Mechanical Properties and Applications of Recycled Polycarbonate Particle Material Extrusion-Based Additive Manufacturing

The Quest for the Holy Grail Of 3D Printing: A Critical Review of Recycling in Polymer Powder Bed Fusion Additive Manufacturing

The benefits of additive manufacturing (AM) are widely recognised, boosting the AM method's use in industry, while it is predicted AM will dominate the global manufacturing industry. Alas, 3D printing's growth is hindered by its sustainability. AM methods generate vast amounts of residuals considered as waste, which are disposed of. Additionally, the energy consumed, the materials used, and numerous other factors render AM unsustainable. This paper aims to bring forward all documented solutions in the literature. The spotlight is on potential solutions for the Powder Bed Fusion (PBF) AM, focusing on Selective Laser Sintering (SLS), as these are candidates for mass manufacturing by industry. Solutions are evaluated critically, to identify research gaps regarding the recyclability of residual material. Only then can AM dominate the manufacturing industry, which is extremely important since this is a milestone for our transition into sustainable manufacturing. This transition itself is a complex bottleneck on our quest for becoming a sustainable civilisation. Unlike previous reviews that primarily concentrate on specific AM recycling materials, this paper explores the state of the art in AM recycling processes, incorporating the latest market data and projections. By offering a holistic and forward-looking perspective on the evolution and potential of AM, this review serves as a valuable resource for researchers and industry professionals alike.

Exploring the Potential of Recycled Polymers for 3D Printing Applications: A Review

The integration of recycled polymers into additive manufacturing (AM) processes offers a promising opportunity for advancing sustainability within the manufacturing industry. This review paper summarizes existing research and developments related to the use of recycled materials in AM, focusing on distinct polymers, such as polylactic acid (PLA), polyethylene terephthalate (PET), and acrylonitrile butadiene styrene (ABS), among others. Key topics explored include the availability of recycled filaments on the market, challenges associated with material variability and traceability, and efforts toward establishing ethical product standards and sustainability characterization methodologies. Regulatory considerations and standards development by organizations such as ASTM and ISO are discussed, along with recommendations for future advancements in improving the sustainability of filament recycling and achieving net-zero emissions in AM processes. The collective efforts outlined in this paper underscore the potential of recycled polymers in AM to foster a more sustainable and environmentally friendly manufacturing industry.

Valorization of Tomato Agricultural Waste for 3D-Printed Polymer Composites Based on Poly(lactic acid)

Agricultural waste is a renewable source of lignocellulosic components, which can be processed in a variety of ways to yield added-value materials for various applications, e.g., polymer composites. However, most lignocellulosic biomass is incinerated for energy. Typically, agricultural waste is left to decompose in the fields, causing problems such as greenhouse gas release, attracting insects and rodents, and impacting soil fertility. This study aims to valorise nonedible tomato waste with no commercial value in Additive Manufacturing (AM) to create sustainable, cost-effective and added-value PLA composites. Fused Filament Fabrication (FFF) filaments with 5 and 10 wt.% tomato stem powder (TSP) were developed, and 3D-printed specimens were tested. Mechanical testing showed consistent tensile properties with 5% TSP addition, while flexural strength decreased, possibly due to void formation. Dynamic mechanical analysis (DMA) indicated changes in storage modulus and damping factor with TSP addition. Notably, the composites exhibited antioxidant activity, increasing with higher TSP content. These findings underscore the potential of agricultural waste utilization in FFF, offering insights into greener waste management practices and addressing challenges in mechanical performance and material compatibility. This research highlights the viability of integrating agricultural waste into filament-based AM, contributing to sustainable agricultural practices and promoting circular economy initiatives.

Mathematical simulation of damage detection for fighting athletes and equipment based on conjugated polymer development

Traditional combat sports equipment usually uses synthetic materials, such as polyurethane and synthetic leather. Although these materials have a certain degree of strength and durability, they have poor flexibility and antibacterial properties, making it difficult to provide stable support and protection for athletes. In order to enhance the antibacterial properties and flexibility of sports equipment and reduce the risk of injuries to athletes, this article conducts in-depth research on the development of combat sports equipment using conjugated polymers. This article first selects polypropylene (PP) as the base material for sports equipment for combat athletes, and uses the gas phase polymerization method to prepare the material; then uses chitosan as an antimicrobial agent and uses the oxidative degradation method to prepare it; after that, this article coats the chitosan antibacterial agent on the prepared PP material, and uses a combination of dipping and calendering for antibacterial treatment; finally, this article uses the spunbond melt-blown composite method to fill and combine the top equipment of combat athletes to achieve the structural design of sports equipment. In order to verify the effectiveness of the equipment, this article conducted equipment performance testing and sports injury simulation. The results showed that the average diameter of the antibacterial zone of this sports equipment reached more than 1 mm, and in the injury risk test, the risk of athletes' joint and muscle injuries was reduced by 16.9% and 20.5% respectively. Research shows that developing combat sports equipment based on conjugated polymers can help reduce the risk of injury to athletes and improve the safety of combat sports.

Finding Ideal Parameters for Recycled Material Fused Particle Fabrication-Based 3D Printing Using an Open Source Software Implementation of Particle Swarm Optimization

As additive manufacturing rapidly expands the number of materials including waste plastics and composites, there is an urgent need to reduce the experimental time needed to identify optimized printing parameters for novel materials. Computational intelligence (CI) in general and particle swarm optimization (PSO) algorithms in particular have been shown to accelerate finding optimal printing parameters. Unfortunately, the implementation of CI has been prohibitively complex for noncomputer scientists. To overcome these limitations, this article develops, tests, and validates PSO Experimenter, an easy-to-use open-source platform based around the PSO algorithm and applies it to optimizing recycled materials. Specifically, PSO Experimenter is used to find optimal printing parameters for a relatively unexplored potential distributed recycling and additive manufacturing (DRAM) material that is widely available: low-density polyethylene (LDPE). LDPE has been used to make filament, but in this study for the first time it was used in the open source fused particle fabrication/fused granular fabrication system. PSO Experimenter successfully identified functional printing parameters for this challenging-to-print waste plastic. The results indicate that PSO Experimenter can provide 97% reduction in research time for 3D printing parameter optimization. It is concluded that the PSO Experimenter is a user-friendly and effective free software for finding ideal parameters for the burgeoning challenge of DRAM as well as a wide range of other fields and processes.

A Coherent Assessment of the Compressive Strain Rate Response of PC, PETG, PMMA, and TPU Thermoplastics in MEX Additive Manufacturing

In this study, we successfully address a significant research and engineering gap by quantitatively assessing the impact of varying compressive loading rates on the mechanical behavior of four popular thermoplastic polymers in material-extrusion-based (MEX) 3D printing. Raw powders of polycarbonate (PC), polyethylene terephthalate glycol (PETG), polymethyl methacrylate (PMMA), and thermoplastic polyurethane (TPU) were processed through melt extrusion, and the filaments were used to 3D-print the test samples. For completeness, thermogravimetric analysis and a compressive test following the ASTM-D695 standard were conducted. Ultimately, the compressive strength and yield stress, the compressive modulus of elasticity and toughness, and the maximum compressive sensitivity index were thoroughly documented. Specimens were tested in strain rates from 1.3 mm/min to 200 mm/min. The compressive strength (40% for the PMMA) and stiffness (29% for the TPU) increased with the increase in the strain rate in all polymers tested. PC had the highest strain rate sensitivity. Significant variations in deformation and fracture modes were observed and thoroughly documented throughout this study. Our findings can be useful in industrial engineering as valued design optimization input parameters in various applications involving the above-mentioned polymeric materials.

Advancing Plastic Recycling: Challenges and Opportunities in the Integration of 3D Printing and Distributed Recycling for a Circular Economy

The concept of the circular economy has emerged as a promising solution to address the mounting concerns surrounding plastic waste and the urgent need for sustainable resource management. While conventional centralized recycling remains a common practice for plastic waste, centralized facilities may prove inadequate in handling the ever-increasing volumes of plastic waste generated globally. Consequently, exploring alternative recycling methods, such as distributed recycling by additive manufacturing, becomes paramount. This innovative approach encompasses actively involving communities in recycling practices and promotes a circular economy. This comprehensive review paper aims to explore the critical aspects necessary to realize the potential of distributed recycling by additive manufacturing. In this paper, our focus lies on proposing schemes that leverage existing literature to harness the potential of distributed recycling by additive manufacturing as an effective approach to plastic waste management. We explore the intricacies of the recycling process, optimize 3D printing parameters, address potential challenges, and evaluate the mechanical properties of recycled materials. Our investigation draws heavily from the literature of the last five years, as we conduct a thorough critical assessment of DRAM implementation and its influence on the properties of 3D printing structures. Through comprehensive analysis, we reveal the potential of recycled materials in delivering functional components, with insights into their performance, strengths, and weaknesses. This review serves as a comprehensive guide for those interested in embracing distributed recycling by additive manufacturing as a transformative approach to plastic recycling. By fostering community engagement, optimizing 3D printing processes, and incorporating suitable additives, it is possible to collectively contribute to a more sustainable future while combatting the plastic waste crisis. As progress is made, it becomes essential to further delve into the complexities of material behavior, recycling techniques, and the long-term durability of recycled 3D printed components. By addressing these challenges head-on, it is feasible to refine and advance distributed recycling by additive manufacturing as a viable pathway to minimize plastic waste, fostering a circular economy and cultivating a cleaner planet for generations to come.

Open source scientific bottle roller

Proprietary bottle rolling systems automate some laboratory applications, however, their high costs limit accessibility. This study provides designs of an open source bottle roller that is compatible with distributed digital manufacturing using 3-D printed parts and readily-available commercial components. The experimental results show that the open source bottle roller can be fabricated for CAD$210 (about USD$150) in materials, which is 86% less expensive than the most affordable proprietary bottle roller on the market. The design, however, is more robust with enhanced capabilities. The design can be adapted to the user's needs, but is already compatible with incubators with a low profile (dimensions 50 cm x46 cm x8.8 cm) and capable of being operated at elevated temperatures. The systems can be adjusted to revolves from 1 to 200 RPM, exceeding the rotational speed of most commercial systems. The open source bottle roller as tested has a capacity greater than 1.2 kg and can roll twelve 100 mL bottles simultaneously. Validation testing showed that it can operate for days at 80 RPM without human intervention or monitoring for days at both room temperature and elevated temperatures (50 °C). Future work includes adapting the designs for different sizes and for different fabrication techniques to further reduce costs and increase flexibility.

Experimentation and Numerical Modeling of Peak Temperature in the Weld Joint during Rotary Friction Welding of Dissimilar Plastic Rods

Rotary friction welding (RFW) could result in lower welding temperature, energy consumption, or environmental effects as compared with fusion welding processes. RFW is a green manufacturing technology with little environmental pollution in the field of joining methods. Thus, RFW is widely employed to manufacture green products. In general, the welding quality of welded parts, such as tensile strength, bending strength, and surface hardness is affected by the peak temperature in the weld joint during the RFW of dissimilar plastic rods. However, hitherto little is known about the domain knowledge of RFW of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) polymer rods. To prevent random efforts and energy consumption, a green method to predict the peak temperature in the weld joint of dissimilar RFW of ABS and PC rods was proposed. The main objective of this work is to investigate the peak temperature in the weld joint during the RFW using COMSOL multiphysics software for establishing an empirical technical database of RFW of dissimilar polymer rods under different rotational speeds. The main findings include that the peak temperature affecting the mechanical properties of RFW of PC and ABS can be determined by the simulation model proposed in this work. The average error of predicting the peak temperature using COMSOL software for five different rotational speeds is about 15 °C. The mesh element count of 875,688 is the optimal number of meshes for predicting peak temperature in the weld joint. The bending strength of the welded part (y) using peak welding temperature (x) can be predicted by the equation of y = -0.019 x² + 5.081x - 200.75 with a correlation coefficient of 0.8857. The average shore A surface hardness, impact energy, and bending strength of the welded parts were found to be increased with increasing the rotational speed of RFW.

Hangprinter for large scale additive manufacturing using fused particle fabrication with recycled plastic and continuous feeding

The life cycle of plastic is a key source of carbon emissions. Yet, global plastics production has quadrupled in 40 years and only 9 % has been recycled. If these trends continue, carbon emissions from plastic wastes would reach 15 % of global carbon budgets by 2050. An approach to reducing plastic waste is to use distributed recycling for additive manufacturing (DRAM) where virgin plastic products are replaced by locally manufactured recycled plastic products that have no transportation-related carbon emissions. Unfortunately, the design of most 3-D printers forces an increase in the machine cost to expand for recycling plastic at scale. Recently, a fused granular fabrication (FGF)/fused particle fabrication (FPF) large-scale printer was demonstrated with a GigabotX extruder based on the open source cable driven Hangprinter concept. To further improve that system, here a lower-cost recyclebot direct waste plastic extruder is demonstrated and the full designs, assembly and operation are detailed. The <$1,700 machine's accuracy and printing performance are quantified, and the printed parts mechanical strength is within the range of other systems. Along with support from the Hangprinter and DUET3 communities, open hardware developers have a rich ecosystem to modify in order to print directly from waste plastic for DRAM.

FDM-based additive manufacturing of recycled thermoplastics and associated composites

Hailed since the fourth industrial revolution, three-dimensional (3D) printing or additive manufacturing (AM) has been extensively implemented in various manufacturing sectors. This process is popular for generating regular products and incorporating innovative designs into the components like auxetic structures, such as fabrication of engineering products, customized implants and sophisticated biomedical devices. Over the years, one of the interesting outputs of this emerging technology is the reuse of waste thermoplastic materials to produce competent products through the fused deposition modeling (FDM) technique. The strength of FDM components produced from thermoplastic waste is lower than that of virgin plastic FDM counterparts. So, there is a need to understand the significant changes in the recycled thermoplastic material during subsequent extrusions, which are chain scission, change in viscosity and breaking strength. The use of additives has been a promising solution to improve the performance of recycled material for 3D printing applications. Hence, this study aims to provide an overview of reusing plastic waste through FDM-based 3D printing. This review summarizes the current knowledge about the effect of processing on thermo-mechanical properties of recycled plastic FDM parts and the use of various additives to improve the overall quality. In addition, two case studies from open literature have been demonstrated to explain the use of FDM and associated technology for plastic recycling.

Upcycling of Poly(Lactic Acid) by Reactive Extrusion with Recycled Polycarbonate: Morphological and Mechanical Properties of Blends

Poly(lactic acid) (PLA) is one of the most promising renewable polymers to be employed to foster ecological and renewable materials in many fields of application. To develop high-performance products, however, the thermal resistance and the impact properties should be improved. At the same time, it is also necessary to consider the end of life through the exploration of property assessment, following reprocessing. In this context the aim of the paper is to develop PLA/PC blends, obtained from recycled materials, in particular scraps from secondary processing, to close the recycling loop. Indeed, the blending of PLA with polycarbonate (PC) was demonstrated to be a successful strategy to improve thermomechanical properties that happens after several work cycles. The correlation between the compositions and properties was then investigated by considering the morphology of the blends; in addition, the reactive extrusions resulting in the formation of a PLA-PC co-polymer were investigated. The materials obtained are then examined by means of a dynamic-mechanical analysis (DMTA) to study the relaxations and transitions.

Characterization of 3D Printed Polylactic Acid by Fused Granular Fabrication through Printing Accuracy, Porosity, Thermal and Mechanical Analyses

Fused Granular Fabrication (FGF) or screw-extrusion based 3D printing for polymers is a less diffused alternative to filament-based Additive Manufacturing (AM). Its greatest advantage lies in superior sustainability; in fact, polymer granules can be used to directly feed an FGF printer, reducing the time, cost and energy of producing a part. Moreover, with this technology, a circular economy approach involving the use of pellets made from plastic waste can be easily implemented. Polylactic Acid (PLA) pellets were processed at different printing speeds and with different infill percentages on a customized version of a commercial Prusa i3 Plus 3D printer modified with a Mahor screw extruder. For the characterization of the 3D printed samples, rheological, thermal, mechanical and porosity analyses were carried out. In addition, the energy consumption of the 3D printer was monitored during the production of the specimens. The results showed that a higher printing speed leads to lower energy consumption, without compromising material strength, whereas a slower printing speed is preferable to increase material stiffness.

Comparative Analysis of the Solid Conveying of Regrind, Virgin and Powdery Polyolefins in Single-Screw Extrusion

The shape and size of processed materials play a crucial role in the solid conveying characteristics of single-screw extruders. Thus, the increasing amount of plastic regrind leads to new challenges in screw extrusion. This work investigates the conveying behavior of three distinctly different material shapes in an axially as well as a helically grooved solid conveying zone. A uniform virgin polypropylene (PP) granule, an irregularly plate-shaped PP regrind and a powdery polyethylene (PE) are processed at screw speeds up to 1350 rpm. Thereby, frictionally engaged conveying in the grooves is visualized for the utilized powder. Similarly, the virgin granule is subject to forced conveying by interlocking in the grooves. The experimentally determined throughput is furthermore compared to analytical calculations which assume a so-called nut–screw conveying. It is found that these calculations perfectly predict the throughput when processing the virgin granule and the powder in a helically grooved barrel. In contrast, the analytical calculation significantly underestimates the throughput for the regrind. This underestimation is expected to be mainly caused by its plate shape and a difference in bulk density. The actual bulk density in the extruder is probably significantly higher due to both orientation and compaction effects compared to the measured bulk density that is used for the analytical calculation. Additionally, the regrind exhibits a fluctuating throughput due to the non-constant bulk density, which results from an irregular regrind shape and a broad size distribution.

Low cost 3D printing of metals using filled polymer pellets

Nowadays, additive manufacturing of metallic materials is most often carried out using expensive and complex tools that leave the user with limited control and no possibility of modification. In order to make the printing of metal parts more accessible to small structures but also better suited for academic research, the use of a mixture of thermoplastic polymer and metal powder is a good solution as many granular feedstocks already exist for Metal Injection Molding applications. To perform the shaping process, the Fused Granular Fabrication 3D printing technology is set up by diverting the use of a feedstock in the form of pellets that are directly inserted into the print head. This solution, which is less costly, is implemented here by modifying a mid-range printer, the Tool Changer from E3D, and by making the hardware and software adaptations to mount a compact granulates extruder on it, which is also available on the market. The polymer portion present in the green part can then be removed in order to perform the heat treatments that will densify the powder by sintering and give a fully metallic dense object.

The Field Guide to 3D Printing in Optical Microscopy for Life Sciences

The maker movement has reached the optics labs, empowering researchers to create and modify microscope designs and imaging accessories. 3D printing has a disruptive impact on the field, improving accessibility to fabrication technologies in additive manufacturing. This approach is particularly useful for rapid, low-cost prototyping, allowing unprecedented levels of productivity and accessibility. From inexpensive microscopes for education such as the FlyPi to the highly complex robotic microscope OpenFlexure, 3D printing is paving the way for the democratization of technology, promoting collaborative environments between researchers, as 3D designs are easily shared. This holds the unique possibility of extending the open-access concept from knowledge to technology, allowing researchers everywhere to use and extend model structures. Here, it is presented a review of additive manufacturing applications in optical microscopy for life sciences, guiding the user through this new and exciting technology and providing a starting point to anyone willing to employ this versatile and powerful new tool.

Size and print path effects on mechanical properties of material extrusion 3D printed plastics

Print conditions for thermoplastics by filament-based material extrusion (MatEx) are commonly optimized to maximize the elastic modulus. However, these optimizations tend to ignore the impact of thermal history that depends on the specimen size and print path selection. Here, we investigate the effect of size print path (raster angle and build orientation) and print sequence on the mechanical properties of polycarbonate (PC) and polypropylene (PP). Examination of parallel and series printing of flat (XY) and stand-on (YZ) orientation of Type V specimens demonstrated that to observe statistical differences in the mechanical response that the interlayer time between printed roads should be approximately 5 s or less. The print time for a single layer in XY orientation is much longer than that for a single layer in YZ orientation, so print sequence only impacts the mechanical response in the YZ orientation. However, the specimen size and raster angle did influence the mechanical properties in XY orientation due to the differences in thermal history associated with intralayer time between adjacent roads. Moreover, all of these effects are significantly larger when printing PC than PP. These differences between PP and PC are mostly attributed to the mechanism of interface consolidation (crystallization vs. glass formation), which changes the requirements for a strong interface between roads (crystals vs. entanglements). These results illustrate how the print times dictated by the print path layout impact observed mechanical properties. This work also demonstrated that the options available in some standards developed for traditional manufacturing will change the quantitative results when applied to 3D printed parts.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40964-022-00275-w.

Additive manufacturing technology of polymeric materials for customized products: recent developments and future prospective

The worldwide demand for additive manufacturing (AM) is increasing due to its ability to produce more challenging customized objects based on the process parameters for engineering applications. The processing of conventional materials by AM processes is a critically demanded research stream, which has generated a path-breaking scenario in the rapid manufacturing and upcycling of plastics. The exponential growth of AM in the worldwide polymer market is expected to exceed 20 billion US dollars by 2021 in areas of automotive, medical, aerospace, energy and customized consumer products. The development of functional polymers and composites by 3D printing-based technologies has been explored significantly due to its cost-effective, easier integration into customized geometries, higher efficacy, higher precision, freedom of material utilization as compared to traditional injection molding, and thermoforming techniques. Since polymers are the most explored class of materials in AM to overcome the limitations, this review describes the latest research conducted on petroleum-based polymers and their composites using various AM techniques such as fused filament fabrication (FFF), selective laser sintering (SLS), and stereolithography (SLA) related to 3D printing in engineering applications such as biomedical, automotive, aerospace and electronics.

Parametric Open Source Cold-Frame Agrivoltaic Systems

There is an intense need to optimize agrivoltaic systems. This article describes the invention of a new testing system: the parametric open source cold-frame agrivoltaic system (POSCAS). POSCAS is an adapted gardening cold-frame used in cold climates as it acts as a small greenhouse for agricultural production. POSCAS is designed to test partially transparent solar photovoltaic (PV) modules targeting the agrivoltaic market. It can both function as a traditional cold frame, but it can also be automated to function as a full-service greenhouse. The integrated PV module roof can be used to power the controls or it can be attached to a microinverter to produce power. POSCAS can be placed in an experimental array for testing agricultural and power production. It can be easily adapted for any type of partially transparent PV module. An array of POSCAS systems allows for the testing of agrivoltaic impacts from the percent transparency of the modules by varying the thickness of a thin film PV material or the density of silicon-based cells, and various forms of optical enhancement, anti-reflection coatings and solar light spectral shifting materials in the back sheet. All agrivoltaic variables can be customized to identify ideal PV designs for a given agricultural crop.

Design, Materials, and Extrusion-Based Additive Manufacturing in Circular Economy Contexts: From Waste to New Products

The transition toward circular economy models has been progressively promoted in the last few years. Different disciplines and strategies may significantly support this change. Although the specific contribution derived from design, material science, and additive manufacturing is well-established, their interdisciplinary relationship in circular economy contexts is relatively unexplored. This paper aims to review the main case studies related to new circular economy models for waste valorization through extrusion-based additive manufacturing, circular materials, and new design strategies. The general patterns were investigated through a comprehensive analysis of 74 case studies from academic research and design practice in the last six-year period (2015–2021), focusing on the application fields, the 3D printing technologies, and the materials. Further considerations and future trends were then included by looking at the relevant funded projects and case studies of 2021. A broader number of applications, circular materials, and technologies were explored by the academic context, concerning the practice-based scenario linked to more consolidated fields. Thanks to the development of new strategies and experiential tools, academic research and practice can be linked to foster new opportunities to implement circular economy models.

Bibliographic mapping of post-consumer plastic waste based on hierarchical circular principles across the system perspective

The current dominating production and consumption model is based on the linear economy (LE) model, within which raw materials are extracted-processed-consumed-discarded. A circular economy (CE) constitutes a regenerative systemic approach to economic development which views waste as a valuable resource to be reprocessed back into the economy. In order to understand the circular strategy for a systemic change from an LE to a CE as a means of resolving the issue of plastic waste, this research aims to map current circular strategy trends across the system perspective contained in the literature relating to plastic CE literature. The novelty of the research lies in the mapping and review of the distribution of comprehensive circular strategies within the 9R framework across the entire system perspective (e.g. micro-meso-macro) down to its sub-levels in the literature on a plastic CE. The bibliographic mapping and systematic literature review iindicateed that the majority of the research focused on recycle (R8), followed by refuse (R0), reuse (R3), and reduce (R2). Certain circular strategies are more appropriate to handling certain plastic materials, despite CE's favoring of prevention and recycling over incineration. Recover (R9) is often used to process mixed and contaminated plastic. Recycling (R8) is the most popular circular strategy and the most applicable to plastic material with three recycle trends, namely; mechanical recycling, chemical recycling and DRAM (Distributed-Recycling-and-Additive-Manufacturing). Prolonging the product life through refurbishing (R5) is not applicable to plastic due to its material limitations. Reduce (R2) popularity as circular strategy reflects the preference to reduce consumption, either by launching campaigns to prevent waste or increasing production efficiency. Research on Rethink (R1) has largely focused on rethinking product design, consumer and organization behavior and perceptions of CE. Refuse (R0) strategy is an adoption of bio-based plastics which have a similar function to fossil-based plastics.

Screw-assisted 3D printing with granulated materials: a systematic review

This paper presents a systematic review on extrusion additive manufacturing (EAM), with focus on the technological development of screw-assisted systems that can be fed directly with granulated materials. Screw-assisted EAM has gained importance as an enabling technology to expand the range of 3D printing materials, reduce costs associated with feedstock fabrication, and increase the material deposition rate compared to traditional fused filament fabrication (FFF). Many experimental printheads and commercial systems that use some screw-processing mechanism can be found in the literature, but the design diversity and lack of standard terminology make it difficult to determine the most suitable solutions for a given material or application field. Besides, the few previous reviews have offered only a glimpse into the topic, without an in-depth analysis about the design of the extruders and associated capabilities. A systematic procedure was devised to identify the screw-assisted EAM systems that can print directly from granulated materials, resulting in 61 articles describing different pieces of equipment that were categorized as experimental printheads and commercial systems, for small- and large-scale applications. After describing their main characteristics, the most significant extruder modifications were discussed with reference to the materials processed and performance requirements. In the end, a general workflow for the development of 3D printers based on screw extrusion was proposed. This review intends to provide information about the state-of-the-art screw-assisted EAM and help the academy to identify further research opportunities in the field.

A Systematic Literature Review on Additive Manufacturing in the Context of Circular Economy

Additive Manufacturing (AM) is, undoubtedly, one of the most promising and potentially disruptive technologies of the Industry 4.0 era, able to transform the traditional manufacturing paradigm and fuel the generally accepted and necessary shift towards the conceptualisation, design and adoption of sustainable and circular business models. The objective of this paper is to contribute to the structure of the scientific field residing in the intersection of AM and Circular Economy (CE), by determining the status of its current state-of-the-art, proposing an initial typology in an attempt to contribute to the existing efforts of structuring this rather novice research area and pinpointing research gaps where more focus should be put, and highlighting areas with a significant potential for added-value future research. To that end, a sample of 206 papers, published from 2014 to 2020, was retrieved from the Scopus and Google Scholar databases. After studying and critically evaluating their content in full, contributions were classified into six thematic categories, providing a first typology of the current literature, followed by a detailed section highlighting and taxonomizing existing review studies. Next, contributions of the three categories of interest are discussed followed by a critical evaluation of the study’s contribution, inherent limitations and future research potential.

Open Source 3D-Printable Planetary Roller Screw for Food Processing Applications

Historically, open source agriculture (OSA) was based on grassroots technology generally manufactured by hand tools or with manual machining. The rise of distributed digital manufacturing provides an opportunity for much more rapid lateral scaling of open source appropriate technologies for agriculture. However, the most mature distributed manufacturing area is plastic, which has limited use for many OSA applications. To overcome this limitation with design, this study reports on of a completely 3D-printable planetary roller screw linear actuator. The device is designed as a parametric script-based computer aided design (CAD) package to allow for the easy adaption for a number of applications such as food processing at different scales. The planetary roller screw is fabricated in dishwasher-safe polyethylene terephthalate glycol (PETG) on an open source machine and tested using an open source testing platform to determine if it could maintain a constant load without slipping and the maximum force. Then, this output is compared to a direct screw press using the same materials. The results found that the maximum force is more than doubled for the roller screw actuator using the same materials, making them adequate for some food processing techniques. Future work is outlined to improve the performance and ease of assembly.

Waste Valorization through Additive Manufacturing in an Industrial Symbiosis Setting

Given the current environmental concerns related to manufacturing, the introduction to the industrial symbiosis concept brought purpose to waste, instead of disposing it in landfills or eliminating it through incineration. The waste generated by industrial processes, or end-of-life products, is redirected to be used as a “new” input in another process by one or more organizations, which is a mutual benefit or a “symbiosis”. Despite its relevancy, the industrial symbiosis concept is marginally explored in the context of additive manufacturing; this emerging technology has disruptive potential regarding the use of different materials as secondary raw materials. This paper presents a systematic literature review regarding industrial symbiosis and additive manufacturing. The main objective is to identify how wastes can be used as input materials to additive manufacturing processes and what exchanges of resources occur in an industrial symbiosis setting. A final sample of 32 documents was reached and analyzed. Five examples of using waste streams in additive manufacturing processes to produce goods were highlighted and explored.

Open source high-temperature RepRap for 3-D printing heat-sterilizable PPE and other applications

Thermal sterilization is generally avoided for 3-D printed components because of the relatively low deformation temperatures for common thermoplastics used for material extrusion-based additive manufacturing. 3-D printing materials required for high-temperature heat sterilizable components for COVID-19 and other applications demands 3-D printers with heated beds, hot ends that can reach higher temperatures than polytetrafluoroethylene (PTFE) hot ends and heated chambers to avoid part warping and delamination. There are several high temperature printers on the market, but their high costs make them inaccessible for full home-based distributed manufacturing required during pandemic lockdowns. To allow for all these requirements to be met for under $1000, the Cerberus - an open source three-headed self-replicating rapid prototyper (RepRap) was designed and tested with the following capabilities: i) 200 °C-capable heated bed, ii) 500 °C-capable hot end, iii) isolated heated chamber with 1 kW space heater core and iv) mains voltage chamber and bed heating for rapid start. The Cereberus successfully prints polyetherketoneketone (PEKK) and polyetherimide (PEI, ULTEM) with tensile strengths of 77.5 and 80.5 MPa, respectively. As a case study, open source face masks were 3-D printed in PEKK and shown not to warp upon widely home-accessible oven-based sterilization.

Open source high-temperature RepRap for 3-D printing heat-sterilizable PPE and other applications

Thermal sterilization is generally avoided for 3-D printed components because of the relatively low deformation temperatures for common thermoplastics used for material extrusion-based additive manufacturing. 3-D printing materials required for high-temperature heat sterilizable components for COVID-19 and other applications demands 3-D printers with heated beds, hot ends that can reach higher temperatures than polytetrafluoroethylene (PTFE) hot ends and heated chambers to avoid part warping and delamination. There are several high temperature printers on the market, but their high costs make them inaccessible for full home-based distributed manufacturing required during pandemic lockdowns. To allow for all these requirements to be met for under $1000, the Cerberus - an open source three-headed self-replicating rapid prototyper (RepRap) was designed and tested with the following capabilities: i) 200 °C-capable heated bed, ii) 500 °C-capable hot end, iii) isolated heated chamber with 1 kW space heater core and iv) mains voltage chamber and bed heating for rapid start. The Cereberus successfully prints polyetherketoneketone (PEKK) and polyetherimide (PEI, ULTEM) with tensile strengths of 77.5 and 80.5 MPa, respectively. As a case study, open source face masks were 3-D printed in PEKK and shown not to warp upon widely home-accessible oven-based sterilization.

Reich M, Fiedler MJ, Snabes SL, Pearce JM. Towards Distributed Recycling with Additive Manufacturing of PET Flake Feedstocks

This study explores the potential to reach a circular economy for post-consumer Recycled Polyethylene Terephthalate (rPET) packaging and bottles by using it as a Distributed Recycling for Additive Manufacturing (DRAM) feedstock. Specifically, for the first time, rPET water bottle flake is processed using only an open source toolchain with Fused Particle Fabrication (FPF) or Fused Granular Fabrication (FGF) processing rather than first converting it to filament. In this study, first the impact of granulation, sifting, and heating (and their sequential combination) is quantified on the shape and size distribution of the rPET flakes. Then 3D printing tests were performed on the rPET flake with two different feed systems: an external feeder and feed tube augmented with a motorized auger screw, and an extruder-mounted hopper that enables direct 3D printing. Two Gigabot X machines were used, each with the different feed systems, and one without and the latter with extended part cooling. 3D print settings were optimized based on thermal characterization, and both systems were shown to 3D print rPET directly from shredded water bottles. Mechanical testing showed the importance of isolating rPET from moisture and that geometry was important for uniform extrusion. The mechanical strength of 3D-printed parts with FPF and inconsistent flow is lower than optimized fused filament, but adequate for a wide range of applications. Future work is needed to improve consistency and enable water bottles to be used as a widespread DRAM feedstock.

Systematic Literature Review: Integration of Additive Manufacturing and Industry 4.0

The research trend in additive manufacturing (AM) has evolved over the past 30 years, from patents, advances in the design, and layer-by-layer materials, to technologies. However, this evolution is faced with some barriers, such as the implementation of additive manufacturing (AM) in operations, its productivity limitations, and economic and social sustainability. These barriers need to be overcome in order to realize the full potential of AM. The objective of this study is to analyze the bibliometric data on these barriers through a systematic review in two study areas: business model innovation and sustainability in AM from Industry 4.0 perspective. Using the most common keywords in these two study areas, we performed a search on the Web of Science (WoS) and Scopus databases and filtered the results using some inclusion and exclusion criteria. A bibliometric analysis was performed for authorship productivity, journals, the most common keywords, and the identified research clusters in the study areas. For the bibliometric analysis, the BIBEXCEL software was used to extract the relevant information, and Bibliometrix was used to determine the research trend over the past few years. Finally, a literature review was performed to identify future trends in the study areas. The analysis showed evidence of the relationship between the study areas from a bibliometric perspective and areas related to AM as an enabler for Industry 4.0.

Open-Source Grinding Machine for Compression Screw Manufacturing

Some of the most promising distributed recycling and additive manufacturing (DRAM) technical systems use fused particle fabrication (FPF) or fused granular fabrication (FGF), where compression screws force post-consumer waste plastic through a heated nozzle for direct 3D printing. To assist the technical evolution of these systems, this study provided the details of an invention for a low-cost, easily replicable open-source grinding machine for compression screw manufacturing. The system itself can be largely fabricated using FPF/FGF following the self-replicating rapid prototyper (RepRap) methodology. This grinding machine can be made from a cordless cut-off grinder and < $155 in parts. The new invention is demonstrated to be able to cut custom screws with variable (i) channel depths, (ii) screw diameters, (iii) screw lengths, (iv) pitches, (v) abrasive disk thicknesses, (vi) handedness of the screws, (vii) and materials (three types of steel tested: 1045 steel, 1144 steel, and 416 stainless steel). The results show that the device is more than capable of replicating commercial screws as well as providing makers with a much greater flexibility to make custom screws. This invention enables the DRAM toolchain to become even more self-sufficient, which assists the goals of the circular economy.

Distributed Manufacturing of Open Source Medical Hardware for Pandemics

Distributed digital manufacturing offers a solution to medical supply and technology shortages during pandemics. To prepare for the next pandemic, this study reviews the state-of-the-art of open hardware designs needed in a COVID-19-like pandemic. It evaluates the readiness of the top twenty technologies requested by the Government of India. The results show that the majority of the actual medical products have some open source development, however, only 15% of the supporting technologies required to produce them are freely available. The results show there is still considerable research needed to provide open source paths for the development of all the medical hardware needed during pandemics. Five core areas of future research are discussed, which include (i) technical development of a wide-range of open source solutions for all medical supplies and devices, (ii) policies that protect the productivity of laboratories, makerspaces, and fabrication facilities during a pandemic, as well as (iii) streamlining the regulatory process, (iv) developing Good-Samaritan laws to protect makers and designers of open medical hardware, as well as to compel those with knowledge that will save lives to share it, and (v) requiring all citizen-funded research to be released with free and open source licenses.

A review of open source ventilators for COVID-19 and future pandemics

Coronavirus Disease 2019 (COVID-19) threatens to overwhelm our medical infrastructure at the regional level causing spikes in mortality rates because of shortages of critical equipment, like ventilators. Fortunately, with the recent development and widespread deployment of small-scale manufacturing technologies like RepRap-class 3-D printers and open source microcontrollers, mass distributed manufacturing of ventilators has the potential to overcome medical supply shortages. In this study, after providing a background on ventilators, the academic literature is reviewed to find the existing and already openly-published, vetted designs for ventilators systems. These articles are analyzed to determine if the designs are open source both in spirit (license) as well as practical details (e.g. possessing accessible design source files, bill of materials, assembly instructions, wiring diagrams, firmware and software as well as operation and calibration instructions). Next, the existing Internet and gray literature are reviewed for open source ventilator projects and designs. The results of this review found that the tested and peer-reviewed systems lacked complete documentation and the open systems that were documented were either at the very early stages of design (sometimes without even a prototype) and were essentially only basically tested (if at all). With the considerably larger motivation of an ongoing pandemic, it is assumed these projects will garner greater attention and resources to make significant progress to reach a functional and easily-replicated system. There is a large amount of future work needed to move open source ventilators up to the level considered scientific-grade equipment, and even further work needed to reach medical-grade hardware. Future work is needed to achieve the potential of this approach by developing policies, updating regulations, and securing funding mechanisms for the development and testing of open source ventilators for both the current COVID19 pandemic as well as for future pandemics and for everyday use in low-resource settings.

A review of open source ventilators for COVID-19 and future pandemics

Coronavirus Disease 2019 (COVID-19) threatens to overwhelm our medical infrastructure at the regional level causing spikes in mortality rates because of shortages of critical equipment, like ventilators. Fortunately, with the recent development and widespread deployment of small-scale manufacturing technologies like RepRap-class 3-D printers and open source microcontrollers, mass distributed manufacturing of ventilators has the potential to overcome medical supply shortages. In this study, after providing a background on ventilators, the academic literature is reviewed to find the existing and already openly-published, vetted designs for ventilators systems. These articles are analyzed to determine if the designs are open source both in spirit (license) as well as practical details (e.g. possessing accessible design source files, bill of materials, assembly instructions, wiring diagrams, firmware and software as well as operation and calibration instructions). Next, the existing Internet and gray literature are reviewed for open source ventilator projects and designs. The results of this review found that the tested and peer-reviewed systems lacked complete documentation and the open systems that were documented were either at the very early stages of design (sometimes without even a prototype) and were essentially only basically tested (if at all). With the considerably larger motivation of an ongoing pandemic, it is assumed these projects will garner greater attention and resources to make significant progress to reach a functional and easily-replicated system. There is a large amount of future work needed to move open source ventilators up to the level considered scientific-grade equipment, and even further work needed to reach medical-grade hardware. Future work is needed to achieve the potential of this approach by developing policies, updating regulations, and securing funding mechanisms for the development and testing of open source ventilators for both the current COVID19 pandemic as well as for future pandemics and for everyday use in low-resource settings.

Recycled Glass Fiber Composites from Wind Turbine Waste for 3D Printing Feedstock: Effects of Fiber Content and Interface on Mechanical Performance

This research validates the viability of a recycling and reusing process for end-of-life glass fiber reinforced wind turbine blades. Short glass fibers from scrap turbine blades are reclaimed and mixed with polylactic acid (PLA) through a double extrusion process to produce composite feedstock with recycled glass fibers for fused filament fabrication (FFF) 3D printing. Reinforced filaments with different fiber contents, as high as 25% by weight, are extruded and used to 3D print tensile specimens per ASTM D638-14. For 25 wt% reinforcement, the samples showed up to 74% increase in specific stiffness compared to pure PLA samples, while there was a reduction of 42% and 65% in specific tensile strength and failure strain, respectively. To capture the level of impregnation of the non-pyrolyzed recycled fibers and PLA, samples made from reinforced filaments with virgin and recycled fibers are fabricated and assessed in terms of mechanical properties and interface. For the composite specimens out of reinforced PLA with recycled glass fibers, it was found that the specific modulus and tensile strength are respectively 18% and 19% higher than those of samples reinforced with virgin glass fibers. The cause for this observation is mainly attributed to the fact that the surface of recycled fibers is partially covered with epoxy particles, a phenomenon that allows for favorable interactions between the molecules of PLA and epoxy, thus improving the interface bonding between the fibers and PLA.

Open Source Waste Plastic Granulator

In order to accelerate deployment of distributed recycling by providing low-cost feed stocks of granulated post-consumer waste plastic, this study analyzes an open source waste plastic granulator system. It is designed, built, and tested for its ability to convert post-consumer waste, 3D printed products and waste into polymer feedstock for recyclebots of fused particle/granule printers. The technical specifications of the device are quantified in terms of power consumption (380 to 404 W for PET and PLA, respectively) and particle size distribution. The open source device can be fabricated for less than $2000 USD in materials. The experimentally measured power use is only a minor contribution to the overall embodied energy of distributed recycling of waste plastic. The resultant plastic particle size distributions were found to be appropriate for use in both recyclebots and direct material extrusion 3D printers. Simple retrofits are shown to reduce sound levels during operation by 4dB-5dB for the vacuum. These results indicate that the open source waste plastic granulator is an appropriate technology for community, library, maker space, fab lab, or small business–based distributed recycling.

Desktop Fabrication of Strong Poly (Lactic Acid) Parts: FFF Process Parameters Tuning

The current study aims to evaluate the possibilities to increase part strength by optimizing the Fused Filament Fabrication (FFF) process parameters. Five different CAD models of parts with the same coupling dimensions but of different shape inherited from a recent study were converted into test samples with Ultimaker 2 3D printer. The main measure of success was the sample strength, defined as the load at which the first crack in the stressed area of the part appeared. Three different modifications to the FFF process with verified positive effect on interlayer bonding were applied. The first modification included raising the extrusion temperature and disabling printed part cooling. The second modification consisted of reduction in the layer thickness. The third modification combined the effects of the first and the second ones. For four out of five shapes tested the applied process modifications resulted in significant strengthening of the part. The shape that exhibited the best results was subject to further research by creating special printing mode. The mode included fine-tuning of three technological parameters on different stages of the part fabrication. As a result it was possible to increase the part strength by 108% only by tuning printing parameters of the best shape designed with increasing its weight by 8%.