Foaming Bio-Polymers

NatureWorks LLC, a subsidiary of Cargill, had been trying to foam their bio-resin, polylactic acid ("PLA") and because they were not satisfied with field tests they had been conducting with conventional technology foam screws, approached us in January of 2005.

The scientists from NatureWorks® told us they needed low shear screw technology and they believed that Turbo-Screws® technology foam screws would fit the bill.

Three months later, trials began at one of our Turbo-Screws® technology licensees' food packaging operations in North America. Trials were conducted on a standard 4.5" x 6.0" tandem extrusion system.

NatureWorks® has three types of PLA foam resin: (i) low heat or amorphous PLA; (ii) mid-heat or semi-crystalline PLA; and (iii) high heat or high-crystalline PLA. Each has its own challenges.

Turbo-Screws® technology feed screws successfully foamed the amorphous and semi-crystalline PLA resins. Trials are continuing on the high-crystalline PLA resin and we are very confident we will shortly be announcing a successful conclusion to those trials.

The trials for the amorphous and semi-crystalline PLA were so successful that in June of 2006, Plastic Engineering Associates Licensing, Inc. signed its first Turbo-Screws® technology license for the commercial production of foam PLA. A second Turbo-Screws® technology license for the commercial production of foam PLA quickly followed in 2007 from a major North American food packager.

Although most of the details of the development trials are still subject to a confidentiality agreement between NatureWorks® & Plastic Engineering Associates Licensing, Inc., some general observations can be disclosed about our experience with PLA.

First, there is no doubt that a tandem foam extrusion system is the preferred melt delivery system for extrusion of foamed PLA. Second, because of the low glass transition temperature of PLA, the ability to obtain and maintain melt temperature is critical to achieving success; thus, to be successful in foaming PLA it is vital to have technologically superior screw technology such as what Turbo-Screws® presents. In fact, Turbo-Screws® technology is listed as a preferred equipment partner on NatureWorks®, LLC's site. Finally, keep in mind that PLA is not polystyrene! You will need help in transitioning and there is no better company to go to for foam expertise than Plastic Engineering Associates Licensing, Inc.; after all, NatureWorks® LLC did, so why shouldn't you?

If you would like to keep up with our company's PLA Foam development trials, click here to receive our company's PLA Foam newsletter.

Click here to view a conference paper on our new Turbo-Screws® technology for processing NatureWorks' Bio-Polymers.

We are pleased to offer to the industry commercial licenses of Turbo-Screws® technology for processing NatureWorks® Bio-Polymers. Click here for more information.

Turbo-Screws® technology is the preferred extrusion screw technology for processing Natureworks® LLC Bio-Polymers. There are two commercial scale licensees, both located in North America, using Turbo-Screws® technology for foaming Natureworks® bio-polymers. We are entering our fourth year of development of specialized hardware and process technology (screws, dies, downstream tooling) for PLA foaming by direct gas injection using the tandem foam extrusion process. We currently offer a 4.50" x 6.00" (120mm x 150mm) and 6.00" x 8.00" (150mm x 200mm) sized Turbo-Screws specifically designed for this family of bio-polymers. Output rates are presently in the 75% to 85% range of industry standard polystyrene output when using the current generation Turbo-Screws® for PLA foaming.

Natureworks® bio-polymer resins, as marketed under the Ingeo® brand name, are available in a variety of grades depending upon the end applications, e.g. injection molding, solid sheet extrusion, bi-ax extrusion, extrusion and injection blow molding and of course for direct gas injection extrusion foaming. Technical data sheets and in many cases, processing guides may be found on their web site at www.natureworksllc.com. The foam processing guides are being given directly to end user customers on a case by case basis, so they will not be found on their website yet.

Presently there are commercial foam grades of Natureworks® Bio-Polymers that we would refer to as "semi-crystalline" having a heat range of up to 55 to 60 degrees C. We have seen no practical density limitation in foaming, as we have achieved densities in both sheet extrusion and thermoforming significantly below those that we run in polystyrene foam applications for meat trays and hinged lid containers, etc.

For example, a sheet density of 3.0 lbs. per cubic foot ( 48 kg/m3) is easily achieved, although for meat tray type materials we typically run higher densities, more in line with current North American industry standards. Closed cell counts of 90% and greater are achievable, although it is also possible to make a high percentage of open cell structures with this material too. As for the thickness range, we have run from a low of 0.020" (0.5mm) all the way to a thickness > 0.200" (~5mm), essentially the typical range for thermoformed food containers. The material is easily thermoformed and trimmed into useful finished containers. Many of the traditional blowing agents used in direct gas foaming have been run, although most of our experience to date has been with hydrocarbons.

Higher heat capacity resins (> 60 degrees Centigrade with a target > 100 degrees Centigrade) have been in development for some time, and in fact we have run a number of them with our second and third generation Turbo-Screws® technology screws specifically designed for PLA foam extrusion. The end goal applications are for hot food contact. This family of resins we refer to as "high crystalline" Natureworks® Bio-Polymers. Since all of the grades in this family are experimental, there is no way to order them commercially yet. These efforts are development projects that have been on-going for some time now.

As for resin pricing and sales, we recommend speaking to the global business development manager at NatureWorks® LLC, Mr. Koen Bastiaens. His email is Koen_Bastiaens@natureworksllc.com. Mr. Bastiaens is responsible for the foams business development and is the appropriate first point of contact for all commercial matters regarding the Natureworks® Bio-Polymer range.

Below is a short movie showing some of our PLA foam extrusion development work. Click on the picture to play.

Here's some photographs from our latest PLA foam development efforts.