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The processing and performance of multilayer films containing post‐consumer recycled polypropylene (rPP1 and rPP2) materials are investigated to understand the effect of layer multiplying elements (LMEs), die temperature, virgin polypropylene (vPP%) content, and polyethylene (PE) contamination in flexible packaging applications. Three‐layer coextruded films were created with virgin polypropylene (vPP) consistently applied as the outer layers while the core layer comprised recyclates with varying concentrations of polyethylene as an unintended contaminant to polypropylene. To enhance layer uniformity and interfacial interaction, a layer multiplying element (LME) was employed to increase the number of coextruded film layers from 3 to 9. Tensile properties (elongation at break, yield stress, and modulus) were characterized in both machine direction (MD) and transverse direction (TD); after which, multiple linear regression analyses were conducted on 45 observations to model the effect of each factor. The results indicated that the LME significantly enhanced elongation at break in TD by 1280% strain, while temperature and vPP fraction also contributed positively to ductility in TD (+341% and +2373%, respectively). However, PE contamination had a substantial negative impact on elongation in MD (−2449%) underscoring its embrittling role due to lack of compatibility with the PP matrix. Critically, LME partially mitigated the negative PE effect via an interaction term (PE*LME), improving elongation in MD by +3101%. Scanning Electron Microscopy (SEM) revealed a distinct, regular pattern of alternating polyethylene (PE) and polypropylene (PP) domains forming ribbon‐like fibrillar structures. This unique morphological arrangement suggests a self‐organizing behavior driven by immiscibility and flow‐induced alignment under extrusion conditions. The presence of regular alternating domains at near equal concentrations implies a balance among shear‐driven orientation, phase separation kinetics, and crystallization phenomena, resulting in an ordered micro‐fibrillar structure. Importantly, both monolayer and multilayer films containing rPP2 or rPP1/rPP2 blends exhibited these aligned, ribbon‐like fibrils oriented in the machine direction (MD). SEM analysis of fractured specimens further indicated that brittle failure was often associated with interfacial delamination, particularly in recyclate‐rich regions, whereas ductile failure exhibited entangled reinforcing fibrils, suggesting improved energy absorption and interlayer cohesion. Understanding and controlling this self‐organized microstructure could significantly enhance processing stability, mechanical properties, and potential applications of recycled polyolefin blends, offering novel strategies for tailoring recyclate morphology and performance. 

This article presents the first use of shape forming elements (SFEs) to produce architected composites from multiple materials in an extrusion process. Each SFE contains a matrix of flow channels connecting input and output ports, where materials are routed between corresponding ports. The mathematical operations of rotation and shifting are described, and design automation is explored using Bayesian optimization and genetic algorithms to select fifty or more parameters for minimizing two objective functions. The first objective aims to match a target cross-section by minimizing the pixel-by-pixel error, which is weighted with the structural similarity index (SSIM). The second objective seeks to maximize information content by minimizing the SSIM relative to a white image. Satisfactory designs are achieved with better objective function values observed in rectangular rather than square flow channels. Validation extrusion of modeling clay demonstrates that while SFEs impose complex material transformations, they do not achieve the material distributions predicted by the digital model. Using the SSIM for results comparison, initial stages yielded SSIM values near 0.8 between design and simulation, indicating a good initial match. However, the control of material processing tended to decline with successive SFE processing with the SSIM of the extruded output dropping to 0.023 relative to the design intent. Flow simulations more closely replicated the observed structures with SSIM values around 0.4 but also failed to predict the intended cross-sections. The evaluation highlights the need for advanced modeling techniques to enhance the predictive accuracy and functionality of SFEs for biomedical, energy storage, and structural applications. 

Abstract This study aims to establish a systematic approach for characterizing recycled polyolefins of unknown composition, with a specific focus on predicting their performance in film extrusion. We explore various characterization techniques, including differential scanning calorimetry (DSC), Fourier‐transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and rheometry to assess their effectiveness in identifying the polyethylene (PE) fractions within polypropylene (PP) recyclates. By integrating experimental data with modeling techniques, we aim to provide insights into the predictive capabilities of these techniques in determining processing behaviors. The research highlights the superior fidelity of DSC in predicting the relative fraction and type of PE in a PP recyclate. FTIR is also identified as a high‐fidelity approach, albeit requiring application‐specific calibration. TGA, capillary, and oscillatory rheometry are recognized for their ability to distinguish between grades of recycled polyolefins but provide aggregate behaviors rather than detailed constituent information. 3D flow simulation of the cast film extrusion investigated the effect of the viscosity characterization method, non‐isothermal assumption, and process settings but could not fully replicate the observed variations in the cast film processing of two industrial polyolefins with similar melt flow rates and viscosity behaviors. This underscores the practical challenge of predicting processing issues prior to actual processing, necessitating reliance on reliable instrumentation suites and human expertise for diagnosing and remedying variations. HighlightsTwo industrial recycled polypropylene materials having similar melt flow rates exhibit drastically different cast film processing behaviors.DSC and FTIR provide reasonable approaches for identifying constituent materials.Modeling of the melt viscosities characterized by capillary and parallel plate rheology suggests that viscosity variations relative to the power‐law behavior assumed in the coat hanger die design is a predominant driver of cast film instabilities. 

Data on thermal contact resistance of thermoplastic materials used in material extrusion additive manufacturing 

This work investigated material extrusion additive manufacturing (MatEx AM) of specialized fluoroelastomer (FKM) compounds for applications in rubber seals and gaskets. The influence of a commercially available perfluoropolyether (PFPE) plasticizer on the printability of a control FKM rubber compound was studied using a custom-designed ram material extruder, Additive Ram Material Extruder (ARME), for printing fully compounded thermoset elastomers. The plasticizer’s effectiveness was assessed based on its ability to address challenges such as high compound viscosity and post-print shrinkage, as well as its impact on interlayer adhesion. The addition of the PFPE plasticizer significantly reduced the FKM compound’s viscosity (by 70%) and post-print shrinkage (by 65%). While the addition of the plasticizer decreased the tensile strength of the control compound, specimens printed with the plasticized FKM retained 34% of the tensile strength of compression-molded samples, compared to only 23% for the unplasticized compound. Finally, the feasibility of seals and gaskets manufacturing using both conventional and unconventional additive manufacturing (AM) approaches was explored. A hybrid method combining AM and soft tooling for compression molding emerged as the optimal method for seal and gasket fabrication. 

In this work, an additive manufacturing process for extruding fully compounded thermosetting elastomers based on fluorine-containing polymer compositions is reported. Additive manufacturing printers are designed with a dry ice container to precool filaments made from curable fluoroelastomer (FKM) and perfluoroelastomer (FFKM) compounds. A support tube guides the stiffened filament towards the printer nozzle. This support tube extends near the inlet to a printer nozzle. This approach allows low-modulus, uncured rubber filaments to be printed without buckling, a phenomenon common when 3D printing low-modulus elastomers via the fused deposition modeling (FDM) process. Modeling studies using thermal analyses data from a Dynamic Mechanical Analyzer (DMA) and a Differential Scanning Calorimeter (DSC) are used to calculate the Young’s modulus and buckling force, which helps us to select the appropriate applied pressure and the nozzle size for printing. Using this additive manufacturing (AM) method, the successful printing of FKM and FFKM compounds is demonstrated. This process can be used for the future manufacturing of seals or other parts from fluorine-containing polymers. 

Abstract Material extrusion is popular for its low barriers to entry and the flexibility it gives designers relative to traditional manufacturing techniques. Material extrusion is a transient process with a high frequency of starts, stops, and accelerations. This work presents transient data collected by an instrumented printhead and models the data by way of system identification. First-order and second-order control system models are proposed. The work also includes principal component analysis to determine which model coefficients correlate with the main effect, models the first-order model coefficients as a function of the experimental factors by regression, and predicts the apparent viscosity using a fitted static gain and known parameters. Flow rate, hot end temperature, nozzle diameter, and acceleration are the factors selected for the experiment. Each of these factors influences the steady state pressure, except for acceleration. The system identification models predict the melt pressure’s transient behavior well, with standard errors less than 4% of the mean melt pressure. Statistical analysis of the first-order model coefficients verifies that the static gain and time constant are statistically significant responses of the factors. The modeled apparent viscosity follows rheological expectations, showing the trends typically seen for viscosity as a function of shear rate. 

Current material extrusion systems can produce complex parts but lack instrumentation for observability and control. To investigate methods for observing the material extrusion process, a printer is instrumented to examine the dependency chain from the motor shaft torque to the infeed load and finally the melt pressure and temperature. The transient rheological and thermal behavior of the material extrusion process and the effect of volumetric flow rate, nozzle orifice diameter, and temperature setpoint on the pressure estimate from each point in the dependency chain are reported. The work also presents pressure predictions from COMSOL Multiphysics non-isothermal flow simulations and an analytical (Poiseuille) model. The pressure estimated by the motor shaft torque is greater than the downstream pressure estimated by the infeed load, which is greater than the downstream melt pressure in the hot end. In other words, both the torque sensor and the infeed load significantly overpredict the melt pressure. Significant variations in the pressures are also observed and explained. The findings demonstrate low and high frequency variation in the process, which can be attributed to gear eccentricity and teeth-to-filament engagement. The melt pressure variation is also observed to increase significantly at lower temperature set-points and higher flow rates, both of which reduce the melt temperature and thereby increase the viscosity. The increase in viscosity tends to reduce the viscous damping such that the variations in the filament infeed are transmitted through the hot end to the extrudate.