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To optimize the thermal conductivity of high-density polyethylene, 15 hybrid filler composites containing either aluminum oxide, graphite, expanded graphite, carbon nanotubes or a combination of the former, have been studied using an extrusion-compression processing tandem. The experimental density of the cube-shaped specimens is substantially lower than the theoretical density calculated by the linear mixing rule, mainly for the composites with high filler contents. The morphology of the composites, as studied by scanning electron microscopy (SEM), highlighted a good dispersion quality and random orientation of the fillers in the test specimens but also revealed air inclusions in the composites, explaining the density results. It is shown that the addition of filler(s) increases both the melt viscosity (up to ca. 270%) and the thermal conductivity (up to ca. 1000%). Hence, a very strong increase of TC can be practically hampered by a too high viscosity to enable processing. Supported by ANOVA analysis, the application of response surface methodology (RSM), assuming a perfect compression, indicates that all fillers have a significant effect on the thermal conductivity and synergistic effects can be achieved. The regression model obtained can adequately predict the thermal conductivity of composites of various compositions, as already confirmed based on three validation experiments in the present work.

The combination of recycled fiber reinforcement with recycled polymer as a feedstock material for extrusion-based additive manufacturing creates an opportunity for a more sustainable material use. In this study, recycled short carbon fibers were combined with recycled poly(ethylene terephthalate) (PET) to obtain carbon fiber-reinforced PET filaments via melt extrusion. The carbon fiber content of the extruded filaments ranged from 0.4 to 40.7 wt%. The molar mass and the degree of crystallinity after processing were determined to evaluate the influence of the extrusion process on the physico-chemical and mechanical properties of the reinforced PET filaments. Furthermore, pressure-volume-temperature measurements were carried out to investigate the influence of the carbon fibers on the shrinkage of the semi-crystalline PET. Samples were printed and their superior mechanical properties, including a 390% increase in tensile modulus, were confirmed via tensile testing. Analysis via X-ray micro-computed tomography indicated that the fiber length reduced with increasing fiber content. The high degree of fiber alignment that was observed in the extruded filaments, was slightly reduced after deposition. Scanning electron microscopy data showed that fiber pull-out was the governing failure mechanism, indicating a weak interface between the carbon fibers and the matrix. The results show the potential of extrusion-based additive manufacturing to valorize recycled PET and recycled carbon fibers.

An important polymer processing technique is additive manufacturing (AM), which enables shape-free design of complex final parts with limited waste during the development change, at least if the impact of molecular degradation reactions is minimized. In the present work, polystyrene (PS) and acrylonitrile butadiene styrene (ABS) polymer have been processed via: (i) fused filament fabrication (FFF), separately accounting for the prior single screw extrusion (SSE) filament production; and (ii) pellet-based additive manufacturing (PBAM), which are two important AM techniques. The influence of printing temperature, layer thickness, printing velocity, and printing technique on the degradation of both polymeric materials is studied by means of thermogravimetric analysis (TGA), size exclusion chromatography (SEC), small amplitude oscillatory shearing tests (SAOS), Fourier-transform infrared spectroscopy (FTIR), and yellowness index (YI) measurements. For ABS, SSE-FF leads to more fission (higher mechanical loading) whereas PBAM results in more cross-linking (more thermal loading). For PS, fission is always dominant and this more evident under FFF conditions. ABS also exhibits yellowing upon processing, indicating thermo-oxidative degradation although below the FTIR sensitivity limit. The selected PBAM conditions with PS are already delivering printed specimens with good mechanical properties and lower degradation. For ABS, a further PBAM optimization is still desired compared to the FFF countercase, taking into account layer-by-layer adhesion.

To reduce the lead time and costs for developing short run production injection moulding tools the potential of additive manufactured mould inserts is investigated. These hybrid moulds are compared...

To extend the diversity of commercial materials relevant for fused filament fabrication (FFF), the relation of nozzle temperature and layer thickness with respect to final product mechanical perfor...

Advanced metamaterials are designed upon the combination of (1) carbon nanotube (CNT) foam, which is obtained from chemical vapor deposition by fully consuming the initial nickel foam, and (2) nanosilver/silicone resin or graphene (Gr) foam. The CNT foam/nanosilver/silicone composite simultaneously exhibits a negative permittivity and permeability in the frequency range from 1 MHz to 1 GHz provided that the appropriate CNT foam amount is considered (20 m%). Double-negative performance in a similar frequency range is obtained with both 3/1 and 1/1 (mass basis) Gr/CNT-based composites. On the other hand, 3/2 (mass basis) Gr/CNT exhibits a negative permeability in the shared frequency range from 6 × 102 MHz to 1 GHz with still negative permittivity in the full range. The Gr amount allows to control the frequency behavior, with a variation in absolute permittivity and permeability values and a switch between a concave and convex behavior. Hence, the work contributes to the further expanding of the application range of metamaterials.

To reduce plastic waste generation from failed product batches during industrial injection molding, the sustainable production of representative prototypes is essential. Interesting is the more recent hybrid injection molding (HM) technique, in which a polymeric mold core and cavity are produced via additive manufacturing (AM) and are both placed in an overall metal housing for the final polymeric part production. HM requires less material waste and energy compared to conventional subtractive injection molding, at least if its process parameters are properly tuned. In the present work, several options of AM insert production are compared with full metal/steel mold inserts, selecting isotactic polypropylene as the injected polymer. These options are defined by both the AM method and the material considered and are evaluated with respect to the insert mechanical and conductive properties, also considering Moldex3D simulations. These simulations are conducted with inputted measured temperature-dependent AM material properties to identify in silico indicators for wear and to perform cooling cycle time minimization. It is shown that PolyJetted Digital acrylonitrile-butadiene-styrene (ABS) polymer and Multi jet fusioned (MJF) polyamide 11 (PA11) are the most promising. The former option has the best durability for thinner injection molded parts, and the latter option the best cooling cycle times at any thickness, highlighting the need to further develop AM options.

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.

Recent development in the field of additive manufacturing, also known as three-dimensional (3D) printing, has allowed for the incorporation of continuous fiber reinforcement into 3D-printed polymer parts. These fiber reinforcements allow for the improvement of the mechanical properties, but compared to traditionally produced composite materials, the fiber volume fraction often remains low. This study aims to evaluate the in-nozzle impregnation of continuous aramid fiber reinforcement with glycol-modified polyethylene terephthalate (PETG) using a modified, low-cost, tabletop 3D printer. We analyze how dimensional printing parameters such as layer height and line width affect the fiber volume fraction and fiber dispersion in printed composites. By varying these parameters, unidirectional specimens are printed that have an inner structure going from an array-like to a continuous layered-like structure with fiber loading between 20 and 45 vol%. The inner structure was analyzed by optical microscopy and Computed Tomography (µCT), achieving new insights into the structural composition of printed composites. The printed composites show good fiber alignment and the tensile modulus in the fiber direction increased from 2.2 GPa (non-reinforced) to 33 GPa (45 vol%), while the flexural modulus in the fiber direction increased from 1.6 GPa (non-reinforced) to 27 GPa (45 vol%). The continuous 3D reinforced specimens have quality and properties in the range of traditional composite materials produced by hand lay-up techniques, far exceeding the performance of typical bulk 3D-printed polymers. Hence, this technique has potential for the low-cost additive manufacturing of small, intricate parts with substantial mechanical performance, or parts of which only a small number is needed.

Sustainability and recyclability are among the main driving forces in the plastics industry, since the pressure on crude oil resources and the environment is increasing. The aim of this research is to develop a sustainable thermoformable multilayer food packaging, based on co-polyesters, which is suitable for hot-fill applications and allows for recycling in a conventional waste stream. As a polymer material for the outer layer, we selected a modified polyethylene terephthalate (PETM), which is an amorphous co-polyester with a high glass transition temperature (±105 °C) and thus high thermal stability and transparency. The inner layer consists of 1,4-cyclohexylene dimethanol-modified polyethylene terephthalate (PETg), which is allowed to be recycled in a PET stream. Multilayers with a total thickness of 1 mm and a layer thickness distribution of 10/80/10 have been produced. To test the recyclability, sheets which contained 20% and 50% regrind of the initial multilayer in their middle PETg layer have been produced as well. The sheet produced from virgin pellets and the one containing 20% regrind in the middle layer showed no visible haze. This was not the case for the one containing 50% regrind in the middle layer, which was confirmed by haze measurements. The hot-fill test results showed no shrinkage or warpage for the multilayer trays for all temperatures applied, namely 95, 85, 75 and 65 °C. This is a remarkable improvement compared to pure PETg trays, which show a visible deformation after exposure to hot-fill conditions of 95 °C and 85 °C.

Zeolites are crystalline metallosilicates displaying unique physicochemical properties with widespread applications in catalysis, adsorption, and separation. They are generally obtained by a multi-step process that starts with primary mixture aging, followed by hydrothermal crystallization, washing, drying, and, finally, a calcination step. However, the zeolites obtained are in the powder form and because of generating a pressure drop in industrial fixed bed reactors, not applicable for industrial purposes. To overcome such drawbacks, zeolites are shaped into appropriate geometries and desired size (a few centimeters) using extrusion, where zeolite powders are mixed with binders (e.g., mineral clays or inorganic oxides). The presence of binders provides good mechanical strength against crushing in shaped zeolites, but binders may have adverse impacts on zeolite catalytic and sorption properties, such as active site dilution and pore blockage. The latter is more pronounced when the binder has a smaller particle size, which makes the zeolite internal active sites mainly inaccessible. In addition to the shaping requirements, a hierarchical structure with different levels of porosity (micro-, meso-, and macropores) and an interconnected network are essential to decrease the diffusion limitation inside the zeolite micropores as well as to increase the mass transfer because of the presence of larger auxiliary pores. Thus, the generation of hierarchical structure and its preservation during the shaping step is of great importance. The aim of this review is to provide a comprehensive survey and detailed overview on the binder-containing extrusion technique compared to alternative shaping technologies with improved mass transfer properties. An emphasis is allocated to those techniques that have been less discussed in detail in the literature.

To improve the product quality of polymeric parts realized through extrusion-based additive manufacturing (EAM) utilizing pellets, a good control of the melting is required. In the present work, we demonstrate the strength of a previously developed melt removal using a drag framework to support such improvement. This model, downscaled from conventional extrusion, is successfully validated for pellet-based EAM—hence, micro-extrusion—employing three material types with different measured rheological behavior, i.e., acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA) and styrene-ethylene-butylene-styrene polymer (SEBS). The model’s validation is made possible by conducting for the first time dedicated EAM screw-freezing experiments combined with appropriate image/data analysis and inputting rheological data. It is showcased that the (overall) processing temperature is crucial to enable similar melting efficiencies. The melting mechanism can vary with the material type. For ABS, an initially large contribution of viscous heat dissipation is observed, while for PLA and SEBS thermal conduction is always more relevant. It is highlighted based on scanning electron microscopy (SEM) analysis that upon properly tuning the finalization of the melting point within the envisaged melting zone, better final material properties are achieved. The model can be further used to find an optimal balance between processing time (e.g., by variation of the screw frequency) and material product performance (e.g., strength of the printed polymeric part).

This paper aims to increase the through-plane thermal conductivity of polymer composites by adjusting the filler orientation. Two methods were tested: a combination of immiscible polymers (PP-PET) ...

Carbon nanotube (CNT) foams with negative permittivity and permeability are successfully prepared by chemical vapor deposition (CVD) and post-treatment. A double negative metamaterial in the 1–1000 MHz frequency range with double continuous structure results by effectively compounding the CNT foam with a polymer material, i.e. epoxy or nanosilver silicone resin. The negative permeability is specifically attributed to the three-dimensional CNT interactions as clear from the study of the relation of the material microstructure and the macroscopic measurements. Compared to CNT foam/epoxy composites, CNT foam/nanosilver/silicone composites have a lower permeability but a more excellent electrical conductivity or permittivity. It is also shown that the carbon source time during CVD and post-pressurization can be adjusted to allow for both negative permittivity and permeability. This contribution highlights a convenient method to obtain a metamaterial in a much larger frequency range (ca. 1 to 1000 MHz) than the state-of-the-art. It thus supports the expansion of the application range of metamaterials and simplifies their preparation, which is of great significance for the wider use of these materials.

The relevance of 3D numerical simulations for the isothermal flow of neat polypropylene through a slit die and the subsequent swelling upon die exit is highlighted based on the finite element method using the ANSYS Polyflow software package. The input parameters of (i) the generalized Newtonian constitutive model with the Cross law viscosity function and (ii) the multimode viscoelastic Phan-Thien-Tanner (PTT) constitutive model are estimated from rheological data obtained with rotational and capillary rheometers. Model validation is performed based on die pressure and real time experimental HD imaging for 3D die swell characterization. The evolution of the swell ratios in both width and height directions is investigated downstream the die exit. It is demonstrated that the PTT based swell ratio in the width direction increases in a much lower rate than the swell ratio in the height direction until equilibrium is achieved in both directions. Therefore, the distance from the die exit in which the final extrudate shape is obtained strongly depends on the die width, which is ignored in conventional 2D numerical simulations. The findings are underpinned through a detailed analysis of the simulated 3D stress and velocity field distributions.

Polyacrylics have been considered for a broad range of material applications, including coatings, dental applications, and adhesives. In this experimental study, the casting potential of a group of (co)monomers belonging to the acrylic family has been explored to enable a more sustainable use of these polymer materials in the medical and veterinary science field. The individual contributions of each comonomer have been analyzed, the reaction conversion has been studied via gas chromatography (GC), the rheological behavior has been characterized via stress-controlled measurements, and the final mechanical properties have been obtained from tensile, flexure, and impact tests. The GC results allow assessing the pot life and thus the working window of the casting process. For the rheological measurements, which start from low-viscous mixtures, a novel protocol has been introduced to obtain accurate absolute data. The rheological data reflect the time dependencies of the GC data but facilitate a more direct link with the macroscopic material data. Specifically, the steep increase in the viscosity with increasing reaction time for the methyl methacrylate (MMA)/ethylene glycol dimethyl methacrylate (EGDMA) case (2% crosslinker) allows maximizing several mechanical properties: the tensile/flexure modulus, the tensile/flexure stress at break, and the impact strength. This opens the pathway to more dedicated chemistry design for corrosion casting and polyacrylic material design in general.

Several mixed recycled plastics, namely, mixed bilayer polypropylene/poly (ethylene terephthalate) (PP/PET) film, mixed polyolefins (MPO) and talc-filled PP were selected for this study and used as matrices for the preparation of microfibrillar composites (MFCs) with PET as reinforcement fibres. MFCs with recycled matrices were successfully prepared by a three-step processing (extrusion&mdash, cold drawing&mdash, injection moulding), although significant difficulties in processing were observed. Contrary to previous results with virgin PP, no outstanding mechanical properties were achieved, they showed little or almost no improvement compared to the properties of unreinforced recycled plastics. SEM characterisation showed a high level of PET fibre coalescence present in the MFC made from recycled PP/PET film, while in the other MFCs, a large heterogeneity of the microstructure was identified. Despite these disappointing results, the MFC concept remains an interesting approach for the upcycling of mixed polymer waste. However, the current study shows that the approach requires further in-depth investigations which consider various factors such as viscosity, heterogeneity, the presence of different additives and levels of degradation.

Personalized medicine, produced through 3D printing, is a promising approach for delivering the required drug dose based on the patient's profile. The primary purpose of this study was to investigate the potential of two different extrusion-based additive manufacturing techniques – fused filament fabrication (FFF) and screw-based 3D printing, also known as direct extrusion additive manufacturing (DEAM). Different ethylene-vinyl acetate (EVA) copolymers (9 %VA, 12 %VA, 16 %VA, 18 %VA, 25 %VA, 28 %VA, and 40 %VA) were selected and loaded with 50% (w/w) metoprolol tartrate (MPT). Hot-melt extrusion was performed to produce the drug-loaded filaments. These filaments were used for FFF in which the mechanical and rheological properties were rate-limiting steps. The drug-loaded filament based on the 18 %VA polymer was the only printable formulation due to its appropriate mechanical and rheological properties. As for the highest VA content (40 %VA), the feeding pinch rolls cause buckling of the filaments due to insufficient stiffness, while other filaments were successfully feedable towards the extrusion nozzle. However, poor flowability out of the extrusion nozzle due to the rheological limitation excluded these formulations from the initial printing trials. Filaments were also pelletized and used for pellets-DEAM. This method showed freedom in formulation selection because the screw rotation drives the material flow with less dependence on their mechanical properties. All drug-loaded pellets were successfully printed via DEAM, as sufficient pressure was built up towards the nozzle due to single screw extrusion processing method. In contrast, filaments were used as a piston to build up the pressure required for extrusion in filament-based printing, which highly depends on the filament's mechanical properties. Moreover, printing trials using a physical mixture in powder form were also investigated and showed promising results. In vitro drug release showed similar release patterns for MPT-loaded 3D printed tablets regardless of the printing technique. Additionally, pellets-DEAM enabled the production of tablets with the highest VA content, which failed in FFF 3D printing but showed an interesting delayed release profile.

One of the challenges for single-screw micro-extrusion or additive manufacturing (AM), thus 3D printing, of polymers is controlling the melting efficiency so that energy and equipment costs can be minimized. Here, a numerical model is presented for AM process design, selecting acrylonitrile&ndash, butadiene&ndash, styrene (ABS) as viscoelastic reference polymer. It is demonstrated that AM melting is different compared to conventional melting due to variation in extrusion dimensions, leading to a different balance in heating by conduction and viscous heat dissipation as caused by the shearing between the melt layers in the associated film layer near the barrel. The thickness of this melt film layer is variable along the screw length, and it is shown that simplified models assuming an overall average value are too approximate. It is highlighted that the screw frequency, pitch angle and compression ratio are important process parameters to control the point of melt finalization. In addition, the power-law index reflecting the shear thinning nature of the polymer melt is showcased as a key parameter. Moreover, AM process results assuming constant and temperature dependent specific heat capacities and thermal conductivities are compared. The current work opens the door for on-line AM process control, addressing all relevant operating and material parameters.

Highly sensitive conductive polymer composites for piezoresistive sensing are developed by a design of the formulation variables of extrusion-based manufacturing (filler type/amount, polymer amount) and annealing (a), considering thermoplastic polyurethane (TPU) and/or olefin block copolymer (OBC) as polymer matrix and carbon black (CB) as conductive filler. With ternary composites - based on a CB type with stronger filler-matrix interactions and an appropriate OBC/TPU blend mass ratio (40/60 with CB amount of 5–10 m%; 50/50 with CB amount of 10 m%), the challenging region of both high sensitivity and static strain (maximal gauge factors (GFmax) > 50 and emax > 100%) can be realized: GFmax > 104 and emax = 20–240%. OBC binary composites with a high CB2 amount (e.g. 15 m%) are however needed for ultrahigh static strains (emax > 600%). Well-designed ternary composites (e.g. OBC40-CB/TPU60-7-a and OBC30-CB/TPU70-7-a) possess a large dynamic resistance change, negligible hysteresis and high stability and display strain sensor application potential. Highly CB2 loaded binary (≥12 m%) and ternary composites (10 m%) exhibit a more obvious strain-dependent dynamic hysteretic behavior, as they switch from a dual peak to single peak pattern toward the sensing strain limit, which is interesting for self-diagnose.

In the food industry, extrusion cooking finds numerous applications thanks to its high productivity and nutrient retention. More specifically, cereal extrusion, e.g., for savory snacks and breakfast products has an important market share. For such applications, rheology, which addresses viscous and elastic contributions, plays an important role in developing, optimizing, and controlling the extrusion manufacturing technique. In this context, conventional off-line rheometers are not ideal for providing data, as the goal is to replicate the exact thermomechanical history to which the food is subjected in the extrusion process. Hence, to achieve reliable analyses, in-line viscometers that have mostly been tested using oil-based polymers were introduced. Biopolymers (e.g., starch), however, are highly sensitive to both heat and mechanical degradation, and the viscometer design has to be adapted accordingly to produce an accurate measurement. Alongside a discussion of the different designs available, this review will address the most common methodologies for measuring the steady shear viscosity, extensional viscosity, and the first normal stress difference for food applications, providing researchers in the biopolymer and food engineering fields with a general introduction to this emerging topic.

For composites based on polypropylene (PP) filled with short carbon fibres (CF), extrusion-based additive manufacturing provides a promising and cost-effective manufacturing technique that utilises the flow-induced orientation of the fibres for their targeted alignment through the control of the printing direction. This study investigates the impact of the fibre orientation on mechanical properties and thermal conductivity of 3D-printed PP composites filled with short-CF. Provided a homogeneous fibre-dispersion and a good fibre-matrix adhesion, the composites showed considerably improved mechanical properties compared to neat PP regardless of the fibre orientation. However, for the different printing orientations, a strong anisotropy in terms of flexural and impact properties and thermal conductivity was observed. For example, it was found that the thermal conductivity along the printing and, thus, the fibre direction was three times higher than perpendicular to that direction. The present work provides a key to the fabrication of parts with tailored, orientation-dependent properties.

Highly sensitive conductive polymer composites (CPCs) are designed employing a facile and low-cost extrusion manufacturing process for both low- and high-strain sensing in the field of, for example, structural health/damage monitoring and human body movement tracking. Focus is on the morphology control for extrusion-processed carbon black (CB)-filled CPCs, utilizing binary and ternary composites based on thermoplastic polyurethane (TPU) and olefin block copolymer (OBC). The relevance of the correct CB amount, kinetic control through a variation of the compounding sequence, and thermodynamic control induced by annealing is highlighted, considering a wide range of experimental (e.g., static and dynamic resistance/scanning electron microscopy/rheological measurements) and theoretical analyses. High CB mass fractions (20 m %) are needed for OBC (or TPU)-CB binary composites but only lead to an intermediate sensitivity as their conductive network is fully packed and therefore difficult to be truly destructed. Annealing is needed to enable a monotonic increase of the relative resistance with respect to strain. With ternary composites, a much higher sensitivity with a clearer monotonic increase results, provided that a low CB mass fraction (10-16 m %) is used and annealing is applied. In particular, with CB first dispersed in OBC and annealing, a less compact, hence, brittle conductive network (10-12 m % CB) is obtained, allowing high-performance sensing.

The production of plastic has grown exponentially over the past few decades and with it the amount of plastic waste leaking in the environment, where it fragments into micro- and nanoplastics. This problematic situation stresses the need for increased plastic collection, recycling and reuse rates. Extrusion-based additive manufacturing (AM) and especially fused filament fabrication (FFF) offer an efficient and effective method to reuse and upcycle recycled plastic. This study focuses on poly(ethylene terephthalate) (PET), which has a broad application window and its recycling is therefore environmentally and economically favorable and sustainable. Therefore, this study involves the thermal and mechanical behavior of recycled PET after extrusion and 3D printing. The extrusion parameters are optimized by performing a complete physico-chemical and thermal analysis of the obtained filaments and they were compared with commercial virgin and recycled PET. Moreover, the influence of the applied processing conditions on the degree of crystallinity and mechanical properties is investigated. The filaments are then used for FFF, where various printing parameters are altered to obtain the optimum printing conditions (i.e. printing temperature, the build plate temperature, fan cooling and printing directions). The effect of the degree of crystallinity of semi-crystalline PET is investigated via altered printing parameters, showing superior mechanical properties for an increasing degree of crystallinity. To verify the portability of the obtained optimized print parameters, two different FFF printers are used. The use of recycled PET as feedstock for FFF supports the efforts for improving the sustainability of plastics by valorizing PET waste, and prolonging the lifecycle of PET.

Recycling of solid plastic waste composed of post-consumer mixed polyolefines (polypropylene and polyethylene) was carried out by injection moulding of secondary material streams. The materials have been characterized by melt flow index (MFI), tensile, bending and impact measurements, density and differential scanning calorimetry (DSC). The sink-float technique was used to separate the polyethylene fraction, which was then blended into virgin polyethylene at different ratios and processed anew. The mechanical and physicochemical properties were likewise determined and these results were compared to theoretical values, predicted by the law-of-mixtures. It was found that the different postconsumer mixed polyolefines were of similar quality and had comparable properties. Furthermore, it was demonstrated that the tensile and bending properties of blends consisting of recycled separated polyethylene and virgin polyethylene follow the law-of-mixtures, while the impact strength does not and is in fact strongly reduced by the presence of different phases within the injection moulded part.

One of the challenges for the manufacturing processes of polymeric parts is the dedicated control of composite melt flow. In the present work, the predictive capability of the Phan-Thien-Tanner (PTT) viscoelastic model is evaluated in relation to the extrudate swell from slit dies at 200 °C, considering polypropylene and graphite filler, and applying ANSYS Polyflow software. It is shown that for sufficiently low filler amounts (below 10%, volumetric) the PTT accurately reflects the viscoelastic interactions, but at higher filler amounts too large swellings are predicted. One can although obtain insights on the swelling in the height direction and consider a broader range of swelling areas compared to virgin materials. Guidelines are also provided for future experiments and model development, including the omission of the no-slip process boundary condition.

The melt flow index (MFI) of seven commercial poly(lactic acid) (PLA) grades is investigated in view of 3D printing quality. A threshold value of 10 g (10 min)−1 (2.16 kg; ISO 1133) is put forward for a successful printing (190–220°C), enabling a fast and practical screening of PLA materials. It is however shown that a sole focus on MFI is insufficient, as the plasticiser type and crystallinity also play a role after the polymer melt deposition. The latter is supported by scanning electron micromorphology and differential scanning calorimetry measurements. In particular, blending with poly(hydroxyl butyrate) (PHB; 20 m%) allows to control both MFI and crystallinity without the need for annealing.

Thermoplastics composites show vast promise as an alternative for thermal management applications in the scope of the development of next-generation electronics and heat exchangers. Their low cost, reduced weight, and corrosion resistance make them an attractive replacer for traditionally used metals, in case their thermal conductivity (TC) can be sufficiently increased by designing the material (e.g., filler type and shape) and processing (e.g., dispersion quality, mixing, and shaping) parameters. In the present contribution, the relevance of both types of parameters is discussed, and guidelines are formulated for future research to increase the TC of thermoplastic polymer composites. POLYM. ENG. SCI., 58:466–474, 2018. VC 2017 Society of Plastics Engineers

Flexible plastic films from food packaging trays make up one of the largest fractions of the plastic waste stream and recycling is one of the most important actions to deal with this fraction, reducing the impact of these plastics on the environment. However, the recyclability of multi-layered films is not straightforward and in most of the cases these fractions are landfilled or incinerated. Recycling of discarded mixed polymers without previous separation often results in low mechanical properties which have lead researchers to investigate novel solutions for recycling. In this research, the concept of microfibrillar composites (MFCs) was investigated aiming to upcycle mixed polymer waste streams. A blend based on polypropylene (PP) and poly(ethylene terephthalate) (PET) at a weight ratio of 80/20 PP/PET was studied. The final step of the MFC processing was conducted using a conical twin screw extrusion. The morphological results confirmed the presence of PET microfibrils in the composites, leading to an improvement in mechanical properties such as in the tensile yield strength and strain at break. Subsequently, the MFC samples were successfully moulded into trays via thermoforming., This research was financially supported by Ghent University, Belgium. We acknowledge the University of Minho, Portugal for collaboration on the project. M. K. would like to thank prof. Carla Isabel Martins for supervising her during the stay at the University of Minho and Paulo Lopes for the support with the Raman measurements.

The reinforcement of recycled polypropylene (rPP) with mineral fillers, to obtain modulus values of 3000–4000 MPa has proven challenging for recyclers, whereas this is common practice for virgin PP...

A challenge for polymer rheology is the reliable determination of shear dependent first normal stress difference (N-1 values) at high shear rates (>10 s(-1)). Here, we evaluate the correctness of the commonly applied exit pressure method focusing on polypropylene and high and low density polyethylene melts at 200 degrees C. It is demonstrated that the linear extrapolation of pressure values toward the die exit, which is a key step in the application of the exit pressure method, is affordable to determine N-1 values despite that these extrapolated exit pressure values are characterized by a relative deviation of 25%-40%. The validity of the exit pressure method is further supported by an excellent match with rheological data from the Laun rule (exponent close to 0.7) and a representative simulation of extrudate swelling data in the width and height direction, considering tuned parameters for the Phan-Thien-Tanner constitutive model. Also, the absence of a significant viscous heating effect near the die exit is highlighted based on numerical analysis. (c) 2020 The Society of Rheology.

Commercially mass-polymerized acrylonitrile&ndash, butadiene&ndash, styrene (ABS) polymers, pristine or modified by stabilization systems, have been injection molded and repeatedly exposed to ultravilolet A (UVA) radiation, mechanical recycling, and extra injection molding steps to study the impact of such treatments on the physicochemical, mechanical, colorimetric, and thermal-oxidative characteristics. The work focus on mimicking the effect of solar radiation behind a window glass as relevant during the lifetime of ABS polymers incorporated in electrical and electronic equipment, and interior automotive parts by using UVA technique. The accelerated aging promotes degradation and embrittlement of the surface exposed to radiation and causes physical aging, deteriorating mechanical properties, with an expressive reduction of impact strength (unnotched: up to 900%, notched: up to 250%) and strain at break (&gt, 1000%), as well as an increase in the yellowing index (e.g., 600%). UV-exposition promotes a slight increase in the tensile modulus (e.g., 10%). The addition of antioxidants (AOs) leads to a limited stabilization during the first UVA aging, although the proper AO formulation increases the thermal-oxidative resistance during all the cycles. Mechanical recycling promotes an increase in strain at break and unnotched impact strength alongside a slight decrease in tensile modulus, due to disruption of the brittle surface and elimination of the physical aging.

Purpose This study aims to evaluate and compare the macroscopic properties of commercial acrylonitrile-butadiene-styrene (ABS) processed by two different types of additive manufacturing (AM) machines. The focus is also on the effect of multiple closed-loop recycling of ABS. Design/methodology/approach A conventional direct-drive, Cartesian-type machine and a Bowden, Delta-type machine with an infrared radiant heating system are used to manufacture test specimens molded in ABS. Afterward, multiple closed-loop recycling cycles are conducted, involving consecutive AM (four times) and recycling (three times). The rheological, mechanical, morphological and physicochemical properties are investigated. Findings The type of machine affects the quality of the produced parts. The machine containing an infrared radiant system in a temperature-controlled chamber produces parts showing higher mechanical properties and filling fraction, although it increases the yellowing. Closed-loop recycling of ABS for AM is applicable for at least two cycles, inducing a slight increase in tensile modulus (ca. 5%) and in tensile strength (ca. 13%) and a decrease in the impact strength (ca. 14%) and melt viscosity. An increase in the filling fraction of the AM parts promotes an increase in tensile strength and tensile modulus, although it does not influence the impact strength. Furthermore, multiple closed-loop recycling does not affect the overall chemical structure of ABS. Practical implications Controlling the environmental temperature and using infrared radiant heating during AM of ABS improves the quality of the produced parts. Closed-loop recycling of ABS used in AM is feasible up to at least two recycling steps, supporting the implementation of a circular economy for polymer-based AM. Originality/value This study shows original results regarding the assessment of the effect of different types of AM machines on the main end-use properties of ABS parts and the influence of multiple closed-loop recycling on the characteristics of ABS fabricated by the most suited AM machine with an infrared radiant heating system and a temperature-controlled environment.

Hollow activated carbon fiber (HACF) with high specific surface area and high charge storage capability was prepared by pre-oxidation, carbonization and KOH-activation from polyacrylonitrile (PAN). HACF was used as self-supported working electrode directly without any binder and conductive agent. The effect of the activation time on specific surface area of HACF was studied intensively. The results show that the specific surface area of HACF increased with the increase of activation time from 0.5 h to 1.5 h, and then decreased with further increase of activation time. Highest specific surface area of 1873 m(2)g(-1) and micropore volume of 0.61 cm(3)g(-1) were obtained in HACF activated for 1.5 h. Electrochemical properties of HACF can be improved with increase of activation time, but excessive activation results in the decrease of specific surface area and increase of internal resistance of HACF. The self-supported electrode of HACF possesses a large specific capacitance of 323 F g(-1) at 0.05 A g(-1) and 216 F g(-1) at 1 A g(-1). Therefore, HACF can be a promising self-supported electrode for high performance supercapacitors.