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]...

Mistakes in science often lead to inventions. Polymer science is no exception. Around 1961, a laboratory scientist processing fluoroelastomers and polyolefins on the same extrusion line, discovered that for some reason he was able to process the most difficult polyolefins obtaining good appearance at higher throughput rates.  An important patent was granted as a result of this work; the patent claimed the addition of small amounts of fluoropolymers (0.1 – 2.0 wt %) to polyolefins gave amazing processing benefits [1]. This is how fluoropolymers and fluoroelastomers gained their fame as polymer processing aids (PPA).

The beginning – Goodbye to melt fracture

After the patent rights expired around 19841, a flood of activity centered around this modification to polyolefin processing.  The early focus was on Linear Low Density Polyethylene (LLDPE) blown films and high-speed wire & cable extrusion.   This is a result of the well-known challenges to process LLDPE. At that time, several polymer manufacturers, high-end compounders and film processors began contacting suppliers of fluoroelastomers made from vinylidene fluoride (VF2) and hexafluoropropylene (HFP).  They began creating high quality low density polyethylene products at up to triple previous production rates on extrusion machines that had previously been only used to process LLDPE using narrow die gaps.

figure_1_split screen_photo1 

Figure 1:  Split screen photo of hexene-based LLDPE plus masterbatch containing 1% of Kynar Flex® 2821 PPA: left side before adding the PPA and right side almost immediately after adding the PPA

A split screen photograph taken in 1987 (Figure 1), shows the immediate effects of adding a fluorinated PPA to a LLDPE blown film, which has been running for 40 minutes full of melt fracture.  It cleared up in less than 4 minutes after the addition of a 1% masterbatch of LLDPE + Kynar Flex® 2821-00.  With such dramatic improvements, it is understandable why polyethylene extrusion and polyolefin resin manufacturers and compounders got excited.

These benefits resulted in a flurry of research on fluoropolymer PPAs that produced rapid results.   Fluorinated resin manufacturers were exploring new monomers, varying VF2 and HFP ratios, varying molecular weights, changing levels of PPA addition, studying the effects of particle size, investigating the importance of particle distribution, and analyzing the effects of processing temperature while using fluorinated PPAs.

The next important patented breakthrough resulted from the study of interactions of common polyolefin additives in blends with PPA. Researchers found that polyethylene glycol had a synergistic effect on the performance of the PPA.  It helped to reduce the levels of PPA required to minimize sharkskin defects, torque, gauge control, processing temperatures and pressure, while increasing processing throughput, and film transparency2.

During the same year, the Kynar® PVDF PPA team at Pennwalt (now Arkema) commissioned a blown film extruder. The technical staff of the supplier stated that based on existing knowledge it would be impossible to run LLDPE on a 2.5”, 30/1 LD extruder with a 10” diameter die and a 0.025” die gap.  Figure 2 shows the actual reduction trend of pressure versus temperature in the virgin hexene-based LLDPE having less than 1 MI (Melt Index) with the same resin with and without 1% Kynar Flex® 2821 masterbatch.  The masterbatch compound contained a let down ratio of 22:1 into the host resin resulting in 450 ppm concentration of Fluorinated PPA.  The results were outstanding but typical of the results that film processors were obtaining in the 1980s.  It is interesting to observe that the pressure reduction shift is almost a parallel line with 800 – 1200 PSI pressure reduction regardless of the melt temperature of the extrusion.

figure_2_extruder pressure comparison1

Figure 2:  Extruder Pressure Comparison of Virgin LLDPE and LLDPE with 450 PPM Fluorinated PPA at a range of Melt Temperature

In the same study, the output of clear film without sharkskin (surface melt fracture) had more than tripled (i.e. from 66 pounds per hour to 204 pounds per hour) at the same melt temperature. Output was limited by the equipment’s throughput since screw speed could only be increased from 34 RPM to 102 RPM (see Table 1).

table1_ppa data table revised 

Table 1:  Processing Parameters Comparison of LLDPE Control vs. LLDPE with 450 ppm of Fluorinated PPA

Figure 2 and Table 1 show how fluorinated PPAs bring large benefits to LLDPE processors through benefits that include equipment longevity, production capacity improvement, higher strength, improved appearance, and reduced scrap. In addition, these additives enabled the use of existing equipment to be used to manufacture products made from more than one version of a polymer.  Figure 3 gives an example of a microscopic view of a PE film with a visible melt fracture that was processed without a fluorinated PPA and a comparison with the same PE resin extruded with just 300 ppm of fluorinated PPA.

As the industry soared along with this technology, manufacturers with less obvious issues began considering that fluorinated PPAs could have incremental benefits that would differentiate them from their competitors.  Compounders started to supply PPA compounds for extruding LDPE, HDPE, UHMW-PE and Cross-linked polyethylene (PEX) that could improve the appearance of marginally smooth products.  Injection and blow molders could fill molds by up to 8% more easily, without going to a higher melt flow rate resin with lower performance properties.  In all types of processing, other processing aids like stearates that were affected by chemicals and sunlight could be replaced by fluorinated PPAs, thus reducing longer-term exposure problems of the polymer.   The use of fluorinated PPAs has been extended to applications with Polypropylene, Polyurethane, and PVC in addition to the various polyethylene resins.

 figure_3_under microscope_left1   figure_3_view under microscope right1

Figure 3:  Microscopic comparison of extruded metallocene PE film before (left) and after addition of 300 ppm of Kynar® 5300 PPA (right)

 

Continued Development

Fluoropolymer producers have made great efforts to focus on the form of the additives to allow good mixing with any synergists to obtain the best mixing and proper dispersion of the small amounts of PPA to gain the desired effects.  The dispersion of PPA in the polymer matrix is critically important and should be considered carefully.  Much has been written on combining the concentrates and the fluorinated PPA. There are many patents in this area; one important patent is US 8053502 B23 which reports that PPA reduces or eliminates extrusion defects without causing deterioration in the yellowing index of the extruded resin.  If the polymer or the master batch containing the PPA does not match up well with the melt flow rate of the host polyolefin, the PPA can lose its ability to coat the die and aid in the reduction of melt fracture.  In other words, the PPA can add to the problem. Studies have shown that surface melt fracture is a die exit phenomenon4. It has been reported5 that visualizing polymer/die interfaces in high resolution images of PPA/PE blends can show that PPA coating occurred in 3 stages.

 

The Future - Can PPA help in reducing die build-up?

Die build up is the newest phenomenon that fluorinated PPAs are helping to avoid.  Companies extruding pipes and profiles with relatively slow extrusion speeds normally would not see any production speed benefit or increased product gloss by using a fluorinated PPA, yet they are now turning to these additives to reduce unwanted buildup on the die that can compromise the integrity of the final product.  Die buildup can do more than create unsightly residue on the extrusion. It can attach to the product and generate a weak point. It can accumulate and degrade at the die creating safety issues.  Die build up can be an acute problem in products containing high levels of fillers and additives.  

Research is continuing on fluorinated PPAs to address the concern that die build up adds to the complexity of the process.  Processors still want good film, wire, or pipe with lower stresses on their extruder, but also, they want to avoid the negative effects of die build up.  PPAs that work best for processing effects may not be optimal for reduction of die build up, and some PPAs that may reduce die build up well may not be very effective in reducing melt fracture.  As a result, this has become a major area of study in 2018, leading to the introduction of newer grades of fluorinated PPA materials. These are designed with specific melting points, molecular weights, and ratios of co-monomer, and VF2-based polymers rather than elastomers.  Figures 4 & 5 show examples of die build up from a capillary and tube extrusion without PPA and Figure 6 shows a comparative reduction over time of die build up with the use of a specific fluorinated PPA.

 figure_4                                             figure_5

Figure 4:  Example of die build up in highly filled Polyethylene                      Figure 5:  Common problem of die build up in tubing extrusion

                                             figure_ 6 split screen of die build up left        figure_6 split screen of die build up right

Figure 6:  Die build up in a capillary of highly calcium carbonate filled PE without PPA (left) and 30 minutes after the introduction of 1260 ppm of Kynar® 705 PPA (right)

 

Die build up is caused by many variables such as concentration and weight of additives, temperature of extrusion, rate of extrusion, molecular weight of the host resin, and design of the dies. The selection of the loading of the fluorinated PPA becomes even more critical to the elimination of melt fracture.  Too much PPA may add to die build up, and not enough PPA may mean the effect is severely restricted by the other components in the compound.  Additionally, if the choice of molecular weight of the fluorinated PPA is not made very carefully,  too much PPA can pass through the process without getting to the die wall in time to compete with the other additives in the stream.  It is common to add as much as 1200 ppm of fluorinated PPA to reduce the die build up. In contrast, some processors have eliminated melt fracture and improved pressure reduction in the melt with levels as low as 150-400 ppm.

Summary

Since the idea of fluorinated PPAs used in polyolefins was accidentally discovered in 1961 and was used by one company for about the next 23 years, the market for these products is now in the thousands of tons globally.  Today, the breadth of its use is commonly presented at conferences on every continent.  What started out as a dramatic processing improvement additive for one polymer (LLDPE), has emerged as a standard processing additive for countless others.  The current trend is for continued incremental improvements in either the processing, appearance or performance properties of the final polyolefin product in injection molding, blow molding, extrusion, and casting.

 

References

1. Blatz, P.S., US Patent 3,125,547 (March 17, 1964)
2. Duchesne, D., Johnson, B. V., US Patent 4,855,360 (August 8, 1989)
3. Bonnet, A., Laffargue, J., Triballier, K., Beaume, F., US Patent 8053502 B2 (November 8, 2011)
4. Cogswell, F.N. ; J. Non-Newtonian Fluid Mech. 2, pp. 37-47, 1977
5. Meillon, M.G., Morgan, D., Bigio, D., Migler, K., ANTEC Proceedings, PP. 96-100, 2005

 

Contributors

David A. Seiler received his B.S. in Chemical Engineering from Penn State University in 1983.  He is employed for Arkema Inc as the Americas Business Manager Industrial / Global Manager Polymer Processing Aids, and has worked in the area of Fluoropolymers for 34 years. 

Jason Pomante graduated from Lafayette College in 2002 with a B.S. in Chemical Engineering and MBA from Saint Joseph’s University in 2010.  Jason has worked at Arkema for 15 years and is currently the North American Market Manager in the Technical Polymers Division.

Robert Lowrie graduated in May of 2017 with a B.S. in Chemical Engineering from Villanova University. He is currently a Technical Marketing Specialist for Arkema Inc. in the Technical Polymers Division.

david a. seiler jason pomante robert lowrie
       David A. Seiler        Jason Pomante                 Robert Lowrie