This year'sNational Plastics Exposition in Chicago (June 22-26) willbe a great place to scout new green materials' technologies. Look for the latest engineering ideas rangingfrom bioplastics to new materials and processes that reduce component weight.

Onepromising idea for design engineers is microcellular foam, which will be demonstratedat the Engel booth (24000) in McCormick Place South.

Controlleduse of supercritical gases such as nitrogen during injection molding produces a 10-percent-or-more reduction in part weight and significant energy savings. And becausecycle times are reduced, presses are 20 to 33 percent more productive. The technology, originally developedat MIT, is targeted at precision and engineered plastic components with maximumwall thicknesses of less than 3 mm.

Key qualityparameters such as flatness and warpage are also improved because pack andhold phases in the injection cycle are eliminated.

Engineersat Southco, a major fastening technologycompany, are among the super users of the MuCell foam process. "We typically seek to achieve a five-percentweight reduction, but our customers aren't overly concerned with that," saysSouthco's Principal Engineer Glenn Anderson. "They're primarily afterimproved quality. We do experience cycle-time savings to some degree based onthe part being produced, but that's more of a side benefit at this point intime." Andersonsays Southco has achieved as much as a 40-percent reduction in part weight.

Southcoachieved improved torque strength and better dimensional control on aglass-filled nylon push-to-close part, in addition to improved manufacturingefficiency. Warping and sink marks caused by thick cross sections wereeliminated with the MuCell process. Andersonsays another major benefit is aesthetics.

Auto lever

Southcoleveraged the technology improvements to win business in the automotiveindustry.

"I'm alwayslooking for a competitive edge for potential programs," says Bill Sokurenko,business development manager at Southco. "The automotive industry is high oninnovation, but they're also very conservative. MuCell helped us win business onlarge automotive programs because of the benefits we gained." Southco has mademore than six million parts a year for automotive customers with the MuCellprocess.

"We'restill looking at highly engineered, functionaltouch points in vehicles that areA-surface components (where MuCell could be applied), whether they're on theinstrument panel or in an around the general cockpit area," says Sokurenko.

The big newpush for the microcellular foam will be in large-part automotive applications.

At the NPE,Engel will be showing parts made on a 1,000-ton press using the "core-back"process, in which the back of the mold is partially extracted after an initialmold filling. The foam continues to expand, creating a multilayer structure.

Mazdaannounced the core-back process reduced component weight up to 30 percentand will be used on parts for 2011 model-year cars. Initial target applicationsfor the process include instrument panel retainers and door panel liners.

"When youcombine core-back and the MuCell process, you can essentially saturate the polymerwith super-critical fluid, or gas in its super-critical state, while keeping themold closed under pressure," says David Bernstein, president of Trexel, whichwas granted an exclusive license to market the MuCell process. The mold canthen be precisely opened to get maximum expansion. "You get a much thickerpart, but one that is much less dense, in fact as much as 75 percent lessdense," says Bernstein.

The bubbles in the outerlayer are microscopic to ensure necessary strength and rigidity, while the sizeof the bubbles in the core layer can be adjusted to reduce its density asdesired. Because the core back process controls the foam's structure, it can beused to enhance the heat insulation and acoustic characteristics of plasticparts, according to Mazda.

SteveBraig, president of Engel's North American operations, says the process issuited for any flat parts. "Design engineers can now re-think the mechanics onsome existing applications in plastic because dramatic weight reductions arerealistic," Braig says. Trials can be conducted at Engel's factory in York, PA, one of tworemaining factories in the United States that make injection-molding machines.

Implementationof the MuCell process is not easy. Southco's Glenn Anderson says, "A personimplementing the MuCell technology really has a steep learning curve tounderstand how to make the process work and how to ensure reliable output.Also, if you're making a plastic bucket, for example, you may not really carethat much about the mechanical properties. You're interested in how does itlook and how much money can I save. With engineered fasteners, we need to makesure we have the design margins where we need them so that we don't have anyissues downstream. Each tool brought itsown characteristics in terms of how you would mold solid or in MuCell."

Engel'sBraig says, "To succeed with core-back, you need precision machine technology."Position and clamp force need to be precisely controlled.

More than300 machines globally are now making parts with the MuCell process. Othercommercial parts include electrical components, electronics, business equipmentand printer components, as well as packaging containers.  

The processis totally different from gas-assist injection molding, in which gas goes intoa mold cavity following resin injection and is used to push the melt stream tothe cavity wall. In the MuCell process, supercritical fluid is injected in thebarrel, and is part of the melt stream.

The MuCellprocess works without chemical blowing agents, hydrocarbon-based physicalblowing agents, nucleating agents or reactive components. As a result, theTrexel process can handle a wider range of melt indexes than conventionalfoaming processes.

In one ofthe newer developments, MuCell can now be applied to long-fiber reinforcedthermoplastics (LFRT) from Ticona.

"Virtuallywarp-free, light-weight parts molded of Celstran LFRT are now a viable optionfor OEM designers and injection molders developing large parts and structuralprofiles," says Steven Bassetti, marketing manager for Ticona. "The Ticona team, working in conjunction withTrexel, developed extensive data for the Celstran LFRT grades usingpolypropylene and nylon 6 and that will help customers predict the performanceof parts made with the MuCell process using the new screw."

Ticonaproduces LFRT grades through use of  pultrusion technology that fully impregnatesthe long fibers to deliver optimal reinforcement to the plastic matrix. Unlike conventional short-fiber reinforcedmaterials, the longer fibers present in molded parts mechanically interact witheach other to form an internal glass fiber "skeleton" that limits anisotropicshrinkage and greatly reduces warpage.

The newscrew design uses a lower compression ratio, 2.0:1 as compared to 2.5:1, andincorporates significant changes to the center restriction element and thewiping and mixing sections to reduce shear.Testing on these screws has been done using the MuCell process with upto 0.6-percent nitrogen in a Celstran LFRT grade that uses 40-percent glass-fiber-filled polypropylene without observing process variations.

Bioplastics surge

Among othergreen highlights at the National Plastics Exposition will be new plastics made from renewableresources. Some of the key players include:

DuPont (West Hall, booth 113011) isexpected to exhibit its latest plastics made from agriculturally sourced polylacticacid. Sorona EP, HytrelRS and Zytel RS include renewably sourced biobased ingredients and can deliveradditional benefits, such as improved stain resistance, appearance and betterdurability when compared to their petroleum-based counterparts. For example, Sorona EP polymers containbetween 20-percent and 37-percent renewably sourced material (by weight)derived from corn. Initial grades with 15-percent and 30-percentglass reinforcement were made available last year for development programs.

Metabolix (West Hall, booth 119020) willshow products made from its Mirel polymers, which are harvested from vats ofgenetically modified microbes that feed on glucose from plants, such as corn. Metabolixand Archer Daniels Midland Co. arecommercializing Mirel through a joint venture called Telles. The firstcommercial-scale Mirel production plant is being constructed adjacent to ADM'swet corn mill in Clinton, IA. Commercial product is expected to beavailable from the plant this year.  

Dow Chemical (WestHall, booth 13a) has hooked up with Brazilian sugar cane producer CrystalSev tobuilda 700 million lbs/yr polyethylene plant in Brazil – the biggest such plant evercontemplated. The molecular structure of the sugar-derived polymer will beidentical to the structure of plastics made from naphtha or natural gas liquids.Dow is the biggest producer of PE in the world. The plant is expected to startproduction in 2011 and will have a capacity of 350,000 metric tons annually.