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]...

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Polymer products are metallized by many different means for many different reasons ranging from decoration, light reflection, light barrier, to supply protection from light and gasses, to lower surface resistance, the storage of electrical charge, for control of energy dissipation during microwave cooking and many other applications. Metallized plastics are all around us in our everyday lives. In general the polymer surface is completely covered with the metal but pattern metallized surfaces are becoming more popular for both decorative and technical reasons such as antenna for security devices and control of browning reactions during microwave cooking. In general the metal most widely used in commercial applications is aluminum but large amounts of copper, silver and stainless steel alloys are also used commercially for the production of flexible circuits, reflective mirrors and susceptors for microwave pop corn. The metal is generally deposited onto a treated plastic surface by the physical vapor deposition from an evaporation source where the metal is melted in a high vacuum chamber and allowed to condense on the polymer surface which is moving above the evaporation source. In some instances the metal is sputtered off a solid metal target by impacting it with high energy ions formed with (often an argon gas) plasma generated above the metal target. Sputtering is slower than evaporation for many materials but is important for deposition of alloys or for better quality metal layers than may be achieved by evaporation. Metallized plastics are everywhere and can be found in snack packages, window films, capacitors, mirrors, Holograms, Automobile headlights, wrapping paper, bottle labels, decorative metal replacement, CD's etc.

Why metallization and how it evolved

Perhaps the most widely used metallized products today are the metallized films used in flexible snack packaging where volume has been growing since the early 1980's to replace clear barrier packaging such as Saran coated films. One of the most important reasons for using metallized films over the existing clear barrier films is the excellent light barrier which is added to the packaging material by the metal layer. Metallized films are produced such that the typical light transmission rate is less than 1% of the ambient light (Optical density of 2.0 or higher) which has been determined to be important for snack packaging. In fact, many of the first snacks were packaged in cans to supply a light barrier and then managed with distribution to minimize stale and rancid products. In the absence of the light barrier, at the level of metallized films, many of our snack foods would be quickly ruined not by the moisture gain or loss (staling) or oxygen gain (oil oxidation giving rancidity) but because the visible and UV light would attack the oils and give an accelerated rancidity reaction. So without the light barrier the need for improved moisture and oxygen barrier are not needed.

 

In general the level of light barrier for snacks is about 1% transmission (an optical density [OD] of 2.0) or perhaps slightly higher1 depending on additional moisture and oxygen barrier requirements. In comparison, a bright reflective, or decorative, layer would generally be formed at about 2.5% light transmission or an optical density of 1.6. Optical density (OD) is defined as in equation 1 and is used as an indirect measure of the aluminum layer thickness2 Figure 1 plots the relationship between optical density and aluminum layer thickness for a polyester film3. Similar, but different curves will exist for other substrates and Figure 1 should not be considered a universal relationship for the substrate surface energy and evaporation process conditions will determine the relative optical density for a given evaporation rate for the aluminum. From figure 1, for the polyester film, an OD of 2.0 the aluminum layer is approximately 150 angstroms thick.

 


OD = Log10(1/T) ……………. Equation 1

 


where: T is the transmittance defined as P/P0
P
is the unabsorbed energy remaining in the light beam passing through the sample, and P0 is the energy of the incident light beam

 

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Figure 1: Plot of Optical Density verses Aluminum layer thickness for metallized Polyester film, Data of Scharr Industries figure 2.3a of reference 2

 


While the permeation barrier properties of a given metallized film will generally be a function of optical density, Figure 2, the barrier properties are a stronger function of the surface on which the metal is deposited4. This is especially true for oxygen barrier but also holds for moisture barrier as well and is displayed in Figure 3. In the early days of metallization of polypropylene films it was widely expected that the barrier properties of metallized PET and metallized OPP would be the same due to the deposited metal layer. However, this was found not to be the case as shown in Figure 3. Ignoring the SiO2 barrier samples, there are two main branches for the barrier properties which display the relationship of oxygen barrier on metallizing surface. The upper branch consists of 70MET/60MAC, Al/APET/OPP, Al/amPA/OPP & Met PET. The first three films are coextruded biaxially oriented polypropylene (OPP) films where the surface polymer metallized are 3.5% ethylene propylene copolymer, amorphous polyester and amorphous polyamide respectively and the last is metallized polyethylene terephthalate. What these four samples show that while the moisture barrier remains about the same the oxygen barrier changes over many orders of magnitude and the more polar the surface layer the better the oxygen barrier. This allowed metallized OPP to replace metallized PET in many applications where the moisture barrier was more important than the oxygen barrier because the product failure was to go stale before rancid. If the product is stale first then there is no real value to the oxygen barrier and the less expensive OPP is a better choice than metallized PET.

 

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Figure 2. Moisture and Oxygen barriers for 48 gauge metallized polyester film as a function of optical density. Data courtesy Camvac International as figure 3.2 of reference 2 (WTR unit is g/m2 24 hrs)

 

In the second branch are two films MET-UHB and MET-HB which show an order of magnitude better moisture barrier than our first four example films and a range of oxygen barrier. These two films are EVOH/OPP and HDPE/OPP coextrusions metallized on the EVOH and HPDE surfaces. Based upon the work to show the barrier results of the first films and the importance of the film surface free energy the metallized EVOH coextrusion was discovered to have excellent oxygen and moisture barrier5. As EVOH is essentially partially oxidized polyethylene, in that it contains hydroxyl groups (-O-H) attached to carbon atoms along the polymer backbone.

 

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WVTR: ASTM test method F1249-90, 37.8 °C (100 °F) and 90% relative humidity (RH).
OTR: ASTM test method D 3985-81, 23 °C (73.4 °F) and 0% RH.

 

Figure 3: Plot of moisture barrier as a function of oxygen barrier showing the variation in oxygen barrier at constant moisture barrier from reference 4

 

This invention lead to the invention of flame treated HDPE surfaces6 which makes an EVOH like surface by the incorporation of hydroxyl groups on the HDPE film surface. It is hypothesized from these results that it is the hydroxyl groups on polyethylene (EVOH and flame treated HDPE) which give the optimum metallized barrier properties7. It turns out that the improved moisture barrier level of the MET-HB creates a situation where the snacks no longer become stale faster than they become rancid if the films oxygen permeation is greater than approximately 0.39 cc/m2/day/atmmosphere (6 cc/100in2/day/atm) and benefit from gas flushing to extend shelf life and improved packaging seals. After this discovery, work in metallized packaging films focused on improving MET-HB oxygen barrier as the most cost effective barrier film for snacks in the North American market. The success of the MET-HB then drove research to improve other films moisture and oxygen barrier by surface functionalization8 and by using improved surface treatment technologies such as plasma treatment in the metallizing chamber9 which has had good success for many films. Much of the new film product design and surface modification technology is finding acceptance and wide spread use in Europe and South America.

 

Looking ahead

While metallized films have seen wide spread growth in packaging due to the excellent cost benefit compared to other barrier packages, growth continues as PVDC coated films are replaced by metallized films where the combination of light, moisture and oxygen barrier create a unique combinations of effective product protection. Films such as the MET-UHB are expensive to produce due to material costs but are capable of replacing foil and can compete effectively where packaging weight is taxed, where chemical and flavor barrier are needed or where distribution cycles are long giving a technical need for the more expensive product.

 

Because of the unique combination of barrier properties (light, moisture & oxygen) and the excellent product protection achievable with a single film component, metallized films will enjoy more growth as the more complex laminated structures are replace with simpler, less expensive combinations containing metallized films and as new high barrier packaging applications are generated.

 

List of Terms

  • OTR Oxygen transmission rate
  • WVTR Water vapor transmission rate
  • HDPE High density polyethylene
  • EVOH Poly(ethylene) vinyl alcohol copolymer
  • PET Polyethylene terephthalate

References

1. Gavitt, I.,F., "Vacuum Coating Applications for Snack Food Packaging," Proceedings of the 36th Annual Technical Conference of the Society of Vacuum Coaters (93), pp254-258
2. Mount III, Eldridge M., editor, AIMCAL Metallizing Committee Metallizing Technical Reference, 3rd ed., The Association of Industrial Metallizers, Coaters and Laminators, March 2001.
3. Scharr Industries Inc. Publication, "Conversion Table Metallized Film (Aluminum)", 1985.
4. Mount III, Eldridge, M., Wagner, John R., "Aroma, Oxygen and Moisture Barrier Behavior of Coated and Vacuum Coated OPP Films for Packaging", J. Plastic Film & Sheeting, V17(July), 2001, pp 221-237.
5. Migliorini, R.A. U.S. Patent 5,153,074, Oct. 6, 1992
6. Migliorini, R.A., Mount III, E.M., U.S. Patent 5194,318 March 16, 1993
7. Amon, M., Mount III, Eldridge M., Tran, F., US Patent 6,420,041, Issued July 16, 2002, " Film With Metallizable Skin Layer".
8. Yializis, A., Mikhael, M.G., Ellwanger, R.E., Mount III, E. M., "Surface Functionalization of Polymer Films", 42nd Annual Technical Conference Proceedings Society of Vacuum Coaters, 1999, pp 469-474.
9. Mount III, E. M., "Plasma pre-treatment for metallizing packaging film", Converting, V19 (3), 2001, pp124-128.

 

Eldridge M. Mount III

Eldridge M. Mount III, EMMOUNT Technologies, LLC,88 Country Downs Circle,Fairport, NY 14450, USA

Eldridge's career in Plastics began in the summer of 1970, at General Electric, as a summer engineer working with Epoxy/glass filament winding. He worked two years as a synthetic Chemist for Sterling Drug and then went to Rennselear Polytecnic to perform an experimental and theoretical study of the melting and extrusion behavior of solid polymers to earn his advanced degrees. From 1978 to 2000 he has worked for ICI Americas and Mobil Chemical Films Division in the area of Extrusion, Coextrusion, orientation technology and product development for biaxially oriented films.



Eldridge has been a member of Society of Plastics Engineers (SPE) since 1975, when he joined as a student member. He presented the results of his Masters thesis at the 1976 ANTEC and his Ph.D. thesis at the 1979 ANTEC. Since then he has presented Papers at ANTEC in 1981, 1987, 1992, 2000 as well as at several RETEC's and TOPCON.



He was elected to the Extrusion Division Board of Directors in 1980. While a member of the Board he helped index the Consultants Corner book, developed a data base of Extrusion Division ANTEC papers, oversaw the Fellows process, worked to develop the TAPPI paper exchange as Films Focus Chairman, and served as 1988 ANTEC Program Chairman, Division Chairman 1990-91, and Division Councilor for two 3 year terms ending in 1998. Currently he is overseeing the Fellows Process and is the Chairman of the Packaging Focus Group. At the 2000 ANTEC he became a Fellow of the Society. From 2001 to 2004 he served as a Vice President and Executive Board Member of the Society of Plastics Engineers.



Dr. Mount is now an independent consultant in polymer extrusion, film converting and intellectual property. Currently, he holds six US and two European Patents in the field of Metallized Films.

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