Recycling Plastics in Fabrication & Design: 3D Printing Raw Materials from Plastic Waste

Alaeddine Oussai, Zoltán Bártfai, László Kátai, and István Szalkai explore ways to improve recycling in 3D printing, releasing the details of their recent study in ‘Development of 3D Printing Raw Materials from Plastic Waste.’

Using plastic and dealing with the trash it produces has become normal around the world—leaving many to look back on the years when we enjoyed products in reusable glass containers—like milk, for example. The authors point out that while plastic waste, regarding type and quality, varies around the world, many types are suitable for re-use. For 3D printing, however, recycling processes are still being heavily explored:

“The current applications for using recycled plastics in fabrication and design are fairly limited, on a small scale, plastics (such as ABS, HDPE, or PET) are shredded and formed into pellets, and then either extruded into lament to be used in existing 3D printers, or injection molded into small parts and pieces of larger components.”

“At a large scale, recycled HDPE is melted into sheets and either used directly as sheets in construction, or then heat formed from a sheet into components for construction. These methods of fabrication using recycled plastics are the norm because of their affordability and straightforward processes, yet each method leaves some complexity to be desired.”

For this study, the researchers focused on both polyethylene terephthalate (PET), often referred to as polyester, and polylactic acid (PLA). While it is true that recycling can be both complicated and confusing for consumers everywhere, there are four basic exercises associated with the process:

  • Mechanical reprocessing into equivalent products
  • Secondary processing into products with ‘lower properties’
  • Chemical constituent recovery
  • Quaternary energy recovery

PET recycling circle

Known as a #1 recycling plastic, PET is made of monomer ethylene terephthalate. This is a material often used to make plastic bottles, as well as thin films and solar cells, offering high mechanical strength and temperature resistance.

End markets for PET recirculates in Europe and in the USA (Petcore, 2011; Napcor, 2011).

PLA is one of the most common types of 3D printing filament, known for its plant-based nature and resulting biodegradability. And while its true nature in terms of degrading are still being explored, this material is used widely by users and researchers too, featured in studies exploring the potential for a more circular economy, development of biodegradable blends, direct waste printing with pellets, and much more.

“Although PLA is a biodegradable material, which would significantly reduce environmental pollution associated with its waste, the knowledge behind this material recycling and changes in the properties of PLA upon its multiple processing is a very important subject of discussion,” state the authors.

Other materials like polyvinyl chloride (PVC) can break down in only several days. PVC is also affordable and offers the potential for making high-performance parts. Polyethylene’s PE’s are also commonly used, offering density, toughness, and flexibility.

Today, overall recycling efforts, and within 3D printing also, are geared toward less use of energy, less sorting during the process, and the eventual inclusion of what are now non-recyclables. Currently only poly (ethylene terephthalate) (PET) and polyethylene (as 9 and 37% of the annual plastic produced) are being mechanically processed.

The researchers mention a previous research solution as they developed a ‘crusher,’ for re-using plastic. The device consists of a crusher and extruder, along with 12 blades.

overview of the complete design of the crusher

Overview of the complete design of the extruder

Other recycling methods include chemical technology; however, the researchers point out that right it is considered to be too expensive due to the amount of energy it consumes. They point out that incineration is an option too.

“In the current scenario there is growing demand and interest towards chemical recycling methods with low energy demand along with compatibility of mixed plastic waste to overcome the need for sorting and expanding the recycling technologies to traditional non-recyclable polymers,” concluded the researchers.

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[Source / Images: ‘Development of 3D Printing Raw Materials from Plastic Waste’]

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3D Printing: Successful Scaffolds in Bone Regeneration

In ‘Comprehensive Review on Full Bone Regeneration through 3D Printing Approaches,’ the authors review new developments and solutions in tissue engineering for the formation of cells, as well as proposing an optimized temporary support geometry for treatment.

Fused Filament Fabrication (FFF) process.

Bone regeneration continues to challenge researchers in their work as well as medical professionals attempting to improve patient treatment:

“Many research groups have been working on bone regeneration for over 10 years, but this has not led to effective therapy in a clinical setting. If it was successful, it would enhance the quality of life for millions of people and significantly reduce the absence to work due to fractures which are considered the second higher cause of working day lost,” state the authors.

“When there are fractures with a bone defect exceeding a critical size, the bone is not able to self-regenerate and, therefore, requires the use of a temporary implant (natural and/or synthetic) to serve as support and cells to help bone regeneration. In this way, tissue engineering (TE) has emerged.”

While scaffolds are used in tissue engineering for transporting nutrients and secretion of waste, the cells must be able to imitate true tissue biology, morphology, and functionality.

Exploring the usefulness of temporary implants, the authors state that in tissue engineering for patients, it is first critical to examine native bone tissue and mechanical properties.

Human long bone properties.

3D printed implants must be able to sustain cell viability in a secure environment, and scaffolds must possess suitable elasticity for matching regular bone. High porosity is desired in most tissue engineering, along with the use of materials that are not only biocompatible but also biologically active. During trials, animal models of fractures are often used in vivo before procedures are attempted on humans.

“Animal studies are needed to understand bone regeneration. Variables such as the amount of bone formation and its kinetics, mechanical properties and safety obtained by the scaffold, including the presence of toxic degradation in different organs and in terms of inflammatory response need to be understood in detail,” explained the researchers.

“However, bone fractures performed in animals do not represent the complexity of healing human fractures. The potential of each different type of cells both in vitro and in vivo plays here a key role.”

Even more interesting though, the authors point out that growth factors are unnecessary, with cells showing the potential to secrete optimal extracellular matrix (ECM) components.

“In vitro studies are advantageous because they offer a controlled environment to experimental test molecular and cellular hypotheses,” stated the researchers. “However, cells cultured in vitro are not replicates of their in vivo counterparts.”

While tissue engineering can be a delicate process overall in terms of working to keep cells alive, bone generation is particularly challenging—and scaffolds must be relied on to maintain the same role as tissue. Biomaterials must be able to mimic the natural environment, along with possessing identical mechanical properties of the initial bone. Appropriate levels of degradation are critical for bone regeneration, and are also dependent on corrosion resistance and materials.

Characteristics of the different materials used to produce a scaffold.

Suitable materials include poly(ε-caprolactone) (PCL) or polylactic acid (PLA), both approved by the FDA and offering stability, biocompatibility, and biodegradability. Scaffolds must be osteoinductive for sustaining cells as well as being osteoconductive, providing growth. They must also serve to:

  • Fill bone defect
  • Ensure pore connectivity
  • Encourage bone formation
  • Promote bone growth

Natural organization of long bones.

Designed in SolidWorks, the structures exhibited ‘superior advantages’ over what could be produced conventionally.

“Considering all types of materials available, associated with the desired bone regeneration and the use of synthetic polymers, as PCL or PLA, combined with collagen type I for the trabecular region and Hap for cortical region, seems to be the best strategy to follow,” concluded the researchers.

“Among the most commonly used bioreactors for bone regeneration, perfusion bioreactors appear as the most suitable, because it improves osteogenic proliferation and differentiation due to improved mass transfer and adequate shear stress. When making a design proposal for bone regeneration, it is necessary to study the mechanical effects, such as stress and tension, and link them.”

Cylindrical scaffold

DNA chain-inspired cylindrical scaffold.

Tissue engineering continues to be an enormous area of study, from seeding human dermal fibroblasts, promoting hydrogel microenvironments, to bioprinting structures for soft tissue engineering applications.

Scaffold requirements in terms of response (left) and what should be taken into account (right) (adapted from [106]).

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[Source / Images: ‘Comprehensive Review on Full Bone Regeneration through 3D Printing Approaches’]

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3D Printing with Bioplastics: Engineering Biodegradable PHA Blends

Jackie Anderson offers a review regarding one of the most critical 3D printing topics today: materials. As innovation continues to grow, so do the options regarding software, hardware, and different types of plastics (along with many other alternatives today).

In ‘Engineering Biodegradable PHA Blends,’ Anderson explores issues with plastic waste, and the need to use more environmentally friendly materials as 3D printing filaments.

While other plastics such as acrylonitrile butadiene styrene (ABS) are often used in 3D printing, bioplastics like polylactic acid (PLA) are popular due to their ability to biodegrade, but still, there are other materials superior in that area; in fact, previous research has shown that thin films of other bioplastics like polyhydroxyalkanoates (PHA) may degrade in as little as 1.2 to 2.4 months. This is promising in eliminating the amount of waste that could emerge from 3D printing discards, with Anderson reminding us that plastics can take ‘hundreds to thousands of years to degrade,’ causing harm to every living creature.

“Plastic is a toxic pollutant that causes damage on a wide scale to many different species and environments, and it is necessary that solutions are found to reduce this impact,” states Anderson.

Bioplastics are used in so many different projects today, from marine applications to medical implants to manufacturing. Produced from vegetables, food by-products, or micro-organisms, bioplastics are preferable to oil-based printing materials, environmentally. They are also conventionally used in making items like packaging, cutlery, straws, and even fishing net.

In using man-made plastics like PLA, biodegradability is a bonus, but printed parts can take years to break down:

“This makes it an undesirable material for products that require high rates of biodegradation,” states Anderson.

PHA is not as well-known overall, and especially not with novice users. This material biodegrades faster but is more expensive, not as accessible for consumers, and Anderson points out that it is often challenging to use on a larger scale. PHA also presents drawbacks in comparison to other bioplastics, offering less strength, less flexibility, and inferior melting properties. It can, however, be beneficial when added to other materials like PLA.

“There are other similar PHA blends that have been designed for similar purposes and have also shown great potential for commercial use, yet more research needs to be done on different PHA blends to expand this potential,” states Anderson.

Algae-based biopolymers, while still considered more of a novel material, are like PHA as they are produced naturally and biodegrade easily. Along with 3D printing materials, algae plastics are also used to make films, cutlery, and plastic bags.

“Algae plastic is just one of the many new bioplastics being developed and researched to help reduce plastic pollution. These products are beginning to be marketed more frequently and will help minimize plastic pollution if used on large scales to replace oil-based plastics,” explains Anderson.

Still, PLA is a favorite within the 3D printing industry, due to accessibility, affordability, efficiency in production, and some semblance of biodegradability:

“If PLA materials were to be discarded into landfills or abandoned in the environment, they would take several years to degrade, causing pollution like that of regular plastics,” states Anderson.

“This is deceiving because companies claim that PLA can degrade in about 40-90 days, but this is not the case if the materials are not in a controlled lab setting (PLA, 2019). PLA can only degrade efficiently in specific industrial composting conditions with temperatures at or above 55-70 degrees.”

Using PHA and PLA to create a composite for greater strength and biodegradability could be a good solution, allowing users the best of both worlds.

“While these bioplastics each have their own negative qualities, they can be blended together in different ratios to form a desirable new plastic with the beneficial qualities of each of them,” concluded Anderson.

“These new blends could be used for a wide range of applications, from food packaging to 3D printing filaments. Bioplastics cannot solve the plastic waste crisis altogether, but they can limit the future pollution caused by plastic use and help reduce the damage that humans have caused.”

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An example of a PLA/PHA filament (colorFabb’s Sky Blue PLA/PHA), from ‘Climate Disrupted: The Promise of PHA?’)

[Source / Images: ‘Engineering Biodegradable PHA Blends’]

 

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Analyzing Parameters of Pure and Reinforced 3D Printed PLA and ABS Samples

If you want high-quality 3D printed parts, then you need to choose the right print parameters. Research on this topic is ongoing, and the latest comes from the University of Manchester. Chamil Abeykoon, Pimpisut Sri-Amphorn, and Anura Fernando, with the Northwest Composite Centre in the Aerospace Research Institute, published “Optimization of fused deposition modeling parameters for improved PLA and ABS 3D printed structures,” about their work studying various properties and processing conditions of 3D printed specimens made with different materials.

There are multiple variables involved in 3D printing, and changing just one parameter could cause “consequential changes in several other parameters” at the same time. Additionally, the most commonly used FDM printing materials are thermoplastic polymers with low melting points – not ideal for “some high performance applications.”

“Therefore, attempts have been made to improve the properties of printing filaments by adding particles such as short-fibres, nanoparticles and other suitable additives [18]. Thanks to these extensive researches and developments in the area of FDM, fibre-reinforced filaments are becoming popular and are currently available for practical applications,” they explained.

In order to optimize parameters and settings for these new reinforced materials, the team says we need more 3D printing research and development. In their study, they investigated the process using seven infill patterns, five print speeds, and four set nozzle temperatures, and observed and analyzed the mechanical, thermal, and morphological properties.

They used five commercially available materials, with 1.75 mm diameters:

  • Polylactic acid (PLA)
  • Acrylonitrile butadiene styrene (ABS)
  • Carbon fiber-reinforced PLA (CFR-PLA)
  • Carbon fiber-reinforced ABS (CFR-ABS)
  • Carbon nanotube-reinforced ABS (CNT-ABS)

The samples were designed with SOLIDWORKS and printed on a MakerBot Replicator 2, MakerBot Replicator 2X, and MakerBot Replicator Z18.

3D CAD images of test specimens: (a) Tensile, (b) Bending, and (c) Compression.

The team studied seven infill patterns – catfill, diamond, hexagonal, Hilbert, linear, moroccocanstar, and sharkfill –  and infill densities of 25%, 30%, 40%, 50%, 70%, 90%, and 100%. Two shell layers were used for all samples, and the print bed temperature was between 23-70° for CFR-PLA, and 110°C for the three types of ABS material, to help reduce shrinkage and warping.

“At each test condition of all the types of tests (mechanical, rheological and thermal), 3 test specimens were prepared and tested, and then the average value was taken for the data analysis to improve the accuracy and reliability of the experimental data,” the team wrote.

Appearance of the printed compression test specimens: (a) PLA, (b) ABS, (c) CFR-PLA, (d) CFR-ABS, and (e) CNT-ABS.

First, the 3D printed samples underwent mechanical testing to determine tensile modulus, flexural modulus, and compression properties. Using differential scanning calorimetry (DSC), the researchers measured melting and crystallization behaviors in a liquid nitrogen atmosphere, and found “the volume fractions of the reinforcement and matrix of the composite filaments” with the help of thermal gravimetric analysis (TGA).

Appearance of printed tensile test specimens: (a) PLA, (b) ABS, (c) enlarged view of PLA, and (d) enlarged view of ABS.

Using a thermal imaging camera, they detected how much heat was released as the figure above was printed with 100% infill density, 20 mm/s infill speed, and 215°C set nozzle temperature. Finally, they used scanning electron microscopy (SEM) to observe and perform morphological testing on the surfaces of the 3D printed specimens that were broken during mechanical testing.

Infill density affects the strength of 3D printed parts. By increasing infill density, you then increase the tensile modulus and decrease porosity, which increases the “strength of the mechanical bonding between layers.”

Relationship between tensile modulus and infill density for PLA.

“For pure PLA, parts with 100% infill density obtained the highest Young’s modulus of 1538.05 MPa,” the researchers note.

But, structure gaps can occur more frequently with low infill densities, which reduces part strength. In the figure below, you can see “the changes in porosity of the structure with the infill density.”

3D printed specimens with infill densities: (a) 25% (b) 50% and (c) 100%.

“Of the tested infill speeds from 70 to 110 mm/s; 90 mm/s infill speed gave the highest Young’s modulus for pure PLA,” they wrote.

Print speeds over 90 mm/s could cause polymer filament to melt, and result in poor adhesion and lower strength. To avoid this, the print speed must be compatible with the set nozzle temperature, and an appropriate combination of speed and set nozzle temperature “can reduce the shrinkage of the parts being printed.”

Relationship between tensile modulus and infill speed for PLA.

3D printed PLA samples were tested with the different infill patterns at 50% infill density, 90 mm/s speed, and 215°C set nozzle temperature.

3D printed samples with infill patterns: (a) Linear, (b) Hexagonal, (c) Moroccanstar, (d) Catfill, (e) Sharkfill, (f) Diamond, and (g) Hilbert.

“Among these seven patterns, the linear pattern gave the highest tensile modulus of 990.5 MPa. This can be justified as the linear pattern should have the best layer arrangement (in terms of the bonding between the layers) with the lowest porous structure,” the team explained.

They found that the print temperature has “a significant effect on the tensile modulus.” 215°C provided the best tensile performance, as lower temperatures might cause poor melting, and thus weak bonding. The set nozzle temperature and print speed correlate, and “should be chosen carefully based on the material being used and the part geometry being printed.”

To study the effect on tensile properties, they were printed with the following parameters: 90 mm/s infill speed, linear pattern, 10% infill density, and 215°C set nozzle temperature for PLA, and 230°C for ABS. The researchers found that the tensile modulus of pure PLA (1538.05 MPa) was far higher than for pure ABS.

“In this study, CFR-PLA gave the largest tensile modulus of 2637.29 MPa while pure ABS (919.52 MPs) was the weakest in tensile strength,” they wrote.

Tensile modulus of the five printing materials.

Reinforcing ABS and PLA with fiber causes higher tensile modulus, though pure PLA was stronger than the CNT-ABS.

Even at 90° of bending, the PLA and ABS samples only had a small crack in the middle, and did not break.

3D printed specimen in bending test.

At 1253.62 MPa, the CFR-PLA had the highest bending modulus, while pure PLA was the lowest at 550.16 MPa.

During compression tests, none of the materials were crushed or broken, and pure ABS was found to be the toughest.

“As evident, pure PLA gave the highest compressive strength while the compressive modulus of CFR-PLA (1290.24 MPa) is slightly higher than that of pure PLA (1260.71 MPa) (higher gradient of the liner region). CFR-ABS and CNT-ABS follow the same trend but CNT-ABS is slightly tougher than CFR-ABS,” the team explained. “Pure ABS shows the lowest compressive strength and modulus (478.2 MPa) but shows the most ductile behavior of the five materials.”

Compressive stress-strain curves of test materials.

Finite element analysis (FEA) by ANSYS was used to visualize stress distribution for the tensile, bending, and compression testing of PLA.

Equivalent stress distribution for tensile test.

“The stress distribution shows that a uniform stress is created in the gauge length of the test piece,” they explained.

“Higher compressive loading will cause the material to have internal crack initiations thereby allowing the PLA to buckle excessively.”

The team concluded through DSC analysis that “the strength of the 3D printed samples is dependent upon the set printing parameters and the printing materials more than the crystallisation.” While the infill speeds differ, the glass transition temperature (Tg) of the samples were similar.

“In this study, cooling of 3D printed parts occurred naturally by releasing heat to the surroundings while printing without any control on the cooling rate,” they stated.

DSC curves of PLA parts printed at different set nozzle temperatures.

As expected, the set nozzle temperature did not significantly effect the Tg, and material crystallization at different temperatures didn’t really affect part strength. But, the tensile modulus did change with the temperature.

TGA was used to analyze the weight loss variation of the composite materials against increased print temperature.

TGA diagrams of short fiber-reinforced composite filaments.

“Degradation temperatures (Td) of these materials can be determined from the mid-point of the descending part of each curve, which is approximately 331.85 °C for PLA. This value showed some sort of agreement to the value reported in commercial PLA data sheets – 353 °C,” they wrote.

Pure PLA typically has a higher Young’s modulus than pure ABS, so it can help to add “a higher volume fraction of reinforcement into the ABS matrix.” Brittle CFR-PLA and CFR-ABS filaments could have their flexibility affected if more carbon fiber is added, which can cause filament feed issues.

Thermal image during 3D printing.

An infrared thermal camera was used to observe 3D printing. The yellow area is the brightest, and hottest: this is where the polymer was extruded from the nozzle. The color changes to orange where the material starts to solidify, and the “red, pink, purple, and blue areas are at lower temperatures, respectively.” The red circle marks the temperature at the printer wall – less than the sample actually being printed.

“SEM images showed that the strength of the printed samples was dependent upon the arrangement of their layers,” the team noted.

Normal and SEM images of fracture surfaces of PLA samples: (a) 25% and (b) 100% infill density.

Observing the fracture surfaces of broken PLA samples with SEM showed that “the air gaps of 25% infill density sample is larger than that of 100% infill density.”

Looking at infill speed with SEM, the team noted that “the best orderliness” comes from 90 mm/s infill speed.

Incompatibility between the material matrix and the reinforcement can cause porosity in the 3D printed samples, but the latter can “contribute in increasing the mechanical properties by bearing the load.” You can see below that the pure PLA has a more regular layer alignment when compared to pure ABS.

SEM images of 3D printed parts at 19X magnification: (a) PLA, (b) ABS, (c) CFR-PLA, (d) CFR-ABS, and (e) CNT-ABS.

CFR-ABS is more porous than CFR-PLA, and both are rougher than the materials in their pure forms.

“Meantime, CNT-ABS shows a better arrangement of individual layers than the other two carbon fibre reinforced materials and also than the pure ABS as well,” they explained.

The last SEM images compare the size of the carbon fiber and carbon nanotube reinforcements. The fracture surface of the CNT-ABS shows some small holes, “due to the embedded carbon nanotubes in the matrix.”

“Compared to the matrix-reinforcement compatibility, both materials show some sort of incompatibility by having cracks and voids between the fibre and matrix,” they wrote.

“On the other hand, although the overall strength of CNT-ABS is improved by CNT particles, the flexibility of this material was decreased compared to the pure ABS as CNT-ABS being more brittle.”

SEM images of fracture surfaces at 1.00 KX magnification: (a) CFR-PLA and (b) CNT-ABS.

They found that the optimal settings to improve the performance of the five 3D printing materials were 100% infill density, 90 mm/s infill speed, 215 °C of set nozzle temperature, and linear infill. Of the five materials, CFR-PLA had the strongest tension, bending, and compression, with the highest modulus.

Overall, it is obvious that the set printing parameters can significantly influence the mechanical properties of 3D printed parts. It can be claimed that the printing speed and set nozzle temperature should be matched to ensure proper melting of filaments and also to control the material solidification process,” the researchers concluded.

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For a Personalized Look, Try a 3D Printed Pompillon Bow Tie

There’s something fantastically dapper about a bow tie, and a 3D printed version definitely takes this fashionable look the extra mile. Ties and bow ties, along with ascots and scarves, were born from the cravat, and can quickly elevate an outfit. But using 3D printing to make these fashion-forward accessories means that you can easily play with the shape and texture of the tie for a more unique aesthetic.

Pompillon, a clothing brand based in Italy and Germany, was founded in 2017, based on an idea from bow tie collector and aerospace engineer Luca Pompa, also the founder of the brand. That idea, of course, was to use 3D printing to make more creative, customizable bow ties. The name Pompillon is a playful merger between the surname Pompa and ‘papillon,’ which the website explains is “the French name of the beloved bow tie.”

“The vast assortment of colors of bow ties and combinable ribbons wants to encourage everyone’s imagination to the maximum, to personalize his style with a small accessory with attention to every detail,” the Pompillon Facebook page states. “Moreover, the various editions will allow collecting them in all its lines.”

3D printed Pompillon bow ties merge classic shapes with creativity, experimentation, and technology; add in attention to detail and a wide range of ribbons and tie colors, and the sky is the limit when it comes to personalizing your style. The Pompillon tie takes the typical bow tie silhouette, reduces it down to the most essential lines, and reinterprets the accessory with 3D printing.

The brand uses another Italian original to fabricate its bow ties – Sharebot 3D printers. Pompillon bow ties are 3D printed using a hexagon infill shape. Several of these six-sided polygons, all with sides of equal length, are joined together to make the bow tie and optimize “structural packing to the maximum.”

3D printed Pompillon bow ties are perfect for classic, everyday style, and for more formal occasions as well. The brand’s ideal clientele are those who appreciate a personalized and colorful look, as they enjoy dressing in a refined way, without being boring.

The bow ties are 3D printed out of plant-based, biodegradable PLA material from renewable resources, which keeps them lightweight. In the future, Pompillon will make special editions of its bow ties out of carbon fiber, marble powder, and even wood.

Pompillon has two versions of its bow tie – the filled Gentlemen and the open Rebel. When you combine the two, it makes the Unique model. The brand also offers a Gala Edition bow tie, which appear to only come in black and white for more sophisticated evenings, à la James Bond. These 3D printed bow ties are completely customizable with a variety of colors, clips, and ribbon, so you have a lot of choices to play around with in making your own unique accessory.

You can visit the brand’s online shop page to see what’s available. Two of the looks I really like are the Pompillon Dark Rebel, which is a red ribbon and black bow tie combination for just €24.90, and the Pompillon Unique White Snow & Blue Ocean, also at a price of €24.90. A 3D printed Gala Edition bow tie will set you back just €26.90, and several of the Pompillon Gentlemen ties, including my favorite in the limited edition Nature Green color, only cost €19.90.

They even look good on dogs!

“Have fun using them in bulk or combined with our other Pompillon. Make it unique and customizable for every look and mood,” the shop page says.

“Take a picture wearing it and post it on social media. If you send it to info@pompillon.it, it will be published and advertised on our social networks! plus you will have the chance to win a free one…be Lucky!”

Would you wear a 3D printed Pompillon bow tie? Let us know! Discuss this story and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the Facebook comments below.

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PLA: The Effects of Annealing & Autoclaving on Mechanical Behavior of Desktop FDM Parts

Researchers from the University of California delve into a very important area of 3D printing for the medical field, experimenting with how sterilization processes affect materials. They released their findings in the recently published ‘Identifying a commercially-available 3D printing process that minimizes model distortion after annealing and autoclaving and the effect of steam sterilization on mechanical strength.’

3D printed models are currently changing the face of medicine in terms of patient-specific treatment, allowing for better diagnosis, education for patients and their families (and medical students), along with acting as pre-planning tools and surgical guides.

In relation to FDM 3D printing in medicine, the authors refer back to previous studies concluding that PLA was weakened by sterilization yet strengthened in annealing, explaining that the next viable step would be to find a 3D printing material that can withstand heat treatment and steam sterilization.

The team fabricated four 30 mm cubes as samples for the study, each featuring different infill—designed in Tinkercad and then 3D printed on a LulzBot Mini 3D printer.

Manufacturer temperature (°C) recommendations for FDM 3D printing materials

Samples were printed all at once, using 0.38 mm layer height and a 0.5 mm printhead nozzle. Materials tested included:

  • ColorFabb Woodfill
  • Dragons Metallic PLA in All That Glitters Gold
  • Essentium PLA in Gray
  • Maker Series PLA in Food Safe FDA OK Clear
  • Maker Series PLA in White HOT White
  • Proto-Pasta HTPLA in White
  • Raptor Series PLA in HD Vivid Blue

a) Infill geometries clockwise beginning from top-left: tetrahedral, triangles, grid, zig-zag and b) 3D printed cubes

Each sample was bathed in hot water, with the annealing treatment performed via an 800 W Strata Home sous vide circulating precision cooker.

“The cubes were removed from the hot water-bath and allowed to cool to room temperature without interference. The X, Y, and Z dimensions of the cubes were measured again to quantify deformation and calculate percent changes, a positive percent change indicating expansion and a negative percent change indicating shrinkage,” explained the researchers.

“In order to quantify distortion in either direction, we took the absolute value of these percentages. Subjective observations were noted such as spherical ‘balloon-like’ expansion. We also analyzed whether certain materials consistently expanded or contracted in every axes.”

Samples were then placed in autoclave sterilization pouches and deposited into a Tuttnauer 2540 M autoclave for 45 minutes at 134 °C and a pressure of 375 PSI. Afterward, the samples were cooled to room temperature and then examined for any signs of deformation.

a) Standard Army-Navy retractor and b) strength-optimized Army-Navy retractor designs in inches created in AutoDesk Fusion 360 obtained from Chen et al. c Retractor orientation on the build plate to eliminate need for support material

a) Standard retractors warping after hot water-bath annealing and b) after autoclaving. c) Strength-optimized retractor without intervention (right) and warping after hot water-bath annealing (left)

The material exhibiting the least amount of deformation was Essentium PLA Gray. The highest deformation was noted in Maker Series PLA White HOT White.

Quantifying absolute deformation in 30 mm cubes across 3D printing materials after annealing

“After hot water-bath annealing for 30 mm cubes, the infill that deformed the least was ‘grid,’ and the infill pattern that deformed the most was ‘zig-zag.’ After both annealing then autoclaving for 30 mm cubes, the material that deformed the least was Essentium PLA Gray. The material that deformed the most was Maker Series PLA White HOT White. After both annealing then autoclaving for 30 mm cubes, the infill pattern that deformed the least was ‘grid,’ and the infill pattern that deformed the most was ‘tetrahedral.’”

Quantifying absolute deformation in 30 mm cubes across 3D printing materials after annealing then autoclaving

Quantifying absolute deformation in 30 mm cubes across infill geometries after annealing then autoclaving

Maker Series PLA White HOT White was the only material noted to expand in every axis—despite the infill geometry or intervention. Every other material showed variances due to infill. Expansion after annealing usually seemed to suggest ‘direction of distortion’ after autoclaving.

“We acknowledge that dimensional changes and strength limitations may not be a challenge at a lower autoclave cycle, which would require further testing. We have also yet to understand the mechanical behavior of the 3D printed models in this study when they are subjected to multiple cycles of autoclaving and whether they will continue to undergo dimensional change. However, regardless of whether 3D printed PLA surgical instruments are determined to be single or multi-use, these instruments may still be valuable in fields such as aerospace medicine where space limitations exist, or in resource-limited situations where additional instruments are needed,” stated the researchers.

“This study is intended as a pre-clinical evaluation of the mechanical behavior of FDM 3D printing materials following hot water-bath annealing treatment and autoclave sterilization. For FDM 3D printed Army-Navy retractors, further sterilization and biocompatibility validation will be necessary for it to be applied clinically.”

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[Source / Images: ‘Identifying a commercially-available 3D printing process that minimizes model distortion after annealing and autoclaving and the effect of steam sterilization on mechanical strength’]

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Researchers Create Low-Cost 3D Printed Polarimeter for Use in Chemistry Classrooms

The adoption of 3D printing in the classroom has opened up new horizons for creating teaching tools. Science teachers, in particular, can make personalized models of nanostructures, and educational tools like colorimeters. But there haven’t been any 3D printable designs for polarimeters, which measures the angle of rotation of polarized light once it’s passed through an optically active solution or substance. Paweł Bernard from Jagiellonian University and James D. Mendez from Indiana University – Purdue University Columbus published a paper about their creation of a low-cost 3D printed polarimeter.

“3D printing and simple electronics were used to create a polarimeter suitable for a variety of chemistry courses,” they wrote. “This device allows instructors to demonstrate optical activity but is also easy to use and low cost enough to be widely available for student use, as well. The instrument uses an LED light source and detector housed in a 3D-printed base. By rotating the top piece, users can visually detect changes in brightness or measure this directly with a multimeter.”

A polarimeter consists of a sample chamber, monochromatic light, and a polarizing filter before, and a rotatable one behind, the sample. This second filter can be adjusted to the angle of the rotated light, after it’s passed through a sample, in order to “minimize or maximize the transmitted light.”

Basic polarimeter schematic and working theory.

High school and college teachers normally demonstrate the optical activity of substances using overhead projection, as most regular polarimeters are too expensive for use in a school laboratory setting. One researcher created a no-cost polarimeter using sunglasses and a mobile phone, which was good for demonstration purposes, but not for student experiments. Another inexpensive polarimeter was made using a shoebox, but it wasn’t durable enough.

“Therefore, the use of 3D printing technology is a perfect solution,” the researchers stated. “The body of a polarimeter can be printed in a reasonable time; the price of the plastic and electronics is low, and the actual assembly of the elements is relatively simple.”

3D printed polarimeter schematic.

A basic polarimeter can use either a test tube or 3D printed cuvette, and light detection can be merely eyeballed, or precisely measured with a low IR radiation sensitivity photodiode. Both are compatible with low-voltage, inexpensive LEDs; the RBG diode at the bottom can be plugged into a 4.5 or 5 V battery, or a standard 9 V battery can be used with a simple circuit.

9 V power supply circuit schematic.

“In the construction, two layers of polarizing filters (polarizing film) are used. It is a low-cost, commercially available material, used for the construction of 3D glasses among other things,” Bernard and Mendez explain. “Our experience shows that it is easier to identify the lowest (rather than highest) intensity of the light passing through the sample; therefore, we advise arranging two layers of polarizing film rotated by 90°. In such a setup at neutral position (0° angle) without a sample, or with a sample of optically nonactive substance, it is dark, showing the lowest light intensity. 

“The construction of the device using a test tube as a sample container is simpler but also more problematic in use. The bottom of a test tube scatters the light. Usually, the center of the light spot is darker, but there is an unpolarized light ring around it.”

A test tube does not ensure a complete blackout at the minimum light point, so a 3D printed container with a flat bottom is useful. The researchers 3D printed the elements out of ABS and PLA filaments, which were black to ensure stable light readings. PVA supports and a dual extruder printer were used to 3D print the rotary cup and main body.

(a) Operating 3D printed cuvette polarimeter with photodiode detector at zero position (minimum signal); (b) operating 3D printed test tube polarimeter (maximum signal); (c) operating 3D printed test tube polarimeter (min signal); (d) operating the 3D printed cuvette polarimeter (max signal); (e) operating 3D printed cuvette polarimeter (min signal).

The researchers tested 50 high school chemistry students in Poland and 15 organic chemistry university students in the US on taking measurements with the 3D printed polarimeter. Working in groups of 2-3, they ran measurements with pure liquids first, and then aqueous solutions. It’s quick and easy to use – the students can change samples and adjust a cap rotation in less than a minute, though they must be told which way to rotate the tool for different substances as “the device gives the same readings in both directions (90° = −270°).”

“It is also advised to adjust the concentration of the sample solution and path length so that the readings are in the range of the provided rotation scale (from −180° to +180°). Using measured rotation and simple mathematical relations, students can calculate a substance’s specific rotation,” the researchers said.

The students used (R)-limonene, fructose, and sucrose, and ran initial measurements both visually and with the 3D printed polarimeter, which allowed them to take measurements with three colors thanks to its RBG diode. They made 4 to 6 measurements for a sample and after dilation for the aqueous solutions.

“The results were a starting point for a discussion on optical rotatory dispersion phenomena. Calculating the specific rotation of the substances was homework, verified by the teacher during subsequent classes,” the researchers stated.

Measured rotation for aqueous solutions of sucrose in the concentration range of 0.05–0.35 g·mL, a series for red, green, blue light measured with a 3D printed polarimeter, and accompanied by results from commercial polarimeter with a sodium lamp 589 nm.

In another project, instructors prepared kits with all of the materials needed to assemble the polarimeter, including breadboards and the 3D printed body. 16 chemistry majors in Poland and four US undergrad students constructed the device, working in pairs, and none had previous experience using breadboards or building measuring devices. But they followed detailed instructions, with some help from teachers, and succeeded in building operational polarimeters in less than one hour.

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Recycling PLA for FDM 3D Printing

Syed Muhammad Raza and Dilawar Singh explore the ongoing potential for recycling 3D printing materials, releasing their findings in the recently published ‘Experimental Investigation on Filament Extrusion using recycled materials.’

As 3D printing becomes increasingly popular around the globe, environmental concerns among users continue to grow despite that less usage of material is often one of the greatest benefits of such new technology. Plastic trash continues to be a growing issue, affecting people, the Earth, and wildlife too. Statistics and information abound on the horrors of polymers, leaving researchers highly motivated to find other materials that may offer higher performance and less waste.

In FDM 3D printing, users have an array of materials to choose from, many of which do have less impact on the environment. While ABS may not be biodegradable, there are different ways to recycle and reuse (even in space), along with the use of innovative solvents, and more. Because there may be many failed prints as users experiment, it is critical to find ways to keep the plastic from piling up in the trash.

PLA is not only biocompatible but biodegradable and is featured in this study due to ‘ease of use compared to other thermoplastics.’

“In the field of medical, PLA is already a widely used material,” stated the authors. “It is being used in application including suture, fixation of bone material, drug delivery and tissue engineering.”

With the goal to recycle PLA discards into useful products, the authors crushed failed or deformed 3D prints, shredded them, and then ‘sieved’ them to get rid of larger pieces. Shredded material was then turned back into filament.

During the study, the researchers realized that basics like parameter, speed, and temperature had a substantial impact on the material and thickness.

Methodology

3Devo Shr3Dit

Process of Dehumidification

In this study, the researchers used a 3Devo Composer 450 filament extruder featuring four heating zones, with one temperature range found suitable for PLA.

“From the lower end of this narrowed range, the range was then increased gradually with an increment of 10oC to identify the ideal temperature for consistent thickness,” said the authors. “The extruder can be easily connected to the laptop/desktop via USB and displays the results on the filament thickness and the process settings using the Arduino software. The effect of temperature and extrusion speed are recorded along with the corresponding filament thickness.”

Experimental scheme

PLA as a 3D printing filament

A series of experiments were performed to attain suitable thickness, with temperatures and speed varied for better results ultimately. Filaments were found to be non-uniform in terms of diameter and exceeded tolerance limits. Stable speed was required was stable extrusion:

“… and with recycled PLA, the flow of pieces and the melting were affecting the rate of extrusion.”

Overall, the team found that diameter was dependent on speed and temperature, and ‘standard deviation’ occurred when speed was constant.

“More experiments should be carried out in order to optimize the variable parameters like heater temperature and speed of the extruder,” concluded the authors.

“The experiment should result in a desirable low thickness filament of recycled PLA to be used for 3D printing facility. It is advisable to have to better way to cool the filament in order to prevent it from getting damaged and losing its shape. The raw material for extrusion must also be tested for moisture content and dehumidified.”

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[Source / Images: ‘Experimental Investigation on Filament Extrusion using recycled materials’]

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3D Printing for COVID-19: ID Badge/Door Opener from 3D LifePrints UK

A number of small companies are attempting to support the supply shortages being faced by hospitals in the face of the COVID-19 outbreak and provide new devices that can reduce the potential risk of contamination for medical professionals. Meanwhile, some large manufacturers that might be deployed for a massive World War Two-style production effort are not stepping up or being government mandated to provide production capacity. In fact, they are even laying off staff in the midst of a health crisis that has also become an economic crisis. (See our comments about GE worker protests in a previous article for an example.)

One such small firm lending a hand to the supply shortages is 3D LifePrints UK, an additive medical device manufacture specialist that makes such items as implants for craniofacial surgery, surgical guides and pre-surgical models for National Health Service trusts, medical device companies, research institutions and others in the U.K., Europe and around the world. 

3D LifePrints has been asked by a number of medical institutions to investigate and provide prototype designs for personal protection equipment (PPE) such as Facial mask connectors, mounts for ICU devices that are being moved into other venues, and a simple 3D printable device called the “Distancer.” This last item makes it possible for healthcare professionals to open a door or swipe an ID card without the need to touch potentially contaminated surfaces. 

“A doctor goes through a door up to 150 times a day in a hospital. The phrase we hear all the time is ‘the doors are like lava.’ The surface retention of COVID-19 is quite high on stainless steel and plastic,” founder and CTO Paul Fotheringham said.

Fotheringham explained that, in addition to the regular protocol for which hospital employees use their IDs, presenting proper identification in healthcare facilities is necessary to prevent the theft of supplies by hospital staff. 

To ensure the maintenance of proper protocol and prevent the spread of the virus, 3D LifePrints UK and the Alder Hey NHS Foundation Trust designed a 3D printed device that can hang off a keychain or lanyard and allow for the slide insert of a user’s electronic ID card. The Distancer features a handle so that the user does not have to touch the actual card, a hook that allows users to open a door, and a flat end for pushing doors closed. 

The company is 3D printing the items from materials that will not deteriorate during the cleaning process, which is essential for items that have exposure to COVID-19: nylon PA 12, ABS or anti-microbial PLA that includes an embedded nano-copper additive. It is available in two designs, either flat-packed with living hinges and one-click assembly, which could be mass produced with injection molding, or a 3D printed version.  

The 3D printed Distancer from 3D LifePrints UK. The file is available for download on the company website. Image courtesy of 3D LifePrints UK.

3D LifePrints is in the process of producing and delivering 4,000 Distancers to NHS hospitals at the moment, while it designs and evaluates other items. The firm is also working with the NHS to develop a specialty connector that can join an off-the-shelf scuba mask to an anesthesia filter that results in a respirator-style device for clinicians (not patients). This is in contrast to the CPAP-type device being developed in Italy using masks from Decathlon. The device is currently being evaluated with the NHS, but it is promising due to the fact that the scuba mask is form fitting and sealed against the face with rubber in a way that is required for the safety of clinicians.  

Fotheringham stressed that 3D LifePrints didn’t simply begin making supplies for the U.K.’s medical facilities out of the blue, but is acting on specific requests from the NHS and British hospitals and is working with medical partners to ensure the safety of the devices, while it is his firm’s job to design, iterate and produce the parts to the needs and specifications of the medical professionals. 

Typically, these devices would require significant clinical testing and approval from the proper regulatory bodies, but due to the emergency nature of the current public health crisis, devices that have not yet received certification are being fast-tracked for approval. 

Other considerations being taken into account are the specific production technologies and materials used to produce parts. More common and less expensive material extrusion printers, for instance, are known to make items that are more porous and have rougher surface finish than those made with selective laser sintering and other polymer powder bed fusion technologies. This reduces the chance for bacteria developing in hidden crevices and makes the parts easier to clean. 

As for materials, the company is focusing on the ability of plastics to withstand the use of chemical disinfectants to minimize the degradation of the part over time. In this case, PLA (the most common polymer used in desktop machines and made from corn starch), is not ideal. However, polypropylene, from which 3D LifePrints intends to injection mold its Distancer, is more durable and can sustain repeated cleanings. 

Fotheringham urged 3D printing enthusiasts and experts to use caution and proper time management when volunteering to combat the COVID-19 supply crisis. He suggested that these devices should be made in conjunction with medical professionals to ensure proper protocol is followed. One way would be to use official channels such as the FDA in the U.S., who we have reached out to in order to learn more about the safety of 3D printed medical devices made in response to the public health crisis. We will cover this topic in greater depth in a follow-up article.

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3D Printed Surfboard: Researchers Test Different Bio-Inspired Core Structures

Just as a New Zealand-based surfer was inspired by the humpback whale and the microgrooves of shark skin when creating his surfboard fins, so too was a team of international researchers inspired by the natural world in their structure study of an on-water sports board. In their recently published paper, “3D Printing On-Water Sports Boards with Bio-Inspired Core Designs,” they explain their work advancing the board by using 3D printing and different bio-inspired core structures, such as the honeycomb.

“Modeling and analyzing the sports equipment for injury prevention, reduction in cost, and performance enhancement have gained considerable attention in the sports engineering community. In this regard, the structure study of on-water sports board (surfboard, kiteboard, and skimboard) is vital due to its close relation with environmental and human health as well as performance and safety of the board,” the researchers wrote.

(a) A natural honeycomb structure; (b) the designed honeycomb core inspired by nature.

3D printing has often been used in the sports field, but in previous studies about 3D printed boards, researchers mainly focused on the geometry, only making small modifications to the equipment. This research team actually introduced different patterns to use as the board’s internal core structure. FDM technology and PLA materials were used to make the first sample board, featuring a uniform honeycomb structure that was created with the help of CATIA V5 software.

Most modern boards feature a sandwich structure, where a thin outer shell covers an inner core made of foam, which allows for increased buoyancy and stability, less weight, and improved bending resistance. These structures typically feature a top shell, the lightweight core, and a bottom shell, but this board merged the bottom shell with the core.

“A smaller scale version of a real on-water sports board was designed,” the researchers wrote. “The board had a 48 mm width and 144 mm length with a 357 mm radius curvature at two sides. A bottom curvature of 600 mm was considered, resulting in a model closer to the real one. The hexagonal honeycomb structure formed the core of the board, and was repeated across the specimen.”

The honeycombs were 3 mm wide, and patterned with 1 mm thick walls, while the bottom and top shells had thicknesses of 5 and 1.5 mm, respectively. The team used an XYZprinting da Vinci 1.0 Pro 3D printer to make the sample board with a uniform honeycomb structure.

(a) Two separate 3D printed parts of the board; (b) two parts glued together with strong adhesive.

Surfboard fractures frequently happen between the surfer’s feet, in the board’s middle section. Usually, this occurs because the lip of the wave impacts in the middle and rips it into two parts after the surfer falls into the water, or because the surfer’s feet get too close together and concentrate their body’s pressure in the middle.

“In both of these circumstances, an immense force acts upon the middle portion of the board, causing large bending stress that may result in breakage,” the researchers explained.

“As both of these breakages are caused by bending stresses, a mechanical three-point bending test could be employed to determine the strength of the board in such loading.”

The board with a uniform honeycomb structure core under three-point bending test.

The team tested the honeycomb board under 3-point loading, though they had to change the grippers for the test.

“The test with the strain rate of 0.001 s1 was carried out at room temperature with an 80 mm distance between two supports. A displacement-controlled test was conducted to get a maximum deflection of 4 mm in the elastic range.”

I-shaped beam and the board with equivalent sections shown with orange lines.

In order to validate these results, and model the structure’s deformation under the test, the researchers developed a “geometrically linear analytical method,” using an equivalent I-shaped section with geometrical stiffness varied along the X-axis, to simulate the honeycomb structure. Then, a geometrically non-linear finite element method, based on ABAQUS software, simulated the boards with a variety of different core structures under the three-point bending test.

Boundary conditions of the finite element method model.

A bending test was simulated to validate the FEM model, and the team performed a mesh sensitivity analysis to make sure the numerical results were accurate. Then, they applied the same test to the sample board with the honeycomb core for a 4 mm maximum deflection. The maximum stress of ∼40 MPa, found in the middle of the board, was low enough to keep the board “in the desired elastic region.” For comparison, the PLA had a yield test level of 60 MPa.

Von Mises stress contour of the board with the uniform honeycomb core.

“The force–deflection curve for the experimental, geometrically non-linear numerical, and geometrically linear analytical results are plotted and compared to each other in Figure 13,” the researchers explained. “The preliminary conclusion drawn from this figure is the fact that the PLA board shows a linear elastic deformation up to 300 N force, beyond which the material yields, followed by plastic deformation that is manifested as a plateau after 500 N.”

Comparison of the experimental, numerical, and analytical load–deflection curves for the three-point bending test of the honeycomb and fully-filled boards.

Once the team had validated the geometrically non-linear FEM model for the board with the honeycomb core structure, they simulated other patterns for the bottom shell’s core. Performing the three-point bending test with the geometrically non-linear FEM software package ABAQUS, while the board’s total volume was kept constant, helped them find the structure with the maximal bending resistance. The different structures they tested were:

  • Hexagonal-Rhomic (HR) Structure
  • Triangular Honeycomb Structure
  • Hexagonal Carbon Lattice
  • Pine Cone and Sunflower-Inspired Patterns
  • Spiderweb-Inspired Pattern
  • Functionally Graded (FG) Honeycomb Structure

“For all of the structures, the mesh convergence study was conducted and the appropriate number of elements for the FEM model was selected,” the researchers wrote. “Furthermore, the maximum stresses of all boards with various core structures were figured to have shown a maximum stress lower than the yield stress of the PLA material.”

(a) A pinecone with two 8-number and 13-number opposite directional spirals; (b) Sunflower with Fibonacci spiral; (c) Pinecone-inspired structure designed using Fibonacci spirals.

They found that the board with the FG honeycomb structure had the best bending performance – 31% better, in fact, than the board with the uniform honeycomb structure at 500 N force. This means that it can tolerate maximum forces, as opposed to an intermediate force like the rest of the structures.

“Due to the absence of similar designs and results in the literature, this paper is expected to advance the state of the art of on-water sports boards and provide designers with structures that could enhance the performance of sports equipment,” the researchers concluded.

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