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The beneficial use of computer simulations to track the microstructural evolution of individual species is highlighted in view of macromolecular engineering and design, considering two case studies on catalytic polymerization, and both "low" (<100) and "high" (>100) chain lengths, that is, i) atom transfer radical copolymerization of n-butyl acrylate and styrene aiming at the synthesis of functional macrospecies of "identical' chain length; and ii) chain shuttling polymerization of ethylene and 1-octene toward the production of segmented block copolymers with "soft" and "hard" segments. Model parameters are validated and/or tuned based on literature data. The modeling strategy supports the future identification of chemical structure-polymer property relationships and is based on the combination of principles from polymer reaction engineering, chemistry, and physics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Short carbon fiber (sCF)-based polymer composite parts enable one to increase in the material property range for additive manufacturing (AM) applications. However, room for technical and material improvement is still possible, bearing in mind that the commonly used fused filament fabrication (FFF) technique is prone to an extra filament-making step. Here, we compare FFF with direct pellet additive manufacturing (DPAM) for sCF-based composites, taking into account degradation reactions, print quality, and energy usage. On top of that, the matrix is based on industrial waste polymers (recycled polycarbonate blended with acrylonitrile butadiene styrene polymer and recycled propylene), additives are explored, and the printing settings are optimized, benefiting from molecular, rheological, thermal, morphological, and material property analyses. Despite this, DPAM resulted in a rougher surface finish compared to FFF and can be seen as a faster printing technique that reduces energy consumption and molecular degradation. The findings help formulate guidelines for the successful DPAM and FFF of sCF-based composite materials in view of better market appreciation. [ABSTRACT FROM AUTHOR]

Kinetic Monte Carlo (kMC) modelling is ubiquitous to simulate the time evolution of (bio)chemical processes, specifically if populations are involved. A recurring task is the selection of the smallest control volume that leads to convergence, which means that the model outputs are accurate and sufficiently free from stochastic noise and do not significantly change upon further increasing this volume. Selecting a too high (safe) control volume leads to an excessive simulation time, while many small incremental control volume increases are inefficient. This work therefore presents an automated tool to determine the smallest control volume leading to convergence. The tool is illustrated for (intrinsic) free radical and nitroxide mediated polymerization (FRP/NMP), in which the chain length distribution (CLD) is a crucial output. The algorithm starts with a very low volume to then check if the desired (monomer) conversion can be reached, the number average chain length is accurate, and finally the signal‐to‐noise (SNR) ratio at the CLD level is below a threshold. The execution time of the algorithm is less than twice the time of running the converged simulation directly, hence, saving tremendous time in setting up a kMC simulation and facilitating benchmark studies even beyond polymer reaction engineering applications. [ABSTRACT FROM AUTHOR]

As societal interest in recycling of plastics increases, modeling thermochemical recycling of vinyl polymers, e.g., via pyrolysis or reactive extrusion, becomes increasingly important. A key aspect remains the reliability of the simulation results with fewer evaluation studies regarding convergence as in the polymerization or polymer reaction engineering field. Using the coupled matrix-based Monte Carlo (CMMC) framework, tracking the unzipping of individual chains according to a general intrinsic reaction scheme consisting of fission, β-scission, and termination, it is however illustrated that similar convergence demands as in polymerization benchmark studies can be employed, i.e., threshold values for the average relative error predictions on conversion and chain length averages can be maintained. For this illustration, three theoretical feedstocks are considered as generated from CMMC polymer synthesis simulations, allowing to study the effect of the initial chain length range and the number of defects on the convergence demands. It is shown that feedstocks with a broader chain length distribution and a long tail require a larger Monte Carlo simulation volume, and that the head–head effects play a key role in the type of degradation mechanism and overall degradation rate. A minimal number of chains around 5 × 105 is needed to properly reflect the degradation kinetics. A certain degree of noise can be allowed at the higher carbon-based conversions due to the inevitable decrease in number of chains. [ABSTRACT FROM AUTHOR]

Acrylonitrile butadiene styrene (ABS) based polymeric composites consisting of mono‐ and hybrid nano‐compounds, that is, graphene nanoplatelets (GNP's), multi‐walled carbon nanotubes (CNT's), and titanium dioxide (TiO2), are studied for fused filament fabrication (FFF). Rheological analysis in a screening step reveals that nanocomposites containing CNT result in a better nano‐filler dispersion within the matrix and enhanced matrix interaction. The addition of GNP and TiO2 leads to a better coalescence between the deposited filaments. For the actual FFF specimens, emphasis is on the tensile, flexural and impact properties as well as the void content. It is shown that the joint addition of GNP, CNT, and TiO2 gives rise to a remarkable synergistic effect, leading to an improved dispersion and an increased tensile modulus and strength of 3D printed ABS by 16 and 20%. Decreasing the layer thickness increases the mechanical properties of the materials, while the printing temperature does not lead to major variations of the mechanical properties, due to a dominant effect of the addition of nanoparticles. It is also shown that for well‐designed composites the slower sintering and higher void content is overruled by the reinforcement effect. [ABSTRACT FROM AUTHOR]

Population balance modeling is very popular in several branches of modern science, including (bio)chemical engineering, geography, and demography. A growing trend is the use of stochastic solvers (e.g., kinetic Monte Carlo), but care should be taken upon inputting and outputting distributed data for the populations involved. In the present contribution, several procedures and guidelines are formulated facilitating such data treatment. The solutions are exemplified through polymerization and polymer modification case studies, taking the molar mass or chain length as core stochastic variable. It is shown that rediscretization is often necessary, as experimentally measured distributions are not directly interpretable at the input side of stochastic solvers. This rediscretization should take place both for the abscissa and ordinate values of the distributions. As stochastic solvers often display noisy data as model output, attention is paid to the smoothening of the output distributions as well. It is highlighted that the kernel‐smoothening method is very promising, as it can reliably tackle postprocessing of nonsymmetric distributions. Guidelines are formulated regarding the correct interpretation of the distribution tail both for the input and output modifications. [ABSTRACT FROM AUTHOR]

Extending photovoltaic (PV) module lifetimes beyond 30 years is a goal of significant priority. A challenge that must first be addressed, however, is the development of a predictive reliability model that captures the synergy of terrestrial stressors on module degradation, particularly at encapsulant interfaces. Using a metrology designed specifically for PV modules, a comprehensive study of the widely used ethylene vinyl acetate encapsulant was performed in which encapsulant adhesion was evaluated as a function of environmental stressors (UV exposure, temperature, and humidity) for modules aged both under accelerated lab and internationally located field conditions for months to nearly 3 decades. Mechanical and chemical characterization methods are combined with fundamental polymer reaction engineering to unravel the degradation processes active at the molecular scale that lead to encapsulant delamination. An analytical and modular model framework is put forward enabling the prediction of long‐term PV module durability, starting from fundamental principles at the molecular level and explicitly accounting for bond rupture events in the bulk encapsulant and at the encapsulant interfaces. Successful parameter tuning to adhesion data indicates a dominant occurrence of deacetylation, β‐scission, and hydrolytic depolymerization, respectively. The model contributes to the longstanding challenge of predicting module lifetimes in any geographic location while minimizing time‐consuming and costly aging studies. Mechanisms of encapsulant adhesive degradation are characterized through mechanical testing and chemical analysis of lab‐ and field‐aged photovoltaic modules. Using fundamentals of polymer reaction kinetics, a modular and analytical model is then developed that captures the synergy of molecular degradation processes to fully characterize and predict adhesive reliability for long‐term field deployment. [ABSTRACT FROM AUTHOR]

Based on kinetic Monte Carlo simulations of the monomer sequences of a representative number of copolymer chains (≈ 150,000), optimal synthesis procedures for linear gradient copolymers are proposed, using bulk Initiators for Continuous Activator Regeneration Atom Transfer Radical Polymerization (ICAR ATRP). Methyl methacrylate and n-butyl acrylate are considered as comonomers with CuBr2/PMDETA (N,N,N',N",N"-pentamethyldiethylenetriamine) as deactivator at 80 °C. The linear gradient quality is determined in silico using the recently introduced gradient deviation () polymer property. Careful selection or fed-batch addition of the conventional radical initiator I2 allows a reduction of the polymerization time with ca. a factor 2 compared to the corresponding batch case, while preserving control over polymer properties ( ≈ 0.30; dispersity ≈ 1.1). Fed-batch addition of not only I2, but also comonomer and deactivator (50 ppm) under starved conditions yields a below 0.25 and, hence, an excellent linear gradient quality for the dormant polymer molecules, albeit at the expense of an increase of the overall polymerization time. The excellent control is confirmed by the visualization of the monomer sequences of ca. 1000 copolymer chains. [ABSTRACT FROM AUTHOR]

The importance of diffusional limitations in controlled radical polymerization at laboratory scale and in homogeneous medium is highlighted using different diffusion models. In particular, a coupled 'parallel' encounter pair model is introduced which allows a rigorous description of the influence of diffusional limitations on the activation/deactivation process. Diffusional limitations on termination have a significant influence, whereas those on the activation/deactivation process can disturb the regular growth pattern at high conversion if the mediating agent is a sufficiently bulky species. Diffusional limitations on initiation are only important in case radical initiator is still present at high conversion. [ABSTRACT FROM AUTHOR]

State of the-Art for Extrudate Swell of Molten Polymers: From Fundamental Understanding at Molecular Scale toward Optimal Die Design at Final Product Scale B Front Cover b : In article number 2000340, Dagmar R. D'hooge and co-workers highlight both the experimental and theoretical capabilities to control extrudate die swell for polymer material production by extrusion, which is a leading technology in the materials engineering field. Swelling takes place as polymer molecules are viscoelastic, implying that when they exit the extrusion equipment they recoil changing the dimensions and thus the product stability. [Extracted from the article]

In article number 1807434, Dagmar R. D'hooge, Karen De Clerck, and co‐workers develop a direct route to control the interfacial bonding between two polymeric materials through molecular diffusion during in situ chemical formation of one of those materials. This route is used to create nanofibrous hybrid materials that have excellent toughness. The image shows a nanofibre ligament bridging a microcrack, resulting in highly toughened hybrid materials. [ABSTRACT FROM AUTHOR]

A 5-dimensional Smith-Ewart based model is developed to understand differences for reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization with theoretical agents mimicking cases of slow fragmentation, cross-termination, and ideal exchange while accounting for chain length and monomer conversion dependencies due to diffusional limitations. The focus is on styrene as a monomer, a water soluble initiator, and a macro-RAFT agent to avoid exit/entry of the RAFT leaving group radical. It is shown that with a too low RAFT fragmentation rate coefficient it is generally not afforded to consider zero-one kinetics (for the related intermediate radical type) and that with significant RAFT cross-termination the dead polymer product is dominantly originating from the RAFT intermediate radical. To allow the identification of the nature of the RAFT retardation it is recommended to experimentally investigate in the future the impact of the average particle size (dp) on both the monomer conversion profile and the average polymer properties for a sufficiently broad dp range, ideally including the bulk limit. With decreasing particle size both a slow RAFT fragmentation and a fast RAFT cross-termination result in a stronger segregation and thus rate acceleration. The particle size dependency is different, allowing further differentiation based on the variation of the dispersity and end-group functionality. Significant RAFT cross-termination is specifically associated with a strong dispersity increase at higher average particle sizes. Only with an ideal exchange it is afforded in the modeling to avoid the explicit calculation of the RAFT intermediate concentration evolution. [ABSTRACT FROM AUTHOR]

To understand how the thermal conductivity (TC) of virgin commercial polymers and their composites with low graphite filler amounts can be improved, the effect of material choice, annealing and moisture content is investigated, all with feasible industrial applicability in mind focusing on injection molding. Comparison of commercial HDPE, PP, PLA, ABS, PS, and PA6 based composites under conditions minimizing the effect of the skin-core layer (measurement at half the sample thickness) allows to deduce that at 20 m% of filler, both the (overall) in- and through-plane TC can be significantly improved. The most promising results are for HDPE and PA6 (through/in-plane TC near 0.7/4.3 W·m−1K−1 for HDPE and 0.47/4.3 W·m−1K−1 for PA6 or an increase of 50/825% and 45/1200% respectively, compared to the virgin polymer). Testing with annealed and nucleated PA6 and PLA samples shows that further increasing the crystallinity has a limited effect. A variation of the average molar mass and moisture content is also almost without impact. Intriguingly, the variation of the measuring depth allows to control the relative importance of the TC of the core and skin layer. An increased measurement depth, hence, a higher core-to-skin ratio measurement specifically indicates a clear increase in the through-plane TC (e.g., factor 2). Therefore, for basic shapes, the removal of the skin layer is recommendable to increase the TC. [ABSTRACT FROM AUTHOR]

In article number 1804138, Karen De Clerck and co‐workers describe how silica nanofibrous membranes produced by direct electrospinning of a sol‐gel solution without a sacrificing polymer allow high‐end separation and purification due to a high thermal and chemical resistance. The water repellent or absorbing nature can be tuned by applying a humidity or thermal treatment. It is showcased that fast gravity driven membrane separation of heterogeneous azeotropes can be achieved. [ABSTRACT FROM AUTHOR]

In this work, the feasibility of ultra-high drug loaded amorphous solid dispersions (ASDs) for the poorly soluble itraconazole, mebendazole and celecoxib via solvent electrospinning in combination with poly(2-ethyl-2-oxazoline) and fenofibrate in combination with polyvinylpyrrolidone is demonstrated. By lowering the polymer concentration in the electrospinning solution below its individual spinnable limit, ASDs with a drug content of up to 80 wt% are obtained. This is attributed to drug-polymer interactions not being limited by default to hydrogen bonds, as also Van der Waals interactions can result in high drug loadings. The theoretically predicted miscibility by the Flory-Huggins theory is corroborated by the experimental findings based on (modulated) differential scanning calorimetry and x-ray diffraction. Globally, the maximally obtained amorphous drug loadings are higher compared to the loadings found in literature. Additionally, non-sink dissolution tests demonstrate an increase in solubility of up to 50 times compared to their crystalline counterparts. Moreover, due to the lack of precipitation biocompatible PEtOx succeeds in stabilizing the dissolved drug and inhibiting its instant precipitation. The current work thus demonstrates the broader applicability of the electrospinning technique for the production of physically stable ASDs with ultra-high drug loadings, a result which has been validated for several Biopharmaceutics Classification System class II drugs. [Display omitted] • Poly(2-ethyl-2-oxazoline) has shown to be a promising excipient for electrospun amorphous solid dispersions. • High drug loadings are achieved by lowering the polymer concentration below spinning concentrations of pure PEtOx. • Theoretical Flory-Huggins based miscibility is experimentally corroborated. • Biocompatible PEtOx stabilizes and inhibits instant drug precipitation upon dissolution. • Non-sink dissolution tests demonstrate an increase in solubility of up to 50 times. [ABSTRACT FROM AUTHOR]

• Cloud point validation of the Flory-Huggins theory using turbidimetry and DLS. • Ternary diagrams as a solvent selection tool in polymer dissolution recycling. • Theoretical and experimental construction of ternary phase diagrams. • Inclusion of a ternary interaction parameter to conform the model to the experiments. One of the recycling methods for polymer waste is the dissolution-precipitation process, which is based on dissolving the polymer in a suitable solvent followed by contaminant removal by, optionally filtration, and polymer precipitation through the addition of a nonsolvent. As showcased for poly(vinyl chloride) (PVC), a polymer used in the construction sector and for packaging, the current work makes clear that the less studied ternary phase diagrams are a very promising tool for the ideal solvent-nonsolvent selection. Such ternary phase diagrams provide compositional information concerning the phase separation process pushing forward the dissolution-precipitation recycling technology. It is demonstrated that these diagrams can be constructed by connecting the Flory-Huggins theory, Hansen solubility parameters and UNIQUAC activity coefficients. Model validation is performed via cloud point measurements for which one can utilize labour-intensive visual inspection or, as demonstrated in this work, one can also apply dynamic light scattering and turbidimetry, with the latter as the preferred method that is cheaper and faster. Ternary phase diagrams for multiple solvent-nonsolvent systems are theoretically constructed and experimentally validated, considering cyclohexanone-ethanol and THF-ethanol as solvent-nonsolvent pairs. It follows that PVC phase diagrams are inherently different compared to other, more commonly studied polymers, such as polyethersulfone (PES) and that for PVC the addition of a ternary interaction parameter might be required. [ABSTRACT FROM AUTHOR]

An innovative model-based design strategy to synthesize well-defined sequence-controlled polymers is presented, enabling selection of both the most appropriate mediating agent and reaction conditions. In combination with experimental analysis, advanced kinetic Monte Carlo simulations are conducted, allowing a visualization of the connectivity of all monomer units of ca. 105 individual copolymer chains. The product quality can therefore be uniquely and unambiguously predicted for the first time at the molecular level, explicitly accounting for chain-to-chain deviations. The strategy is illustrated for BlocBuilder MA-initiated nitroxide-mediated polymerization, with styrene and N-benzylmaleimide as comomomers, and is generally applicable for all reversible deactivation radical polymerization (RDRP) techniques. Further design of the nitroxide-mediating capabilities and the reaction conditions allows the realization of a targeted (multi)functionalization pattern, including an increase of the contribution of trifunctionalized chains above 75%. The reported results are interpreted in terms of the individual activation-growth-deactivation cycles and provide an unprecedented mechanistic understanding of RDRP in general. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coupled matrix based Monte Carlo as powerful tool for grafting/crosslinking kinetics. • Unique and successful model validation under FRP and FRIG conditions. • Need of shooting model to rapidly update average apparent rate coefficients. • Molar mass bimodality due to chain length difference for vinyl and graft copolymer. • High relevance of chain length and monomer conversion dependencies. In radical (co)polymerization and polymer recycling processes with branch and crosslinking formation easily more than two macroradical types exist, defining a variety of termination reaction possibilities. However, in many kinetic modeling studies the termination of each distinct radical pair is described by the same average (apparent) rate coefficient formula, only acknowledging polymer mass fraction variations but ignoring chain length dependencies. In the present work, it is demonstrated that coupled matrix-based Monte Carlo (CMMC) simulations can reliably predict the termination behavior of distinct radical pairs. This is illustrated for free-radical induced grafting (FRIG) of polybutadiene with styrene, distinguishing six termination (by recombination) reaction channels as defined by (conventional) polystyrene radicals, polybutadiene mid-chain radicals, and grafted end-chain radicals. Model validation is uniquely performed under both free radical polymerization (FRP) and FRIG conditions, highlighting that the CMMC simulations should be applied with the so-called shooting method, in which each average apparent termination rate coefficient is updated per reaction event to capture to dynamic changes of all chain length distributions in the FRIG process. These updates should be done based on the composite k t (diffusion) model while considering better-tuned chain transfer kinetic parameters, as recommended based on recent developments in the polymer reaction engineering field. It is showcased that the FRIG reaction conditions have a clear impact on the kinetic importance of all radical types and their termination pattern determining the evolution of the bimodal log-molar mass distribution. The current work further enhances the stochastic modeling field to accurately represent (de)polymerization kinetics with several macroradical types and topological variations. [ABSTRACT FROM AUTHOR]