Newsflash

The drive for lightweight materials to reduce overall cost and environmental impact for automotive manufacturers is nothing new.  Fuel economy attracts car buyers too. That is how majority of steel parts have been replaced in F-150 pickup truck by aluminum parts, reducing overall weight over 500 pounds. Then there are alloys, carbon fiber and plastics composites.The ambition for lighter vehicles did not stop with alloys (magnesium, aluminum), and/or composites (glass, carbon fibers).  Recently, Japanese researchers at Kyoto University led by Professor Hiroaki Yano along with its industrial partners (Denso Corporation and Daikyo-Nishikawa Corporation) reported that they were developing cellulose nanofiber based materials for automotive as well as aircraft parts to reduce environmental footprint while increasing product performance.Inevitable questions are: 1) would these materials be cost effective? 2) What would be the service life of these products compared to the current ones? 3) How about the parts’ safety in situations like crash or fire?A final question that an automaker has to ask is: what would be the pay back time to replace current production line (machinery) to CNF based plastics line?Reference: https://www.japantimes.co.jp/news/2017/08/15/business/researchers-japan-use-wood-make-cellulose-nanofiber-auto-parts-stronger-lighter-metal/#.WbAIKeTXuUm...
We know polycarbonates mostly from its use in plastics water bottles, safety goggles, smart phones, structural panels (glazing) and the list goes on.  A quick look at Wikipedia gives a spectrum of applications.However, polycarbonates have its weaknesses along with the BPA (bis-phenol) controversy. Polymers such as polysulfates and polysulfonates have similar if not better mechanical properties than polycarbonates.  The issue has been how reliably scale-up the manufacturing process of polysulfates and polysulfonates?“Click chemistry” is a concept in organic chemistry by which highly reactive reactions provide high yielding products and require little to no purification.  The concept was introduced by Nobel Prize winner Professor K. Barry Sharpless in 2001.A recent work published in Nature Chemistry, by a team of researchers from The Scripps Research Institute (La Jolla), Lawrence Berkley National Laboratory (Berkley), California and Shanghai Institute of Organic Chemistry & Soochow University, China claimed that reduced cost of catalyst, product purity, and by-product recycling make their work ready to move from laboratory research to industrial process.Chemists are at work indeed!References:https://en.wikipedia.org/wiki/PolycarbonateK. Barry Sharpless et al; Nature Chemistry, 2017 DOI: 10.1038/nchem.2796...
In a recent The Atlantic interview Bill Gates made a wish on an energy miracle, “Here’s a source of energy that is cheaper than your coal plants, and by the way, from a global-pollution and local-pollution point of view, it’s also better”.  The race is on to find that source. One such energy source is solar energy. We all know that solar energy can be harnessed to generate thermal energy or electrical energy for use in the residential and/or in the commercial applications.  Any material that can store Solar Thermal Energy is called Solar Thermal Fuel (STF).  The quest to harvest solar energy, store the same and use it when needed has been the focus of research in industry and academia alike. For the first time, Professor Grossman’s team at MIT, Cambridge (USA) has come up with a new approach which uses polymer Solar Thermal Fuel (STF) storage platform utilizing STF in its solid-state.  According to the published article, researchers stated, “Closed cycle systems offer an opportunity for solar energy harvesting and storage all within the same material. This approach enables uniform films capable of appreciable heat storage of up to 30 Wh kg?1 and that can withstand temperature of up to 180 °C.”How the STF process works?Certain molecules (chemicals) can have 2 different stable structural forms. These structures are called conformations.  When original molecular conformation is exposed to sunlight, the molecule gets charged and the original conformation changes to the other and stay in that charged conformation for a long period.  The charged molecule snaps back to their original shape (conformation), when triggered by a very specific temperature or other stimulus generating heat in the process. Currently, developed polymeric film can release heat about 10 degree C above the surrounding temperature. Film property improvements are underway. German auto company BMW, has sponsored this research. Where the potential application lies - your guess is as good as mine.References:The Atlantic, p 56, November 2015Zhitomirsky, D., Cho, E. and Grossman, J. C. (2015), Solid-State Solar Thermal Fuels for Heat Release Applications. Adv. Energy Mater., 1502006. doi:10.1002/aenm.201502006...
In a recent The Atlantic interview Bill Gates made a wish on an energy miracle, “Here’s a source of energy that is cheaper than your coal plants, and by the way, from a global-pollution and local-pollution point of view, it’s also better”.  The race is on to find that source. One such energy source is solar energy. We all know that solar energy can be harnessed to generate thermal energy or electrical energy for use in the residential and/or in the commercial applications.  Any material that can store Solar Thermal Energy is called Solar Thermal Fuel (STF).  The quest to harvest solar energy, store the same and use it when needed has been the focus of research in industry and academia alike. For the first time, Professor Grossman’s team at MIT, Cambridge (USA) has come up with a new approach which uses polymer Solar Thermal Fuel (STF) storage platform utilizing STF in its solid-state.  According to the published article, researchers stated, “Closed cycle systems offer an opportunity for solar energy harvesting and storage all within the same material. This approach enables uniform films capable of appreciable heat storage of up to 30 Wh kg?1 and that can withstand temperature of up to 180 °C.”How the STF process works?Certain molecules (chemicals) can have 2 different stable structural forms. These structures are called conformations.  When original molecular conformation is exposed to sunlight, the molecule gets charged and the original conformation changes to the other and stay in that charged conformation for a long period.  The charged molecule snaps back to their original shape (conformation), when triggered by a very specific temperature or other stimulus generating heat in the process. Currently, developed polymeric film can release heat about 10 degree C above the surrounding temperature. Film property improvements are underway. German auto company BMW, has sponsored this research. Where the potential application lies - your guess is as good as mine.References:The Atlantic, p 56, November 2015Zhitomirsky, D., Cho, E. and Grossman, J. C. (2015), Solid-State Solar Thermal Fuels for Heat Release Applications. Adv. Energy Mater., 1502006. doi:10.1002/aenm.201502006...
Reliable and high performance lithium ion batteries commonly known as LIBS are highly sought after product by industries. We all have heard stories about laptops, electric vehicles, airplanes catching fires due to LIBS. Underlying problem is the battery overheating. Preventing batteries from overheating is crucial to the public safety.  Now a team of researchers at Stanford University designed a thermo-responsive (heat sensitive) plastic composite film made from polyethylene and spiky nickel microparticles coated with graphene which shuts down the battery if the temperature is too high.         In a recently published work led by Yi Cui and Zhenan Bao of Stanford University, USA concluded “Safe batteries with this thermoresponsive polymer switching (TRPS) materials show excellent battery performance at normal temperature and shut down rapidly under abnormal conditions, such as overheating and shorting.” How practical this design approach is? Time will tell.References: Y. Cui, Z. Bao et al Nature Energy vol.1, Article number: 15009 (2016); DOI: 10.1038/nenergy.2015.9Chemical & Engineering News, Page 7, January 18, 2016...
In aviation industry, the focus is how to improve fuel safety and handling. Mike Jaffe and Sahitya Allam gave their perspective on safer fuels by integrating polymer theory into design (Science, 350, No. 6256, p. 32, 2015).Mist (generated from the fuel) is much more flammable than the liquid and that is why anti-misting kerosene interferes with mist formation when a low percentage of a polymer is added into it.  The problem however, is that the polymer chain undergoes scission during handling and can’t assist in suppressing mist formation. The answer comes from a recent paper published in the Journal Science by Professor Julia Kornfield and her cross-functional team at Caltech, Pasadena, USA. The group designed a megasupramolecules having polycyclooctadiene backbones and acid or amine end groups (telechelic polymer) which is short enough to resist hydrodynamic chain scission while protecting covalent bonds through reversible linkages. Yes, polymers can be designed to suit our societal needs including aviation fuel safety.Reference: M-H Wei, B. Li, R.L. Ameri David, S.C. Jones, V. Sarohia, J.A. Schmitigal and J.A. Kornfield; Science, 350, (6256), pp. 72-75 (2015)...
At the TED conference, Carbon3D, a Vancouver based company touted a radical 3D printing technology and named it CLIP or Continuous Liquid Interface Product. CLIP grows parts instead of printing them layer by layer. It harnesses light and oxygen to continuously grow objects from a pool of resin.  The result: make commercial quality parts at game-changing speed.  CLIP is 25 to 100 times faster than traditional 3D printing technique.  To make the point, Carbon3D web site provides a head-to-head comparison of CLIP to Polyjet, SLS and SLA.[Press release: March 16, 2015, Vancouver, Canada.  www.carbon3D.com]...
Self-healing plastics has been around for a while. Applications include self-healing medical implants, self-repairing materials for use in airplanes and spacecrafts. Even scientists have made polymeric materials that can repair itself multiple times. A recent report in Science describes a significant advance in self-healing plastics. The authors describe a product that mimics how blood can clot to heal a wound. When the plastic is damaged a pair of pre-polymers in channels combines and rapidly forms a gel, which then hardens over 3 hours.The authors demonstrated that holes up to 8 millimeters wide can be repaired. The repaired parts can absorb 62% of the total energy absorbed by undamaged parts.  Science never stops.Reference:S. R. White, J. S. Moore, N. R. Sottos, B. P. Krull, W. A. Santa Cruz, R. C. R. Gergely; Science, Restoration of Large Damage Volumes in Polymers, Vol. 344 no. 6184 pp. 620-623; (9 May 2014). ...
Knowingly or unknowingly, flexible electronics has become a part of our daily life.  Transparent conductive films (TCFs) are used in mobile phones, tablets, laptops and displays.  Currently, Indium Tin Oxide or commonly known as ITO is the material of choice.  But use of ITO has some major disadvantages and these are brittleness, higher conductivity at greater transparency, and supply of Indium.  This is where non-ITO materials come into play. Based in St. Paul, Minnesota (USA), Cima NaoTech’s uses its SANTETM nanoparticle technology, a silver nanoparticle conductive coating which self-assembles into a random mesh like network when coated onto a flexible substrate such as PET and PC.  According to a recent press release, the company stated SANTETM nanoparticle technology enabled transparent conductors in a multitude markets from large format multi-touch displays to capacitive sensors, transparent and mouldable EMI shielding, transparent heaters, antennas, OLED lighting, electrochromic and other flexible applications.  Cima NanoTech is working with Silicon Integrated Systems Corp. (SIS) of Taiwan and using its highly conductive SANTE FS200TM touch films to develop large format touch screens.References: Press release, San Diego, June 03, 2014; www.cimananotech.com ; http://www.cimananotech.com/sante-technology ; http://www.sis.com/...
In an article appeared today (January 29, 2014) in The Guardian newspaper, Stuart Dredge wrote, “From jet parts to unborn babies, icebergs to crime scenes, dolls to houses: how new technology is shaking up making things”1. Mr. Dredge was speaking about 3D printing technology.  The heart of this technology is the 3D printer itself. Stratasys, a company headquartered in Minneapolis, USA is the manufacturer of 3D printers.  It recently announced the launch of Color Multi-material 3D Printer, the first and only 3D printer to combine colors with multi-material 3D printing.  According to the press release2, by using cyan, magenta, and yellow, multi-material objects can be printed in hundreds of colors.  The technology is based on proven Connex technology.  While the base materials are plastics and elastomers, they can be combined and treated to make finished products of wide ranging flexibility and rigidity, transparency and opacity.  Designers, engineers and manufacturers can create models, mold, and parts that match the characteristics of the finished production part. This includes achieving excellent mechanical properties.  According to the manufacturer, print job in the newly revealed printer can run with about 30 kg of resin per cycle and prints as fine as 16 micron layers for models.  No wonder why some call the new Color Multi-material 3D printer a groundbreaking stuff.References: 1. www.theguardian.com.technology/2014/jan/29/3d-printing-limbs-cars-selfies (January 29, 2014)2. http://investors.stratasys.com/releasedetail.cfm?ReleaseID=821134 (August 3, 2014)...
Instead of stitches or skin staples, doctors use skin glue to close wounds. The glue joinsthe edges of a wound together while the wounds heal underneath. Most of the timeskin glue is used for simple cuts or wounds. According to the paper published inScience Translational Medicine, there are no clinically approved surgical glues thatare non-toxic, bind strongly to tissue, and work well in wet and highly dynamicenvironments within the body. This is the reason why this published work is promisingwhere infants born with heart defects would benefit tremendously. Researchers at the Brigham and Women’s hospital in Boston have engineered ‘bio-inspired’ gluethat can bind strongly to tissues on demand, and work well in the presence ofactively contracting tissues and blood flow. The authors of the paper show howthe glue can effectively be used to repair defects of the heart and blood vessels during minimally invasive procedures. [References: P. J. del Nido et al; Sci. Transl. Med., DOI: 10.1126/scitranslmed.3006557; See also, www.geckobiomedical.com/news/gecko-biomedicals-co-founde.html]...
Stability of organic electronics in water is a major research challenge. For this reason,organic electronics has yet to see any sensing application in aqueous environment.However, as understanding of underlying mechanism of stability aspect is becomingclearer, new developmental efforts to make water compatible organic polymer devicesare taking place. Recently, Professor Zhenan Bao’s group in the department of chemical engineering at Stanforduniversity revealed in a paper published in the journal of Nature Communications thatsolution- processable organic polymer could be stable under both in freshwater andin seawater. Developed organic field-effect transistor sensor is able to detect mercury ionsin the marine environment (high salt environment). Researchers believe that the work hasthe potential to develop inexpensive, ink-jet printed, and large-scale environmental monitoring devices. [References: O. Knopfmacher, M.L. Hammock, A.L. Appleton, G. Schwartz, J. Mei, T. Lei, J. Pei,and Z. Bao; Nature Communications, 5, 2954, January 6, 2014; DOI: 10.1038/ncomms3954]...
Insulin, the wonder medicine for diabetes was discovered about a century ago.Since insulin does not get into the blood stream easily, diabetes patients oftenhave injected themselves with insulin. Now a group of scientists led by Dr. Sanyog Jainat the Center for Pharmaceutical Nanotechnology of National Institute of Pharmaceutical Education and Research in Punjab, India has designed a polymerbased package for oral insulin administration. The package design addresses two major obstacles, 1) digestive enzymes must notdegrade insulin prior to its action and 2) the insulin gets into the blood stream.The package contained folic acid functionalized insulin loaded in liposomes.To protect the liposomes (lipids or fat molecules) they were alternately coated withnegatively charged polyacrylic acid (PAA), and positively charged poly allylamine hydrochloride. Studies were conducted to compare the efficacy of bothdelivery systems: designed polyelectrolyte based insulin and standard insulinsolution. Effects of oral administration lasted longer than that of injectedinsulin, authors reported in a recent article in Biomacromolecules. [Reference: A.K. Agarwal, H. Harde, K. Thanki, and S. Jain; Biomacrmolecules, Nov. 27, 2013;DOI: 10.1021/bm401580k]...
Research in the area of stretchable electronics is heating up!  Thanks to polymers. Led by Professor George M. Whitesides of Harvard University (USA), a team of researchers have demonstrated in a recently published paper in Science that ionic conductors can be used in devices requiring voltages and frequencies much higher than commonly associated with devices using ionic conductors.  The team showed for the first time that electrical charges carried by ions and not electrons, can be utilized in fast-moving, high voltage devices.As a proof of concept, the authors of the study built a transparent loudspeaker that produces sound across the full audible range i.e., 20 Hz to 20 kHz.  Components [such as VHB 4910 tape (acrylic tape with PE liner), polyacrylamide hydrogel containing NaCl electrolyte] used for the high speed, transparent actuators are described in the paper.Tissues and cells are soft and require stretchable conductors for biological systems. Many hydrogels are biocompatible which makes this work particularly an important one. The design of gel-based ionic conductors is highly stretchable, completely transparent and offer new opportunities for designers of soft machines.   [Reference: C.Keplinger, J-Y. Sun, C.C. Foo, P. Rothemund, G.M. Whitesides, and Z. Suo; Science, 341 (6149), pp. 984-987 (2013); DOI: 10.1126/science.1240228]...
Interweaving biological tissue with functional electronics, one can make bionic ears.  NASA has tested 3D-printed rocket engine part.  Then why not 3D print yourself?Well, Twinkind, a German start-up company is now offering enthusiasts statues of themselves for display.  How this works?  A full body scanner takes an image of the customer’s body, transfers the file to the printer after which 3D printer laser sinters a composite powder layer by layer into the customer image.Can we dare to say that Madame Tussauds wax figure of Voltaire can now be 3D printed in polymers soon!  [Reference: www.twinkind.com ]...
Polymer membranes have become a leading contender in numerous separation processes.  Be it in gas (air, hydrogen etc.) or be it in water purifications (salinated water, waste water etc.).  Not only polymer membrane technology helps reducing the environmental impact but also it is cost-effective.  Fracking in shell gas is one of many examples. New advances in drilling technology (such as horizontal drilling) have led to new hydraulic fractures called fracking.  Hydraulic fracturing requires about 2.5 to 5 million gallons of water per well.  Water management and its disposal are major costs for producers.One major challenge, however, of the membrane technology is the fouling (damage caused by contaminants) mitigation.  This has been recently studied by a group of researchers from University of Texas at Austin led by Professor Benny Freeman to address efficiency and reuse of water for fracking in shale gas plays.Researchers modified polydopamine coated UF (ultrafiltration) module by grafting polyethylene glycol brushes onto it.  The result is more hydrophilic surfaces which in turn improved cleaning efficiency relative to unmodified modules. The coating improves the membrane life, and can easily be applied to membrane surface by rinsing it through the recycling system.[References: D.J. Miller, X. Huang, H. Li, S. Kasemset, A. Lee, D. Agnihotri, T. Hayes, D.R. Paul, and B. Freeman; J. Membrane Sci., 437, pp. 265-275 (2013); Also see www.advancedhydro.net ]...
Flexible electronics can change the way we use electronic devices.  It is a term used for assembling electronic circuits by mounting electronic devices on a flexible plastic. A recent review article captured the advancement of CNT and graphene based flexible thin film transistors from material preparation, device fabrication to transistor performance control compared to traditional rigid silicon1. Silicon is used almost exclusively in electronic devices.Now Prof. Ali Javey led a team at the University of California, Berkley to develop a printing process to make nanotube transistors at room temperature with gravure printer.  The plastics used is polyethylene terephthalate (PET). The device exhibited excellent performance with mobility and on/off current ratio of up to ~9 cm2/ (V s) and 105 respectively.  Also, maximum bendability is observed.  The paper authors conclude that this high-throughput printing process serves as enabling nanomanufacturing scheme for range of large-area electronic applications based on nanotube networks2. References:1. D-M. Sun, C. Liu, W-C. Ren and H-M Cheng; Small, DOI: 10.1002/smll.2012031542. P.H. Lau, K. Takei, C. Wang, Y. Zu, J. Kim, Z. Yu, T. Takahashi, G. Cho, and Ali Javey; Nano Letters, 13 (8), pp. 3864-3869 (2013); DOI. 10.1021/nl401934a...
Drinking coffee from paper cups are as common as drinking water from plastics bottle. The issue however, is recycling of disposable cups. The disposable cups are made up of 90-95% of high strength paper (fibers) with a 5% thin coating of plastic (PE).To address the recycling issue, James Cropper Speciality Papers of UK have developed a process which involves softening the cup waste, and separating the plastic coating from the fiber.  After skimming off the plastic, remains are pulverised and recycled, leaving water and pulp behind.  According to the company news release, the high grade pulp is reused in luxury papers and packaging materials.An innovative approach to address a common problem.[Reference: www.jamescropper.com/news ]...
A search for an alternative to rigid silicon wafers gave birth to the area of flexible or bendable electronics. Research has been intense for the past few years in the area flexible electronics as it opens up multitude of new applications. Polymers play an important role to exciting field of flexible electronics.In a recent research report, a team of scientist led by Prof. Ali Javey of University of California, Berkeley (USA)  has shown for the first time user-interactive electronic skin or e-skin can conformally wrap irregular surfaces and spatially map and quantify various stimuli through a built-in active matrix OLED display.  Three electronic components namely thin film transistor (uniform carbon nanotube based), pressure sensor, and OLED arrays (red, green, and blue) are integrated over a plastic substrate.  Spin coated and cured polyimide on a silicon wafer is used as the flexible substrate.  Details are in the paper.This work essentially provides a technology platform where integration of several components (organic and inorganic) can be done at a system level on plastic substrates. According to the paper, this e-skin technology could find applications in interactive input/control devices, smart wallpapers, robotics, and medical/health monitoring devices.    [Ref: C. Wang, D. Hwang, Z. Yu, K. Takei, J. Park, T. Chen, B. Ma, and Ali Javey; Nature Materials, Published online July 21, 2013; DOI: 10.1038/NMAT3711]...
Recent buzz in the technology world is 3D printing.  Researchers to designers are creating new products everyday using 3D printing technology.  Even eBay has unveiled its services to those looking to make their own creations using 3D printing App.Since ages composites have played a crucial role in our society. Inspired by natural (biological) composites such as bone or nacreous abalone shell, researchers from MIT (USA) and Stratasys have developed composite materials that have fracture behaviour similar to bones.  Using computer model with soft and stiff polymers, the team has come up with a specific topological arrangements (hierarchical structures) of polymer phases to boost the mechanical behaviour in the composites.Interestingly, the team has been able to manufacture (thanks to 3D printing) a composite material that is more than 20 times larger than its strongest constituent.  The referenced paper showed that one can use computer model to design composite materials of their choice, tailor the fracture pattern and then use 3D printing technology to manufacture the composites.[Ref: L.S. Dimas, G.H. Bratzel, I. Eylon, and M.J. Buehler; Advanced Functional Materials, Published online June 17, 2013; DOI: 10.1002/adfm.201300215]...

3dprinting_connex3_figure4Over the past two decades, additive manufacturing (AM) technology has become fully ingrained into pop culture, with  Do it Yourself (DIY) applications for the home, schools and other locations in addition to industrial applications  for the aerospace, automotive, and biomedical industries.  While AM can be used to fabricate objects from metals, polymers, and ceramics, polymeric materials are currently the most common.  ASTM Standard F2792-12a1 describes techniques that can convert polymeric materials into useful products: 1) sheet lamination; 2) material extrusion; 3) vat photopolymerization; 4) powder bed fusion (with polymers); 5) binder jetting; and 6) material jetting.  The automotive industry was an early adopter of 3D printing of polymeric materials, for example in the early 1990s a Japanese manufacturers2,3 used a commercialized vat photopolymerization process (widely known as stereolithography (SL)) to manufacture prototype door panels.  More recently, an extrusion-based AM system was used on the International Space Station (ISS)4.

Many different processes are used to process polymeric materials for additive manufacturing.  The AM process of sheet lamination involves the layering of single sheets of material, cutting out a shape by either a laser or blade and then laying subsequent sheets which are bound by an adhesive.  Material extrusion, also widely known as Fused Deposition Modeling (FDM), is the most common extrusion technology used for AM. It entails the extrusion of a thermoplastic monofilament, which is then deposited layer by layer to create a 3D object.  In stereolithography, a 3D object is created by curing a photocurable resin, layer by layer, with an ultraviolet (UV) laser.  In binder jetting, material in powder form is joined together by the deposition of an adhesive, while in material jetting, a photocurable resin is deposited in a manner similar to that of a conventional ink-jet printer and locally cured by a UV source.  The interested reader of the variety of technologies is encouraged to review ASTM F2792-12a1 as well as Wong and Hernandez5.

AM provides many key advantages over conventional manufacturing technologies. These include an ability to create unique geometries and to print objects with moving parts without part-specific tooling or in many cases, the assembly of the final part.  In order to enable an increased level of multi-functionality of parts fabricated using AM, advancements in two critical areas must occur: 1) the increase of printer-compatible materials with a diverse range of physical properties; and 2) integration of processing steps within AM systems beyond material deposition or fusion.  The work presented in this paper describes two strategies employed in the use of two polymeric based AM technologies: 1) FDM; and 2) SL, to achieve a higher level of functionality, usefulness, and benefit to society of additive manufacturing.  The work presented here is not an exhaustive review of the area of polymeric AM, but rather an overview of the material and process development work performed at the W.M. Keck Center for 3D Innovation (keck.utep.edu).

Multi-material Additive Manufacturing

The combination of multiple material types in a single printed component is a key aspect to achieving multifunctionality.  As demonstrated by Choi, et al.6 as well as Wicker and MacDonald7 multi-material stereolithography was achieved by the development of an SL system with four individual vats on a rotary system which facilitated printing of components of up to four individual resin types.  When combined with other manufacturing methods, namely direct write (DW); where conductive and insulating inks and pastes are deposited via printing methodologies, polymeric AM technologies have been used to create the novel genre of 3D structural electronics8-13.  Here, the stop-start ability of the AM process allows for the deposition of conductive or passive media along with the insertion of commercial-off-the-shelf electronic components such as microprocessors, accelerometers, magnetometers, etc.  Figure 1 shows examples of structural electronic components.

3delpasofigure1Figure 1. Examples of structural electronic components

The evolution of the structural electronics manufacturing process involving thermoplastic materials has led to the development of wire embedding processes where wire is directly inserted into 3D printed thermoplastic substrates by way of an ultrasonic or ohmic heating method.  An example of 3D structural electronics created through the integration of this wire embedding technique with FDM is shown in Figure 2; further details can be found our group’s other publications14-17.

3delpasofigure2

Figure 2. Example of a 3D structural electronic device manufactured by integrating a wire embedding process with thermoplastic 3D printing

In addition to allowing inserting conductive paths into the thermoplastic, there are several other benefits, namely the ability to locally strengthen the material, which arise from this process.  As a reinforcement, wire can be embedded into 3D printed parts either during an interruption of the printing process or after the printing.  The degree of reinforcement is dependent on wire materials, orientation, gage, and degree of embedding.  With the use of composite theory, the expected performance of the composite (polymer matrix and wire reinforcement) can be calculated so that performance metrics are satisfied.  The example below demonstrates a wire embedding process for reinforcing 3D printed plastic parts along the layer stacking direction by using a nickel chromium alloy (Nichrome or NiCr).

Here, a Fortus 400mc (Stratasys, Eden Prairie, MN) equipped with T16 tips and polycarbonate (PC) was used to build ASTM D638 Type I specimens in the ZXY orientation. For more information pertaining to coordinate-terminology related to AM processes, we suggest the reader refer to the ASTM standard 52921-1318. To prevent specimens from falling over during the building process, surround support was used.  All other processing parameters were not changed from their default settings.  After fabrication, a sample set of five specimens were conditioned at 25 ± 2°C and 50 ± 10% relative humidity for at least 40 hours.  The specimens were then tested under tensile loading conditions in accordance to ASTM D638 using an Instron 5866 material testing machine using a 10kN load cell and a ramp rate of 5mm/min.

Another sample of five specimens was subjected to the wire embedding process in which five Nichrome wires (28 AWG) were embedded axially on two, opposite sides of the specimen.  The wire embedding tool uses thermal energy to simultaneously heat the plastic surface and copper wire.  The head is mounted on an automation motion system to facilitate the embedding process directly from a CAD file.  In the same fashion, the specimens were conditioned and tensile tested.

The results of these experiments are shown in Figure 3 where it can be seen that the main effect of the reinforcement was noted in the ultimate tensile stress (UTS).  In Figure 3, each bar represents the average of five specimens and the error bars represent plus or minus one standard deviation.  In this case, the average UTS of the wire-reinforced specimens was 41% greater than the non-reinforced specimens.  Likewise, there was an increase in ductility and elasticity by the inclusion of wires.

3delpasofigure3

Figure 3. Mechanical properties of polycarbonate (PC) and NiCr-wire-reinforced PC specimens: a) ultimate tensile strength, b) % elongation at maximum load, and c) modulus of elasticity

From this example it can be concluded that the inclusion of NiCr wires in PC specimens provided a 41% increase in UTS.  This is of particular interest since the interlayer bonding is the weakest location within the fabricated part19,20.  With the wire embedding process demonstrated here, one can imagine a structure such as an Unmanned Aerial Vehicle (UAV) where the locations susceptible to failure, like where a wing joins to the fuselage, can be reinforced with embedded wires to extend the life of a structure.

Polymeric Materials Development

Combining technologies such as SL and FDM with other manufacturing methods is one way to expand the applicability of polymeric AM systems. Advancements can be made through bulk material augmentation.  Efforts to manipulate the physical properties of SL materials were demonstrated by Sandoval et al.21, 22 where multi-walled carbon nanotubes were combined with photo-curable resins.  Though the weight percent of nanotubes added to the resin was small (0.05% and 0.5%), a substantial increase of storage modulus of the material was observed at temperatures above 200°C.

The creation of polymer matrix composites (PMC)s and the creation of novel polymeric blends are two approaches that have been used to advance material extrusion 3D printing based on FDM technology.  The goal of both of these approaches has been to create material systems with a broad range of physical properties while retaining compatibility with current FDM-type 3D printing systems.  Both approaches have relied heavily on thermoplastic extrusion via a twin screw extruder/compounder system (Collin ZK 25T).  We have successfully demonstrated a capability to create 3D printable polymer matrix composites from acrylonitrile butadiene styrene (ABS) and PC with a broad range of filler materials such as metals, metal oxides, and plant fibers 19, 20, 23 and also demonstrated an ability to manipulate the elasticity of ABS through blending with the thermoplastic rubber, styrene ethylene butylene styrene (SEBS) 24.

Part of this research included work to perform failure analysis in order to understand the effect of additives on the fracture behavior of a given novel polymeric material system.  The main method for achieving this has been the performing of fractography on the fracture surfaces of 3D printed test coupons with the aid of a scanning electron microscope (SEM).  Examples include the documentation of a brittle fracture mode caused by loading ABS with TiO219,20 though, on the other hand, loading PC with tungsten did not significantly influence the fracture surface morphpology23.  Key to our work has been the use of variants of SEBS where the effect of adding this material to ABS has been the emergence of a fracture surface indicative of a large amount of plastic deformation and dominated by the presence of fibrils19,20,24.

  
Of pertinence to 3D printing has been the understanding of the mechanical property anisotropy of these novel thermoplastic material systems.  Inherent to 3D printing is a difference in mechanical properties depending on build orientation19,20.  Our work has found that a ternary polymeric blend composed of ABS, SEBS, and ultra high molecular weight polyethylene (UHMWPE) yields a material which exhibits similar mechanical properties for samples printed in the XYZ and ZXY build direction;19,20 specifically for a blend created from a mixture of (by weight ratio) 75:25:10 ABS:UHMWPE:SEBS.  The compounding of these three polymeric systems led to a polymer/polymer composite where  UHMWPE particles were distributed within a matrix composed of blended ABS and SEBS due to the lack of miscibility of UHMWPE within this system20,24.  As seen in Figure 4, the presence of UHMWPE particles and the rheological characteristics of this ternary blend leads to random failure rather than failure within the inter-print layer zone which is the main mode of failure for samples printed in the ZXY direction.  While the ternary blend yields tensile test data that are lower than samples printed from the ABS base resin alone, the strategy may lead to the development of materials with isotropic qualities without a loss of overall mechanical strength.  Another advantage of the ternary blend over ABS was found to be the capability to print smoother inclined planes as verified by surface roughness measurements24,25.

3delpasofigure4

Figure 4. a) SEM micrograph of a 3D printable ternary polymeric blend composed of ABS, SEBS, and UHMWPE particles of this blend as compared to ABS

Other notable achievements have been the development of 3D-printable radiation shielding material based on PC where the attenuation of the material can be tuned by the loading (by weight percent) of tungsten powder23 and the development of printable ferrimagnetic material through the addition of the iron oxide, magnetite (Fe3O4) to ABS25.  In both instances bonding of the filler material was improved with the aid of a silane coupling agent; a process we borrowed from the manufacturing process of glass reinforced polymers. 3delpasofigure5The key point of augenting the physical properties of 3D printable materials is that when they are used in conjunction with one another, a pathway to multifunctionality can be realized as seen in Figure 5 where an ABS/SEBS blend is used in conjunction with the magnetite loaded ABS to make a simple magnet driven actuator.

                 Figure 5. A simple 3D-printed magnet-driven actuator

Aspects of Equipment

While our group has access to state-of-the-art material extrusion AM equipment manufactured by Stratasys, the rheological differences of our novel material systems as compared to stock 3D printer filament20,24,25 oftentimes necessitates the use of open source material extrusion 3D printers.   In most instances, we have relied upon desktop grade material extrusion 3D printers, namely a MakerBot Replicator 2X (MakerBot Industries, Brooklyn, NY, USA), a LulzBot Taz 4 (Aleph Objects, Inc., Loveland, CO, USA) and a Rostock Max (SeeMe CNC, Goshen, IN, USA).  In general, there are typically two types of deposition systems found on desktop-grade material extrusion 3D printers: 1) a Bowden extrusion system where the drive mechanism is far away from the liquifier; and 2) a direct drive extrusion system where the filament drive mechanism is directly above the liquefier (Figure 6a and 6b respectively).  3delpasofigure6Figure 6a) Material extrusion 3D printer with a Bowden-type filament drive system located away from the liquiefierassembly and b) a direct drive 3D printer where the drive system for the filament is integrated with the liquiefier in a single print head assembly

The latter extrusion system is similar to that found on industrial grade FDM systems.  We have had more success utilizing direct drive-based systems when printing elastomeric material systems developed by our group due to the lack of rigidity of the material which leads to incompatibility with Bowden-type systems.  We have borrowed heavily from the learnings of DIY users of 3D printing technology as the current state is an extremely large community of practice composed of hobbyists and entrepreneurs pushing the development of new technologies.  Key examples have been the modification of direct drive systems (Fig. 7a), the integration of custom drive gear systems and the print head modifications of with a high temperature liquefier (E3D V6, E3D-Online Limited, Chalgrove Oxfordshire, UK) to enable print temperatures on the order of 400?C (Fig. 7b) where most stock desktop printers are only capable of print temperatures on the order of 260°C to 280°C due to the fact that ABS and PLA are currently the materials most widely utilized by desktop grade systems.

3delpasofigure7

Figure 7. DIY community inspired modifications: a) cantilever system added to a direct drive-type material extrusion 3D to increase the pressure on the filament by the drive gear and b) addition of a high-temperature liquefier and cooling system to a Bowden-type material extrusion 3D printer

Future Trends

The development of new manufacturing approaches and 3D printable polymer systems with a wide range of physical properties is resulting in a constant flow of new applications for the production of polymer products with 3D printing.

The development of integrated fabrication systems where advanced wire embedding techniques, micromachining, and component insertion are combined with polymer material extrusion 3D printing in a single manufacturing platform is anticipated.

3D printable polymeric materials development is focusing on developing system with tunable electromagnetic, thermal, mechanical, and rheological properties. This is being achieved by compounding new polymer blends containing filler materials with the given desired physical properties.  Additionally, the development of polymeric systems in which the mechanical properties are less sensitive to build orientation are providing materials with greater tensile strength.

Our future research efforts are designed to facilitate the rapid advancement of required technology that demands an integration of polymer science, novel manufacturing techniques, and advanced engineering.  The community of hobbyists and the DIY community cannot be ignored as their contributions in this area can be easily integrated into research efforts.

References

1. ASTM Standard F2792-12a: Standard Terminology for Additive Manufacturing Technologies, ASTM International, West Conshohocken, PA, (2012).
2. Nakagawa, T.; Makinouchi, A.; Wei, J. 3-D Plotting of Finite Element Sheet Metal Forming Simulation Results by Laser Stereolithography. CIRP Annals - Manufacturing Technology 1992, 41 (1), 331–333.
3. Nakagawa, T. Recent Developments in Auto Body Panel Forming Technology. CIRP Annals - Manufacturing Technology 1993, 42 (2), 717–722.
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6. Choi, J.-W.; Kim, H.-C.; Wicker, R. Multi-Material Stereolithography. Journal of Materials Processing Technology 2011, 211 (3), 318–328.
7. Wicker, R. B.; MacDonald, E. W. Multi-Material, Multi-Technology Stereolithography. Virtual and Physical Prototyping 2012, 7 (3), 181–194.
8. A.J. Lopes, M. Navarrete, F. Medina, J. A. Palmer, E. MacDonald, and R. B. Wicker, Expanding rapid prototyping for electronic systems integration of arbitrary form, 17th Annual Solid Freeform Fabrication Symposium, University of Texas at Austin, Austin, TX, Aug, 2006, pp. 14–16.
9. Lopes, A. J.; Lee, I. H.; MacDonald, E.; Quintana, R.; Wicker, R. Laser Curing of Silver-Based Conductive Inks for in Situ 3D Structural Electronics Fabrication in Stereolithography. Journal of Materials Processing Technology 2014, 214 (9), 1935–1945.
10. DeNava, E.; Navarrete, M.; Lopes, A.; Alawneh, M.; Contreras, M.; Muse, D.; Castillo, S.; MacDonald, E.; Wicker, R. Three-Dimensional off-Axis Component Placement and Routing for Electronics Integration Using Solid Freeform Fabrication. In Proceedings of Solid Freeform Fabrication Symposium, The University of Texas at Austin, Austin TX; 2008; pp 362–369.
11. Amit Joe Lopes, Eric MacDonald, and Ryan B. Wicker, “Integrating stereolithography and direct print technologies for 3D structural electronics fabrication,” Rapid Prototyping Journal, 18 (2), pp. 129–143, 2012.
12. S. Castillo, D. Muse, F. Medina, E. MacDonald, and R. Wicker, “Electronics integration in conformal substrates fabricated with additive layered manufacturing,” in Proceedings of the 20th Annual Solid Freeform Fabrication Symposium, University of Texas at Austin, Austin, TX, 2009, pp. 730–737.
13. M. Navarrete, A. Lopes, J. Acuna, R. Estrada, E. MacDonald, J. Palmer, and R. Wicker, “Integrated layered manufacturing of a novel wireless motion sensor system with GPS,” in Proceedings of the 18th Annual Solid Freeform Fabrication Symposium, University of Texas at Austin, Austin, TX, 2007.
14. D. Espalin, D. W. Muse, E. MacDonald, and R. B. Wicker, “3D Printing multifunctionality: structures with electronics,” Int J Adv Manuf Technol, vol. 72, no. 5–8, pp. 963–978, Mar. 2014.
15. C. Kim, D. Espalin, A. Cuaron, M. A. Perez, M. Lee, E. MacDonald, and R. B. Wicker, “Cooperative Tool Path Planning for Wire Embedding on Additively Manufactured Curved Surfaces Using Robot Kinematics,” J. Mechanisms Robotics, vol. 7, no. 2, pp. 021003–021003, May 2015
16. C. Shemelya, F. Cedillos, E. Aguilera, D. Espalin, D. Muse, R. Wicker, and E. MacDonald, “Encapsulated Copper Wire and Copper Mesh Capacitive Sensing for 3-D Printing Applications,” IEEE Sensors Journal, vol. 15, no. 2, pp. 1280–1286, Feb. 2015.
17. C. Shemelya, F. Cedillos, E. Aguilera, E. Maestas, J. Ramos, D. Espalin, D. Muse, R. Wicker, and E. MacDonald, “3D printed capacitive sensors,” in 2013 IEEE SENSORS, pp. 1–4.
18. American Society for Testing and Materials, ASTM 52921-13 Standard Terminology for Additive Manufacturing-Coordinate Systems and Test Methodologies ASTM International, West Conshohocken, PA (2013).
19. Torrado, A. R.; Roberson, D. A.; Wicker, R. B. Fracture Surface Analysis of 3D-Printed Tensile Specimens of Novel ABS-Based Materials. J Fail. Anal. and Preven. 2014, 14 (3), 343–353.
20. Torrado, A. R.; Shemelya, C. M.; English, J. D.; Lin, Y.; Wicker, R. B.; Roberson, D. A. Characterizing the Effect of Additives to ABS on the Mechanical Property Anisotropy of Specimens Fabricated by Material Extrusion 3D Printing. Additive Manufacturing 2015, 6, 16–29.
21. J. Hector Sandoval; Ryan B. Wicker. Functionalizing Stereolithography Resins: Effects of Dispersed Multi?walled Carbon Nanotubes on Physical Properties. Rapid Prototyping Journal 2006, 12 (5), 292–303.
22. Sandoval, J. H.; Soto, K. F.; Murr, L. E.; Wicker, R. B. Nanotailoring Photocrosslinkable Epoxy Resins with Multi-Walled Carbon Nanotubes for Stereolithography Layered Manufacturing. J Mater Sci 2007, 42 (1), 156–165.
23. Shemelya, C. M.; Rivera, A.; Perez, A. T.; Rocha, C.; Liang, M.; Yu, X.; Kief, C.; Alexander, D.; Stegeman, J.; Xin, H.; et al. Mechanical, Electromagnetic, and X-Ray Shielding Characterization of a 3D Printable Tungsten–Polycarbonate Polymer Matrix Composite for Space-Based Applications. Journal of Elec Materi 2015, 1–10.
24. Rocha, C. R.; Torrado Perez, A. R.; Roberson, D. A.; Shemelya, C. M.; MacDonald, E.; Wicker, R. B. Novel ABS-Based Binary and Ternary Polymer Blends for Material Extrusion 3D Printing. Journal of Materials Research 2014, 29 (17), 1859–1866.
25. David Roberson; Corey M Shemelya; Eric MacDonald; Ryan Wicker. Expanding the Applicability of FDM-Type Technologies through Materials Development. Rapid Prototyping Journal 2015, 21 (2), 137–143.

 

David A. Roberson, Ph.D.

3delpasoroberson2015 Dr.Roberson is an Assistant Professor in the Department of Metallurgical and Materials Engineering at The University of Texas at El Paso.  He currently directs the Polymer Extrusion Lab in the W.M. Keck Center for 3D Innovation where he performs research related to the development of novel polymer matrix composites and polymer blends for additive manufacturing applications

Prior to his academic career, Dr. Roberson spent eight years working as an engineer in the semiconductor industry for Intel Corporation (2001-2006) and Qimonda NA (2006-2009). Dr. Roberson earned his B.S. in Metallurgical and Materials Engineering (1999), his M.S. in Metallurgical and Materials Engineering (2001), and his Ph.D. in Materials Science and Engineering (2012) from The University of Texas at El Paso, USA.

 

David Espalin

3delpasodespalin2015 Mr. Espalin is the Center Manager for the W.M. Keck Center for 3D Innovation.  He received the B.S. and M.S. degrees in mechanical engineering from the University of Texas at El Paso (UTEP), in 2010 and 2012, respectively, and is currently pursuing a Ph.D. in Materials Science and Engineering. 

Mr. Espalin's research within additive manufacturing has focus on fused deposition modeling, multi-material fabrication, embedded electronics, and hybrid manufacturing.

Ryan Wicker, Ph.D., P.E.

3delpasoryan2015 Dr. Wicker is the endowed Mr. and Mrs. MacIntosh Murchison Professor of Mechanical Engineering at the University of Texas at El Paso (UTEP), and Director and Founder of the UTEP W.M. Keck Center for 3D Innovation (Keck Center).  He is also Editor-in-Chief and Founding editor of Additive Manufacturing, an Elsevier journalRyan received degrees in mechanical engineering from The University of Texas at Austin (B.S., 1987) and Stanford University (M.S., 1991, and Ph.D., 1995), worked at General Dynamics Fort Worth Division (1987-1989), and has spent his entire academic career at UTEP

The Keck Center (www.keck.utep.edu) represents a world-class research facility that focuses on the use and development of additive manufacturing technologies for fabricating 3D objects that are plastic, metal, ceramic, of bio-compatible materials, composite materials, or that contain electronics.  Major research efforts are underway at the Keck Center in the areas of additive manufacturing technology development; closed-loop process control strategies for additive manufacturing; additive manufacturing of various powder metal alloy systems; development of new polymers for use in additive manufacturing; and 3D structural electronics in which electronics, and thus intelligence, are fabricated within additive manufacturing-fabricated structures.