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Carbon fiber reinforced polyetheretherketone (CF-PEEK) samples were fabricated using material extrusion. These additive manufactured green bodies are later processed to their final application as ceramic matrix composites (CMC) by the liquid silicon infiltration (LSI) route. Past studies showed that the application of material extrusion for the fabrication of CMC requires an additional stabilization-step after 3D-printing in order to prevent the remelting of CF-PEEK during the high temperature process of pyrolysis. The thermally induced crosslinking of the CF-PEEK parts ensured shape accuracy and avoided remelting during the pyrolysis afterwards but is limited by the melting temperature of PEEK (Tm ∼ 343 °C). The study revealed a correlation between the annealing conditions time and temperature and the degree of crosslinking. Based on the analytical results from differential scanning calorimetry (DSC), a kinetic model was calculated, allowing predictions in dependence of the annealing temperature and time. Rheological and shape stability investigations of thermally annealed specimens verified the analytic results. The main findings of the study highlight an increasing degree of crosslinking with increasing annealing temperature and time.

Polymeric materials have long been at the forefront of materials science due to their exceptional physical and chemical properties. Designing new polymeric materials traditionally relies on a combination of physical and chemical principles along with empirical trial and error methods. A big issue in this approach is that the traditional trial and error experiments/simulations are often time consuming and sometimes inefficient in order to achieve targeted properties. Machine learning (ML) offers a promising solution to this issue. By leveraging ML algorithms, researchers can accelerate the design process, predict material properties more rapidly, and optimize formulations. ML approaches can analyze vast amounts of data, uncover hidden patterns, and generate predictive models that significantly reduce the time needed to develop materials with desired properties. This paradigm shift allows for more efficient exploration of the material space and faster innovation in polymeric material design. The current review article focuses on the application of ML methods to help design polymeric materials, more especifically, thermosets, thermoplastics and elastomers. Additionally, the review explores future possibilities and opportunities arising from the state-of-the-art advancements in ML, offering perspectives on how these technologies might evolve and influence the polymer science domain.

Flame retardants are often developed for epoxy resins and then transferred into their fiber-reinforced composites with uncertain results. Understanding this transfer in detail represents a critical scientific challenge. This study systematically compares epoxy resins with their glass-fiber reinforced composites, focusing on bisphenol A diglycidyl ether with the hardener dicyandiamide, the flame retardants melamine polyphosphate, ammonium polyphosphate, and silane ammonium polyphosphate, along with inorganic silicate. The research investigates changes in pyrolysis (thermogravimetry), flammability (UL 94, limiting oxygen index), and fire behavior (cone calorimeter) while also examining the flame-retardant modes of action and overall fire performance. The findings reveal that alterations in the amount of fuel, thermal properties, melt flow, and protective layer significantly impact ignition, flammability, and fire load, with a critical reduction in carbonaceous char within the composites preventing intumescence. This study quantifies the effects and provides a fundamental scientific understanding of the complex transfer process of flame retardants from resins to composites, offering essential insights that are of major importance for developing more effective flame-retardant materials.

This study presents a thermoset moulding compound designed for electrical machines with high power densities. The compound reduces residual stresses induced by the difference in thermal expansion during use and by shrinkage in the compound during the manufacturing process. To reduce the internal stresses in the compound, in the electrical sheet lamination and at their interface, first the moulding’s coefficient of thermal expansion (CTE) must match that of the lamination because the CTE of the electrical sheets cannot be altered. Second, the shrinkage of the compound needs to be minimized because the moulding compound is injected around a prefabricated electrical sheet lamination. This provides greater freedom in the design of an electric motor or generator, especially if the thermoset needs to be directly bonded to the electrical sheet. The basic suitability of the material for the injection moulding process was iteratively optimised and confirmed by spiral flow tests. Due to the reduction of the residual stresses, the compound enables efficient cooling solutions for electrical machines with high power densities. This innovative compound can have a significant impact on electric propulsion systems across industries that use laminated electrical sheets.

Substrate materials for printed circuit boards must meet ever-increasing requirements to keep up with electronics technology development. Especially in the field of high-frequency applications such as radar and cellular broadcasting, low permittivity and the dielectric loss factor are key material parameters. In this work, the dielectric properties of a high-temperature, thermoplastic PEEK/PEI blend system are investigated at frequencies of 5 and 10 GHz under dried and ambient conditions. This material blend, modified with a suitable filler system, is capable of being used in the laser direct structuring (LDS) process. It is revealed that the degree of crystallinity of neat PEEK has a notable influence on the dielectric properties, as well as the PEEK phase structure in the blend system developed through annealing. This phenomenon can in turn be exploited to minimize permittivity values at 30 to 40 wt.-% PEI in the blend, even taking into account the water uptake present in thermoplastics. The dielectric loss follows a linear mixing rule over the blend range, which proved to be true also for PEEK/PEI LDS compounds.

Abstract The interest in bio‐based alternatives to classical polyesters such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) is steadily growing to achieve a more sustainable approach to polymer materials. In this study, PBT/poly(butylene furanoate) (PBF) blends are prepared, characterized and extrusion foamed. PBF as a bio‐based polyester offers two advantages. The ecological footprint of the material is reduced, and additionally, it can be used in Diels‐Alder reactions at the blend surface to support fusion of the foamed beads. The blending behavior of the polyesters is investigated using samples prepared in a microcompounder, particularly focused on the miscibility of the blends and transesterification reactions. The blends are thermodynamically immiscible but show a certain degree of transesterification according to nuclear magnetic resonance (NMR) spectroscopy. The morphology of blend beads produced by an extrusion foaming process is analyzed regarding their cell density, cell size distribution, and open‐cell content. It is shown that PBF has a positive effect on the bead foam morphology. The use of a bifunctional linker designed for chemical fusion of the bead surfaces allows to obtaining of molded parts, in contrast to beads containing pure PBT.

Polysilazane-based coatings exhibit excellent mechanical properties and chemical resistance, but thermal curing limits their range of applications. Therefore, the aim of the study was to evaluate the more resource-efficient curing of polyorganosilazane-based coatings on a stainless-steel substrate by photo-induced thiol-ene “click” reaction at room temperature compared to the conventional thermally induced polymerization using a radical initiator. As expected crosslinking at higher temperatures led to the formation of a pronounced Si-O-Si network. However, crosslinking via UV radiation at room temperature suppressed the incorporation of oxygen remarkably also after a subsequent additional treatment at 135 °C in air. Both the chemical stability of the layers cured by means of UV radiation and the mechanical properties are comparable to those of the thermally crosslinked coatings. Therefore, curing using UV radiation at low temperatures is a suitable alternative method for producing protective coatings on substrates with limited thermal stability.

Abstract Herein, a simple melt‐blending method is utilized to disperse of halloysite nanotubes (HNTs) in polystyrene/polyolefin elastomer (PS/POE) blends. Based on morphological studies, the PS/POE/HNT nanocomposite containing up to 3 phr HNTs shows excellent nanofiller dispersion, while those filled with 5 phr HNTs exhibit nanofiller aggregation. To overcome the nanofiller aggregation issue, the polypropylene‐grafted‐maleic anhydride (PP‐g‐MA) compatibilizer is added to the PS/POE/HNT nanocomposite, which results in improved mechanical properties for the nanocomposite sheets. Furthermore, the addition of compatibilized HNTs to the PS/POE blends leads to decreased O2 and N2 gas permeabilities. Besides, incorporating POE, HNTs, and PP‐g‐MA leads to a decrease in water vapor transmission of PS. In the end, the experimentally‐determined mechanical properties and gas permeabilities of the nanocomposite sheets are compared to those predicted by prevalent theoretical models, revealing a good agreement between the experimental and theoretical results. Molecular‐dynamics simulations are also carried out to calculate the gas diffusion coefficients in the different sheets to further support the experimental findings in this study. Overall, the PS/POE/HNT/PP‐g‐MA nanocomposite sheets fabricated in this work demonstrate excellent mechanical and gas barrier properties; and hence, can be used as candidate packaging materials. However, the strength of the resulting PS/POE blend may be inferior to that of the virgin PS.

Abstract Polymers are omnipresent in our everyday lives. For specific applications, their properties can be extensively modified by various types of additives, e.g., processing stabilizers, antioxidants, UV-stabilizers, flame retardants, and plasticizers. While several additives are nowadays considered to be toxic or persistent in the environment, quantitative data characterizing plastic fragmentation and microplastic formation have not yet been discussed in detail. Here, we present a long-term, laboratory-controlled accelerated weathering study on polypropylene (PP) particles with and without processing stabilizers. We were able to identify the stabilizers as Irgafos® 168, and Irganox® 1010. For both PP sample sets, we monitored the degradation using a combination of various analytical methods, such as gel permeation chromatography, particle size distributions, scanning electron microscopy, solid-state 13C magic-angle spinning NMR and liquid-state 1H, 13C, 31P NMR spectroscopy, differential scanning calorimetry and matrix-assisted laser desorption ionization time of flight mass spectrometry. The stabilizers prevent degradation by simulated solar radiation for about 350 h. Then, degradation sets in rapidly, leading to an exponential decrease in molecular weight and particle size, accompanied by an increase in crystallinity and the formation of oxygen-containing functional groups. After 3200 h, representing approximately 2 years of outdoor weathering, both PP samples exhibit comparable characteristics and sizes, regardless if a stabilizer was initially present. During degradation, an extremely large number of 100,000 daughter particles (4 µm) are formed and released from one MP particle of 192 µm diameter. Their physical properties and chemical composition have largely changed, resulting in a very low molecular weight and a hydrophilic character. These particles no longer resemble pristine PP. We thus expect them to be more prone to biodegradation compared to the starting material.

Abstract Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so‐called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.

This study highlights the need for a deeper understanding of the structure-property relationships of carbon fiber reinforced thermosets applications, whenever considered as a functional part for running footwear. This is done, investigating the static and dynamic flexural properties of three different epoxy resins in prepreg-based carbon fiber composite laminates, varying the glass transition temperature (Tg). In this way, the inherent morphology of the resin was correlated with the fatigue properties of the laminate, which is crucial for the design of composite stiffening inlays for running shoes. First, it was shown that the crosslink density and aromatic content of the resin, which correlates with Tg, drastically affect the compressive strength of the matrix and are therefore crucial for the static and dynamic flexural properties of CFRP. Increasing the Tg from 147 °C to 269 °C leads to stiffening of the resin and thus increased resistance to fiber buckling, resulting in improved bending stiffness, flexural strength, bending angle, overall fatigue strength and thus durability of CFRP plates for running shoes. Moreover, the percentage of fibers in the loading direction can be considered as the main factor affecting the flexural properties of the laminate. Here, a quasi-isotropic stacking order leads to an increased bending angle but to a decrease in bending stiffness, flexural strength and fatigue strength compared to a unidirectionally reinforced composite due to a high load bearing capacity of the 0° fibers. This knowledge creates a basis to bridging the gap between composite material and biomechanical sports science for future work.

Nanoclay (NC) has gas barrier properties that, when used in food packaging, protects food against spoilage. Moreover, food packaging frequently makes use of rigid and foamed polystyrene (PS). In this work, reactive blending in a co-rotating twin-screw extruder was used to process PS, polyolefin elastomer (POE), and NC blends, leading to microphase-separated PS/POE/NC nanocomposite films. The structural and CO2 and N2 barrier properties of the resulting films were determined. The distribution of the NC platelets in the blends was theoretically predicted using the wetting coefficients. Nearly all NC platelets were found in the PS phase, in agreement with the theoretical predictions. Moreover, the NC platelets were found to be concentrated at the interfacial zones between the polymer phases when a compatibilizer was added to the blend. Scanning electron microscopy, wide-angle X-ray scattering, and transmission electron microscopy were used to examine the microstructure of the PS/POE/NC nanocomposites. Adding NCs as a gas barrier component to the PS/POE blend resulted in a decrease in CO2 and N2 permeability. For a better understanding of the gas diffusion in the pure PS and POE, as well as PS/POE blend, molecular dynamics simulations were performed to enable the calculation of gas diffusion coefficients in the different systems. The simulation results confirmed the experimental trends observed in this work.

In this study, a latent and tacky epoxy resin (EP) modified with siloxane core-shell-particles was developed and investigated. The use of EP as a towpreg matrix for winding of cryogenic composite vessels requires a certain toughness to resist microcracking. First, the mechanical properties at +90 °C, +22 °C, −50 °C and −196 °C were examined, with emphasis on the fracture toughness at cryogenic temperatures. Although the modulus of the resin increased dramatically, the KIC also increased by + 100% at −196 °C. Compression testing revealed that the associated yield point increased up to 500 MPa at −196 °C. The yield point of the modified resins was reduced by almost 10% which leads to easier yielding and enabling toughening mechanisms. Thus, the KIC value clearly is not the primary property that needs to be improved in cryogenics. Second, the radius of the plastic zone around the crack tip (Rp) was calculated. It decreased mathematically from 1.9 μm to 0.4 μm, due to a reduced energy dissipation resulting from a smaller spatial expansion of the plastic deformation zone. Finally, an optimum value of 3% by volume of polydimethylsiloxane was identified, demonstrating an increase of the Rp to 1.8 μm at −196 °C and proving the necessity of combinatorial methods to understand temperature-dependent failure of epoxy matrices.

Epoxy (EP) resins exhibit desirable mechanical and thermal properties, low shrinkage during cuing, and high chemical resistance. Therefore, they are useful for various applications, such as coatings, adhesives, paints, etc. On the other hand, carbon nanotubes (CNT), graphene (Gr), and their derivatives have become reinforcements of choice for EP-based nanocomposites because of their extraordinary mechanical, thermal, and electrical properties. Herein, we provide an overview of the last decade's advances in research on improving the thermal and electrical conductivities of EP resin systems modified with CNT, Gr, their derivatives, and hybrids. We further report on the surface modification of these reinforcements as a means to improve the nanofiller dispersion in the EP resins, thereby enhancing the thermal and electrical conductivities of the resulting nanocomposites.

This study discusses weathering-induced oxidation of polystyrene with and without different concentrations of the antioxidant Irgafos using Laser-induced Breakdown Spectroscopy (LIBS). By examining the spectral feature of oxidation and due to laser ablation, a systematical analysis of the oxygen content on the sample’s surface and its penetration depth could be conducted. The results show that LIBS can be used as a fast technique for the quantification of weathering-induced oxidation.

Abstract Due to their light‐weight and cost‐effectiveness, cellular thermoplastic foams are considered as important engineering materials. On the other hand, additive manufacturing or 3D printing is one of the emerging and fastest growing manufacturing technologies due to its advantages such as design freedom and tool‐less production. Nowadays, 3D printing of polymer compounds is mostly limited to manufacturing of solid parts. In this context, a merged foaming and printing technology can introduce a great alternative for the currently used foam manufacturing technologies such as foam injection molding. This perspective review article tackles the attempts taken toward initiating this novel technology to simultaneously foam and print thermoplastics. After explaining the basics of polymer foaming and additive manufacturing, this article classifies different attempts that have been made toward generating foamed printed structures while highlighting their challenges. These attempts are clustered into 1) architected porous structures, 2) syntactic foaming, 3) post‐foaming of printed parts, and eventually 4) printing of blowing agents saturated filaments. Among these, the latest approach is the most practical route although it has not been thoroughly studied yet. A filament free approach that can be introduced as a potential strategy to unlock the difficulties to produce printed foam structures is also proposed.

In this study, application relevant toughened epoxy-amine formulations were investigated regarding their mechanical behavior at low temperatures and compared to a non-toughened reference. The application-oriented resins are based on reactive diluent-modified diglycidylether of bisphenol A (DGEBA) which were tested at 22 °C and −50 °C in regard to their fracture toughness (KIC) and fatigue crack propagation (da/dN) behavior. The E′ and E’’ moduli and the corresponding glass transition temperatures Tg were determined via dynamic mechanical thermal analyses (DMTA) which also described the influence of the block copolymeric toughener on the epoxy resin network. The plastic zone size, calculated during crack propagation, reveals the temperature dependent toughener-matrix interaction. The prevailing energy dissipation mechanisms were correlated with the changes of E’. SEM micrographs confirm the superior performance of the toughened system at −50 °C by the decrease of the fatigue cack propagation slopes and highlight the trends of the materials low temperature behavior.