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]...

alex_figure2_1rightbottom   In the previous article, we discussed flame retardant (FR) regulations and how they might be expected to change. Nevertheless, the market is still strong for non-halogenated flame retardants. Therefore, the objective of this second part article is to summarize notable experimental results obtained with commercial Flame Retardants, and approaches that are likely to be important over the coming decade. New Flame Retardants chemistries and approaches will also be discussed.

 

 

New Commercial Non-Halogenated Flame Retardants

 

The novelty of the new non-halogenated flame retardants means that academia and government labs have not done a lot of research with the materials. The information in this section will be based solely upon the limited publically available information.  Most of these new flame retardants are polymeric in structure and their chemical structures have not been published; although manufacturers have sufficient technology to provide general guidelines on how to apply them, it is possible that their structures have not yet been elucidated.

However, these materials would not be commercial at all if they didn’t show significant potential for flame retardant use.

The first new group of non-halogenated flame retardants is polymeric/oligomeric phosphonate compounds made by a company known as FRX Polymers. This company has also commercialised compounds which are copolymers of polycarbonate (poly(phosphonate-co-carbonate))1.

FRX Polymers has a range of polymeric additives and reactive oligomers, all of which can be melt compounded with other polymers, or can be used directly as inherently flame retardant materials. Applications in fibers, electronics, transportation (aerospace, trains), building and construction have been claimed. The polymers which appear to be most effective are those containing oxygen in the polymer backbone, including polycarbonate, polyesters [unsaturated, poly(ethylene terephthalate), poly(butylene terephthalate)], thermoplastic polyurethanes, and epoxies. Little is known about the properties of these flame retardant materials except for the minimal fire safety values provided by LOI (limiting oxygen index) test data. LOI test data does not correlate to any realistic fire scenario2, however, any material with a LOI of 60% or greater is a low heat release / low flammability material with potential as a flame retardant additive. Because of this, these promising flame retardant materials have been commercialized.

Israel Chemicals Limited have recently released Fyrol HF-5, another polymeric non-halogenated flame retardant. Although little is yet known about the material, it contains a high level of phosphorus, which suggested that it could be effective in flexible polyurethane foams used in automotive, mattress, and furniture applications3.

The final new non-halogenated flame retardant of note is FP-2100J, produced by Amfine Chemical Corporation. This material is an intumescent flame retardant additive package optimized for polyolefins. It is not polymeric, but shows efficient intumescent behavior by forming protective chars with very high thermal durability. About 20-25wt% loading of FP-2100J in polypropylene provides UL-94 V-0 performance at 1.6 and 0.8mm. Since polypropylene is flammable (one of the highest heat release polymers known), this level of performance is quite impressive for a non-halogenated material4.

 

New Experimental Non-Halogenated Flame Retardants

 

Outside the commercial arena, there have been two experimental non-halogenated flame retardants that deserve attention. They are boronic acids for polyurethanes, and deoxybenzoin co-monomers. It should be noted that of the new flame retardants reported, these two are truly of new chemistries. There have been other chemistries discussed and published in the past year, but they either build upon well-known chemistry (phosphorus, mineral fillers) or are still too new to science to discuss in detail.

In recent studies, boronic acids have been found to be effective as flame retardants for polyurethanes5. Boronic Acids have a similar structure to carboxylic acids (such as acetic or benzoic acid) but the central carbon has been replaced with boron. An example is provided by the chemical structure in Figure 2-1.

alex_fig_2_1_center                                                                                                                                                                  Figure 2-1: Monoboronic Acid

 

These compounds showed notable reductions in heat release, changes in thermal decomposition behavior (suggesting crosslinking and char formation in the polyurethane), and appeared to have slowed or preventing dripping and flow of the polyurethane during burning. In the figure below, the heat release of the pure thermoplastic polyurethane before and after addition of the boronic acid, flame retardant is shown.

alex_figure_ 2_1_left       alex_figure_ 2_1_middle 

   Figure  2-1: HRR plot of TPU control (left), TPU + Monoboronic Acid (right);  Below: Chars of neat TPU (no FR, left bottom), and TPU + Monobornic acid (right bottom)

alex_figure2_1righttop         alex_figure2_1rightbottom

 

Deoxybenzoin co-monomers (Figure 2-2) are notable in that they can copolymerize with a wide range of polymer chemistries, and they reduce heat release without the use of phosphorus or other typical non-halogen materials.alex_figure_2_2

                                                                                                                                                                   Figure 2-2: Bisphenol Deoxybenzoin Monomer

These materials show very little heat release when they thermally decompose to form a carbon char and water and then burn; therefore they serve mostly as a diluent. A 50/50 blend of deoxybenzoin and bisphenol A epoxy would show a 50% reduction in base heat release, while a 25/75 blend of deoxybenzoin and bisphenol. A epoxy would show a 25% reduction in base heat release. From the results published to date6,7,8,9this strategy appears to be a very promising path to lowering the base flammability of a commodity polymer without compromising mechanical properties or using other flame retardant additives. The chemistry is not yet commercial, but it seems simple to synthesize so that it could be rapidly commercialised in response to the right economic incentives.

 

Protective Coating - New Flame Retardant Approaches

 

Another way to achieve flame retardant protection in thermoplastic materials is through the use of protective coatings. There are two notable approaches relevant to thermoplastics. The first is the use of an infrared reflective coating on a thermoplastic so that the material never heats up enough to thermally decompose and ignite. For example Prof. Bernhard Schartel (of the German Federal Institute for Materials Research and Testing) placed a copper mirror on a thermoplastic material to dramatically delay the time to ignition of the thermoplastic material10. What makes this approach intriguing is that in the absence of flame retardants, significant ignition resistance can be achieved for a thermoplastic simply by reflecting the heat away from the plastic. While interference (EMI) shielding effects for the plastic with this copper mirror have not been measured, it seems likely that this mirror would be of great value for plastics in hand-held communication devices such as smart phones in which EMI and flame retardancy are crucial.

Another protective coating approach is provided by the use of layer-by-layer (LbL) coatings11,12,13,14. These have been used successfully for textiles and foams. With the LbL process, a polymer nanocomposite is built up one layer at a time on foam or textile materials, where it creates an unbroken (conformal) barrier over the polymer. When the material is exposed to a flame, the LbL coating chars and carbonizes to prevent the underlying material from degrading it further. This prevents dripping and/or structural collapse of the underlying material. The technology is a recent discovery and can be tailored to a wide range of polymer chemistries, but may only work well with high-surface area polymer constructions such as foams, and textiles. Flammability of nanocomposite coatings on cotton fabrics as a function of bilayers is shown in Figure 2-3. Some data however, suggests that the LbL coatings will not provide enough protection to a thick (>1mm) plastic material, but more data is needed to confirm this.

 alex_figure_2_3

Figure 2-3: Mass loss and flammability of nanocomposites coatings on cotton fabrics as a function of bilayers (BL), (Li, Y-C; Mannen, S.; Yang, Y-H.; Morgan, A.B.; Grunlan, J.C., "Anti-Flammable Intumescent Nanocoatings on Fabric", Advanced Materials, 2011, 23, 3926-3931)    

 

Polymeric Flame Retardants – Recent Trends

 

As mentioned briefly in part I of this series on flame retardant trends, many producers of flame retardant additives are pursuing polymeric materials. This is because these materials have a better environmental profile when compared to small molecules. All of the major flame retardant producers now have commercial polymeric additives, but the chemistry has not been widely revealed due to the proprietary nature of these additives. Recently commercialized polymeric flame retardant additives are described below.

The Albemarle Corporation15 provides two polymeric flame retardants, both of which are brominated. The first is GreenArmor, a polymeric flame retardant of unknown chemical structure. The chemistry could be based on brominated polystyrene since it contains a high level of bromine and is claimed to be optimal for HIPS and ABS.

The second compound is GreenCrest16, which is optimized to provide flame retardancy for polystyrene insulation foams, like those used in building insulation products. It is marketed as a replacement for hexabromocyclododecane (HBCD), but it is not clear whether this additive can replace HBCD in applications other than polystyrene foam, such as textile back-coatings.

Chemtura / Great Lakes Solutions markets and sells polymeric flame retardants under the“Emerald Innovation” tradename. The first is Emerald Innovation 100017, which shows good flame retardant performance in HIPS, ABS, and PP. It is also likely a brominated polystyrene, but since it shows some promise in PP as well, it may have some other polymer chemistry present which enables it to show good effectiveness in PP for simple ignition resistance tests like UL-94 V.

On the other hand, Emerald Innovation 300018 is optimized to provide flame retardant protection for polystyrene foams, and, like GreenCrest, it is a replacement for HBCD in polystyrene foams. This flame retardant is the material that Chemtura licensed from Dow Chemical a few years back, which suggests that it has been found to be very effective in polystyrene foams.

Israel Chemicals Limited (ICL) has a much wider range of polymeric flame retardants than the other companies19, with either halogenated and phosphorus-based chemistries. Its phosphorus based chemistries include Fyrol HF-5 and Fyrol PNX; both of these are optimized for polyurethanes. A wide range of brominated polymeric flame retardants has been listed on its website, covering brominated polyacrylates, brominated polystyrenes, and some proprietary chemistries as well. The full range of ICL’s offerings can be found at their website.

FRX Polymers has the range of polymeric additives and reactive oligomers that were described in the New Commercial Non-Halogenated Flame Retardants section of this article.

 

Conclusions 

 

As outlined in Part I of this series, new flame retardants are being discovered, optimized, and commercialized. Polymeric flame retardants are dominating the new chemistries from the main commercial vendors (Albemarle, Great Lakes Solutions, ICL) and the new vendors (FRX). Flame retardants with very different chemistry (boronic acids for polyurethanes) and low flammability monomers (deoxybenzoin) are satisfying needs in a number of niches.

Coatings are being developed that provide fire protection through reflection of heat or through the charring of nanocomposite materials. Just as there are multiple ways to provide flame retardant properties to polymers and these must be customized to each application. The advances over the past year strongly suggest that there will continue be multiple solutions to choose from. Material scientists should expect existing flame retardant companies to continue to provide innovation, but they should also watch the literature for new small companies that can be expected to commercialize some of the approaches outlined in this paper.

 

References

1 http://www.frxpolymers.com/(accessed 13 Mar, 2013)

2 “Oxygen Index: Correlations to Other Fire Tests” Weil, E. D.; Hirschler, M. M.; Patel, N. G.; Said, M. M.; Shakir, S. Fire and Materials 1992, 16, 159-167.

3 http://icl-ip.com/?products=fyrol-hf-5(accessed 13 Mar, 2013)

4 http://www.amfine.com/productdetails.asp?ProductID=50(accessed 13 Mar, 2013)

5 “Synthesis and flame retardant testing of new boronated and phosphonated aromatic compounds” Benin, V.; Durganala, S.; Morgan, A. B. J. Mater. Chem. 2012. 22, 1180-1190.

6 “Flame Resistant Electrospun Polymer Nanofibers from Deoxybenzoin-based Polymers” Moon, S.; Ku, B-C.; Emrick, T.; Coughlin, B. E.; Farris, R. J. J. App. Polym. Sci. 2009, 111, 301-307.

7 "Halogen-free, low flammability polyurethanes derived from deoxybenzoin-based monomers" Ranganathan, T.; Cossette, P.; Emirck, T. J. Mater. Chem. 2010, 20, 3681-3687.

8 “Deoxybenzoin-Based Polyarylates as Halogen-Free Fire-Resistant Polymers” Ellzey, K. A.; Ranganathan, T.; Zilberman, J.; Coughlin, E. B.; Farris, R. J.; Emrick, T. Macromolecules 2006, 39, 3553-3558.

9 “Deoxybenzoin-based epoxy resins” Ryu, B-Y.; Moon, S.; Kosif, I.; Ranganathan, T.; Farris, R. J.; Emrick, T. Polymer 2009, 50, 767-774.

10 “Sub-micrometre coatings as an infrared mirror: A new route to flame retardancy” Schartel, B.; Beck, U.; Bahr, H.; Hertwig, A.; Knoll, U.; Weise, M. Fire Mater. 2012, 36, 671-677.

11 “Layer-by-layer assembly of silica-based flame retardant thin film on PET fabric” Carosio, F.; Laufer, G.; Alongi, J.; Camino, G.; Grunlan, J. C. Polym. Degrad. Stab. 2011, 96, 745-750.

12 “Development of layer-by-layer assembled carbon nanofiber-filled coatings to reduce polyurethane foam flammability” Kim, Y. S.; Davis, R.; Cain, A. A.; Grunlan, J. C. Polymer 2011, 52, 2847-2855.

13 “Clay-Chitosan Nanobrick Walls: Completely Renewable Gas Barrier and Flame-Retardant Nanocoatings” Laufer, G.; Kirkland, C.; Cain, A. A.; Grunlan, J. C. ACS Applied Materials & Interfaces 2012, 4, 1643-1649.

14 “Intumescent All-Polymer Multilayer Nanocoating Capable of Extinguishing Flame on Fabric” Li, Y-C.; Mannen, S.; Morgan, A. B.; Chang, S.; Yang, Y-H.; Condon, B.; Grunlan, J. C. Advanced Materials 2011, 23, 3926-3931.

15 http://albemarle.com/Products-and-Markets/Polymer-Solutions/Fire-Safety-Solutions/BFR-0001-GreenArmor-173C183.html (accessed 13 Mar, 2013)

16 http://albemarle.com/Products-and-Markets/Polymer-Solutions/Fire-Safety-Solutions/GreenCrest-Press-Release-%282012%29-956C183.html(accessed 13 Mar, 2013)

17 http://www.chemtura.com/deployedfiles/Business%20Units/Polymer_Additives-en-US/Document%20Downloads/Emerald/EmeraldInnovation1000_Final_web.pdf

18 http://www.chemtura.com/deployedfiles/Business%20Units/Polymer_Additives-en-US/Document%20Downloads/Emerald/EmeraldInnovation_3000_Final_Web.pdf (accessed 13 Mar, 2013)

19 http://icl-ip.com/?page_id=56 (accessed 20 Mar, 2013)

 

Alexander B. Morgan, Ph.D.

After receiving a B.Sc from the Virginia Military Institute (1994) and a Ph.D. from the University of South Carolina (1998), Dr. Morgan has worked for over seventeen years in the areas of materials flammability, polymeric material flame retardancy, fire science, fire testing, and fire safety engineering with an emphasis on chemical structure property relationships and fire safe material design.  His current research areas include New Flame Retardant Technology for Polyurethane Foam and Furniture, New Flame Retardant Technology with Reduced Environmental Impact, Fire Testing Method Development, Waste-To-Energy Pyrolysis and Combustion Science and Thermal Degradation and Stability Behavior of Materials.

Dr. Morgan has helped academic, government, and industrial customers solve their flame retardant and fire safety needs in a wide range of applications.  He is on the editorial review boards for two fire safety journals (Fire and Materials, Journal of Fire Science), and is a member of ASTM, Sigma Xi, International Association of Fire Safety Scientists, and the American Chemical Society.