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Info Center > Story Details

Plastics Technology "Keep it Clean"

Plastics Technology | December 2009
By Matthew H. Naitove, Executive Editor

 "PLA is very sensitive to contamination—even more than PET," cautions McIntosh. "You must keep it clean. All the more so if you run a PET or PS line right next to a PLA line or switch between materials on the same line." Early on, Hazleton shifted back and forth between PET and PLA on one extrusion/thermoforming line. "That's a killer," says McIntosh. PET and PS won't melt at the low temperatures used to process PLA. A speck of unmelted PS will show up white in a clear PLA cup. And a bit of unmelted PET will appear like a dimple. "We had to get everybody on board about this. Workers must learn that this clear cup is not the same as that clear cup, so regrind doesn't get mixed. Putting regrind into a clear product is challenging enough as it is."
 

Above is the giant 7-in. extruder that puts out 4000 lb/hr of PLA sheet, It carries a UnaDyn insulated hopper and additive feeder for blue toner to mask the yellowness of PLA.

When McIntosh talks about getting "everybody on board," he includes the packers of finished cups. PLA is very brittle and tends to shatter into very sharp fragments. McIntosh remembers how his work clothes were shredded by broken shards of PLA in those early days at Hazleton. "The problem was that we started out thinking we could handle PLA after forming just like PET, which is a much more robust material." PLA trims easily because of its brittleness, but finished product must be handled gently. Dustiness of the brittle material remains an issue. "We're even talking with sugar mills to see how they handle the dust," says Dave Grinage, manufacturing development manager.
 

The Hazleton team did find some positives in working with PLA. McIntosh says PLA has better melt strength than PP, and energy consumption in processing is much less than for other materials, owing to the low melt temperatures (390 to 430 F). PLA also can run on the same extruder screw and thermoform tooling as PET.

F-K's Greenware volume grew sufficiently to dedicate a line at Hazleton to PLA full time. After two years, a line in Greenville, S.C., began extruding and forming PLA lids on a part-time basis. But Fabri-Kal needed still more capacity. So in May of 2009, Line 5 was installed at Kalamazoo, dedicated to inline extrusion and forming of PLA. (The other four lines there process a range of rollstock for short runs.) This is the largest line operated by Fabri-Kal and is reportedly the largest used for PLA anywhere. It has a 7-in., 30:1 extruder capable of 4000 lb/hr. Built by PTi/Processing Technologies International, it extrudes 53-in.-wide sheet, which goes into a 50-in.-wide mold that has 80 cavities for cups of 12 to 24 oz. (The line at Hazleton runs 48-in.-wide PLA sheet on a 6-in. Welex extruder at under 3000 lb/hr).

"We started up a brand-new line with a new mold and a new crew of people," recalls McIntosh. Thanks to the experience gained at Hazleton, "It was actually a better startup than any we've had with PS. It took two weeks, which is normal, and we were running zero scrap within six weeks."

"It's one of the best lines in the plant in uptime efficiency," says senior process technician Ray Torres. Workers on Line 5, like Torres, Don Drenten, and Clemente Vigil wear T-shirts that jokingly proclaim, "Survivor of Line 5 Launch, May 2009."

"We're proud of them," sums up plant manager Lisa Shincariol.

The PTi extrusion system feeds a thermoformer from Thermoforming Systems, a trim press from Brown Machine, and a Brown lip roller. The lip roller had to be fine-tuned for running PLA at high speeds. "We had to find the right balance of heating and cooling and the right auger screw design," says McIntosh.

A granulator under the trim press sends PLA regrind to a surge bin and then to a Maguire blender, where it is combined with virgin PLA pellets. The mix is conveyed 4000-lb/hr UnaDyn crystallizer with a cyclone separator to remove the dust. After the crystallizer comes a UnaDyn dryer, and then material is conveyed to an insulated hopper atop the extruder with a UnaDyn color concentrate feeder to add a blue tint to mask the yellowness of PLA. Quality engineer Mike Saunders notes that color checks are a new QC task for the plant since PLA was brought in.

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