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Researchers gather to discuss advances in organic photovoltaics (OPV)

IKV researchers report thermoplastic/metal hybrid materials for Direct manufacturing electronic part

Are you interested in self-healing polymers – must read reviews

How computer modelling & 3D printing create fracture resistant composites – reports Stratasys and MIT researchers

A review on polymer/bioactive glass nanocomposites provides current trends in polymer research

Mannigton converts large stickers from 2010 winter games into commercial flooring

Siver nanowire electrodes for flexible electronics

McMaster university (Canada) researchers developed flexible solar cell technology

Japanese researchers are developing stereo-block type PLAs for high performance materials

Arkema unveils a range of "green" polymers for its textile market

Chinese researchers made a bendy polymer that could separate aromatics hydrocarbons from aliphatic

Japanese scientists report a unique, smart and self-healing polymer nanocomposite hydrogels

Binder free multilayer graphene based polymer composite for high performance supercapacitor electrodes

Alberta scientists help to make Canada’s first bio-composite based electric vehicle body design

How plastics helping revolutionize stretchable electronics applications – a review, not to be missed!

French scientists tout first use of nano-structured assemblies that could revolutionize dentistry

For the first time, IBM researchers showed 3D molecular structure could be observed

Univ of Texas @ Austin scientists reported method to produce a large scale reduced graphene oxide

Teijin Techno Products claims to be world’s first mass producer of aramid nanofibers

Can you “Cool Your Roof” - reports researchers from Chinese Academy of Sciences, Beijing

Strain Paint: an alternative to strain gauges

Polymers can be used to package insulin into a pill for diabetes treatment reports Indian scientists

USA researchers develop all-polymer multilayer coating to retard fire and to suppress smoke

Work of North Carolina State Univ. researchers shows how to remove radioactive elements from drinking water

MIT researchers develop first Solar Thermal Fuel storage platform in solid-state

James Cropper Speciality Paper touts recycling of disposable coffee cups

Canadian researchers claim world’s most efficient “inverted” OPV solar cells

Polymer bank notes on the rise to avoid counterfeit paper currencies

Polymer helps to designing higher capacity Li-ion battery

Advanced nanocomposite membrane technology of NanoH2O turns it to a Global clean technology company

Practical Devices provide useful power from the body

German researchers unveiled a green approach to electrospinning technique for making biodegradable nanofibres

GM recycles oil soaked booms from the Gulf of Mexico for its Chevrolet Volt under hood parts

Braskem S.A. is leading the way to manufacture biobased polyethylene using catalytic dehydration

Are you an injection moulder, you may want to read the ultimate in mould cooling article

If you follow plastics electronics - follow Unidym’s innovative product lines

Harvard Univ researchers show how soft robotics could navigate a difficult obstacle

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AMI unveils the North American Bioplastics technology agenda

Work of North Carolina State Univ. researchers shows how to remove radioactive elements from drinking water

A new microcellular injection molding process for polycarbonate using water

It is time to make “Perfect Plastic” reports UK researchers

UC Berkley researchers have developed paper thin e-skin that responds to touch

Brazilian scientists are actively pursuing bioplastics research and innovation

Stratasys touts World’s first color multi-material 3D printer for rubber & plastics products

Battelle researchers are improving PLA for injection molding applications

Korean scientists provide a different twist to the “Smart Window” technology

In Milan, art and science get together to showcase Vegetal, weather resistant designer chair

USA researchers report polymeric blood-resistant surgical glue that can repair minimally invasive heart defects

Rice Univ (USA) researchers grew high quality graphene from polystyrene, cookies, grass, cockroach leg & dog feces

University of Texas at Austin researchers show use of polymer membranes for fracking in shale gas

Green Composites - all you wanted to know about

Can polymer reinforced aerogel make a space mission? University of Akron researchers think so!

Researchers develop unique printable thin film supercapacitor using SWCNT

Using biodegradable polymer, University of Basque country researcher report on bone regeneration

ZogglesTM earns Invention of the year 2010 award and keeps the fog away

Stanford Univ researchers make Jell-O-like conducting polymer hydrogels

Umass, Amherst researchers find ways to hold 300 kilograms of weight using sticky tape

Polymers help Addidas to launch lightest soccer boots and 2010 FIFA World cup match ball never seen before in the field

Something old... Something new.... produces an interesting marriage

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Rutgers Univ researchers moves plastic electronics with graphene based PS thin films

A team of researchers demonstrate plastics and graphene can work together to make touch screen device a reality

Bayer uses PC film Makrofol? for it's new Innosec Fusion? technology to stop counterfeiting

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Will your windows generate power one day?

Can polymer reinforced aerogel make a space mission? University of Akron researchers think so!

Can Gas Jet process challenge electrospinning in producing polymeric nanofibers?

Yale scientists develop high performance thin film composite membrane

Harvard University researchers design stretchable, transparent ionic conductors

US and South Korean researchers develop a printing technique to make high performance CNT transistors

Can you 3D print yourself? TwinKinds of Germany shows just that!

Norner touts major research project on polymers based on carbon dioxide

Stanford researchers use cheap plastics film to make safe lithium batteries

How blood can clot to heal a wound - Science reports

Scientists from Sweden and USA showed electronics can truly be organic or say truly be plastics

MIT researchers show how to draw Polyethylene as nanofibers and get a very high thermal conductivity

NIST develops greener solution to challenge commercial fire retardants

Oil-SAP, a novel development to clean-up oil spill & recovery from Penn State University, USA

Non-toxic, liquid bandage from Chesson Labs of Durham, NC is ready for the healthcare market

Plastic Logic sees mass production of flexible display in 2008

Bio-succinic acid is becoming new green platform chemical for plastics

Austrian scientists claim to be the first to have developed an image sensor that is fully transparent

Carbon3D, a Canadian company unveils a breakthrough technology for layerless 3D printing

Cima NanoTech flexes mussels with its non-Indium Tin Oxide, high performance transparent conductors

Current status in graphene based polymer nanocomposites – a review

Swedish researchers show highest reported charge capacities for all polymer paper-based battery

Nanoparticle coating prevents ice build up

Self-healing plastics healing like human skin

US researchers develop shape memory polymer nanocomposites exhibiting fast actuation speed

Can you “Cool Your Roof” - reports researchers from Chinese Academy of Sciences, Beijing

Prof. Alan Heegers group demonstrated the potential of plastics solar cells

Austrian researcher reports new opportunities from Silicon oxide Nanofilms

Researchers show stretchy battery for flexible and stretchable electronics

3D systems introduces non-halogenated flame retardant for aircraft applications

Plastrec, a Quebec recycler unveils recycled PET production combining two plastics technologies

Singapore researchers touts corn starch can help solve body armour and protective sports padding

Plastics help design non-shatter pint glass to prevent pub attacks

New ambipolar polymer beats others: reports US researchers

Sabic Innovative Plastics unveils its newly developed a clear flame retardant Polycarbonate copolymer

World’s first all-plastic LED lamp comes from Japan

Block copolymers could create hard disks with 10 tera-bit-per-Square-inch:Researchers predict

MIT team aims to develop application specific surgical adhesives to seal tissues

Princeton university researchers embedded piezoelectric material onto polymer as energy harvester

Wax could be green too – touts GreenMantra Technolgies!

Current trends and future prospects for flame retardants in polymeric materials

Scientists from IBM and Stanford University are developing new plastics recycling process

UCLA scientists showed how simple it could be to make conducting polymer thin films

Stanford university researchers detect mercury ions in sea water using organic polymer transistor sensor

Caltech researchers show through telechelic polymers how to produce a safer and a cleaner fuel

From Cellular to Microcellular Foam

ImageThe concept or the technology of microcellular thermoplastic foam appears to be an interesting extension of the cross-linked polyethylene foam. Nonetheless, its advantages and recent developments have spurred many commercial uses. Given the uniqueness of the technology, the breadth of application is continuing to grow and the future has practically no limits.

A bit of History

Microcellular thermoplastic foam came to the public in the eighties from MIT1, unique in its cell size (100 - 101 microns) to differentiate from the conventional cellular products with cell size ranging from 102 to 104 microns. It employs inorganic physical blowing agent in its super critical state to create a swarm of bubble in the polymeric matrix. In the midst of ozone depletion concerns, it soon caught public's attention and support. In ten years, it moved from batch mode to continuous process. When Trexel is formed to bring this microcellular thermoplastic foam or Mucell technology to plastics industry, it was clearly focused on the material instead of the product. It turned out to be a clever approach in licensing the Mucell technology to equipment suppliers as well as foam producers, quite promising in bridging the gap between polymeric materials and polymeric foam products2.

 

The Advantages

The unique features of microcellular foam (MCF) are fine cell size, high cell density, inorganic blowing agent, and no nucleating agent. Since the cell is very fine, without careful attention, MCF may be taken as a plastic material rather than a cellular product.

 

When cell is reduced to micron range without using nucleating agent, decreased convection in the cell and less open cell make a uniform structured product with better insulation characteristics. Some mechanical properties, especially propagation related; such as: notch and fatigue, appeared superior to the parent plastic material. It was attributed to cell as propagation absorber. Conventional polymeric foam is known for its high performance/weight ratio, which increases as cell size decreases and cell integrity improves. This evidently enlarges property spectrum3.

 

Mechanisms

Foaming is a phase separation phenomenon governed by thermodynamic-driven kinetics. A common practice is to establish a positive super-heat, or supersaturation, that volatile phase tends to conglomerate into spherical gas bubbles. In general, saturate with gas, then apply vacuum or heat, or both, to induce thermodynamic instability. Bubbles appear. In the eighties, MIT tried carbon dioxide in the super critical state to polystyrene first, owing to its amorphous structure and favorable Tg4, then to various semicrystalline polymers to obtain the microcellular foam. In contrast, traditional cellular foam technology controls nucleation via nucleating agent5, whereas MCF by super critical carbon dioxide, which, namely, plays a dual role; blowing agent and nucleating agent6.

 

X-linked PE foam producers tempted compounding chemical blowing agent (CBA) into PE, and X-linking first to enhance polymeric strength, and then decompose the CBA to liberate nitrogen to form cellular structure. The less the expansion, the finer the cell. Fewer than ten times expansion, ten microns or under can be achieved. At thirty times expansion, the cell is in the hundred microns.

 

Cellular vs Microcellular

The conventional cellular foam (i.e. cell size in mm) is generally blown with non-volatile hydrocarbon blowing agent as opposed to microcellular foam with volatile carbon dioxide or nitrogen. The latter is characterized by aggressive, highly nucleated, and limited expansion in contrast to the former less aggressive, lowly nucleated, and large expansion. It was also noted that the cellular nucleation is heterogeneous in nature (i.e. adding nucleating agent), and microcellular homogeneous (i.e. without nucleating agent). Microcellular foam contains 108 cells/cm3, and cellular foam around 104 - 106 cells/cm3.



The aggressive expansion in microcellular makes the polymeric strength very critical in maintaining cell integrity, even more so in continuous extrusion, cell coalescence becomes otherwise inevitable. Thick cell wall is thus very necessary, and that lays the expansion limit to around ten times, whereas the cellular foaming can achieve over fifty times expansion. Saving materials can justify the material handling investment, therefore, cellular foam is still quite popular in the market.



However, when expansion reduces to 30 to 70% weight reduction, about two to three times expansion, quite a few polymers are qualified for processing and foaming. It became a great opportunity for engineered polymer, where material saving is rather substantial. Nylon, ABS, PC, and filled PP are good examples in MCF injection molding7. Publications in methods and technologies can be found in references6,7.

 

From Pilot to Commercialization

Pilot extrusion results were presented in the nineties. Trexel was formed to take over commercialization. However, consistence in commercial-scale polystyrene MCF extrusion became a concern. In the late nineties, efforts were then shifted to low expansion injection molding with special SCF injection design to render fine cell possible. Excellent cell integrity made unique features over gas-assisted injection molding technology. Other benefits were quite substantial: less tonnage, less cooling time, less residual stress, less warpage, less shrinkage…etc. Combining the processing and material saving benefits, licensing agreements soon expanded into international mode8. In December 2003, some interesting papers were presented in the Polymer-Supercritical Fluid Systems and Foams conference held in Japan9. More recently, plastics machinery manufacturer of Japan (Kawata Mfg. Co., Ltd., Osaka) developed a microcellular foam (MCF) extrusion process for biodegradable polylactic acid (PLA) resin. Kawata's MCF process is claimed to provide controllable expansion of up to 40 times.

 

Current Trends

Trexel has been working in quite a few fronts to advance this technology, especially in injection molding license, hoping to establish a solid material technology. Institute of Plastics Processing (IKV, Aachen, Germany) is committed to make specially designed injection unit for MCF injection molding10.



Lately, Univ. of Toronto formed a consortium for Cellular and Microcellular Plastics, focusing on extrusion, injection molding, and fundamental concepts. Univ. of Wisconsin and Ohio State Univ. are sponsored by National Science Foundation (NSF) to explore the application possibilities for nano particle induced MCF. Other institutes, such as: Kyoto Univ. in Japan, Washington Univ..… are trying to expand the MCF application spectrum.

 

Predictions or Future Realities

When nano-particle becomes a great topic in enhancing polymer's mechanical property, it is a natural combination into microcellular foam. Nano particle could be an ideal nucleating agent, and even dispersion can generate interfacial volume as nucleus for microcellular morphology. This nano-microcellular polymer could be a great product with an impressive performance/weight ratio; excellent physical, mechanical and thermal properties.



The other challenge is to explore the finest cell size, highest cell density, and MCF density. Is nano-cellular possible? It will then be a pure material development. Let's keep our eyes and ears open.

 

References

1. J. E. Martini, Master's thesis, Massachusetts Institute of Technology, 1982
2. N. P. Suh, Foreward, Microcellular Processing, K. Okamoto, Hanser, Munich, GE, 2003
3. N. P. Suh, Ch. 3 "Microcellular Plastics", Innovation in Polymer Processing, ed. J. F. Stevenson, Hanser, Munich GE, 1996
4. K. W. Suh, Ch. 8 "Polystyrene and Structural Foam", Polymeric Foams, ed. Klempner and Frisch, Hanser, Munich, GE, 1991
5. S. T. Lee, Ch. 4 "Foam Nucleation in Gas-Dispersed Polymeric Systems", Foam Extrusion, ed. Lee, CRC Press, Baton Roca, FL, 2000
6. C. B. Park, Ch. 11 "Continuous Production of High-Density and Low-Density Microcellular Plastics in Extrusion", Foam Extrusion, ed. S. T. Lee, CRC Press, Baton Roca, FL, 2000
7. K. T. Okamoto, Ch. 8, "Microcellular Molding: Case Studies", Microcellular Processing, Hanser, Munich, GE, 2003
8. H. Eckardt, "Thermoplastic Structural Foam; Wellknown and New Process", Blowing Agent and Foaming Process 2003 conference, spon. RAPRA, Munich, GE, 2003
9. T. Kanai, H. Kawato, H. Goda, and Y. Otsuki, "Control Factors of Foam Structure and Properties in Microcellular Foaming", Polymer-Supercritical Fluid Systems and Foams, Tokyo, 2003
10. W. Michaeli and S. Habibi-Naini, "Investigation on Foam Injection Moulding with a Special Moulding Nozzle", Blowing Agent and Foaming Process 2003 conference, spon. RAPRA, Munich, GE, 2003

 

Shau-Tarng Lee

Shau-Tarng Lee, Sealed Air Corporation, 301 Mayhill St., Saddle Brook, New Jersey 07663, USA



Dr. Shau-Tarng Lee was born and raised in Taiwan, ROC. He received his Bachelor's degree from National Tsing-Hua University, Master's and Ph. D. from Stevens Institute of Technology in New Jersey, USA. He has over twenty years experience in polymeric foams with over 80 publications, including 21 US patents. He is a fellow of Society of Plastics Engineers, elected in 2001. Currently, Dr. Lee is with Sealed Air Corp., and resides with his wife, Mjau-Lin, and the third son, Tom in New Jersey.