This article discusses the scope biochar’s uses; biochar is a sustainable organic material, rich in carbon, that can be synthesized from various types of biomass feedstock using thermochemical reactions such as pyrolysis or carbonization. Biochar is an eco-friendly filler material that can enhance polymer composites’ mechanical, thermal, and electrical performances. In comparison to three inorganic fillers, namely carbon black, carbon nanotubes (CNT), and carbon filaments, this paper explores the optimal operating conditions for regulating biochar’s physical characteristics, including pore size, macro- and microporosity, and mechanical, thermal, and electrical properties. Additionally, this article presents a comparative analysis of biochar yield from various thermochemical processes. Moreover, the review examines how the surface functionality, surface area, and particle size of biochar can influence its mechanical and electrical performance as a filler material in polymer composites at different biochar loads. The study showcases the outstanding properties of biochar and recommends optimal loads that can improve the mechanical, thermal, and electrical properties of polymer composites.

Enhancing the Potential of Polymer Composites Using Biochar as a Filler: A Review

Polyethylene terephthalate (PET) is an engineering material widely used in packaging and cosmetics, given its excellent mechanical properties, water resistance and recyclability. PET is typically manufactured by injection blow molding but its use in additive manufacturing (AM) is not spread enough due to its (semi)crystalline behavior, which makes it difficult to process by Material Extrusion (ME) technologies. Alternatively, polyethylene terephthalate glycol copolymer (PETG), a fully amorphous material, is used in these technologies. However, PETG has worse mechanical properties than PET. In this context, this work studies the viability of different commercial PET by ME for Large Format Additive Manufacturing (LFAM). While PET for general purposes (PET1 and PET2) could not be printed, a marketable PET for thick-walled products (PET3) allowed to manufacture different objects by ME-LFAM with good dimensional accuracy. DSC and XRD studies evidenced that its slow crystallizing behavior was key to obtaining a proper flow and a successful printing. Young’s modulus and tensile strength of PET3 was significantly higher than those of PETG, both from this work and in previous reports found in the literature, since it remains semicrystalline after printing. This allows expanding the library of materials available for AM, positioning PET as a potential material for those industrial applications where PETG does not meet the necessary mechanical requirements. 

Large Format Additive Manufacturing of Polyethylene terephthalate (PET) by Material Extrusion

Life cycle cost, energy, and carbon emissions of molds for precast concrete: Exploring the impacts of material choices and additive manufacturing

Styrene-acrylonitrile (SAN) is widely used in various applications due to its excellent properties, including thermal stability, dimensional stability, and chemical resistance. However, poor toughness has limited its applications. In this study, an innovative in-situ fibrillation technique was employed to create nanofibers of thermoplastic polyurethane (TPU) in the SAN matrix. Silane was initially grafted onto TPU, followed by the development of nanofibril TPU, and lastly, post-crosslinking was conducted to retain the nanofibril structure. The grafting reaction was analyzed using Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). FTIR and NMR data were used in conjunction with the gel content test to confirm the involved grafting, hydrolysis, and crosslinking reactions. Observations with a Scanning Electron Microscope (SEM) revealed the formation of nanoscale TPU fibers ranging from 90 to 360 nm for various TPU contents. Because of nanofibril TPU's high aspect ratio and the effective SAN-TPU interaction, the required TPU decreased to 1 wt%. Due to the minimal use of rubber, SAN's stiffness was not compromised and compared to pure SAN and a spherical structure with the same concentration, tensile toughness increased by 350% and 200%, respectively. The fracture mechanism was investigated for both the short and long timeframes of deformation, and several potential hypotheses were proposed. Finally, this novel toughened SAN was compared with one of the most effective toughened acrylonitrile butadiene styrene (ABS) materials that contain 40 wt% spherical butadiene rubber (BR) domains. 

Unleashing the power of SAN: Innovative in situ fibrillation and moisture-crosslinking techniques yield stronger, tougher, and Greener material than ABS

Since the take-make-dispose model is leading to significant waste production and environmental impact, circular economy models have been spreading to reduce waste and resource depletion, rethinking the existing resource cycles. Plastic waste created environmental and economic concerns, requiring new recycling methods and strategies to preserve resources. This practice plays a key role in extrusion-based additive manufacturing, converting waste into recycled feedstock. Large-format additive manufacturing represents a promising way to scale up recycling strategies with granulated polymer feedstock, especially considering popular materials, i.e., PLA. However, thermomechanical degradation affects the quality of this secondary raw material, and these effects on large-format systems are scarcely studied. This work investigates the thermal, rheological, and mechanical properties of PLA feedstock for large-format additive manufacturing after multiple recycling processes, i.e., up to six. The effect of material degradation from multiple recycling processes was assessed through Gel Permeation Chromatography, Differential Scanning Calorimetry, flow stress ramp tests, tensile tests, and colorimetry. Some 3D printed parts were fabricated to assess the overall quality of the process, including pieces from potential applications. Lower effects of thermomechanical degradation were found compared to desktop-size 3D printers, mainly by cutting the reprocessing steps to produce secondary raw materials, i.e., making new filaments. Recycled granulate PLA feedstock represents a potential alternative to virgin pellets for new applications in real-world contexts. [copyright information to be updated in production process]. 

Characterization of PLA feedstock after multiple recycling processes for large-format material extrusion additive manufacturing

Carbon fiber filled acrylonitrile butadiene styrene (CF-ABS) is an emerging 3-D printable, recyclable thermoplastic composite. A popular application for CF-ABS is printed molds using large scale additive manufacturing (AM) processes produced for a variety of composites end-users. Other applications have not been fully realized as CF-ABS currently has a higher cost than other polymer composite feedstocks. The cost of CF-ABS could be greatly reduced if recycled CF-ABS material was accepted and utilized industrially, which would further expand its application space. The impacts of mechanical recycling on the properties and performance of CF-ABS after AM or other processes are not yet fully understood. As such, most AM CF-ABS is discarded as waste after use. In this work, AM CF-ABS molds used for concrete castings were recycled using an industrial shredder/granulator system. The granulate was then used as feedstock for large area AM to print test specimens. The elastic moduli in the printing direction and transverse to printing direction after mechanical recycling were found to decrease by 25% and 10%, respectively, most likely caused by reductions in the fiber content and polymer molecular weight. It was found that a significant portion of carbon fiber is lost during mechanical recycling through dust generation, while the thermomechanical extrusion during printing caused the polymer degradation. Although the mechanical performance of CF-ABS was reduced after recycling, the recycled feedstock retained properties for reuse as printed molds using large area AM or another suitable application. 

Recycling polymer composite granulate/regrind using big area additive manufacturing

Large format additive manufacturing (LFAM) necessitates the use of short fiber thermoplastic composites, such as carbon fiber filled acrylonitrile butadiene styrene, to enable printing. Currently, when LFAM parts are machined into their final shape, the machining scrap (i.e., small flake like particles and offcuts) is landfilled. Previous studies have demonstrated the viability of recycling end-of-life LFAM parts by shredding and optionally re-compounding the material back into pellets. However, there is little understanding of the value and performance of recycled material made from LFAM machining scrap, which if pursued could motivate more broad recycling of this waste stream. In this study, recycled in-process machining scrap is explored as an LFAM feedstock source. Herein, it is found that the primary degradation mechanism of the recycled material is significant fiber length attrition during surface machining. While this fiber attrition negatively impacts the mechanical performance of the material in the print direction, it seems that the changes in processing behaviors and print quality, namely the surface roughness of the printed structure associated with shorter fiber lengths, is beneficial to interlayer adhesion. The tensile strength and elastic modulus of the recycled material, in the print direction, decreased 11% and 31% respectively compared to the pristine material. However, in the layer-wise direction it was found that the recycled material exhibited no significant change in elastic modulus and a significant 21% increase in tensile strength – a surprising result. This work indicates that machining waste could be a viable material stream for recycled LFAM feedstock materials. 

Recycling of CF-ABS machining waste for large format additive manufacturing

Rheological Evaluation of Printability for Recycled Carbon Fiber Acrylonitrile Butadiene Styrene

differ for three reasons: casualty risks are different from fatality risk; risks per vehicle registration-year are different from risks per crash; and risks estimated from national data are different from risks from the five states analyzed here. We also examined the effect of driver behavior, crash location, and general vehicle design on risk, as well as sources of potential bias in using the crash data from five states. 

/pdf/printed-strain-gauges-for-anthropomorphic-test-dummies-for-34i7odcr.pdf

Printed Strain Gauges for Anthropomorphic Test Dummies for Vehicle Crash Testing

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Recycling polymer composite granulate/regrind using big area additive manufacturing

Recycling of CF-ABS machining waste for large format additive manufacturing

Rheological Evaluation of Printability for Recycled Carbon Fiber Acrylonitrile Butadiene Styrene

Printed Strain Gauges for Anthropomorphic Test Dummies for Vehicle Crash Testing