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Horizons: what's shakin'?

My first impression of plastics was that of well-chewed chewing gum. They are soft, sticky, and impossible to process. Perhaps the most unappreciated miracle of the twentieth century is the plastics-processing industry. This group of inventive people has mastered the ability to process this stuff, and they do it in so many different ways. Processing machines such as injection molding machines, extruders, and especially those tall blown-film machines leave me in awe. Watching this soft sticky stuff being shoved around is mesmerizing.

We've made exceptional strides in plastics processing, yet there is more that we can learn about what and how particular actions affect plastic materials. Plastics processors need the help of materials engineers. After all, they are dealing with a material that is difficult to process and affected by subtle changes in temperature, moisture, and in-process handling.

For example, vibrations from machinery and the shop floor can help or hinder processing. Most of the time, especially with machines, the engineer tries to eliminate vibrations to keep machines and people in one piece. On the other hand, vibrations can have positive effects. In some cases these positive effects can be cost-effective; and in others they require careful planning and added processing. Vibrations, ranging from a simple shaking to ultrasonics, during processing are important because their effects extend to the molecular level.

Plastics are based on polymers that are made up of very long molecular chains. In the melt or amorphous state these chains form an entangled mass much like a bowl of spaghetti. It is these entanglements that make chewing gum and plastics, especially thermoplastics, so sticky and viscous. By inducing molecular motion, vibrations can untangle the chains and reduce viscosity.

For several years I abstracted papers for SPE's ANTEC. This review gave me a global perspective on the papers being presented. On this basis, Maro presented Future Technology Awards at several ANTECs to celebrate accomplishments and to predict the future. The very first award in 1997 went to Dr. Jean Pierre Ibar for his paper "Melt Viscosity Reduction of Plastics by Vibration during Filling in Injection Molding." He showed, for example, a 40-Hz vibration could reduce polycarbonate viscosity from above 100,000 poise at 175[degrees]C to below 20,000 poise or a viscosity comparable to the 300[degrees]C viscosity. Assuming the 300[degrees]C viscosity was a workable viscosity. A processor now has only to heat the resin to 175[degrees]C, rather than 300[degrees]C, for the same effect. A significant change, wouldn't you say? This development has been fruitful for Dr. Ibar. A quick patent search showed nine Ibar U.S. patents on this subject since 1994.

I suspect that controlled vibrating of the melt is not the easiest thing to do during processing, especially considering the complexity and massiveness of some machines. Still, the potential cost-savings of an order of magnitude drop in viscosity is worth a second look. Our industry is built on inventiveness. One day, someone will figure out an ingenious way to effectively use this concept and bring the plastics industry to a new processing era.

Viscosity is not the only feature of plastics affected by vibration, nor are low-frequency vibrations the only kind of vibration. Among other things we have the wonderful world of ultrasonics. Not only can we see our grandchildren before they are born, but we can weld things, cut things, clean things and so on.

Since 2001, I have collected 45 ultrasonic patents links. This does not include ultrasonic welding or ultrasonic testing. Nine of these seem directly related to processing. U.S. Patent #6,713,600 deals with ultrasonic-induced crystallization; #6,682,660, ultrasonic-induced polymerization: #6,545,060, rubber devulcanization; #6,528,554, polymer blending; #6,511,563, making fiber-reinforced composites; #6,464,485, ultrasonic injection molding of an optical disk: #6,395,216, assisted melt extrusion; #6,365,695, fluidized-bed olefin polymerization; and #6,361,733, ultrasonic injection molding.

Two of the above are by Professor Isayev and colleagues from the University of Akron. The first, #6,713,600, deals with extrusion of slowly crystallizable resins such as polyethylene terephthalate. Subjecting the stream to ultrasonic waves perpendicular to the flow markedly increased crystallization and eliminated later cold crystallization. In # 6,528,554, ultrasonic treatment during blending of dissimilar polymers significantly enhanced their molecular interactions and miscibility.

These few patents indicate some interesting possibilities. Processors, especially those interested in moving beyond the limits of existing technology, should take a look at "What's Shakin'."

Note: I would be pleased to send any interested reader the patent references from the Maro Collection for Vibrations and Processing. Send an email request to cornelrd@bee.net and I will return an email message in which each patent is linked to the text version of the patent on the U.S. Patent website.

Roger D. Corneliussen is Professor Emeritus of Materials Engineering, Drexel University, in Philadelphia. He is editor of Maro Polymer Alerts and the Maro Polymer website (www.maropolymeronline.com). He has been active in SPE since 1962 and has served on the board of the Philadelphia Section and as National Councilor. For his Maro Patent Alerts he reviews all U.S. Patents" weekly, makes links to the polymer-related patents, and sends the links daily to subscribers. There comments in Horizons are based on the weekly selection process. Maro email Alerts are available to SPE members without charge--simply email a request to cornelrd@bee.net.
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Title Annotation:polymer-related patents
Author:Corneliussen, Roger D.
Publication:Plastics Engineering
Geographic Code:1USA
Date:Oct 1, 2004
Words:907
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