High-performance Thermoplastics Research Articles

Sustainable production of the drug precursor tyramine by engineered Corynebacterium glutamicum.

Tyramine has attracted considerable interest due to recent findings that it is an excellent starting material for the production of high-performance thermoplastics and hydrogels. Furthermore, tyramine is a precursor of a diversity of pharmaceutically relevant compounds, contributing to its growing importance. Given the limitations of chemical synthesis, including lack of selectivity and laborious processes with harsh conditions, the biosynthesis of tyramine by decarboxylation of L-tyrosine represents a promising sustainable alternative. In this study, the de novo production of tyramine from simple nitrogen and sustainable carbon sources was successfully established by metabolic engineering of theL-tyrosine overproducing Corynebacterium glutamicum strain AROM3. A phylogenetic analysis of aromatic-L-amino acid decarboxylases (AADCs) revealed potential candidate enzymes for the decarboxylation of tyramine. The heterologous overexpression of the respective AADC genes resulted in successful tyramine production, with the highest tyramine titer of 1.9gL-1 obtained for AROM3 overexpressing the tyrosine decarboxylase gene of Levilactobacillus brevis. Further metabolic engineering of this tyramine-producing strain enabled tyramine production from the alternative carbon sources ribose and xylose. Additionally, up-scaling of tyramine production from xylose to a 1.5L bioreactor batch fermentation was demonstrated to be stable, highlighting the potential for sustainable tyramine production. KEY POINTS: • Phylogenetic analysis revealed candidate l-tyrosine decarboxylases • C. glutamicum was engineered for de novo production of tyramine • Tyramine production from alternative carbon substrates was enabled.

Friction in Oil-Lubricated Rolling–Sliding Contacts with Technical and High-Performance Thermoplastics

Thermoplastics show great potential due to their lightweight design, low-noise operation, and cost-effective manufacturing. Oil lubrication allows for their usage in high-power-transmission applications, such as gears. The current design guidelines for thermoplastic gears lack reliable estimates for the coefficient of friction of oil-lubricated rolling–sliding contacts. This work characterizes the friction of elastohydrodynamic rolling–sliding contacts with technical and high-performance thermoplastics with oil lubrication. The influence of polyoxymethylene (POM), polyamide 46 (PA46), polyamide 12 (PA12), and polyetheretherketone (PEEK), as well as mineral oil (MIN), polyalphaolefin (PAO), and water-containing polyalkylene glycol (PAGW), was studied. Experiments were carried out on a ball-on-disk tribometer, considering different loads, speeds, temperatures, and surface roughness. The results show that, for fluid film lubrication, there is very low friction in the superlubricity regime, with a coefficient of friction lower than 0.01. Both sliding and rolling friction account for a significant portion of the total friction, depending on the contact configuration and operating conditions. In the mixed to boundary lubrication regime, the sliding friction depends on the thermoplastic and rises sharply, thus increasing the total friction.

Fast, Regioselective Aminolysis of Tetrasubstituted Cyclic Carbonates and Application to Recyclable Thermoplastics and Thermosets.

Herein, the long-standing challenge of the ring-opening aminolysis of CO2-derived tetrasubstituted cyclic carbonates at room temperature (r.T) is overcome under catalyst-free conditions. Molecular design of the cyclic carbonate by substitution of an alkyl group by a thioether unlocks quantitative conversion at r.T and ensures total regioselectivity toward highly substituted oxazolidone scaffolds. An in-depth rationalization of the high reactivity of these cyclic carbonate structures and of the aminolysis reaction mechanism is provided by a computational study supporting experimental observations. The high efficiency of the reaction is then translated to the deconstruction of high-performance thermoplastics containing tetrasubstituted cyclic carbonate linkages to deliver building blocks that are reused for designing recyclable thermosets bearing dynamic N,S-acetal linkages.

Adding Rare Earth Oxide Markers to Polyoxymethylene to Improve Plastic Recycling through Tracer-Based Sorting.

Engineering plastics, such as polyoxymethylene (POM), are high-performance thermoplastics designed to withstand high temperature or mechanical stress and are used in electronic equipment, the automotive industry, construction, or specific household utensils. POM is immiscible with other plastics but due to a low volume of production, no methods were developed to separate it from the residual plastic waste stream. Therefore, POM recycling is minimal despite its high market value. This paper provides a proof of concept for tracer-based sorting (TBS) as a potential solution for increasing the separation efficiency of low-volume, high-quality polymers. For this purpose, yttrium oxide (Y2O3) and cerium (IV) oxide (CeO2) have been embedded into the POM matrix. Mechanical tests of samples at varying concentrations (0.1 to 1000 ppm) of both tracers were conducted, followed by an analysis of detectability and dispersibility using a portable X-ray fluorescence spectrometer (p-XRF), subsequently optimizing detection time and tracer concentration. Finally, an experimental scenario was developed to test the fate and potential recovery of the tracer material after the thermal treatment of plastics. A low detectable concentration, short measurement time, low influence on mechanical parameters of the compound, and low loss ratio after simulated recycling prove Y2O3 to be a suitable tracer for the industrial implementation of TBS.

Characterization and modeling of laser transmission welded polyetherketoneketone (PEKK) joints: Influence of process parameters and annealing on weld properties

Welding high-performance thermoplastics has gained popularity across various industries such as automotive, aerospace, and medical. Laser transmission welding (LTW) has emerged as an effective method for joining thermoplastic parts due to its precise control and high joint quality. PAEK (polyaryletherketone) are wide spreading over various industrial applications as a substitute to metals and thermosets when high durability and performance are required. Polyetherketoneketone (PEKK) is one of these PAEK and it has received less attention than PEEK until now. PEKK, being a semi-crystalline thermoplastic, requires additional care during processing due to its propensity to crystallize. This study presents both experimental and numerical investigations into LTW of PEKK molded parts, aiming to understand the influence of welding parameters and crystallinity on weld joint morphology and mechanical properties. PEKK plates, prepared in amorphous and semi-crystalline states, are subjected to LTW using a 975 nm diode laser. Material characterization confirms differences in crystallinity between the samples, which affect their thermal and optical properties, which are crucial for welding. Welding tests are conducted with varying laser power (between 75 and 95 W) and semi-transparent part thickness (2 and 4 mm). The morphology of joints is analysed. Assemblies undergo post-weld annealing treatment to examine its influence on weld crystallinity and consequent mechanical properties. Results reveal an anisotropic distribution of crystallinity within the heat-affected zone (HAZ). The depths of the molten layer (ML) and semi-crystalline layer (scL) vary with laser power and assembly type. A notable decrease in weld strength with laser power is highlighted, while annealing leads to enhanced crystallinity and improved weld strength. Despite variations, high weld strengths are achieved with annealing. Computational modelling elucidates the complex interplay between laser irradiation, temperature distribution, and crystallization kinetics observed experimentally. Overall, this comprehensive investigation provides valuable insights into optimizing LTW parameters for PEKK parts.

High-performance thermoplastic nanocomposites for aerospace applications: A review of synthesis, production, and analysis

Thermoset polymers are cured under natural or synthetic created conditions and retain their solid form when exposed to heat. Unlike thermosets, thermoplastics melt when exposed to heat after production. Thermoplastics are preferred as raw materials because they can be easily shaped after production, have a high shelf life and are recyclable. In this regard, the prominence of high-performance engineering polymers in recent years has led to the preference of alternative polymers to thermosets. High-performance engineering thermoplastics include thermoplastics such as polyphenylene-sulfide (PPS), polyether-ether-ketone (PEEK), polyether-ketone-ketone (PEKK), polyphenylene-ether, polysulfone,polyoxadiazole, polyimide, polyether-amide, polyether-amide-imide, polynaphthalene, and polyamide-imide. These polymers exhibit application potential in aerospace, defense, automotive, marine, energy, and medical sectors. In challenging conditions such as high pressure, temperature, and corrosive environments, they possess high service temperatures, enhanced mechanical and physical properties, preferable chemical resistance as well as out-of-autoclave and rapid processing properties. In this review article, nanomaterial production methods (bottom-up and top-bottom) are mentioned. In the following sections, PPS, PEEK, and PEKK thermoplastics are explained, and carbon- and boron-based nano additives used in constructing nanocomposites are investigated. In the last section, PPS, PEKK, and PEEK polymer nanocomposites are investigated.

Obtaining excellent mechanical properties with additively manufactured short fiber reinforced polyether-ether-ketone thermoplastics through simultaneous vacuum and infrared heating

Additive manufacturing of short fiber reinforced thermoplastic composite with high-performance engineering thermoplastics is important in various industrial sectors because of their ability to manufacture complex and lightweight products. Although extensive studies in the literature are aimed at enhancing the mechanical performance of additively manufactured short fiber reinforced thermoplastics through methods like refining printing parameters, enhancing fiber fractions, and optimizing printing parameters, their mechanical performance remains limited. In this study, the individual effects of vacuum-assisted printing and infrared pre-heater-assisted printing and their combined effects were investigated to substantially increase the mechanical properties, interlaminar performance, and crystallinity ratios. The polyether ether ketone (PEEK) samples were printed with vacuum-assisted, infrared-assisted, and a combination of vacuum and infrared-assisted environments were subjected to three-point bending tests to evaluate their mechanical properties. Synergistic vacuum and infrared-assisted printing significantly enhanced the mechanical properties as the flexural strength increased by 54.58 % compared to printing under vacuum alone. Moreover, the flexural strength and elasticity modulus of samples printed with vacuum-infrared-assisted manufacturing increased by 324.48 % and 239.77 %, respectively, when compared to printing under atmospheric pressure without additional heating. Thermal and structural characterizations of the printed parts revealed that this significant improvement was attributed to reduced porosity ratios and increased crystallinity.

Advancements in Fused Deposition Modeling for Aerospace: Optimizing Lightweight and High- Strength Components

Fused Deposition Modeling (FDM) has emerged as a pivotal technology in aerospace manufacturing, enabling the creation of lightweight and high-strength components. Recent advancements in FDM materials, process optimization, and design methodologies have significantly enhanced its applicability in producing aerospace parts that meet stringent performance criteria. This paper reviews the latest developments in FDM technology, focusing on material innovations, structural optimization techniques, design for additive manufacturing and practical applications in the aerospace sector. Key advancements include the use of high-performance thermoplastics, carbon fiber composites, and hybrid materials, as well as improved printing techniques that reduce defects and enhance mechanical properties. The potential of FDM to revolutionize aerospace manufacturing through cost- effective and efficient production of complex geometries is explored, highlighting ongoing research and future directions in this dynamic field.

Analysis of Performance of Additively Manufactured Reinforced Ablatives

This study investigates reentry conditions for Mars missions, focusing on extreme anaerobic heating. This work studies poly(ether ketone ketone) (PEKK), a high-performance thermoplastics polymer, in both small-scale laboratory and simulated oxyacetylene test bed conditions to eliminate low-performing polymeric materials. Previous research demonstrated PEKK’s superior ablation performance compared to poly(ether ether ketone) (PEEK) and polyetherimide. The aerothermal performance of neat PEKK can be further enhanced with reinforcement materials. This work explores PEKK composite materials reinforced with additives such as carbon nanotubes (CNTs), carbon fibers (CFs), and glass fibers (GFs). The CNT-reinforced (10%wt) PEKK exhibited the highest char yield (69%wt) during thermogravimetric analysis (TGA) in nitrogen, superior to the short CF-reinforced PEKK. Various CF and GF loadings (10% and 20%wt) were tested for their thermophysical and aerothermal performance. Oxyacetylene tests (OTBs) under fuel-rich conditions further validated the results. Except for 10% CF PEEK, the mass loss in OTB tests correlated with TGA and thermal diffusivity measurements. The addition of CF/GF in PEKK enhanced thermal effusivity, but it also led to significant swelling due to increased conductive flux and reduced ablated heat flux. Among the tested materials, CNT-reinforced PEKK displayed the highest char yield, lowest mass loss, and minimal swelling. The unique porous structure of CNTs minimized char expansion and erosion during the OTB tests, making a promising material for reentry flights.

PISOX Copolyesters-Bio- and CO2-Based Marine-Degradable High-Performance Polyesters.

Oxalate esters and isosorbide serve as intriguing polymer building blocks, as they can be sourced from renewable resources, such as CO2 and glucose, and the resulting polyesters offer outstanding material properties. However, the low reactivity of the secondary hydroxyl groups makes it difficult to generate high-molecular-weight polymers from isosorbide. Combining diaryl oxalates with isosorbide appears to be a promising approach to produce high-molecular-weight isosorbide-based polyoxalates (PISOX). This strategy seems to be scalable, has a short polymerization time (<5 h), and uniquely, there is no need for a catalyst. PISOX demonstrates outstanding thermal, mechanical, and barrier properties; its barrier to oxygen is 35 times better than PLA, it possesses mechanical properties comparable to high-performance thermoplastics, and the glass transition temperature of 167 °C can be modified by comonomer incorporation. What makes this high-performance material truly exceptional is that it decomposes into CO2 and biomass in just a few months in soil under home-composting conditions and it hydrolyzes without enzymes present in less than a year in 20 °C water. This unique combination of properties has the potential to be utilized in a range of applications, such as biomedical uses, water-resistant coatings, compostable plastic bags for gardening and agriculture, and packaging plastics with diminished environmental impact.

Mussel-inspired catechol prepolymers as surface primer for enhanced interface bonding to high-performance thermoplastics

High-performance thermoplastics, such as polyether ether ketone (PEEK) and polyester sulfone (PES), are extensively utilized across various industries owing to their exceptional properties. However, their relatively low surface energy often leads to insufficient bonding strength when adhering PEEK or PES. Commonly used surface pretreatments, such as acid-base and plasma treatments, have drawbacks including the use of toxic acids and bases, complex procedures, and poor stability. In this study, we synthesized four catechol-functionalized prepolymers by reacting bisquinone A with dithiols or diamines in a 1:1 M ratio. These catechol-containing prepolymers were employed as surface primers, and the adhesion performance before and after primer treatment was examined using epoxy adhesive for bonding tests. Compared to untreated samples, the lap shear strengths of surface primed PEEK and PES were significantly enhanced by 181 % and 114 %, respectively. These results indicate that the synthesized prepolymers with catechol structures can effectively serve as adhesive primers for bonding.

Surface segregation of rigid polyarylene ether amidoxime on polyurethane nanofiber into hierarchical membranes as substrate of flexible SERS nanosensor for sulfamethoxazole detection

Electrospun polymeric nanofibrous membranes are emerging as the promising substrates for preparation of flexible SERS nanosensors due to their intrinsic nanoscale surface roughness, easy scalability as well as rich surface reactivity. Although the nanofiber membranes prepared from high performance thermoplastics exhibit good mechanical stability, the SERS nanosensors based on these substrates normally have lower signal-to-noise ratio because of the interference from background Raman signals of aromatic moieties. Herein, we synthesized an optically transparent polyurethane (PU) and rigid polyarylene ether amidoxime (PEA), which were electrospun into core-shell nanofibers membranes with a “beads-on-web” morphology. Furthermore, the PU-PEA membranes were coated with ultra-thin silver layer and thermally annealed to prepare the flexible SERS nanosensor without any background noises. In addition, the Raman enhancement of SERS nanosensor can be readily improved by tuning of PU-PEA composition, silver thickness as well as thermal annealing temperature. Finally, the optimized SERS nanosensor enables label-free detection of sulfamethoxazole as low as 0.1 nM with a good reproducibility and detection performance in real water sample. Meanwhile, the optimized SERS nanosensor shows long term anti-biofouling capacity. Thanks to its facile fabrication, competitive analytical performance and resistance to biofouling, the current work basically open new way for design of flexible SERS nanosensors for biomedical applications.

High-performance thermoplastics obtained by fused filament fabrication: effects of harsh environmental conditions of power transformers

High-performance thermoplastics obtained by fused filament fabrication: effects of harsh environmental conditions of power transformers

Synthesis and characterization of long carbon chain polyamide 1012 modified polyamide 6 via melt copolymerization

Polyamide6 is a vital high-performance commercial engineering thermoplastics polymer, but it exhibits low toughness and high hydrophilicity. To improve its disadvantages, the facile melt co-polycondensation method was proposed to synthesis a novel polyamides 6-1012 copolymers (PA6-1012) with different PA1012 salt loading. Experimental results show that the melting temperature (Tm), crystallization temperature(Tc), melting enthalpy(ΔHm), and crystallinity(Xc) decreased with the increase of PA1012 loading in the copolyamides. The size and number of the copolymers’ spherical crystals decrease by the additions of 1012 units, but its crystalline structure and thermal stabilities does not be affected. The hydrophilicity decreases with increasing PA1012 content from 0 to 28 wt% and the highest contact angle value at the PA1012 loading of 28 wt% is 96°, which can be considered as a surface hydrophobic material. Low temperature (−5 °C)mechanical test results reveal that loss in tensile strength is exchanged for a considerable increase in the strain at break. The impact strength of the PA6-1012 copolyamides is notably enhanced by increasing the PA1012 loading in different test temperatures due to the increase of molecular chain flexibility, indicating that the copolyamindes exhibit enough toughness to suitably apply in low temperature environment.

Closing the loop in space 3D printing: Effect of vacuum, recycling, and UV aging on high performance thermoplastics produced via filament extrusion additive manufacturing

The outlook for space exploration, and the long-term sustainable presence of humans in space, rely upon the advancement of in-situ manufacturing capabilities. In-space additive manufacturing (AM) has gained significant attention due to its potential to produce spare parts in-situ and facilitate repairs for extending space missions. However, to date, there is no AM system capable of processing high-performance engineering thermoplastic polymers within uncontrolled space conditions (i.e., reduced gravity, vacuum, and radiation environment). Additionally, the effect of ultra-violet (UV) radiation on printed parts has remained unexplored. In this work, a custom-built filament extrusion AM breadboard has been developed and tested enabling the fabrication of engineering thermoplastic polymers, whereby the machine was placed inside a vacuum chamber to partly mimic the harsh space environment. Mechanical (tensile and flexural) and thermal (thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis) tests were conducted on the printed specimens before and after exposure to UV aging. Moreover, the printed geometries underwent a recycling process involved the shredding of the pristine 3D-printed polymeric samples, the drying of the obtained granulates and finally the extrusion of 3D-printable filaments. The polymeric recycled 3D-printed specimens were then subjected to further mechanical and thermal testing, offering valuable insights into the feasibility of in-space AM and the potential to augment the circularity of the printed parts. The results of the mechanical and thermal tests, together with the effect of vacuum printing, UV aging, and recycling, are provided within the manuscript. This work cements the basic building blocks to sustainably advance on-orbit and in-space infrastructure, and paves the way for long-term human space missions.

High-Performance PEEK/MWCNT Nanocomposites: Combining Enhanced Electrical Conductivity and Nanotube Dispersion.

High-performance engineering thermoplastics offer lightweight and excellent mechanical performance in a wide temperature range. Their composites with carbon nanotubes are expected to enhance mechanical performance, while providing thermal and electrical conductivity. These are interesting attributes that may endow additional functionalities to the nanocomposites. The present work investigates the optimal conditions to prepare polyether ether ketone (PEEK)/multi-walled carbon nanotube (MWCNT) nanocomposites, minimizing the MWCNT agglomerate size while maximizing the nanocomposite electrical conductivity. The aim is to achieve PEEK/MWCNT nanocomposites that are suitable for melt-spinning of electrically conductive multifilament's. Nanocomposites were prepared with compositions ranging from 0.5 to 7 wt.% MWCNT, showing an electrical percolation threshold between 1 and 2 wt.% MWCNT (107-102 S/cm) and a rheological percolation in the same range (1 to 2 wt.% MWCNT), confirming the formation of an MWCNT network in the nanocomposite. Considering the large drop in electrical conductivity typically observed during melt-spinning and the drawing of filaments, the composition PEEK/5 wt.% MWCNT was selected for further investigation. The effect of the melt extrusion parameters, namely screw speed, temperature, and throughput, was studied by evaluating the morphology of MWCNT agglomerates, the nanocomposite rheology, and electrical properties. It was observed that the combination of the higher values of screw speed and temperature profile leads to the smaller number of MWCNT agglomerates with smaller size, albeit at a slightly lower electrical conductivity. Generally, all processing conditions tested yielded nanocomposites with electrical conductivity in the range of 0.50-0.85 S/cm. The nanocomposite processed at higher temperature and screw speed presented the lowest value of elastic modulus, perhaps owing to higher matrix degradation and lower connectivity between the agglomerates. From all the process parameters studied, the screw speed was identified to have the higher impact on nanocomposite properties.

Poly(arylene ether)s-Based Polymeric Membranes Applied for Water Purification in Harsh Environment Conditions: A Mini-Review.

Confronting the pressing challenge of freshwater scarcity, polymeric membrane-based water treatment technology has emerged as an essential and effective approach. Poly(arylene ether)s (PAEs) polymers, a class of high-performance engineering thermoplastics, have garnered attention in recent decades as promising membrane materials for advanced water treatment approaches. The PAE-Based membranes are employed to resist the shortages of most common polymeric membranes, such as chemical instability, structural damage, membrane fouling, and shortened lifespan when deployed in harsh environments, owing to their excellent comprehensive performance. This article presents the advancements in the research of several typical PAEs, including poly(ether ether ketone) (PEEK), polyethersulfone (PES), and poly(arylene ether nitrile) (PEN). Techniques for membrane formation, modification strategies, and applications in water treatment have been reviewed. The applications encompass processes for oil/water separation, desalination, and wastewater treatment, which involve the removal of heavy metal ions, dyes, oils, and other organic pollutants. The commendable performance of these membranes has been summarized in terms of corrosion resistance, high-temperature resistance, anti-fouling properties, and durability in challenging environments. In addition, several recommendations for further research aimed at developing efficient and robust PAE-based membranes are proposed.

Assessment of the tribological performance of glass fibre reinforced polyamide 6 under harsh abrasive environments

High-performance thermoplastics exhibit significant potential to substitute metals in various applications, primarily due to their remarkable tribological, thermal and mechanical characteristics. Nevertheless, their characteristics require further refinement. This research aims to assess and compare the influence of distinct material types on the tribological characteristics of Polyamide 6 composites, as well as their reliance on the PV factor, which is the result of the velocity and pressure product.In the current research, the friction and wear performances of polyamide 6 (PA6) reinforced with glass fibres were examined in adverse PV factors till materials failed. Twin screw extrusion and subsequent injection moulding procedures were utilised to process the materials. The tribo-performance of the materials was assessed in ambient conditions using a pin-on-disc abrasive configuration. The morphological analysis of the abraded surfaces was conducted through field emission scanning electron microscopy (FESEM), and the plausible wear mechanisms contributing to wear are explained. Furthermore, the materials were thoroughly characterised for their tribological, mechanical and physical behaviours.The wear behaviour depended mainly on operating parameters and composition. PA6 proved to be beneficial till moderate PV conditions but not for harsh operating environments as compared to PA6 reinforced with 25% by volume of glass fibres (PA625GF). PA625GF showed PVlimit value of 1.04 MPa m/s which was decisively superior to PA6 (0.78 MPa m/s). Additionally, under a load of 50 N, PA625GF could sustain a higher speed of 800 rpm as compared to PA6 (600 rpm). The results showed that under all testing conditions glass fibres can minimise the coefficient of friction. Under low PV settings, the specific wear rate of PA625GF was remarkably reduced owing to the presence of glass fibres, reflecting superior anti-wear properties. Notably, the wear resistance of PA6 was considerably improved by glass fibres, particularly under high PV conditions, resulting in a PVlimit of 1.04 MPa m/s. The enhancement in PVlimit was attributed to the protective function of the fibres on the matrix and their superior mechanical properties. PA625GF proved to be tribo-potential materials in abrasive wear mode under extreme conditions in terms of low specific wear rate (8.484 ×10−3 mm3/N.m) and PVsafe value (0.78 MPa*m/s). This study is expected to pave the way for the development of novel self-lubrication composite materials for harsh service environments.

Characterization and modelling of the crystallization behavior of PEEK for polymer processing techniques

This study examines the crystallization behavior of high-performance thermoplastics under both isothermal and non-isothermal conditions. The accurate prediction of the crystallization kinetics in conjunction with process simulation tools can create new methods for defining the key process parameters in various polymer processing techniques. By simulating the thermal history of the materials, optimal process parameters can be assigned at specific time points, resulting in a more homogeneous process and improved material properties, while avoiding costly and time-consuming trial-and-error experimentation or post-processing. Here, flash differential scanning calorimetry (DSC) was used to capture the rapid crystallization of Luvocom 3F PEEK 9581 NT, and various isothermal and non-isothermal models were applied to mimic its crystallization behavior, highlighting the differential form of the dual Nakamura model as the most suitable option. To accurately predict the absolute crystallinity, the maximum achievable enthalpy was introduced in the model, and weight factors were assigned to the primary and secondary crystallization mechanisms. The differential form of the model is suitable for efficient implementation in process simulation tools, because it is independent of the total crystallization time. This research has the potential to significantly improve the selection of proper process parameters in complex polymer processing techniques, e.g., material extrusion.

Material Extrusion 3D Printing of PEEK-Based Composites.

High-performance thermoplastics like polyetheretherketone (PEEK), with their outstanding thermal stability, mechanical properties and chemical stability, have great potential for various structural applications. Combining with additive manufacturing methods extends further PEEK usage, e.g., as a mold insert material in polymer melt processing like injection molding. Mold inserts must possess a certain mechanical stability, a low surface roughness as well as a good thermal conductivity for the temperature control during the molding process. With this in mind, the commercially available high-performance thermoplastic PEEK was doped with small amounts of carbon nanotubes (CNT, 6 wt%) and copper particles (10 wt%) targeting enhanced thermomechanical properties and a higher thermal conductivity. The composites were realized by a commercial combined compounder and filament maker for the usage in a material extrusion (MEX)-based 3D-printer following the fused filament fabrication (FFF) principle. Commercial filaments made from PEEK and carbon fiber reinforced PEEK were used as reference systems. The impact of the filler and the MEX printing conditions like printing temperature, printing speed and infill orientation on the PEEK properties were characterized comprehensively by tensile testing, fracture imaging and surface roughness measurements. In addition, the thermal conductivity was determined by the laser-flash method in combination with differential scanning calorimetry and Archimedes density measurement. The addition of fillers did not alter the measured tensile strength in comparison to pure PEEK significantly. The fracture images showed a good printing quality without the MEX-typical voids between and within the deposited layers. Higher printing temperatures caused a reduction of the surface roughness and, in some cases, an enhanced ductile behavior. The thermal conductivity could be increased by the addition of the CNTs. Following the given results, the most critical process step is the compounding procedure, because for a reliable process-parameter-property relationship, a homogeneous particle distribution in the polymer matrix yielding a reliable filament quality is essential.