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1. Examining the mass loss and thermal properties of 3D printed models produced by fused deposition modeling and stereolithography under elevated temperatures

   https://doi.org/10.1108/RPJ-01-2022-0007  

   Hsieh, Shu-An ; Anderson, Jared L. ( June 2022 , Rapid Prototyping Journal)

   Purpose This paper aims to study the mass loss of three-dimensional (3D) printed materials at high temperatures. A preconcentration and analysis technique, static headspace gas chromatography-mass spectrometry (SHS-GC-MS), is demonstrated for the analysis of volatile compounds liberated from fused deposition modeling (FDM) and stereolithography (SLA) 3D printed models under elevated temperatures. Design/methodology/approach A total of seven commercial 3D printing materials were tested using the SHS-GC-MS approach. The printed model mass and mass loss were examined as a function of FDM printing parameters including printcore temperature, model size and printing speed, and the use of SLA postprocessing procedures. A high temperature resin was used to demonstrate that thermal degradation products can be identified when the model is incubated under high temperatures. Findings At higher printing temperatures and larger model sizes, the initial printed model mass increased and showed more significant mass loss after thermal incubation for FDM models. For models produced by SLA, the implementation of a postprocessing procedure reduced the mass loss at elevated temperatures. All FDM models showed severe structural deformation when exposed to high temperatures, while SLA models remained structurally intact. Mass spectra and chromatographic retention times acquired from the high temperature resin facilitated identification of eight compounds (monomers, crosslinkers and several photoinitiators) liberated from the resin. Originality/value The study exploits the high sensitivity of SHS-GC-MS to identify thermal degradation products emitted from 3D printed models under elevated temperatures. The results will aid in choosing appropriate filament/resin materials and printing mechanisms for applications that require elevated temperatures. 

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2. Design, synthesis, and characterization of vinyl-addition polynorbornenes with tunable thermal properties

   https://doi.org/10.1039/D1PY01050F  

   Wang, Xinyi ; Jeong, Yewon L. ; Love, Christopher ; Stretz, Holly A. ; Stein, Gila E. ; Long, Brian K. ( October 2021 , Polymer Chemistry)

   Unfunctionalized vinyl-addition polynorbornene (VAPNB) possesses many outstanding properties such as high thermal, chemical, and oxidative stability. These features make VAPNB a promising candidate for many engineering applications. However, VAPNB has a small service window between its glass transition temperature ( T g ) and decomposition temperature ( T d ), and it cannot be readily processed in a melt state. In this work, we demonstrate that the service window of VAPNBs can be tailored through the use of norbornene monomers bearing alkyl, aryl, and aryl ether substituents. The vinyl addition homopolymerization and copolymerization of these functionalized norbornyl-based monomers yielded VAPNBs with high T ′ g s (>150 °C) and large service windows ( T d – T g > 100 °C), which are comparable to other commercial engineering thermoplastics. To further establish the feasibility of melt processing, a functionalized VAPNB material with T g = 209 °C and a service window of 170 °C was successfully extruded and molded into bars. Subsequent characterization of the bars by dynamic mechanical analysis (DMA), nuclear magnetic resonance spectroscopy (NMR), and gel permeation chromatography (GPC) revealed only minor signs of polymer degradation. These studies suggest that substituted VAPNBs could be developed into a new class of engineering thermoplastics that is compatible with workhorse melt processing techniques such as extrusion and injection molding, as well as emerging techniques such as extrusion-based 3D printing. 

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3. Low‐temperature compounding of flax fibers with polyamide 6 via solid‐state shear pulverization: Towards viable natural fiber composites with engineering thermoplastics

   https://doi.org/10.1002/pc.25184  

   Wakabayashi, Katsuyuki ; Vancoillie, Simon H. E. ; Assfaw, Mekdes G. ; Choi, David H. ; Desplentere, Frederik ; Van Vuure, Aart W. ( December 2018 , Polymer Composites)

   Low‐temperature compounding of natural fiber/thermoplastic composites via solid‐state shear pulverization (SSSP) is explored for the first time, with a goal of processing temperature‐sensitive natural fibers with high temperature‐melting engineering thermoplastics without fiber degradation. The model study was based on polyamide 6 (PA6) as the matrix material and short flax fibers as the filler materials; flax fiber type was varied to provide a range of comparison. Composite structural characterization was conducted using computer tomography, optical microscopy, and scanning electron microscopy, while mechanical property measurements were performed on injection molded specimens in both tension and bending. SSSP demonstrated robust and effective processing results in model PA6/flax composites, especially when compared with conventional extrusion. SSSP was able to isolate unmodified scutched fibers into individual elementary fibers with minimal scission, and effectively distribute them in the polymer matrixin situ. The dispersed and distributed filler morphology led to mechanical property enhancements, including 230% and 40% increases in Young's modulus and tensile strength, respectively, compared with neat PA6, at a 20 vol% fiber content. POLYM. COMPOS., 40:3285–3295, 2019. © 2018 Society of Plastics Engineers

    

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4. Strategic cost and sustainability analyses of injection molding and material extrusion additive manufacturing

   https://doi.org/10.1002/pen.26256  

   Kazmer, David ; Peterson, Amy M. ; Masato, Davide ; Colon, Austin R. ; Krantz, Joshua ( January 2023 , Polymer Engineering & Science)

   Economic and environmental costs are assessed for four different plastics manufacturing processes, including cold and hot runner molding as well as stock and upgraded material extrusion three dimensional (3D) printers. A larger stock 3D printer was found to provide a melting capacity of 14.4 ml/h, while a smaller printer with an upgraded extruder had a melting capacity of 36 ml/h. 3D printing at these maximum melting capacities resulted in specific energy consumption (SEC) of 16.5 and 5.28 kWh/kg, respectively, with the latter value being less than 50% of the lowest values reported in the literature. Even so, analysis of these respective processes found them to be only 2.9% and 3.8% efficient relative to their theoretical minimum energy requirements. By comparison, cold and hot runner molding with an all‐electric machine had SEC of 1.28 and 0.929 kWh/kg, respectively, with efficiencies of 9.9% and 13.6% relative to the theoretical minima. Breakeven analysis considering the cost and carbon footprint of mold tooling found injection molding was preferable at a production quantity of around 70,000 units. Parametric analysis of model inputs indicates that the breakeven quantities are robust with respect to carbon tax incentives but highly dependent on mold costs, labor costs, and part size. Dimensional and mechanical properties of the molded and 3D printed specimens are also characterized and discussed.

    

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5. HIGH TEMPERATURE CHARACTERIZATION OF FIBER BRAGG GRATING SENSORS EMBEDDED INTO METALLIC STRUCTURES THROUGH ULTRASONIC ADDITIVE MANUFACTURING

   Schomer, J.J. ; Dapino, M.J. ( September 2018 , Proceedings of the ASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems)

   Embedded fiber Bragg grating (FBG) sensors are attractive for in-situ structural monitoring, especially in fiber reinforced composites. Their implementation in metallic structures is hindered by the thermal limit of the protective coating, typically a polymer material. The purpose of this study is to demonstrate the embedding of FBG sensors into metals with the ultimate objective of using FBG sensors for structural health monitoring of metallic structures. To that end, ultrasonic additive manufacturing (UAM) is utilized. UAM is a solid-state manufacturing process based on ultrasonic metal welding that allows for layered addition of metallic foils without melting. Embedding FBGs through UAM is shown to result in total cross-sectional encapsulation of the sensors within the metal matrix, which encourages uniform strain transfer. Since the UAM process takes place at essentially room temperature, the industry standard acrylate protective coating can be used rather than requiring a new coating applied to the FBGs prior to embedment. Measurements presented in this paper show that UAM-embedded FBG sensors accurately track strain at temperatures higher than 400 C. The data reveals the conditions under which detrimental wavelength hopping takes place due to non-uniformity of the load transferred to the FBG. Further, optical cross-sectioning of the test specimens shows inhibition of the thermal degradation of the protective coating. It is hypothesized that the lack of an atmosphere around the fully-encapsulated FBGs makes it possible to operate the sensors at temperatures well above what has been possible until now. Embedded FBGs were shown to retain their coatings when subjected to a thermal loading that would result in over 50 percent degradation (by volume and mass) in atmospherically exposed fiber. 

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