By Jan H. Schut
Imagine molding plastic with no energy cost – zero, zip, nadda, as the saying goes. Karl von Kries, CEO of startup LightManufacturing LLC (www.lightmanufacturingsystems.com) in Pismo Beach, CA, has done just that. He’s invented the world’s first solar-heated plastic molding and is launching solar-heated rotational molding commercially this month at SPE’s GPEC (www.sperecycling.org) conference in New Orleans, LA, on March 20-22. The patent-applied-for technology (U.S. Pat. Applic. # 20120104658) was first presented last November at the Association of Rotational Molders conference in Minneapolis, MN.
Don’t confuse von Kries’s approach with using solar electric power to mold, which has been done before. Penninsula Packaging (www.penpack.com) in Exeter, CA, generates about a third of its power for sheet extrusion and 14 thermoforming machines with a field of hundreds of solar panels. Instead von Kries concentrates sunlight directly onto molds to melt and mold the plastic. Cycle time is only slightly longer than conventional rotomolding, he says—25 minutes vs. 19 minutes for the same part. “We’re seeing now how much faster we can go,” he says. “If we add more Heliostats, we think we can drop cycle time a lot.”
Also at GPEC, two new environmentally friendly materials will be introduced: “hyperbranched” recycled PLA with melt strength better than, or comparable to, virgin PLA by Interfacial Solutions (www.interfacialsolutions.com), a contract R&D firm in River Falls, WI, and new developmental 25% to 50% starch-filled soft elastomers down to 55-65 Shore A from bio-plastic compounder Cereplast Inc. (www.cereplast.com), El Segundo, CA.
THE ICARUS FACTOR
LightManufacturing’s game-changing solar rotational molding machinery is built into a shipping container. It needs no building, electrical hook up, or even concrete pad. The container can be deposited on flat ground or in a customer’s parking lot (anywhere there’s enough sun) and mold parts closer to where they’re needed. It can’t run at night, and it can’t run in many parts of the country, but von Kries figures it will work on almost half of the earth’s land surface, certainly throughout the South and Southwest United States.
In the early ‘90s, von Kries worked in engineering and new product development at rotational molder Hardigg Industries Inc. in South Deerfield, MA, now part of Pelican Products Inc. (www.pelican.com), Torrance, CA. In 1994, he took a project for portable sound equipment for the military and spun it off as a separate company, called Technomad LLC (www.technomad.com) with offices in Boston, MA, of which von Kries is still CEO.
Technomad’s audio products were housed in rugged ¼ to 3/8-inch-thick, rotomolded medium density PE cases, molded by Hardigg. von Kries moved to California in 2005 and saw solar mirrors, or heliostats, heating steam turbines with reflected sunlight. He got the idea to heat rotational molds that way, too, saving a lot on energy. By 2009, he set up LightManufacturing with investors and was designing the first solar-heated roto-molding.
He started using commercially available heliostats, but the supplier went out of business. So he and his team spent two years designing their own heliostats, which he says are the lowest cost per reflected watt on the market—2,000 watts of heat for about $1,400, or $1.60 per watt. The firm’s H1 Heliostats became a separate product selling to architects and home owners for green home heating.
H1 Heliostats are 2.3 square meter mirrors made of aluminum-coated PET film stretched over a frame. The reflective film has a threaded rod on the back that adjusts the mirror shape to focus light on a larger or smaller area to fit mold size. “If you walk around in the beams of light, which I do all the time, they feel like a strong space heater,” von Kries explains. Heliostats can stand 20 mph steady wind and gusts to 60 mph, or up to 95 mph in “safe position” sideways to the wind, LightManufacturing says. If they’re damaged, it’s relatively easy to replace the reflective film.
MOVE HEAT, NOT MOLDS
Solar molds aren’t mounted on massive articulated arms on a central rotor and moved in and out of a convection oven like conventional rotomolding. The solar rotational molding machine has two chambers, each with a molding station and a large Lexan polycarbonate window on one side to let light in. Solar-heated molds rotate on two axes, but in fixed position.
Twenty heliostats are assembled and installed in an array in front of the windows to direct sunlight first onto one mold, then onto the other, while the first mold cools. Radiant heat from sun light goes into the mold without heating the surrounding air or the framework holding the molds, so cooling is faster than with conventional molding, von Kries says. Temperature inside the molding chamber reaches only about 180 degrees F compared to 500 degrees F in a gas-fired convection oven for conventional rotational molding.
The solar machine uses standard aluminum or steel molds up to 48 in. on the diagonal, coated with black heat-absorbing material. Optional wireless thermocouples can provide real-time temperature data. Solar panels installed on top of the enclosure power motors, cooling fans and electronics.
LightManufacturing now has 10 employees and several solar rotational molding machines in beta test sites in the U.S. for over 18 months, producing parts commercially for Technomad and other customers. They have molded medium density PE and LLDPE, but haven’t yet tried PP or high heat materials like nylon. A turnkey system costs “well under” $100,000, von Kries says, including two molding stations, 20 H1 Heliostats, two photovoltaic panels, and wireless computer controls. A conventional rotational molding machine with a convection oven costs around $300,000.
Because solar rotational molding runs off-grid, it could be attractive in third world markets or for disaster relief, molding things like water tanks or sectional emergency housing without needing outside power. But von Kries argues that the competitive advantage is most compelling in a developed market with high energy costs. “Once a few companies have it, they’ll eat the competition,” he predicts.
“Rock-and-roll” type rotational machines with multiple arms could be adapted to solar heat using “a single large horizontal window,” von Kries says, “and large parts could be molded in site-assembled enclosures, instead of the shipping container approach.” Direct solar heat could also be applied to other molding processes by putting solar arrays onto factory roofs and using light pipes to bring radiant heat into the building. Thermoforming and compression molding could be adapted fairly easily to solar heat, he thinks: “Those are the next things we’re going to look at.”
NEW RECYCLED PLA, NEW SOFTER STARCH-FILLED ELASTOMERS
Interfacial Solutions’ technical director, Adam Pawloski, is introducing new post-consumer and post-industrial recycled PLA compounds at GPEC, made with the company’s reactive process for hyperbranching PLA. Interfacial introduced its patent-applied-for hyperbranching chemistry (International Pat. Applic. # WO 2010/1080760 A2) five years ago in compounds with virgin PLA to improve melt strength for durable applications and extrusion without a penalty for processability. Hyperbranching is now being used with scrap PLA to improve mechanical properties “to meet or exceed those of virgin PLA,” Pawloski says.
Hyperbranching adds lots of short chains onto linear PLA molecules, increasing melt strength without increasing viscosity and die pressure, according to tests done by the Macosko group at the University of Minnesota (research.cems.umn.edu) in Minneapolis, MN. This gives hyperbranching an advantage compared to several commercial chain extending additives for PLA like CESA-extend masterbatches from Clariant Corp. (www.clariant.com), Charlotte, NC and Joncryl ADR from BASF Group (www.basf.com) in Germany, which increase PLA’s melt strength, but also increase shear viscosity and die pressure.
Interfacial is commercializing several new grades of hyperbranched post-industrial recycled PLA in its “de Terra bio-based polymer” product line. For the new recycled PLA grades, Interfacial tested reclaimed PLA from eight post-industrial and one post-consumer source and reports this data as well. Post-industrial sources tested include mixed reground card stock, recycled water bottles and cups, and recycled reground gift cards. Properties of the scrap materials, especially melt flow index and impact strength, vary widely, but can be adjusted using hyperbranching to meet the needs of an application. Interfacial will make custom recycled PLA on a toll basis for customers or license its technology for companies to use in-house.
Cereplast’s chief technology officer Kelvin Okamoto is introducing softer starch-filled elastomers than the company has presented before. Its patent-applied-for (U.S. Pat. Applic. # 20090048368) starch-content elastomers were introduced at NPE 2012 last March in Orlando with two grades, Hybrid 111D with 25% starch and Hybrid 112D with 50% starch. Both elastomers, however, only go down to 85-95 Shore A in softness for injection molded applications like soft-grip handles and soft-touch automotive parts.
|Tensile Strength @ Yield||MPa||4.4||5.7||4.2|
Cereplast is introducing new 25% starch-filled TPEs as soft as 55-65 Shore A hardness and thinks the elastomers can be made even softer–down to 30 Shore A–still with 25% starch.
Cereplast has since developed even softer elastomers with 25% starch down to 55-65 Shore A hardness in a range of melt flow indices for injection molding and extrusion applications. These softer elastomers don’t have commercial grade names yet, but are available for testing. Cereplast’s Okamoto believes they can go even softer–down to a 30 Shore A.