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Improved FDM 3D Printing with Lignin Biocomposites

In the recently published ‘Lignin: A Biopolymer from Forestry Biomass for Biocomposites and 3D Printing,’ international researchers Mihaela Tanase-Opedal, Eduardo Espinosa, Alejandro Rodríguez, and Gary Chinga-Carrasco explore a very specific area of materials related to biopolymers.

As composites are used more often these days to improve existing materials—especially in 3D printing—alternative materials like wood are being experimented with also. Fiber-based biocomposites and lignin can be better options than petrochemical-based products. For this study, the authors gleaned lignin from spruce trees being reduced to pulp. They used the material to create composite filaments, printing sample dogbones to test mechanical properties.

Natural-fiber biocomposites offer the following:

  • Affordability
  • Good mechanical properties
  • No emission of toxins
  • Light weight

PLA is a popular polymer used in 3D printing, and as the authors remind us, it is actually a biopolymer—featuring good mechanical properties, biodegradability, easy melt-processability, and much more; however, it is also not always cost-effective or suitable for every project. As a composite, however, PLA becomes more versatile.

“Each year, over 50 million tons of lignin are produced worldwide as a side product from biorefineries, of which 98% are burned to generate energy. Only 2% of the lignin has been used for other purposes, mainly in applications such as dispersants, adhesives, and fillers,” state the researchers.

“Without modification, lignin can be directly incorporated into a polymeric matrix, such as UV-light stabilizer, antioxidant, flame retardant, plasticizer, and flow enhancer to reduce production cost, reduce plastic, and potentially improve material properties.”

As 3D printing brings so many advantages forth to industrial users, with the ability to create affordable and complex structures, as well as leaving behind less waste and energy usage, materials like lignin are attractive for use when mixed with other polymers. For this study, the researchers focused on PLA/soda lignin biocomposite filament for 3D printing.

“A motivation for selecting soda lignin is that it is sulphur-free. Soda lignin was thus expected to reduce the typical smell that is experienced when melt-processing biocompounds containing kraft lignin or lignosulfonates,” stated the researchers.

Samples were assessed for:

  • Mechanical (tensile testing)
  • Thermal (TGA, DSC analysis)
  • Morphological (SEM)
  • X-ray diffraction
  • Antioxidant properties

An original Prusa i3 MK3S was used in FDM 3D printing of the dogbone samples, with a length of 63mm and width of 3mm. Three sets were printed, as well as a phone case. The biocomposite demonstrated an increase in mechanical properties when temperatures were increased, with elastic modulus decreasing by 25% to 32%. Lignin offered an improvement in ductility, but a decrease in plasticity.

Mechanical properties of PLA and PLA/Lignin biocomposites.

 

Stress−strain curves for the different biocomposites

Antioxidant properties were also confirmed, showing that 3D printed samples with lignin had even more antioxidant capability than PLA, meaning there is the potential for use for other applications such as food packaging.

“The suitability of the PLA/lignin biocomposite filament for 3D printing was also tested, by printing a smartphone protective case,” stated the researchers. “The printing process revealed a good performance of the lignin-containing filament, and a functional protective case was effectively 3D printed. PLA/Lignin filaments are a plausible option for lignin utilization with potential in, e.g., rapid prototyping and consumer products. It is worth to mention that the typical smell from some lignins was not detected during the extrusion of the filaments or during the printing process, which is an additional advantage of using soda lignin in PLA biomaterials.

“Biocomposites exhibited good extrudability and flowability with no observable agglomeration of the lignin. This suggests that lignin-containing biocomposites are plausible alternatives for 3D printing applications.”

3D printing of a smartphone protective case with PLA/lignin biocomposite filament

The use of composites today is a growing trend due to the ability to improve prototypes and parts, from glass composites to copper metal to particle reinforced nanocomposites. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images – ‘Lignin: A Biopolymer from Forestry Biomass for Biocomposites and 3D Printing’]

 

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CRP Technology Used SLS 3D Printing and Windform XT 2.0 to Make Aircraft Model for Wind Tunnel Testing

The new AW609 wind tunnel model designed for Leonardo HD by Metaltech S.r.l. and 3D printed by CRP Technology

CRP Technology, part of the larger CRP Group, is well-known for its 3D printing applications in the automotive sector, but lest we forget that it is also accomplished in aerospace 3D printing, the company has come out with a new case study about its work creating a new 3D printed wind tunnel model (1:8.5 scale) of the Leonardo TiltRotor AW609 for the Leonardo Helicopter Division (Leonardo HD, formerly known as AgustaWestland).

According to the case study, CRP Technology was able to “highlight the perfect union” between its advanced SLS 3D printing technology and high-performance, composite Windform materials – particularly its Windform XT 2.0, a polyamide-based carbon fiber reinforced composite. Metaltech S.r.l. designed the model.

The goals of Leonardo HD’s project included:

  • design and manufacture an internal main structure out of aluminum alloy that can easily have new geometries added
  • complete the work in a very short timetable, but with an extremely high level of commonality and reliability
  • make components out of materials with high mechanical and aerodynamic characteristics

3D printed aircraft propeller spinners

These goals are why Leonardo HD was referred to CRP Technology – it would be able to meet these goals while 3D printing the external parts for the wind tunnel model, which was designed, manufactured, and assembled in order to complete a series of dedicated low-speed wind tunnel tests. Some of the parts that were 3D printed for the wind tunnel model include nose and cockpit components, fairings, external fuel tanks, rear fuselage, wings, and nacelles.

The level of detail that went into these 3D printed parts “is crucial to the applied loads to be sustainable,” as the wind’s aerodynamic loads in the tunnel are high. So load resistance was one of the more important project aspects, along with maintaining good dimensional tolerances, under load, of large components.

“It is important to remember that the performance of these components affects the final performance of the entire project, especially because the external fairings have to transfer the aerodynamic loads generated by the fuselage to the internal frame,” CRP Technology wrote in the case study.

3D printed tail fairing

The tests needed to cover the standard range of flight attitudes at Leonardo HD’s Michigan wind tunnel facility, in addition to Politecnico di Milano, and varying external geometries were changed during testing, so that technicians would be able to gain a better understanding of “aerodynamic phenomena.”

Today, the CAD-CAM approach is used to design models for wind tunnel testing, before an internal structural frame of aluminum and steel is milled and assembled. Then, 3D printing is used to obtain all external geometries. Because Leonardo HD used CRP Technology’s advanced 3D printing and Windform XT 2.0 material the project was completed much more quickly, with “excellent results and with high-performing mechanical and aerodynamic properties.”

CRP analyzed the dimensional designs that Leonardo HD had sent in order to make the best composite material recommendation: its Windform XT 2.0, with high heat deflection, increased tensile strength and modulus, superior stiffness, and excellent detail reproduction.

“The choice of the Windform XT 2.0 composite material was not casual, all the goals required by Leonardo HD were considered, such as the importance of a short realization time, good mechanical performances and also good dimensional characteristics,” CRP Technology wrote in the case study.

It was necessary to 3D print the single parts separately, as “some components were dimensionally superior to the construction volume of the 3D printing machines,” but CRP Technology was able to complete the project with no time delays. The company used CAD to evaluate the working volume’s functional measures in order to determine which parts to split, and to figure out how to maximize contact surface where structural adhesive would be added to the model.

3D printed aircraft nose and cockpit

It only took four days to 3D print the various parts of the components.

The case study noted, “Different confidential efficiencies, which are an integral part of CRP Technology’s specific know-how, allowed the reduction of the delivery lead time and allowed CRP to minimize the normal tolerances of this technology, and eradicate any potential problem of deformation or out of tolerance.”

The completed model underwent surface finishing, before it was assembled by Metaltech S.r.l. and mounted directly onto a rig assembly, so any small imperfections resulting from single components being put together could be optimized. Thanks to CRP Technology, this step was finished very quickly, and Leonardo HD was able to efficiently flatten the model’s surface and treat it with a special liquid to both prepare for painting and make the model waterproof.

Leonardo HD needed to review the behavior of the aircraft, and so completed a high-speed wind tunnel test campaign, which encompassed speeds Mach 0.2-Mach 0.6, on a new 1:6 scale model at NASA Ames Unitary Plan 11′ x 11′ transonic wind tunnel. The company called on CRP USA, based in North Carolina, to speed up the process, using its partner company’s SLS 3D printing and Windform XT 2.0 composite material to make the external fuselage and some additional components.

3D printed model installed in the 11’x 11’ test section at NASA Ames

While the architecture of the new 3D printed model, which spanned nearly 2 meters, is similar to the original AW609 version, some improvements were made so remote controls could be used for the wing flaperons and elevator surfaces. Additionally, by using four different 6-component strain gauge balances, all the loads were able to act on the complete model, the nacelle, the tail surfaces, and the wing alone.

The model was constructed in such a way as to be mounted in the transonic wind tunnel on a single strut straight sting support system.

Discuss this news and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

[Images: Leonardo HD]

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UK Researchers Develop Responsive Cellulose-Based Ink for 4D Printing

Graphical abstract

We’ve seen the results of 3D printing research about responsive materials, but what about with 4D printing, where 3D printed objects can move and change shape of their own volition? A collaborative team of researchers from the University of Bristol and the University of Bath recently developed a responsive ink for 4D printing that’s both cost-effective and sustainable – important features for the adoption of 4D printing. The ink’s hydrogel matrix has a high total cellulose content, and a good dispersion of cellulose fibers as well.

The team discussed the development of their new composite ink in a paper, titled “Responsive cellulose-hydrogel composite ink for 4D printing,” that was recently published in the Materials & Design journal.

The abstract reads, “This paper focuses on the development of a cellulose-hydrogel composite ink for additive manufacture, presenting the development and physical characterisation (stability, swelling potential and rheology) of the cellulose-hydrogel composite to establish its suitability for 4D printing of responsive structures. The use of a carboxymethyl cellulose (CMC) hydrocolloid with incorporated cellulose pulp fibres resulted in an ink with a high total cellulose content (fibre volume fraction ≈50% for the dehydrated composite) and good dispersion of fibres within the hydrogel matrix. The The composite ink formulation developed in this study permitted smooth extrusion using an open source 3D printer to achieve controlled material placement in 3D space while retaining the functionality of the cellulose. The addition of montmorillonite clay not only resulted in enhanced storage stability of the composite ink formulations but also had a beneficial effect on the extrusion characteristics. The ability to precisely apply the ink via 3D printing was demonstrated through fabrication of a complex structure capable of morphing according to pre-determined design rules in response to hydration/dehydration.”

Stimulus-response of pine cones.

There are existing examples of 4D structures, or 3D structures that can morph over time, in nature, such as a pinecone’s ability to attract and hold water molecules from the surrounding environment. In order to realize this kind of responsive system following the design principles of nature, there are two requirements: a compliant stimuli responsive material, and a process that allows for the controlled placement of this material in order to achieve the response. Cellulose, which is the most abundant bio-macromolecule found in nature, is such a compliant stimuli-responsive material.

“Introduction of water to cellulose can result in plasticisation of the amorphous regions by weakening or relaxing hydrogen bonding through formation of competitive hydrogen bonds,” the researchers explained. “These intercalating water molecules result in swelling throughout the material, which can be used to drive the reversible actuation of specific architectures created by these materials.”

To achieve this second requirement of a responsive system, 3D printing can be used. The technology offers plenty of control over placing materials in space, which makes it possible to design hybrid structures with “the hierarchical structural complexity characteristic of functional biological systems.”

Unfortunately, cellulose is not compatible in its natural form with most 3D printing methods. So, in order for 4D printing to continue advancing, we need to develop more stimuli responsive, 3D printable smart materials.

“To address this, this paper focuses on the development of a cost-effective, compliant “ink” material that can enable 3D printing of stimuli responsive complex forms to create programmable 4D structures. Moreover, the cellulosic ink will be specifically tailored for 3D printing using low-cost, open-source 3D printers ensuring the cellulosic composites thus fabricated are able to be further developed and extensively adopted in 4D printing research,” the researchers wrote.

“In this work, we have developed a stimuli responsive cellulosic pulp-hydrogel composite ink that is cost effective and bio-degradable. This composite ink is formulated for 3D printing and the stability, rheology and swelling potential of the ink has been characterised. A functional complex shape was fabricated using 3D printing to achieve precise material placement of the cellulosic ink, and the actuation via exposure to water demonstrated the ability to use this ink to produce 4D structures capable of programmable transformation.”

For their study, the team used sodium carboxymethyl cellulose (CMC-Na/CMC), a biocompatible, cellulose-derived polymer with great self-healing properties that’s often used as a thickening agent in the food and drug industry. Cotton derived pulp linters were used as a cellulosic fibre component, and the hydrogel was stabilized with clay. The resulting cellulose-hydrogel composites were able to be manually extruded through a syringe, and the team investigated the swelling response of the formulations, in addition to its rheological behavior.

Then, a custom off-axis direct driven paste extruder was integrated with a Prusa i3 MK2 3D printer, and the team validated the 3D printing capabilities, and subsequent 4D morphing, of their cellulose formulations with a morphing petal architecture, which has a programmed ‘through-thickness strain mis-match,’ which drives transformations. The specimen dried at room temperature, which initiated its transformation, and was later rehydrated in a room temperature water bath; it switched back to its 3D configuration once dry.

This actuation between the flat and 3D configurations of the object can be repeated several times, which shows that the team’s new composite ink has shape memory behavior.

The researchers wrote, “The development of a compliant composite cellulosic hydrogel integrating a high proportion of cellulosic material allowed use of a standard 3D printer to control material placement without compromising the responsiveness of the cellulose to hydration.”

By using 3D printing, researchers can achieve greater material placement precision, along with more complex architectures and actuation pathways for 4D printing. Because 3D printing parameters and design choices can significantly impact a material’s morphing behavior, it’s important to have a comprehensive understanding of just how these things can occur.

“Presently, the authors are exploring and devising experimental procedures to determine the influence these parameters; this will be reported in a subsequent publication,” the researchers concluded.

Co-authors of the paper are Manu C. Mulakkal, Richard S. Trask, Valeska P. Ting, and Annela M. Seddon.

Discuss this research and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.