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Pulsed laser polymerization (PLP) has emerged as a leading technique to determine radical polymerization characteristics. Here we present a concise overview of the potential of this polymerization technique mainly in combination with size exclusion chromatography (SEC) analysis. Focus is not only on the traditional determination of intrinsic propagation reactivities for radical polymerizations with one dominant macroradical type based on inflection point data but also on (i) the determination of such intrinsic reactivities if multiple dominant radical types are present (e.g. , for radical polymerization with branch formation and copolymerization); and (ii) the exploitation of the complete SEC trace to obtain information on the quantum yield, chain initiation and (apparent) termination reactivity. General guidelines are provided how to increase the accuracy of PLP-SEC measurements and to combine such measurements with advanced kinetic modeling and ab initio calculations to further increase our understanding of radical polymerization chemistry and to construct chemical structure-reactivity relationships. [ABSTRACT FROM AUTHOR]

Pulsed laser polymerization (PLP) has emerged as a leading technique to determine radical polymerization characteristics. Here we present a concise overview of the potential of this polymerization technique mainly in combination with size exclusion chromatography (SEC) analysis. Focus is not only on the traditional determination of intrinsic propagation reactivities for radical polymerizations with one dominant macroradical type based on inflection point data but also on (i) the determination of such intrinsic reactivities if multiple dominant radical types are present (e.g. , for radical polymerization with branch formation and copolymerization); and (ii) the exploitation of the complete SEC trace to obtain information on the quantum yield, chain initiation and (apparent) termination reactivity. General guidelines are provided how to increase the accuracy of PLP-SEC measurements and to combine such measurements with advanced kinetic modeling and ab initio calculations to further increase our understanding of radical polymerization chemistry and to construct chemical structure-reactivity relationships. [ABSTRACT FROM AUTHOR]

The strength of multi-scale modeling to support the fundamental understanding and design of radical polymerization processes is illustrated, considering both controlled and free radical polymerization (CRP/FRP) in non-dispersed (bulk/solution) and dispersed (suspension/emulsion) media. At the molecular scale, the importance of joint experimental and theoretical studies is highlighted. At the micro-scale, the concept of apparent rate coefficients is elaborated to account for the possible influence of diffusional limitations on the local reaction rates. At the meso-scale, the key characteristics to fundamentally describe the evolution of the particle size distribution are covered and the possible interaction with the micro- and macro-scale is discussed. At the macro-scale, the main mathematical tools to assess the relevance of mixing and temperature gradients are provided. Several examples on CRP and FRP processes are included to showcase the modeling capabilities for each scale, focusing both on laboratory and industrial reactors. [ABSTRACT FROM AUTHOR]

A systematic kinetic investigation of the living cationic ring-opening polymerization (CROP) involving 2-ethyl-2-oxazoline, 2-methyl-2-oxazoline, and 2-phenyl-2-oxazoline employing a series of alkyl sulfonate initiators with variation of the alkyl initiating fragment (methyl, ethyl, iso -propyl) and the leaving group/counterion (tosylate, nosylate, triflate) is reported. The study reveals that the initiation and propagation reactivity increases in the order tosylate < nosylate < triflate. Slow initiation is observed for EtOTs, while EtONs is a sufficiently fast initiator even for 2-phenyl-2-oxazoline. It is thus recommended to avoid the use of alkyl tosylates, except MeOTs, as initiators for the CROP of 2-alkyl-2-oxazolines. Although triflates are generally the best initiators, the use of the more stable and easier synthesizable nosylates provides a suitable alternative for the design of functional initiators for the CROP of 2-alkyl-2-oxazolines. [ABSTRACT FROM AUTHOR]

Highlights: [•] Assessment of end-group functionality in ATRP of NiPAm. [•] Synthesis of well-defined “smart” amphiphilic block copolymers. [•] Relevance of side reactions and diffusional limitations in ATRP of NiPAm. [ABSTRACT FROM AUTHOR]

Flexible and stretchable piezoresistive strain sensors which can translate mechanical stimuli (strain changes) into electrical signals (resistance changes) provide a simple and feasible detection tool in the field of health/damage monitoring, human motion detection, personal healthcare, human-machine interfaces, and electronic skin. Herein a detailed overview is presented on both strategies for sensing performance improvement and progress to medium or large-scale fabrication. A broad range of matrices/substrates and incorporated nanomaterials is covered and attention is paid to the current state-of-the-art of feasible but low-cost manufacturing methods. The sensor design parameters include sensitivity (gauge factor), stretchability, linearity, hysteresis, biocompatibility, and self-healing potential. Starting from fundamental sensing mechanisms, i.e. the tunneling effect, the disconnection mechanism, and the crack propagation mechanism, examples are provided from lab to application scale. [ABSTRACT FROM AUTHOR]

Highlights • Relevance of 3D numerical simulations for slit die swell. • Interplay of viscous and elastic effects using the PTT constitutive model. • Model validation based on die pressure and real time experimental HD imaging. Abstract 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. [ABSTRACT FROM AUTHOR]

The development of well-designed polylactic acid (PLA) based composite filaments through fused filament fabrication (FFF) is crucial, as PLA printed parts are characterized by a high brittleness. Here we focus on FFF composite formation using ductile poly (butylene adipate-co-terephthalate) (PBAT), the nanoclay cloisite and the chain extender Joncryl. A high modulus, flexibility, toughness and notched impact strength result upon combining PLA/PBAT (80:20; mass basis) with a sufficiently high cloisite amount (1–5 phr) supported by a suited Joncryl amount (0.3 phr). A fine PBAT dispersion is then ensured, as confirmed by scanning and transmission electron microscopy. For high cloisite amounts (e.g. 10 phr) the crystallinity and vicat softening temperature enhance but cloisite aggregation is unavoidable, leading to a strong reduction in tensile strain and toughness. Annealing increases crystallinity thus material strength, rigidity and impact, at least partially overruling the need of a fine dispersion. Novel radar charts are also reported to select an optimal bio-based blend suitable for different end-user applications by adjusting the composition and possible post-annealing of printed products. Image 1 Innovative bio-based fused filament fabrication (FFF) of composite PLA-based filaments. • Design of PLA-based composite filaments for high quality FFF. • Morphology control for both PLA matrix and PBAT dispersed phase. • Introduction of radar charts for composite filaments in view a desired application [ABSTRACT FROM AUTHOR]

Polyolefin (PO) blends are difficult to separate due to density and chemical structure similarities. The associated waste treatment in the context of mechanical recycling is therefore complicated by the establishment of multi-phase morphologies that are not yet fully understood. In the present work, a high density polyethylene (HDPE) with a very high melt flow index (MFI) and a polypropylene (PP) with a very low MFI are deliberately mingled to better understand the full spectrum of morphological variations for PO blending. The linkage with the control over injection mold-based mechanical properties such as tensile strength, elasticity modulus, elongation at break, and impact strength is made. This is done supported by the connecting of experimental analyses at different scales, including (i) the molecular scale via size exclusion chromatography and Fourier transform infrared spectroscopy (FTIR), and (ii) the meso-scale via scanning electron and polarized light microscopy as well as differential scanning calorimetry, including a differentiation between the bulk and surface region. Emphasis is both on blends processed once and re-processed either once, twice or three times. For the single processing, it is demonstrated that in most cases a droplet morphology is obtained, with smaller droplets in case HDPE is the minor component and with a dominance of HDPE at the surface even for 60% PP, due to a better HDPE flowability. It is further shown that the scission of PP chains and crosslinking of HDPE chains respectively facilitates and inhibits crystallization, at least if meso-scale -mixing as more evident during re-processing is not taking over. It is also highlighted that the properties of PP can be enhanced by adding up to 10 wt% HDPE, acting as a filler, and that the (ideally) reprocessed blends remain suitable for application. [Display omitted] • Morphological variations of polyolefin blends with large MFI differences for its components. • More molecular scale degradation but also more macro-scale mixing upon reprocessing. • Analysis at both surface and in bulk region to identify morphological gradients. • Optimized mechanical properties based on composition. • Guidelines on analysis of stability blends in view of mechanical recycling $. [ABSTRACT FROM AUTHOR]

Abstract 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 (GF max) > 50 and ε max > 100%) can be realized: GF max > 104 and ε max = 20–240%. OBC binary composites with a high CB 2 amount (e.g. 15 m%) are however needed for ultrahigh static strains (ε max > 600%). Well-designed ternary composites (e.g. OBC 40 -CB/TPU 60 -7-a and OBC 30 -CB/TPU 70 -7-a) possess a large dynamic resistance change, negligible hysteresis and high stability and display strain sensor application potential. Highly CB 2 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. [ABSTRACT FROM AUTHOR]

• Experimental protocol to determine hydrolytic degradation in polyester. • Half-life times for degradation via regression analysis of the most sensitive data. • Lower chain lengths matter for the material properties during degradation. • Linkage of molecular scale reactions and final part properties at application level. • Relevance of water removal and careful storage for PETG. Poly(ethylene terephthalate glycol) (PETG) is a promising polyester for additive manufacturing (AM) applications. However, an important question is its thermal and hydrolytic stability under storage conditions. The current work investigates which measuring technique is most suited to qualitatively answer this question, completing the field for polyester stability analysis by focusing on more amorphous structures. In combination with regression analysis under lab accelerated conditions to practically estimate characteristic degradation time scales and currently lacking (overall) Arrhenius parameters, a distinction is made between techniques dealing with molecular and larger scale properties, distinguishing between Fourier Transfer Infrared (FTIR) spectroscopy, size exclusion chromatography (SEC), rheological measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It is shown that hydrolytic scission is dominant over thermal scission, and mainly affects the lower mass region of the molar mass distribution. However, the degradation sensitivity can only be assessed using the SEC number average molar mass, and a more pronounced qualitative sensitivity is only obtained applying rheological analysis, with an extrapolated very low half-life time under water-saturated conditions of ca. 3 days in the Newtonian region and of 2 days in the shear thinning region. It is further highlighted that hydrolytic degradation influences the tensile properties of parts fabricated with fused filament fabrication, which is an important AM technique. [ABSTRACT FROM AUTHOR]

A pseudo-steady state based (PSSA) deterministic solution strategy is presented to calculate the concentrations of single and multi-arm macrospecies types in reversible addition fragmentation chain transfer (RAFT) polymerization, accounting for chain length dependent apparent rate coefficients to fully reflect the impact of diffusional limitations. The simulation time is of minute scale and diffusional limitation on termination are accounted for with the RAFT-chain length dependent-termination technique. Based on an extensive set of experimental data (18 conditions), addition and fragmentation kinetic parameters are determined for RAFT polymerization of styrene initiated by 2,2′-azobis(2-methylpropionitrile) and 2-cyano-2-propyl dodecyl trithiocarbonate. Due to higher chain length dependent apparent termination rates, a rate retardation with respect to the free radical polymerization (FRP) results despite that a simplified degenerative mechanism can be considered. This rate retardation is enhanced for polymerizations exhibiting a stronger gel-effect ( e.g. methyl methacrylate). Then even the average RAFT polymerization characteristics cannot be reliably calculated by approximating the macroradical chain length distribution (CLD) through a Poisson or Schulz-Flory distribution. The calculation of the macroradical CLD always requires a full kinetic model taking into account the chain length dependencies for all individual chain lengths. [ABSTRACT FROM AUTHOR]

[Display omitted] The control of the A/B comonomer distribution over individual chains targeting block and/or gradient monomer distributions is essential to control the macroscopic properties of the resulting copolymers. Matrix-based kinetic Monte Carlo simulations allow to compare each chain of a representative copolymer sample with the desired (mathematical) composition, as defined by monomer inclusion probabilities (P A / B) taking the B-functionalization degree (B-Func) as maximally 50%. A so-called average deviation (SD ∗ value) results per chain, with a close to 0 average (normalized) structural deviation 〈 S D 〉 corresponding to an almost perfect structure and a 〈 S D 〉 close to 1 representing the worst case scenario of a B-homopolymer. The previously assigned 〈 S D 〉 transitions from excellent to good and from good to poor are, however, somewhat arbitrary, e.g. for both symmetric gradient and block copolymers a threshold 〈 SD Good / P o o r 〉 of 0.3 is currently utilized and only for specific asymmetric cases (30% B-Func block, block-gradient, and gradient) 〈 SD Exc / G o o d 〉 and 〈 SD Good / P o o r 〉 values have been reported. The present work puts forward an equation driven method to obtain 〈 S D 〉 threshold values, minimizing the arbitrary nature of the quality classification for a given copolymer type and more importantly aligning the quality assessment for any copolymer type containing block and/or gradient elements. Emphasis is on the complete SD distribution (instead of only its average) for (a)symmetric AB gradient, block A-gradient AB, block A-gradient AB-block B, and AB block copolymers by introducing the overall gradient and block fractions (f Gr / B l) as a novel parameter alongside the targeted degree of polymerization (target DP) and B-Func. Ideal theoretical structures with equal chain length and a perfect implementation of the desired P A / B profiles are dealt with, as they represent the best case an actual synthesis recipe could deliver in the limit. It is shown that the log-normal distribution can be reliably used to approximate the SD distribution, as coefficients of determination (R2) very close to one follow for (a)symmetric copolymers. It is further showcased that threshold values for gradient dominant structures must be higher than those for block-like structures and that well-defined symmetric structures are more difficult to achieve than asymmetric ones. It is also recommended to report 〈 S D 〉 together with its standard deviation σ SD. [ABSTRACT FROM AUTHOR]

• Chemical recycling will be one of the most important contributors to solving the problem of solid plastic waste (SPW) disposal within the circular economy approach. • Pyrolysis and gasification are and will remain the leading technologies for the coming decade because of their flexibility, robustness, and advantageous economics. • Four decades of work on detailed kinetic and transport modeling efforts for pyrolysis and gasification of SPW together with related experimental studies show that substantially more work is needed to gain fundamental understanding and improve process design and performance. • Fulfilling the gap between chemical kinetics, fluid dynamics, and reactor modeling aspects will pave the way for innovative reactors design and the industrial-scale implementation of chemical recycling. Chemical recycling of solid plastic waste (SPW) is a paramount opportunity to reduce marine and land pollution and to enable the incorporation of the circular economy principle in today's society. In addition to more conscious behaviors and wiser product design ("design for recycling"), a key challenge is the identification of the leading recycling technologies, minimizing the global warming potential in an industrially relevant context. Chemical recycling technologies based on pyrolysis and gasification are leading the way because of their robustness and good economics, but an improved understanding of the chemistry and more innovative reactor designs are required to realize a potential reduction of greenhouse gas emissions of more than 100 million tonnes of CO 2 -eq., primarily by more efficient use of valuable natural resources. The feed flexibility of thermal processes supports the potential of pyrolysis and gasification, however, the strong variability in time and space of blending partners such as multiple and co-polymers, additives, and contaminants (such as inorganic materials) calls for accurate assessment through fundamental experiments and models. Such complex and variable mixtures are strongly sensitive to the process design and conditions: temperature, residence time, heating rates – severity, mixing level, heat and mass transfer strongly affect the thermal degradation of SPW and its selectivity to valuable products. A prerequisite in improving design and performance is the ability to model conversion profiles and product distributions based on accurate rate coefficients for the dominating reaction families established using first-principle derived transport and thermodynamic properties. These models should also help with the "design for recycling" strategy to increase recyclability, for example by identifying additives that make chemical recycling difficult. Fundamental experiments of increased quality (accuracy, integrity, validity, replicability, completeness) together with improved deterministic kinetic models, systematically developed according to the reaction classes and rate rules approach, provide insights to identify optimal process conditions. This will allow shedding some light upon the important pathways involved in the thermal degradation of the feedstock and the formation/disappearance of desired or unwanted products. In parallel, the intrinsic kinetics of the dominating elementary reaction steps should be determined with higher accuracy, moving beyond single step kinetics retrieved from thermogravimetric analysis experiments. Together with more accurate kinetic parameters, better models to account for heat and mass transfer limitations also need to be further developed, since plastic degradation involves at least three phases (solid, liquid, gas), whose interactions should be accounted for in a more rigorous way. Novel experimental approaches (e.g. detailed feedstock and product characterization using comprehensive chromatographic techniques and photoionization mass spectrometry) and available computational tools (e.g. kinetic Monte Carlo, liquid phase, and heterogeneous theoretical kinetics) are needed to tackle these problems and improve our fundamental understanding of chemical recycling of SPW. [ABSTRACT FROM AUTHOR]

• Relevance of upstream contraction flow on slit die design. • 3D simulation of edge/middle height and width die swell ratio. • Combined effects of die geometry and PTT model parameters on extrudate swell. • Interplay of stress and velocity redistribution on anisotropic swell behavior. The relevance of upstream contraction for extrudate swell behavior of polymer melts is numerically investigated for slit dies with an aspect ratio of 10 and a length-to-height ratio ranging from 2.5 to 40. Three-dimensional (3D) flow simulations are performed with ANSYS Polyflow software at different flow rates and a constant temperature of 200°C, selecting a differential multimode Phan-Thien-Tanner (PTT) constitutive model to describe the viscoelastic behavior of polypropylene. It follows that decreasing the die length results in an opposite trend of the swell ratio in the width and height directions. The width swell ratio decreases up to 28%, whereas the middle height swell ratio increases up to 55% and the edge height contraction increases with 37%, all highlighting the 3D anisotropy of the extrudate swell deformation. However, especially for low flow rates, the area swell ratio remains almost unchanged and cannot be used to capture the anisotropic swelling behavior. This is predominantly attributed to the similar relative redistribution degree of the axial velocity (v x). An analysis of the transversal (v y) and lateral velocity (v z) combined with the stress field variation is performed as well to fully relate the anisotropic extrudate swell behavior to the various die lengths. The current study therefore contributes to completing the understanding of the relation of slit die design parameters and 3D extrudate flow under isothermal conditions, covering both developing and fully developed flow. [ABSTRACT FROM AUTHOR]