Polymer Manufacturing Research Articles

Experimental Analysis and Optimisation of a Novel Laser-Sintering Process for Additive Manufacturing of Continuous Carbon Fibre-Reinforced Polymer Parts

Additive manufacturing of continuous carbon fibre-reinforced polymer (CCFRP) parts enables the production of high-strength parts for aerospace, engineering and other industries. Continuous fibres allow for parts to be reinforced along the load path, multiplying their mechanical properties. However, current additive manufacturing processes for producing CCFRP parts do not optimally meet the requirements of the matrix. With resin- and extrusion-based processes, the time-consuming and costly post-processing required to remove support structures severely limits design freedom, and producing small batches requires increased effort. In contrast, laser sintering has proven to be a promising alternative in an industrial environment, allowing the production of robust parts without support structures in a time-efficient and economical manner for single and small-batch production. Based on a novel laser-sintering machine with the automated integration of continuous fibres, a combination of the advantages of the laser-sintering process and the advantages of continuous fibres is to be achieved. This paper describes an experimental analysis and optimisation of this laser-sintering machine using design of experiments. The processing time for fibre integration could be reduced by a factor of three compared to the initial state.

Direct milling: Efficient, facile, and green method for processing fibrillated cellulose/polymeric nanocomposites with boosted thermomechanical and rheological performance

Bringing biobased nanomaterials into polymer manufacturing is essential to enhance polymers' properties and address the challenges posed by plastic waste. Using polymers such as polyamide 6 (PA6) in advanced industries, e.g., automotive sector, has been impeded as a direct consequence of their inability to meet the required mechanical properties. Herein, we utilize bio-based cellulose nanofibers (CNFs) to enhance the properties of PA6 by green processing, with no footprint on the environment. We address the issue of the dispersion of the nanofillers in polymeric matrices and demonstrate direct milling (cryo-milling and planetary ball milling) to facilitate a thorough integration of the components. Nanocomposites incorporating 1.0 wt% CNF, processed by pre-milling followed by compression molding, are shown to possess a storage modulus of 3.8 ± 0.2 GPa, Young's modulus of 2.9 ± 0.2 GPa, and ultimate tensile strength of 63 ± 3 MPa (all measured at room temperature). To show the superiority of direct milling in achieving these properties, other frequent approaches used to disperse CNF in polymers, such as solvent casting and hand mixing, are meticulously investigated and compared for the performance of their resulting specimens. The ball-milling method is demonstrated to provide PA6-CNF nanocomposites with excellent performance, better than solvent casting, with no associated environmental concerns.

Homotopy analysis of mixed convection flow of a magnetized viscoelastic nanofluid from a stretching surface in non-Darcy porous media with revised Fourier and Fickian approaches

This article addresses theoretically the mixed convection hydromagnetic flow of electrically conducting viscoelastic nanofluid from a vertical permeable stretching sheet in a non-Darcy porous medium with Cattaneo–Christov double-diffusion model to evaluate the heat transfer phenomena in steady boundary layer flow on a stretchable surface. In this regard, thermal and solutal hyperbolic wave relaxation effects are included for non-Fourier and non-Fickian models. Heat absorption is also included in the analysis. The Buongiorno two-component nanoscale model is adopted for simulating Brownian motion and thermophoretic body force effects. A non-Darcy drag force model is employed for the porous medium and the Reiner–Rivlin second-grade model for non-Newtonian characteristics. Via appropriate dimensionless similarity variables, the nonlinear dimensional partial differential conservation equations for momentum, energy and concentration with associated boundary conditions are rendered into a nonlinear dimensionless ordinary differential boundary value problem. The homotopy analysis method (HAM) is utilized to solve the boundary value problem and the impact of emerging parameters including thermal relaxation parameters, non-Newtonian material parameter, Darcy permeability parameter, porous inertial parameter and Hartmann magnetic number on the momentum, heat and mass transfer characteristics are visualized graphically and in tables. A 30th-order approximation for HAM is shown to produce sufficient accuracy for the velocity and temperature fields and a 40th-order estimates is adequate for the concentration field. It is observed that increasing the magnitude of thermal and solutal relaxation parameters has the opposite effect on the thermal and concentration distributions. The novelty of the work is the simultaneous inclusion of multiple effects (non-Fourier and non-Fickian thermal relaxation hyperbolic wave models, non-Darcy drag effects and heat generation/absorption) which are relevant to rheological nanomaterials processing and also the deployment of homotopy analysis as an alternative to conventional numerical methods such as finite differences, finite elements and MATLAB solvers. The study is relevant to the manufacture of electro-conductive polymers (ECPs) and smart (functional) magnetic nano-liquids.

Dual-Band Circular-Polarized Microstrip Antenna for Ultrawideband Positioning in Smartphones With Flexible Liquid Crystal Polymer Process

This article proposes a dual-band circular-polarized (DBCP) microstrip antenna using flexible liquid crystal polymer (LCP) manufacturing process for ON-smartphone ultrawideband (UWB) positioning application. To achieve dual-band circular polarization in a low profile, the proposed antenna is designed with a cross-slot-loaded patch with four L-shaped feeding probes and a sequential phase feeding network. A circle of capacitive via fence is loaded surrounding the patch for area miniaturization, which is adaptive for the limited space of flexible printed circuit (FPC) in smartphones. Based on the UWB positioning protocol, a three-element antenna array is constructed in a low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.015\lambda _{0}$ </tex-math></inline-formula> with required isolation of 17 dB. Experimental results show the overlapped bandwidth of the efficiency and the axial ratio (AR) covering the demand bands of 6.30–6.80 and 7.75–8.10 GHz. With the properties of dual wideband operation, circular polarization, and ultralow profile, the proposed antenna exhibits feasible solutions for the UWB positioning application in space-limited smartphones.

Mechanical and optical performance evaluations of embedded polyimide and PEEK coated distributed optical sensors in glass fibre reinforced composites with vinyl ester resin systems

Embedded optical fibre sensors (OFSs) offer the potential to monitor the internal strains at various stages during the manufacturing and service life of fibre-reinforced polymer (FRP) composite structures. Various aspects associated with the embedment of OFSs, such as integration, material compatibility, and sensing performance of the embedded sensor needs to be investigated to develop reliable OFSs based internal sensing platform for composite structures. In this study, Polyimide (PI) and Polyether ether ketone (PEEK) coated optical fibres (OF) were embedded into glass fibre-reinforced polymer (GFRP) composites to evaluate four important aspects associated with the embedment of OFs, which include; i). Structural integrity of the OFs against chemical reactions from vinyl ester resin and its additives through immersion testing, ii). Methods of integrating the OFs into layered glass fibres for the vacuum resin infusion manufacturing process, iii). Sensing performance of the embedded OFs during manufacturing and structural testing (tensile and compressive), and iv). Internal structural integrity of the embedded OFs and the host composite structure using X-Ray micro-computerised tomography technique (μ-CT). The results from the immersion testing and manufacturing process monitoring showed that both PEEK and PI coated OFs can resist the chemical and mechanical stresses caused by resin polymerisation during curing process. The subsequent mechanical testing showed a similar sensing performance by the PI and PEEK coated OFs. Under tensile loads, the OFs monitored the tensile strain distribution up to 7,000 με and compressive strain distribution up to −1,200 με under flexural loading without compromising their optical performance. Finally, the μ-CT scanning results had shown a minimal structural deterioration of the embedded OFs and host composite structure. The outcomes from this detailed experimental investigation on the embedment of OFS in GFRP structures provided useful information towards the integration and performance of optical sensors in composite structures.

Thermal Intra-Layer Interaction of Discretized Fractal Exposure Strategies in Non-Isothermal Powder Bed Fusion of Polypropylene

Additive manufacturing of material systems sensitive to heat degradation represents an essential prerequisite for the integration of novel functionalized material systems in medical applications, such as the hybrid processing of high-performance thermoplastics and gelling polymers. For enabling an inherent process stability under non-isothermal conditions at reduced ambient temperatures in laser-based additive manufacturing, maintaining a homogeneous layer formation is of vital significance. To minimize crystallization-induced deflections of formed layers while avoiding support structures, the temporal and spatial discretization of the melting process is combined with the subsequent quenching of the polymer melt due to thermal conduction. Based on implementing superposed, phase-shifted fractal curves as the underlying exposure structure, the locally limited temporal and spatial discretization of the exposure process promotes a mesoscale compensation of crystallization shrinkage and thermal distortion, enabling the essential homogeneous layer formation. For improving the understanding of local parameter-dependent thermal intra-layer interactions under non-isothermal processing conditions, geometric boundary conditions of distinct exposure vectors and the underlying laser power are varied. Applying polypropylene as a model material, a significant influence of the spatial distance of fractal exposure structures on the thermal superposition of distinct exposure vectors can be derived, implicitly influencing temporal and temperature-dependent characteristics of the material crystallization and the emerging thermal material exposure. Furthermore, the formation of sub-focus structures can be observed, contributing to the spatial discretization of the layer formation, representing a decisive factor that influences the structure formation and mesoscopic part properties in non-isothermal powder bed fusion of polymers. Consequently, the presented approach represents a foundation for the support-free, accelerated non-isothermal additive manufacturing of both polymers and metals, demonstrating a novel methodology for the mesoscale compensation of thermal shrinkage.

Material Extrusion Additive Manufacturing with Polyethylene Vitrimers.

Polyethylene (PE) is one of the most widely used polymers in conventional polymer manufacturing processes. However, it remains a challenge to use PE in extrusion-based additive manufacturing (AM). Some of the challenges that this material presents include low self-adhesion and shrinkage during the printing process. These two issues lead to higher mechanical anisotropy when compared to other materials, along with poor dimensional accuracy and warpage. Vitrimers are a new class of polymers that have a dynamic crosslinked network, allowing the material to be healed and reprocessed. Prior studies on polyolefin vitrimers suggest that the crosslinks reduce the degree of crystallinity and increase the dimensional stability at elevated temperatures. In this study, high-density polyethylene (HDPE) and HDPE vitrimers (HDPE-V) were successfully processed using a screw-assisted 3D printer. It was demonstrated that HDPE-V were able to reduce shrinkage during the printing process. This shows that 3D printing with HDPE-V will provide better dimensional stability when compared to regular HDPE. Furthermore, after an annealing process, 3D-printed HDPE-V samples showed a decrease in mechanical anisotropy. This annealing process was only possible in HDPE-V due to their superior dimensional stability at elevated temperatures, with minimal deformation above melting temperature.

Combined impacts of thermoelectric and radiation on hydromagnetic nanofluid flow over a nonlinear stretching sheet

Controlling heat transmission in the polymer manufacturing business has always depended on the thermal radiation component and the development of a variety of novel technical processes, such as solar energy technology and combustion of fossil fuels occur at high temperatures. Therefore, it would appear significant to study heat radiation and because of that this research delivers a numerical evaluation of the cumulative influence of Hall current and radiation of heat on MHD fluid flow across stretchable surface which is non-linear. Nevertheless, it has been considered that the fluid conveys tiny (1-100 nm) particles. The model equations have been made non-dimensional using the boundary layer approach and non-dimensional components. Then, using the finite difference approach, the acquired non-dimensional equations are numerically constructed. The solution of the fluid flow is discussed to investigate the primary plus secondary velocity, temperature but also concentration ordination. Skin friction, coefficient of transmission of mass, and coefficient of transmission of heat are some of the significant boundary layer phenomena that are investigated. Streamlines, as well as isothermal lines, have also been employed to display an upgraded representation of the fluid flow. A closer examination reveals that the cumulative effects of the Hall current and radiation parameter have a larger influence on primary and secondary velocity than the individual impacts of the Hall current and radiation factor. It is also revealed that when both radiation and Hall current influences are included, the heat transfer capabilities of the fluid are considerably higher than when only one of them is examined.

Process-Structure-Property Interdependencies in Non-Isothermal Powder Bed Fusion of Polyamide 12

Non-isothermal laser-based powder bed fusion (LPBF) of polymers suggests the potential for significantly extending the range of materials applicable for powder-based additive manufacturing of polymers, relying on the absence of a material-specific processing window. To allow for the support-free manufacturing of polymers at a build chamber temperature of 25 °C, applied processing strategies comprise the combination of fractal exposure strategies and locally quasi-simultaneous exposure of distinct segments of a particular cross section for minimizing crystallization-induced part deflection. Based on the parameter-dependent control of emerging cooling rates, formed part morphologies and resulting mechanical properties can be modified. Thermographic in situ measurements allow for correlating thermal processing conditions and crystallization kinetics with component-specific mechanical, morphological, and microstructural properties, assessed ex situ. Part morphologies formed at crystallization temperatures below 70 °C, induced by reduced laser exposure times, are characterized by a nano-spherulitic structure, exhibiting an enhanced elongation at break. An ambient temperature of 25 °C is associated with the predominant formation of a combined (α + γ)-phase, induced by the rapid cooling and subsequent laser-induced tempering of distinct layers, yielding a periodic microstructural evolution. The presented results demonstrate a novel approach for obtaining nano-spherulitic morphologies, enabling the exposure-based targeted adaption of morphological properties. Furthermore, the thermographic inline assessment of crystallization kinetics allows for the enhanced understanding of process-morphology interdependencies in laser-based manufacturing processes of semi-crystalline polymers.

Coupling ATR-FTIR spectroscopy with multivariate analysis for polymers manufacturing and control of polymers’ molecular weight

Acrylate-based polymers are commonly used in the chemical industry. Consistent manufacturing of these polymers with the help of Process Analytical Technology (PAT) is very desirable. The capability of monitoring polymers’ molecular weight in real-time reduces operation time and eliminates the frequent samplings needed for quality control. Herein, molecular weight (Mw) of glycidyl methacrylate-co-methyl methacrylate (GMA-co-MMA) copolymer was monitored in real-time using mid-infrared ATR-FTIR spectroscopy. The Principal Component Analysis (PCA) and Partial Least Square (PLS) models were then utilized to examine, improve the latent space, and select high-quality spectra. We show that acquiring highly correlated spectra enhances the robustness of the regression model. The developed models demonstrate a satisfied R2 correlation up to ∼87%. This study suggests the potential of robust data-driven techniques for the development of predictive Mw analytics tools.

Finite element mechanism and quadratic regression of magnetized mixed convective Burgers' nanofluid flow with applying entropy generation along the riga surface

BackgroundThe thermal control subject of heat transference encompasses the generation, use, conversion, and transportation of thermal energy. Heat transference is critical in engineering and industrial industries such as food processing, food additive manufacturing, electronic cooling, microturbines, and so on. Because of the intriguing possibilities in sectors such as polymer manufacture, paper production, crystal glass manufacturing, and so on, academics all over the globe have attempted to investigate the influence of heat transmission on fluid past an expanding surface. PurposeWe constructed a symmetric system relating extended Burgers' nanofluid (BNF) with Fourier's and Fick's laws in a symmetric stretchy slip as part of our investigation. The Cattaneo-Christov mass and heat diffusions principle has been considered. The Buongiorno occurrence is also utilized for the symmetric flowing of nanofluids (NFs) in the generalized Burger's fluid, according to the Cattaneo-Christov connection (CCC). FormulationFor the numerical solution, using the similarity transformations, the control system that regulates partial differential equations (PDE) was turned into ordinary differential equations (ODE). Using the COMSOL program, the Galerkin finite element method (G-FEM) is utilized to generate mathematical results for non-linear equations. FindingWe observed greater temperature and concentration for Fourier-Fick's conditions as compared to revised Fourier-Fick's scenarios. The heat field is raised to produce the calculations of the current Biot quantity and generalized BNF factor. To receive results in the form of figures and tables, the parameter values must be between 0.1 ≤ β1 ≤ 0.5, 0.2 ≤ β2 ≤ 0.4, 0.2 ≤ β3 ≤ 0.4, 0.2 ≤ β4 ≤ 0.4, 0.1 ≤ M ≤ 1.2, 0.1 ≤ Nr ≤ 0.9, 0.1 ≤ λ ≤ 0.5, 0.2 ≤ K ≤ 1.6, 0.1 ≤ Rd ≤ 1, 0.1 ≤ λT ≤ 0.3, 0.1 ≤ δ1 ≤ 0.3, 0.1 ≤ E ≤ 1 and 0.1 ≤ Le ≤ 0.9. NoveltyThe G-FEM investigation of Burgers' nanofluid (BNF) in the presence of heat source, thermal radiative heat flux and Cattaneo-Christov mass and heat flux has not been investigated yet in the available literature.

Additively manufactured Bi-functionalized bioceramics for reconstruction of bone tumor defects.

Bone tissue exhibits critical factors for metastatic cancer cells and represents an extremely pleasant spot for further growth of tumors. The number of metastatic bone lesions and primary tumors that arise directly from cells comprised in the bone milieu is constantly increasing. Bioceramics have recently received significant attention in bone tissue engineering and local drug delivery applications. Additionally, additive manufacturing of bioceramics offers unprecedented advantages including the possibilities to fill irregular voids after the resection and fabricate patient-specific implants. Herein, we investigated the recent advances in additively manufactured bioceramics and ceramic-based composites that were used in the local bone tumor treatment and reconstruction of bone tumor defects. Furthermore, it has been extensively explained how to bi-functionalize ceramics-based biomaterials and what current limitations impede their clinical application. We have also discussed the importance of further development into ceramic-based biomaterials and molecular biology of bone tumors to: (1) discover new potential therapeutic targets to enhance conventional therapies, (2) local delivering of bio-molecular agents in a customized and "smart" way, and (3) accomplish a complete elimination of tumor cells in order to prevent tumor recurrence formation. We emphasized that by developing the research focus on the introduction of novel 3D-printed bioceramics with unique properties such as stimuli responsiveness, it will be possible to fabricate smart bioceramics that promote bone regeneration while minimizing the side-effects and effectively eradicate bone tumors while promoting bone regeneration. In fact, by combining all these therapeutic strategies and additive manufacturing, it is likely to provide personalized tumor-targeting therapies for cancer patients in the foreseeable future. STATEMENT OF SIGNIFICANCE: To increase the survival rates of cancer patients, different strategies such as surgery, reconstruction, chemotherapy, radiotherapy, etc have proven to be essential. Nonetheless, these therapeutic protocols have reached a plateau in their effectiveness due to limitations including drug resistance, tumor recurrence after surgery, toxic side-effects, and impaired bone regeneration following tumor resection. Hence, novel approaches to specifically and locally attack cancer cells, while also regenerating the damaged bony tissue, have being developed in the past years. This review sheds light to the novel approaches that enhance local bone tumor therapy and reconstruction procedures by combining additive manufacturing of ceramic biomaterials and other polymers, bioactive molecules, nanoparticles to affect bone tumor functions, metabolism, and microenvironment.

Effects of Chemical Reaction and Joule Heating on MHD Generalized Couette Flow between Two Parallel Vertical Porous Plates with Induced Magnetic Field and Newtonian Heating/Cooling

In this article, the effects of chemical reaction and Joule heating on MHD generalized Couette flow between two vertical porous plates with induced magnetic field and Newtonian heating/cooling have been investigated. The mathematical model used for the MHD generalized Couette flow takes into account the effect of viscous dissipation. The system of nonlinear partial differential equations governing the flow was solved numerically using the finite difference method. The resulting numerical schemes are simulated in MATLAB to obtain the profiles of the flow variables such as velocity, induced magnetic field, temperature, and concentration profiles graphically. Also, the effects of the flow parameters on the skin‐friction coefficient, Nusselt number, and Sherwood number are obtained and discussed numerically through tabular forms. The findings show that an increase in the chemical reaction parameter leads to a decrease in the concentration profiles. Also, increase in the Joule heating parameter and heat generation parameter leads to an increase in the temperature profiles. Induced magnetic field profiles increase with an increase in Reynold’s number. The findings of this study are important due to its application in developing a variety of chemical technologies, including polymer manufacturing, MHD pumps, food processing, chemical catalytic reactors, astronomy, MHD flow meters, and lubrication.

Effect of print direction on mechanical properties of 3D printed polymer-derived ceramics and their precursors

The use of engineering ceramics with intricate geometries is limited by manufacturing processes and lack ease of machinability of ceramics. Additive manufacturing of pre-ceramic polymers which are pyrolyzed into ceramics after 3D printing has recently been used to circumvent traditional manufacturing processes creating ceramics with complex geometries, however, mechanical characterization is limited. Polymer-derived ceramics and their green-body precursors are printed using digital light projection 3D printing in two orientations (0°- and 90°- to the build plate) and mechanically characterized. The results show that mechanical anisotropy exists both in the green-body polymer samples where the 0°-samples are stronger and stiffer than their 90°-counterparts and the final ceramics, where the stronger samples are fabricated at 90° despite isotropic hardness measurements. Through the manufacturing process, it was noted that samples undergoing pyrolysis built in the 90°-orientation have a pyrolysis survival rate of 94% whereas the 0°-samples showed a survival rate of 54%. The results suggest that the build-direction of 3D printed green-bodies plays a role in both material manufacturing and mechanical integrity of the final ceramic materials.

Variability in the inorganic composition of colored acrylonitrile-butadiene-styrene and polylactic acid filaments used in 3D printing.

Fused filament fabrication is a 3D printing technique that has gained widespread use from homes to schools to workplaces. Thermoplastic filaments, such as acrylonitrile-butadiene-styrene (ABS) and polylactic acid (PLA), are extruded at temperatures near their respective glass transition temperature or melting point, respectively. Little has been reported on the inorganic elemental composition and concentrations present in these materials or the methods available for extracting that information. Because inorganic constituents may be included in the aerosolized particulates emitted during the printing process, identifying elements that could be present and at what specific concentrations is critical. The objective of the current research is to determine the range of metals present in thermoplastic filaments along with their relative abundance and chemical speciation as a function of polymer type, manufacturer, and color. A variety of filaments from select manufacturers were digested using a range of techniques to determine the optimal conditions for metal extraction from ABS and PLA polymers. The extraction potential for each method was quantified using by ICP-MS analysis. When possible, further characterization of the chemical composition of the filaments was investigated using X-ray Absorption spectroscopy to determine chemical speciation of the metal. Optimal digestion conditions were established using a high temperature, high pressure microwave-assisted acid digestion method to produce the most complete and repeatable extraction results. The composition and abundance of metals in the filaments varied greatly as a function of polymer, manufacturer, and color. Potential elements of concern present in the filaments at elevated concentration included that could pose a respiratory risk included Si, Al, Ti, Cu, Zn, and Sn. XAS analysis revealed a mixture of metal oxides, mineral, and organometallic compounds were present in the filaments that were being used to increase opaqueness impart color (dyes), polymeric catalysts, and flame retardants. This work shows that a variety of metals are present in the starting materials used for 3D printing and depending on their partitioning into 3D printed products and byproducts as well as the exposure route, may pose a health risk which merits further investigation.

3D printable composites of modified cellulose fibers and conductive polymers and their use in wearable electronics

There are many bioelectronic applications where the additive manufacturing of conductive polymers may be of use. This method is cheap, versatile and allows fine control over the design of wearable electronic devices. Nanocellulose has been widely used as a rheology modifier in bio-based inks that are used to print electrical components and devices. However, the preparation of nanocellulose is energy and time consuming. In this work an easy-to-prepare, 3D-printable, conductive bio-ink; based on modified cellulose fibers and poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), is presented. The ink shows excellent printability, the printed samples are wet stable and show excellent electrical and electrochemical performance. The printed structures have a conductivity of 30 S/cm, high tensile strains (>40%), and specific capacitances of 211 F/g; even though the PEDOT:PSS only accounts for 40 wt% of the total ink composition. Scanning electron microscopy (SEM), wide-angle X-ray scattering (WAXS), and Raman spectroscopy data show that the modified cellulose fibers induce conformational changes and phase separation in PEDOT:PSS. It is also demonstrated that wearable supercapacitors and biopotential-monitoring devices can be prepared using this ink.

Material extrusion additive manufacturing of low-viscosity metallic feedstocks: Performances of the plunger-based approach

In recent years, increasing attention has been directed at the material extrusion additive manufacturing of highly-filled polymers (MEAM-HP). This is because conventional polymer 3D printers, which are low cost and readily available, can easily be adapted for use with metal powder-filled polymer filaments. However, fabricating the latter is time-consuming and their formulations differ from regular metal injection molding (MIM) feedstocks by lower powder solids loadings and higher elastomer contents, thus requiring significant efforts to optimize their debinding and sintering conditions. Favorably, other types of MEAM-HP printers, such as screw- and piston-based ones, can process available MIM feedstocks and apply the debinding and sintering procedures that have already been optimized. In this study, a novel ram extruder-based printer with a 100 mm-diameter ― 250 mm-high build volume was developed to print a low-viscosity MIM feedstock composed of 65% of 17-4PH powder, 23% of paraffin wax, 10% of ethylene vinyl acetate and 2% of stearic acid (all in vol. %). The printer calibration and the process optimization procedures are detailed herein. The kinematic accuracy of the build platform revealed a maximum deviation of 29 and 92 µm in the vertical (Z) and horizontal (XY) directions, respectively. Prior to printing, a relative feedstock density of 99.8% was obtained using a one-minute degassing procedure. During printing, a 52.5°C build platform temperature was used and an 85°C extrusion temperature conferred to the feedstock a viscosity of 142 Pa·s at a shear strain rate of 180 s -1 (Ø0.4 mm E3D V6 nozzle, 1 mm 3 /s flow rate). Indirect measurements of the extrusion pressure using a load cell positioned under the piston allowed to maximize the accuracy of start/stop extrusion sequences by adjusting the retraction volumes. An overlap printing path technique was introduced to eliminate typical MEAM voids between printed lines. Finally, six parts exhibiting complex geometries were printed to validate the capacity of the printer to produce functional components using conventional low-viscosity MIM feedstocks.

Phosphorous‐nitrogen‐boron decorated graphene hybrid for flame retardancy enhancement of epoxy resin

AbstractSoaring development in widely applicable materials raises an urgent demand to develop high‐performance epoxy resin (EP) materials combining superior flame retardancy, smoke suppression and mechanical properties. Phosphorus, boron and nitrogen‐containing flame retardants are high potential environmental‐friendly flame‐retardant additives in polymer manufacturing owing to their low toxicity, molecular diversity, and efficient flame resistance. In this paper, a novel additive flame retardant of RGO‐HCCP@MPB compound was fabricated which involved the functionalization of reduced graphene oxide (RGO) with hexachlorocyclotriphosphazene (HCCP), and the simple complexing RGO‐HCCP with melamine phosphate borate (MPB). The prepared RGO‐HCCP@MPB was then directly mixed with EP matrix to evaluate its flame resistance. It found that the addition of RGO‐HCCP@MPB obviously inhibited the heat release and smoke emission behaviors of EP matrix during combustion. With 5 wt% addition of RGO‐HCCP@MPB in EP, the LOI value of EP/RGO‐HCCP@MPB reached up to 28.4%, the peak heat release rate (PHRR) and the total heat release (THR) decreased by 61.1% and 30.5% compared to neat EP, respectively. Furthermore, the flexural strength and flexural modulus of the EP/RGO‐HCCP@MPB were also promoted compared with that of the pure EP. The flame‐retardant mechanism shows that elements of boron (B), nitrogen (N) and phosphorus (P) in RGO‐HCCP@MPB compound play a synergistic role in the enhancement of the flame retardancy of EP in a combustion.

Kinetics and Thermodynamics of the Pyrolysis of Waste Polystyrene over Natural Clay

Due to the massive increase in polymer manufacture, there has been a remarkable increase in plastic waste. With fewer landfills being used to dump plastic waste each year, it is becoming increasingly important to use effective recycling methods for plastic waste decomposition. In the present work, waste polystyrene was degraded in the presence of natural clay (K&lt;sub&gt;0.02&lt;/sub&gt;, Ca&lt;sub&gt;0.15&lt;/sub&gt; [Mg&lt;sub&gt;0.25&lt;/sub&gt;, Al&lt;sub&gt;0.69&lt;/sub&gt;, Fe&lt;sub&gt;0.06&lt;/sub&gt;], [Si&lt;sub&gt;2.0&lt;/sub&gt;, Al&lt;sub&gt;0.6&lt;/sub&gt;] O&lt;sub&gt;6.8&lt;/sub&gt; (O&lt;sub&gt;10&lt;/sub&gt;) nH&lt;sub&gt;2&lt;/sub&gt;O). The waste polymer was pyrolyzed at different heating rates i.e., 5, 10, 15 and 20°C min&lt;sup&gt;-1&lt;/sup&gt; in an inert environment using nitrogen within the temperature range of 40 to 600°C. Thermogravimetric data were interpreted using various models, including fitting kinetic methods i.e., Coats-Redfern and model-free methods i.e., Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman method. The activation energy determined by Coats-Redfern, Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman models were in the range of 83.22-150.37, 74.52-133.71, 73.16-131.23, and 78.40-140.67 kJmol&lt;sup&gt;-1&lt;/sup&gt;, respectively. Among them, the lowest activation energy for polystyrene degradation was observed using Kissinger-Akahira-Sunose method. The calculated kinetic parameters would be useful in determining the reaction mechanism of the solid-state reactions in a real system.

Chemical and thermodynamic analyses of the surface waxes of ‘Korla’ pears: Relationships between the surface waxes and skin greasiness

The surface waxes of ‘Korla’ pears can become greasy during storage when overripened, and the wax changes are considered to be responsible for this disorder, but the relationship between the wax changes and skin greasiness of ‘Korla’ pears remains unclear. We profiled the chemical and thermal changes in the surface waxes of ‘Korla’ pears as skin greasiness increased when stored at 25 °C. We also recorded the effects of treatment with 1-methylcyclopropene (1-MCP), which is known to interfere with this aetiology. The results show that as skin greasiness increased, there were steady increases in the more fluid wax compounds, mainly of the n-9 olefins (C17, C19, C21, C23 and C25). These fluid olefins were detected only in greasy fruit, and their amounts were highly correlated with greasiness. Separation experiments further confirmed that the accumulation of fluid olefins increased the fluidity of the solid alkanes of the ‘Korla’ pear waxes. The thermodynamic analyses show that melting temperatures and enthalpy both decreased with increases in wax fluidity. Moreover, the chemical and thermal changes in these waxes, along with greasiness can be suppressed by 1-MCP. These results indicate that the accumulation of fluid n-9 olefins raises wax fluidity, while the thermal analyses indicate that this effect could be similar in mechanism to those of the plasticizers used in the manufacture of synthetic polymers.