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]...
Polymers are the backbone of plastics.  The giants of the molecular world, they can be built from simple molecules (monomers) into stars, chains, brushes and trees to generate desired application specific qualities.  The objective of this review is to highlight some examples of exciting, emerging trends of developments in plastics and in their technologies.  The scope is not limited to documenting a series of developments in plastics technology but also to inform readers where these events are taking place.

Plastic nanocomposites

As nanocomposite technology slowly matures - Plastic nanocomposites (PNC) are finding commercial applications in automotive parts, packaging films, appliances, fire retardant electrical enclosures and housings.  These are materials where nanometer (nano comes from Greek word for midget; nanometer means a billionth part of one meter) particles are dispersed in a polymeric matrix.  The matrix can be single or multiphase.  As for definition, a nanoscale particle is a material with at least one dimension in the nanometer range.  The critical reinforcing effects of nanosized particles come from its aspect ratio (ratio of the length or thickness to that of the diameter), very large specific surface area (viz. 800m2/g) and the particle-matrix interactions.  If the aspect ratio of a nano particle is over 500, the reinforcing effect is similar to an infinitely large particle. 
 
In PNCs, natural clays (mainly montmorillonite) and synthetic clays (fluorohectorite) are mostly used as nanoparticles.  The clay is any material (natural or synthesized) having a cation-exchange capacity of 50 to 200 milliequivalent/100g and a large surface area.  Typical example is smectite type of clays.  However, mixing polymers and clays is not a simple process.  There are two reasons for it: immiscibility (like mixing water and oil) and very tight packing of individual clay layers.  When clays are treated with an organic intercalants, the space between clay platelets expands and interactions are enhanced so the dispersion of organoclay may take place.  Intercalant is an oligomer or polymer that is sorbed between platelets of the layered material and complexes with the platelet surfaces to form an intercalate1.
 
The original concepts of PNC sprang from the invention of polyamide-clay composites in the Toyota Research Corporation in 19852.  At that time, the objective was to making under-the-hood heat resistant automotive parts lighter than metal.  However, recent commercialisation of newly developed thermoplastic olefin (TPO) nanocomposite by General Motors has attracted producers from every sector of the polymers industry to reconsider their polymer system.  To include rubber in a thermoplastic matrix is well known.  That is what Basell Polyolefin's' (previously Montell) Catalloy process does with higher levels of rubber particles in a polyolefin matrix (PP).  By incorporating 2.5 wt.% of exfoliated smectite type nano clay particles in TPO, Bassel polyolefins and GM developed a PNC that replaced 15% talc-filled PP, translating into 7-8% weight savings.  Exfoliation is done to delaminate the clay platelets via intercalation. 
 
The process of exfoliation is primarily done via in-reactor polymerization or by melt compounding.  When particles are dispersed into plastic resins, resulting PNC behaves as a single phase and as a single component material.  The property improvements to PNC include stiffness, barrier to liquids and gases, flame retardancy, electrical conductivity etc.  Several application specific examples of PNC involving PET, PP, TPE and nylon were recently presented by Lan et al.3, while Utracki and Kamal1 have detailed clay-containing polymeric nanocomposites.  The clay’s structure gives it a unique position over other particles.  Owing to nano-scale dimension of exfoliated clay platelets, PNC may replace any polymeric matrix (thermoplastic, thermoset or rubbery) in multiphase applications such as alloys, blends, composites, or foams.
 
Exfoliated montmorillonites platelets are about 1 nanometer thick hence below the visible light wavelength and therefore, yield transparent particles – a critical demand for packaging applications.  Furthermore, a gas barrier is easily achieved in PNC due to the platey nature of the clay particle, which enhances polymer crystallization leading to a more tortuous path4.  Another attractive property of PNC is its ability to form char.  This has opened up several possibilities of creating fire retardant (FR) polyolefin nanocomposites3.  From the standpoint of cost, PNC reduces the amount of FR additive package required, while maintaining equivalent fire ratings.  As macro-reinforcements (e.g., glass fibers) the nano-reinforcing clay platelets improve rigidity, strength and significantly reduce shrinkage.  For example, the latter property is of particular concern to dentists – shrinkage of the acrylic filling results in short lifetime of the repairs.  Incorporation of 1 wt% of clay may reduce this shrinkage by a factor of 10.  
 
Another nanoscale particle is hollow carbon nanotubes (CNT) that are thousands of times smaller in diameter than carbon fibers.  CNT can be compounded into thermoplastics to produce nanotube composites with uniform surface resistivity of 104 to 109 ohms/sq.  Uniformity reduces the “hotspots” encountered with carbon fiber filled composites.  Nanotube composites are excellent for automotive applications such as fuel system components and for electrostatic painting.  Johnson et al. inserted single wall CNT to epoxy to make a composite that is 3.5 times harder than original epoxy.  Only 1% of CNT showed 125% increase in thermal conductivity at room temperature5
 
Studies on PNC have taken different unique, application driven, directions such as nanoporous-nanocomposites6 and foamed nanocomposites7.  The future of plastic nanocomposites not only depends on volume based markets such as PP in automotive applications, PVC in pipe or siding, but also in speciality areas like aerospace, electronics and biomedical devices.  These materials can be manufactured by established processes including extrusion, injection molding, reaction injection molding or resin transfer molding.               

Plastic electronics

Conductive plastics is another area that can change modern life.  Plastics are known to be insulators.  This notion has changed since polyacetylene was doped in 19778.  A thin polyacetylene film could be oxidized with iodine vapour to increase its electrical conductivity a billion times.  It is well known that conductivity depends on electronic structures of materials.  Because of the large density of free electrons in metals – they conduct electricity.  This is not the case with polymers.  However, a polymer containing conjugated double bonds along its backbone can behave like a conductor if it is well treated.  When polyacetylenes or polyanilines are doped, they can be made to have conductivity similar to metallic copper.  The list of applications for conductive polymers is on the rise.  For instance, polypyrrole has been tested as microwave absorbing “stealth” (radar invisible) screen coatings9.
 
As an alternate to doping, Schön et al.10 have developed a solution cast process by which polythiophene film becomes superconducting at – 2350C.  This study shows the possibility of tuning the electrical properties of conjugated polymers from insulating to superconducting.  Essentially, conductive polymer molecules at controlled micron length scales can be engineered to behave as Light Emitting Polymers (LEP), photodiodes or as switch, thin film transistors (TFTs) that are changing the way we use cell phone, monitors or TV.  Although organic TFTs are the future, inorganic TFTs on a flexible substrate have already been demonstrated by Rollotronics via "roll-to-roll" manufacturing.  In this technique, a continuous sheet of plastic is unrolled from one spool, covered with circuit-board-like patterns of silicon, and collected on another spool providing flexible transistors on a roll11.  This makes plastic electronics an exciting area12, 13.  Mixing inorganic nano-rods with semiconducting plastics, Alivisatos 14 et al. have produced a new flexible plastic solar cell. 
 
This flexible nature of plastics has overwhelmed its inorganic counterpart along with low cost manufacturing.  Utilising a vacuum coating process (in a single processing sequence) flexible OLED can be produced in rapid throughput, roll-coating systems.  However, challenges are critical to the success of plastic electronics.  Organic Light Emitting diodes (OLED) are known to break up in presence of water and oxygen.  With diffusion barrier materials and substrates based on vacuum polymer deposition flexible and transparent substrates for display is today’s reality15.  Current specifications for permeation rates of substrates for OLED are on the order of 10-3 cm3/m2/day at standard temperature and pressure for oxygen and 10-6 g/m2/day for water vapour16.  Multi-layered organic-inorganic barrier can be engineered to the specific performance requirements into plastics substrate for display applications.  It is claimed that engineered barrier substrates would be comparable in price to the glass substrates currently purchased for use in flat panel displays17,18
 
Another field of interest in display technology is electronic ink.  This is an electronic paper, which appears as a plastic film and reads like a printed paper.  Until now, electronic ink has been used with standard, rigid backplanes designed for liquid crystal displays.  Researchers at Cambridge, MA-based E-Ink have completed the first prototype, a functional electronic ink display on a plastic substrate that can be twisted without disturbing the print image.  This has demonstrated the possibility of a fully flexible electronic paper-like display19.


Self-assembly process

“Self-assembly” is the creation of parts capable of fusing together into a complex system without an outside builder.  The process is simple but can have an enormous impact how we think, live and work.  This is how nature works.  Double helical strands of DNA molecule where chemical bases are attracted selectively to each other (“T” with an “A” or “C” with a “G” and never otherwise), are a case in point.  In a cell, this process is very complex.  However, the underlying principle is “recognition”.  Recognition can be of different types, such as the chemical recognition at the molecular level (example: chemical bases of DNA), or the geometrical recognition at the micro level. 
 
Expanding the latter approach, scientists at Alien Technology deposit integrated circuits across a plastic substrate to manufacture a flexible display for smart cards.  In this fluid self-assembly (FSA) process20, transistors are floated into place across a large surface area having transistors shaped as holes.  As the circuit approaches a hole, it fits into the hole perfectly since it fits only one way.  In this manner a thin, low cost, light plastic film is used instead of costly and brittle glass to continuously produce smart cards.  Whitesides et al. recently used patterned assembly of integrated semiconductor devices (LED) suspended in water to fabricate flexible (using transparent polyimide) cylindrical displays that light up in any desired pattern21.  The study showed the feasibility of assembling 1500 silicon cubes, on an area of 5 square centimeters, in less than 3 minutes, with a defect rate of ~2%. The power of self-assembly concept has also been demonstrated by creating complex structures in minutes.  For example, 15 layers of bubbles of uniform sizes (0.2-2.0 microns in diameter), in 30-40 micron thick polymer films22
 
Polystyrene is an inexpensive plastic and is used for a variety of applications. However, it is brittle.  The technique of self-assembly can change the structure of polystyrene, providing enhanced properties.  When very small amounts of designed molecules, known as dendron rodcoils, are dissolved in styrene monomers, the molecules interact with one another, forming weak bonds and assembling into ribbon-like structures23. Rigid ribbons guide polymer chains line up closely alongside them improving mechanical properties. Furthermore, the presence of thin ribbons makes polystyrene strongly birefringent, a property that moves light in specific directions.  In other words, the modified polystyrene also can reflect and transmit certain wavelengths of light and could become a material for advanced photonics. 
 
Another promising development comes from a group of researchers at Cornell University who used the self-assembly technique to produce a flexible ceramic.  The group of Ulrich Weisner24 used a di-block copolymer with a silica type material to produce a hybrid material of cubic bicontinuous structure. The resulting hybrid material not only has the component properties but may also have other behaviors at different structural levels from battery electrolytes to fuel cells to separating live proteins.   


Fuel cell

The fuel cell is another new technology development area.  The technology offers not only efficiency and cleanliness but also abundant hydrogen and renewable energy.  In principle, fuel cells run on hydrogen and convert chemical energy into electrical energy without using a combustion process.  Hydrogen combines with oxygen from the air to produce electricity, water, heat and no emission (ideally). 
 
Many cells are combined into a fuel cell stack to produce large amounts of electricity. Bipolar plates separate neighboring cells and serve as the anode for one fuel cell and the cathode for the adjacent one.  In a proton exchange membrane (PEM) fuel cell, a plastic thin film (membrane), coated with a catalyst (platinum and / or ruthenium) on both sides generates electricity.  When hydrogen or hydrogen rich gas from the reformer gets to the coated plastic membrane, hydrogen molecules are broken into protons & electrons. The protons penetrate the membrane and combine with oxygen to produce water and heat. However, the membrane does not allow the electrons to pass through. When electrons get around the membrane, they generate direct current (DC).  A power conditioner then transforms the DC power to AC power, reducing voltage spikes and thereby completing the PEM fuel cell structure.


Today’s commercially available plastic membrane is a sulfonated fluoropolymer manufactured by Dupont called Nafion®.  The problem with Nafion® is that above 800C, its conductivity is greatly reduced. This happens due to the lack of humidity.  A similar problem faces sulfonated ethylene styrene interpolymer.  Researchers are working on composites, aromatic polyimide and sulfonated styrene ethylene membranes to address this problem25-27
 

The membrane is not the only involvement of plastic in a PEM fuel cell. End plates holding the PEM fuel cell stack are also made of plastics.  Plug Power Inc., producer of PEM fuel cells for home power generation, uses highly graphite loaded vinyl ester polymeric bulk compounds (BMC 940) for its end plates.  Effective lightweight storage of hydrogen in a minimum space provides plastics further application opportunities.  The potentials for plastic usage in making fuel cells represent future challenges for scientists and engineers alike.  Developing a lower cost membrane, greater operating temperature ranges, without wet environment, injection moldable end plates in bulk, and hydrogen storage tanks are among those challenges.

Tissue engineering

Interestingly, plastics are not limited to material applications.  Soon they may provide spare human body parts.  Plastics, as biomaterials, are at the forefront of current tissue engineering activity.  Motivations stem from the unique properties of polymers and the current need for custom made materials for specific medical applications.  Although biodegradable polymeric bio-materials have gained acceptance in clinical use including regulatory approval for controlled drug delivery, only a modest success has been recorded in sustained protein release – a key to tissue engineering. 
 
The major drawback in designing implantable organs is in providing a blood supply to them.  An effective solution to this problem could be by encouraging surrounding cells and blood vessels to grow into the new organ.  Structural versatility and attractive physico-chemical properties make plastic an excellent candidate for tissue engineering scaffolds, and have become the subject of intense study.  Injecting plastics with proteins known as growth factors could guide and support tissue in-growth.  In the case of a damaged bone, for example, as plastic continues to degrade inside the body, proteins are released.  These growth factors attract blood vessels from the healthy surrounding bone that flood the damaged area, bringing nutrients that the new tissue requires to survive.   That is how periodontists today can utilize biodegradable plastics for tissue regeneration.  Tissue growth is facilitated by a three dimensional framework with properties that encourage favorable cell responses. 
 
Essentially, these 3?D biological interfaces enable specific types of cells to attach themselves to the scaffold, grow, and organize into functional tissue28.  The idea may sound simple but in reality, designing polymeric biomaterials for specific applications offers diverse challenges.  For example, bones at different body locations (a vertebra, a jawbone or a thighbone) require different structural loads and once healed (healthy tissues having been grown), the material should disappear at a predetermined rate without any toxic effect to the body.  Tuning these polymers to disintegrate at the same rate as the new bone is developed is equally crucial. 
 
It is not surprising that no single plastic material can be ideal for tissue engineering scaffolds.  Several polymeric systems have been designed as scaffolds for engineering functional tissues29-32.  However, plastics, as biomaterials, have opened up a considerably more than expected.  Polymers are now being developed with built-in adhesion sites that act as cell hosts in giving shapes that mimic different organs.  It should be possible in the future to use multi-layered polymers that release a series of growth factors necessary for healing an ailing part at predetermined time intervals. 
 
As well, stem cells could be combined to the growth factors in seeding the plastic scaffolds.  Professor Robert S. Langer’s group at MIT is actively pursuing three-dimensional polymer scaffolds for growing human tissues such as skin, cartilage, blood vessels, and nerves.  Likewise, different types of poly (phosphoester)s have been developed by Professor Kam Leong’s group at John Hopkins University that have the attributes of elastomeric, gel-like and crystalline materials for construction of 3?D scaffolds with controlled porous architecture.  Notwithstanding regulatory worries or legal concerns, plastic biomaterials are poised to increase the effectiveness and longevity of our body parts.
 

Combinatorial approach and high through-put technique

                                                                                                                                                                                 The push for a speedy discovery of new materials for applications ranging from nanocomposites to biotechnology has made researchers pursue the “combinatorial” approach actively.  In simple terms, the “combinatorial” approach provides a way to find promising compounds or materials via a route that is faster, better and cheaper. 

To conduct a study in the traditional sense, we imply a few measurements or a few samples at a time.  In the “combinatorial” approach, we are talking about a scale of hundreds and thousands of measurements at a time.  These “high-throughput” solutions are due to the combinations of tools and techniques such as robotics, computation and miniaturization.
 
High-throughput technology, (HTPT) as it is called, has been gestating and growing for over 3 decades.  In fact, Hanak reported33 the first example of a combinatorial approach with increased efficiency for the discovery of new materials in 1970.  Only recently has the technology started to mature for the efficient synthesis and characterization of complex polymeric systems34-35.  Amis et al. have reviewed current advances in combinatorial methods for polymer materials science36.  An important step towards the technique is to create a library of compounds (using robots or automated tools) based on physical and structural properties that are likely to yield the desired polymer molecule.  Many different variables can be inserted e.g., temperature, pressure, time, thickness, composition etc. This library of compounds is then screened for “lead” candidates that could produce the target polymer.   Examples of the many benefits of HTPT are, the design of a new catalyst, the optimization of reaction conditions for the controlled preparation of nanoscale materials (advanced materials), or the production of biodegradable polymer blends with optimum microstructure (tissue engineering). 
 
The technique can be exploited to synthesize polymers that can give functional attributes such as wetability, lubricity, and anti-adhesion properties or enhance the activity of a functional molecule.  Symyx Technologies Inc. has constructed discovery platforms as a part of HTP technology aiming at materials that show high affinity to specific surfaces.  Recently, Symyx has provided a second module of Discovery ToolsTM to GIRSA that performs an average of 48 experiments a day for the development, discovery and optimization of different polymers37.  Soon combinatorial and high throughput technique will be the driving force behind many discoveries.
 

Conclusions


Applications of plastics hold enormous promise for the future, ranging from nanotechnology to biotechnology.  The passive nature of plastics is slowly changing.  Development is taking place where plastics are responding to their changing surroundings - be it water, temperature, light or electricity.  It is the molecular uniqueness that gives plastic the strength to bring science and technology together.  No other material but plastics represents an open book of new ideas and technologies for a brighter tomorrow. 


Acknowledgements

                                                                                                                                                                           The author wishes to thank L.A. Utracki and G. Czeremuszkin for valuable comments.  Helpful suggestions from P.J. Cook and V. Flaris are also appreciated. 


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[This article was originally published in Plastics Engineering in September 2002 – Editor]
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