is characterized using macroscopic tests on bulk samples and compared with nanoindentation performed directly on the lattice material surface. An excellent correlation was found between the rate-dependent mechanical behavior obtained at the two scales, validating microscopic techniques for characterizing the mechanical response of SLS fabricated PA12 parts.

Injection Molding Simulation of Polyoxymethylene Using Crystallization Kinetics Data and Comparison with the Experimental Process

It is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component’s mechanical behavior. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. The simulations are found to be good accordance with the experiments. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. Also, the evolution of these parameters along the flow path is plausible. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts.

Porphyrinic conjugated microporous polymer anode for Li-ion batteries

Porphyrin-based molecules have attracted considerable interests for using as anodes in Li-ion batteries, because of their large π-conjugated aromatic structures, abundant active sites with multi-electron redox activities, and narrow HOMO–LUMO gaps. Herein, a porphyrinic conjugated microporous polymer was prepared through the Sonogashira-Hagihara cross-coupling reaction of Br-functionalized porphyrinic monomer and alkynyl-based monomer. Due to the existence of abundant active sites, rich porosity, narrow bandgap, and inhibition of dissolution in electrolyte, this porphyrinic porous polymer can be used as anode material for Li-ion batteries, and achieves high specific capacity of 1200 mAh g−1 at 1 A g−1, and capacity retention of 242% after 5000 cycles at 3 A g−1. This excellent performance can bear comparison with that of the state-of-the-art organic anode materials. The ex situ X-ray photoelectron spectroscopy tests reveal all of the porphyrin center, benzene ring and alkynyl parts of the porous polymer can be acted as active sites for Li insertion during the cathodic process.

Melt exit flow modelling and experimental validation for fused filament fabrication: From Newtonian to non-Newtonian effects

Fused filament fabrication (FFF) is an important additive manufacturing technique to produce complex polymeric parts in fields such as prototyping, medical devices and sporting equipment. An outstanding challenge is the detailed understanding of the flow behaviour once the filament has been molten, as it determines the structure and stability. Here one can distinguish between the flow downstream the nozzle exit and the shape variations once the flow is deposited on the printing plate. Advanced modelling techniques are recommended but currently one typically assumes Newtonian flow, despite that conventional large-scale extrusion studies have highlighted the relevance of the viscoelastic nature of thermoplastic polymers, specifically upon the die exit. In the present contribution, polypropylene (PP) FFF flow is simulated at a reference FFF temperature of 473 K with ANSYS Polyflow by inputting Phan-Thien-Tanner (PTT) viscoelastic parameters that have been previously validated, based on both rheological and conventional extrusion slit die swell measurements. The suitability of these PTT parameters is further confirmed by comparing simulated and experimental FFF swelling data, with a coefficient of determination of 0.916. Benefiting from this validation, the flow model is reliably used to highlight that both the FFF processing parameters, e.g. temperature and printing speed, and machine parameters, e.g. nozzle length and diameter, have a large impact on the viscoelastic exit flow. A sensitivity analysis on the viscoelastic parameters additionally highlights the relevance of dedicated rheological data to understand FFF swelling and to accurately simulate the subsequent deposition stage.