This research highlights a recently patented rotating nozzle Fused Filament Fabrication (FFF) 3D printing technology that accelerates print speeds and facilitates an isotropic-like fiber-orientation distribution in 3D printed polymer composites. The printer incorporates a 1.1-kilowatt indirect drive system, equipped with sensors for real-time data acquisition of temperature, filament feed rate, nozzle rotational speed, and extrusion force to describe the interrelation between processing parameters and final part performance. Experiments using short glass-fiber-reinforced nylon filament reveal fiber orientation distribution evolution, providing a path to material isotropy. Introducing a rotational nozzle shows improvements in ultimate tensile strength perpendicular to the printing direction by approximately 40 % and accelerates the extrusion processes by reducing the required force for extrusion as viscosity is reduced through shear-thinning. These improvements have the potential to broaden the scope of fused filament fabrication applications, particularly in high-performance engineering sectors such as aerospace and automotive industries which demand custom performance metrics.

You have accessUnderstanding Polymer ProcessingOct 2010Understanding Polymer ProcessingTim A. OsswaldTim A. Osswaldhttps://doi.org/10.3139/9783446446038.fmSectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF ShareFacebookTwitterEmailLinkedIn next chapter FiguresReferencesRelatedDetails 2010Pages: I-XIVPrint ISBN: 978-3-446-42404-3eISBN: 978-3-446-44603-8 Copyright & Permissions© 2011 Carl Hanser Verlag GmbH & Co. KGPDF DownloadLoading ...

Polypropylene (PP) comprises 21% of global plastics production and 18% of plastics waste, yet less than 1% of solid-waste PP is recycled in the United States (U.S.), representing significant environmental and economic challenges. Mechanical recycling, the most prevalent recycling method, subject's materials to thermomechanical stresses, which typically degrade polymer properties, affecting the quality of polymer products. This study replicates the impact of mechanical recycling through multiple extrusion cycles to examine the effects on PP's processing behavior. Dynamic scanning calorimetry (DSC) measurements showed stable melting behavior across all processing conditions, while crystallization analysis exhibited consistent shifts in kinetic parameters. Rheological characterization demonstrated progressive viscosity reductions through successive cycles, particularly pronounced at elevated reprocessing temperatures. The integration of this experimental data into injection molding simulations showed that recycled PP maintains viable processing characteristics. Our findings establish quantitative correlations between processing history and material behavior, enabling optimization of processing parameters directly rather than relying on trial-and-error approaches. While these results reflect idealized recycling conditions with minimal contamination, they provide a framework for understanding fundamental property evolution during mechanical recycling.

The laser powder bed fusion (LPBF) process utilizing a focused Gaussian-shaped beam faces challenges, including pore formation, melt pool fluctuation and liquid spattering. While beam shaping technology has been explored as a potential approach for defect mitigation, the beam-matter interaction dynamics during melting with shaped beams remain unclear. Here, we report the direct observation of ring-shaped beam-matter interaction dynamics, including pore formation, melt pool fluctuation and liquid spattering, and unveil defect mitigation mechanisms in ring-shaped beam laser powder bed fusion process. We find that, by spatially manipulating incident laser rays, the ring-shaped beam controls keyhole morphology, thereby managing the distribution of the reflected rays. This manipulation can effectively eliminate the formation of an unstable cavity at the keyhole tip, stabilizing the keyhole and mitigating keyhole pores. This enhanced keyhole stability effectively reduces the melt pool fluctuation, the formation of liquid breakup induced spatters and liquid droplet colliding induced large spatters in the laser powder bed fusion process. Additionally, the high-energy forefront of the ring-shaped beam effectively melts the powder bed, reducing agglomeration liquid spatter in the laser powder bed fusion process. The discovered defect mitigation mechanisms may guide the design of beam shaping strategies for simultaneously increasing the quality and productivity of metal additive manufacturing.

How reliable is our century-old understanding of natural-rubber latex (NRL) when examined through the lens of modern analytical techniques, such as nuclear magnetic resonance (NMR)? For decades, the scientific community has assumed that NRL comprises a branched/network polyisoprene structure, with covalently linked phospholipids and proteins purportedly responsible for its elasticity, curing kinetics, and film-forming properties. However, this perspective is derived from post-coagulation solids rather than the native colloidal structure found in living latex. In this study, we meticulously re-evaluate native latex in three distinct forms: ammonia-stabilized (pH approximate to 10), ammonia-free (pH approximate to 3.5), and deproteinized/saponified, then re-alkalized, utilizing a series of advanced NMR techniques, including chemical shift (1H/13C and 2D), Diffusion-Ordered Spectroscopy (DOSY), and Relaxation (TD-NMR). Our high-resolution spectra provide compelling evidence for a linear cis-1,4-polyisoprene backbone that lacks any branched structural features. The 31P-1H HMBC results connect phosphorus resonances exclusively to small-molecule protons in the range of 3.6-4.2 ppm. The DOSY analysis effectively attributes these resonances to rapidly diffusing phosphocholine and glycerol-phosphate (D approximate to 5-6 x 10-10 m2s-1), distinctly separated from the immobile rubber matrix. Additionally, the TD-NMR data delineate a microsecond core (T2 approximate to 5 mu s) alongside a millisecond interfacial shell (T2 approximate to 0.8-1.4 ms), which expands in basic conditions and dissipates upon saponification. Importantly, our quantitative inverse-gated 13C measurements indicate that any phosphate-terminated chains exist at concentrations below 0.05 mol%. The accumulated evidence strongly supports a pH-responsive lipid-protein corona encasing a linear polyisoprene core.

This study explores how three distinct preservation techniques affect the microstructure and rheological properties of natural rubber latex. Traditional ammoniated systems were compared against two emerging eco-friendly preservatives developed by AFLatex Technologies, which demonstrated enhanced latex properties reported in Ammonia-Free Latex Compositions, US Patent Application 63/267,167.2022. 2023. Rheological data were modeled using the Cross model to capture the non-linearity of viscosity and the Krieger–Dougherty (K&D) model to describe viscosity as a function of volume fraction. We also proposed an extended K&D model to better fit experimental observations. Additionally, Taylor–Couette flow simulation were performed to investigate shear-induced particle migration, providing insights into the dynamic behavior of particles under varied shear conditions. Our findings showed differences in critical volume fraction; the ammoniated system exhibited a critical volume fraction range of 0.6–0.7, while the ammonia-free systems had a lower range of 0.4–0.55. These values align closely with the predication from the Cross model, which suggests critical volume fraction of 0.4–0.5 for ammonia-free systems and above 0.6 for ammoniated systems. The extended and original K&D models corroborated these findings, with the ammonia-free systems typically reaching a critical volume fraction of 0.55 and the ammoniated systems approaching 0.7. Simulations under simplified assumptions revealed that shear-induced migration can maintain approximately 20% of the particles at a critical volume fraction of around 0.48, underscoring the complex interplay of particle dynamics and preservation technique in determining natural rubber latex material properties.

No AccessUnderstanding Polymer ProcessingOct 2010Modeling Polymer ProcessesTim A. OsswaldTim A. Osswaldhttps://doi.org/10.3139/9783446446038.009SectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF key 'share (en)' returned an object instead of string.FacebookTwitterEmailLinkedIn previous chapternext chapter FiguresReferencesRelatedDetails 2010Pages: 207-279Print ISBN: 978-3-446-42404-3eISBN: 978-3-446-44603-8 Copyright & Permissions© 2011 Carl Hanser Verlag GmbH & Co. KGPDF DownloadLoading ...

No AccessUnderstanding Polymer ProcessingOct 2010Transport Phenomena in Polymer ProcessingTim A. OsswaldTim A. OsswaldSearch for more papers by this authorhttps://doi.org/10.3139/9783446446038.008SectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF key 'share (en)' returned an object instead of string.FacebookTwitterEmailLinkedIn previous chapternext chapter FiguresReferencesRelatedDetails 2010Pages: 165-206Print ISBN: 978-3-446-42404-3eISBN: 978-3-446-44603-8 Copyright & Permissions© 2011 Carl Hanser Verlag GmbH & Co. KGPDF downloadLoading ...

No AccessUnderstanding Polymer ProcessingOct 2017Melt RheologyTim A. OsswaldTim A. OsswaldSearch for more papers by this authorhttps://doi.org/10.3139/9781569906484.003SectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF key 'share (en)' returned an object instead of string.FacebookTwitterEmailLinkedIn previous chapternext chapter FiguresReferencesRelatedDetails 2017Pages: 61-76Print ISBN: 978-1-56990-647-7eISBN: 978-1-56990-648-4 Copyright & Permissions© 2017 Carl Hanser Verlag GmbH & Co. KGPDF downloadLoading ...

Vat photopolymerization (VPP) is one of the most successful additive manufacturing modalities, offering high printing resolution and a wide selection of photo-resins for applications in aerospace, electronics, soft robotics, and biomedical devices. However, conventional photo-resins, primarily derived from fossil resources, present sustainability challenges. They often rely on short-chain oligomers that form brittle, dense polymer networks, limiting their performance in high-demand applications, especially for elastomeric materials. In this study, we developed an ammonia-free natural rubber latex-based photo-resin featuring an ultra-high molecular weight polymer with low viscosity (<10 Pa.s) and rapid curing speed (similar to 11 s, corresponding to gelling point), making it highly suitable for VPP. The printed green parts underwent a two-step process of crosslinking and coagulation, resulting in semi-interpenetrating polymer networks with unique structural properties. Two curing intensities were investigated: 18 and 35 mW/cm(2). Lower intensity resulted in lower 9 x 10(-5) mol/cm(3) in crosslinked density and higher intensity, 1.4 x 10(-4) mol/cm(3) in crosslink density. We systematically investigated multi-scale structure-property relationships using spin-lattice (T1) and spin-spin (T2) relaxation analysis via inversion recovery and Carr-Purcell-Meiboom-Gill. 18 mW/cm(2) with 30 s of curing and drying resulted in two regimens of motion for Rubber polymer with intermediate crosslinking density and intermediate entanglements dominating the network. Also, 35 mW/cm(2) with 30 s of curing and drying resulted in two regimes of Rubber polymer: however, one with a higher crosslinked and a mobile polymer phase. Optimized curing parameters enabled the fabrication of highly stretchable elastomers with 5-7.8 MPa tensile strengths and breaking strains of 750%-900%. These results highlight the potential of biomass-based photo-resins to advance sustainable 3D printing technologies. Furthermore, we demonstrated the feasibility of this formulation by printing complex geometries using a commercially available SLA printer.

Using natural fibers in bio-based product development offers a promising path toward an environmentally sustainable future. This study aims to characterize natural fibers obtained from food processing companies and artisans across Colombian regions, employing a methodology that can be extended to natural fibers characterization worldwide and supporting research focused on sustainable product development based on natural fibers. The thermal, mechanical, morphological, and surface properties of the fibers were measured using advanced techniques such as dynamic mechanical analysis-DMA, thermogravimetry-TGA, computed microtomograph, and 3D-microscopy. The chemical composition was analyzed using Van Soest methodology and TGA thermogram deconvolution. Thermal characterization reveals that natural fibers start their degradation between 227 and 258 degrees C, defining a safe thermal processing range for natural fiber-reinforced polymer composites (NFRPC) products. Mechanical properties were measured at temperatures ranging from -50 to 150 degrees C. Among the tested fibers, pineapple leaf fibers, hemp fibers, and toquilla straw exhibited superior mechanical performance up to 100 degrees C suggesting their potential for developing bioproducts across various applications. In contrast, banana and coir coconut fibers showed lower tensile strength and tensile modulus. Surface roughness differs in the longitudinal and transverse directions, suggesting that chambira straw (Ra 0.067 mm), fique fibers (Ra 0.03 mm), and hemp and pineapple leaf fibers (Ra 0.021 mm) may be of interest for further investigation in NFRPC production. This research highlights the progress and challenges in utilizing natural fibers to develop sustainable products. It positively impacts regional economies, drives technological advancements, and expands the potential applications of natural fiber-reinforced composites.Highlights Novel micro-CT technique reveals accurate cross-sectional areas of natural fibers Colombian natural fibers maintain stable tensile properties from -50 to 125 degrees C Toquilla straw shows highest strength-to-density ratio among studied fibers Thermal analysis offers rapid verification of natural fiber chemical composition Ashby charts allow comparison of natural fibers and their uses in composites.

The quality of elastomeric foams highly depends on specific processing conditions that foster the proper interaction between curing and blowing reactions. Here, we introduce an innovative multi-scale computational platform that optimizes the extrusion of elastomeric materials. This platform uses transport equations informed and parameterized with the time-temperature-transformation-viscosity diagram. The temperature and concentration fields within the two-dimensional extruded profile are obtained from the energy balance and the elastomer cure kinetics. At the same time, a one-dimensional diffusion-reaction equation calculates the bubble size distribution at discrete points within the extruded material. The methodology is illustrated in the context of an industrial-like ethylene-propylene-termonomer rubber compound that enters the vulcanization tunnel after being extruded in three different shapes. The tunnel temperature, the velocity of the conveyor band and the average extruded profile cure degree at the end of the tunnel serve as the controlling parameters that direct the desired bubble size and cure degree distributions. This approach offers fertile grounds for online process optimization and quality control, marking a significant advancement in the field.

Polypropylene (PP) is one of the most widely used plastics, yet its recycling remains limited, with less than 1% of solid waste PP being reprocessed. Mechanical recycling through extrusion is the most practical method, but inconsistent reprocessing conditions introduce variability in material properties. While temperature, screw speed, and residence time influence the thermomechanical stress applied during reprocessing, there are no standardized guidelines for optimizing these parameters. This study examines how these factors shape the properties of recycled PP, using conditions designed to mimic post-industrial recycled (PIR) scrap. Residence time was measured using colorimetric tracking and correlated with molecular weight, viscosity, and mechanical properties over multiple extrusion cycles. Data-driven modeling, including response surface methodology, support vector machines, and artificial neural networks, identified processing temperature as the dominant factor in material degradation, followed by residence time. Mechanical properties remained stable, while viscosity decreased predictably with increasing residence time. By linking reprocessing conditions to property evolution, this study provides a method to optimize processing parameters and reduce variability in recycled PP. These findings help manufacturers improve process control, making recycled PP more predictable for reuse in manufacturing.Highlights Study of PIR-quality PP without additives or compatibilizers. Residence time analysis shows processing temperature drives PP property changes. Mark-Houwink enables quick molecular weight checks for quality control. Models predict mechanical and rheological shifts in reprocessing. Optimized processing parameters minimize property degradation in recycling.

No AccessUnderstanding Polymer ProcessingOct 2017Other Plastics ProcessesTim A. OsswaldTim A. OsswaldSearch for more papers by this authorhttps://doi.org/10.3139/9781569906484.008SectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF key 'share (en)' returned an object instead of string.FacebookTwitterEmailLinkedIn previous chapternext chapter FiguresReferencesRelatedDetails 2017Pages: 171-201Print ISBN: 978-1-56990-647-7eISBN: 978-1-56990-648-4 Copyright & Permissions© 2017 Carl Hanser Verlag GmbH & Co. KGPDF downloadLoading ...

No AccessMaterials Science of Polymers for EngineersSep 2012Mechanical Behavior of PolymersTim A. Osswald, Georg MengesTim A. OsswaldSearch for more papers by this author, Georg MengesSearch for more papers by this authorhttps://doi.org/10.3139/9781569905241.009SectionsAboutPDF ToolsAdd to FavoritesDownload CitationTrack CitationsCopy LTI LinkPDF key 'share (en)' returned an object instead of string.FacebookTwitterEmailLinkedIn previous chapternext chapter FiguresReferencesRelatedDetails 2012Pages: 339-422Print ISBN: 978-1-56990-514-2eISBN: 978-1-56990-524-1 Copyright & Permissions© 2012 Carl Hanser Verlag GmbH & Co. KGPDF downloadLoading ...