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Breakdown breakthrough?

Compostable films made with soy proteins are now technically viable according to new research from Michigan State University. Next up: overcoming scale and cost hurdles.

A new type of soy-based polyester film that biodegrades via composting has been produced on laboratory-scale equipment at Michigan State University's Department of Chemical Engineering East Lansing MI. Initial applications of the technology will focus on product applications such as lawn and leaf bags trash bags and agricultural mulch film. But the films can also be used for packaging applications says Dr. Ramani Narayan who is Professor of Chemical & Biochemical Engineering at MSU and who pioneered the development of the new plastic. Initial packaging applications might include carry-out bags (such as plastic grocery sacks) and cereal bags for bag-in-box applications. Pallet wraps are also possible as are injection-molding applications. (For a new development in biodegradable foodservice packaging see Packaging World August '98 p. 2.) Chemists have long recognized that soy protein and other protein polymers can be cast into films with the aid of plasticizers. However such protein films until now have been brittle with elongation-to-break of around 30% to 50%. Nor could such films be melt-processed in conventional plastics processing equipment without degrading. Narayan believes his research supported in part by the United Soybean Board has overcome processing problems. He claims to have developed thermoplastic blends of soy protein and a certain type of polyester that melt and form a viscous fluid that can be blown or cast into film or injection-molded. Blends tested on the laboratory-scale equipment have consisted of up to 40% soy protein. The main benefit of the protein-based plastic is its ability to completely disintegrate and decompose into CO2 water and biomass in a typical 35- to 40-day composting cycle specified by the ASTM standard for composting. Performance issues So far the protein plastic blend has been tested only on a small-scale extrusion cast film line. "We're using conventional processing equipment but on equipment of a laboratory scale" says Narayan. "Obviously in scaling up production there will be lots of parameters that will need to be optimized. But there's no reason why it shouldn't work on a bigger machine." Narayan says that in theory the films should perform well on form/fill/seal and other packaging equipment although he admits such tests haven't been done since packaging isn't one of the preliminary application focuses. But he maintains that because the protein plastic film "behaves like a pure thermoplastic material" it is heat-sealable like any other. Most important Narayan claims to have overcome elongation and tensile strength weaknesses traditionally inherent in soy protein film blends. Such blends can now elongate up to 500% and exhibit tensile strength of around 2 psi according to Narayan. He says that LDPE elongates to anywhere from 300% to 600% with tensile strength of around 2 to 3 psi. Drawbacks The most significant drawback of course is cost. Narayan estimates that in the beginning protein plastic packaging materials will cost roughly double that of commodity-priced LDPE films. Like any other new technology Narayan expects the cost to come down as volumes go up. Another drawback is that the bag material can't be made completely clear. Instead it would be translucent. Narayan says pigments could be added to make it opaque. A final drawback is susceptibility to extreme humidity and liquid. Narayan admits that the plastic could degrade slightly if left in an extremely hot and humid warehouse for an extended period of time. "If it's a very high-moisture environment and you leave it there for a year or two years there will be some deterioration" he admits. Also "if water comes into contact with the film you'd start to get some degradation." But he argues these are defensible limitations. "If we want something to biodegrade at very fast rates we have to sacrifice somewhere." He claims the films resist infestation despite being made with organic materials. "It is rodent-and insect-proof because of the way the polyester encapsulates all the proteins. It should not attract insects or rodents." Though he admits this has not been tested he says "Once we get the films up and running we'll test that out." Next steps Next up is to produce the films on a pilot line. Full-scale film production in a commercial film plant will follow. Narayan says he's in discussions with resin companies as well as blown-film converters that he prefers not to identify. Companies that supplied the polyesters for testing include Eastman Chemical (Kingsport TN) and Union Carbide (Danbury CT). Narayan reports that his project is about six months away from testing on a commercial processing line. "If you want to go on a commercial line you need at least 500 to 1 pounds of resin. But before we make that much we want to play around with many more formulations to come up with the right one. "The question that hasn't been answered yet is what speeds will the material run at? We may find that we have to cut the speed down by twenty percent or we may have to adjust temperature etc. Those kinds of things we're not sure of yet." What has been demonstrated according to Narayan is that the the protein plastic degrades quite well under a variety of commercial or even backyard composting conditions. "We wanted it to degrade very fast even in a poorly run composting operation" he says. "But we have to be careful when we say that because if you have a very poorly run operation then you're not even going to do a good job biodegrading your organic material let alone the protein plastic." To be considered a true composting operation says Narayan temperatures should reach 50°C to 60°C (122°F to 140°F) for five to seven days after which there is a cool-down and maturation phase. The protein plastic blend degrades through a combination of hydrolysis and microbial biodegradation. Narayan stresses that the protein plastic isn't designed to be a solution to litter. "On concrete it will disintegrate as slowly as any other plastic" he says. "If it comes in contact with soil it will biodegrade but much slower than in a composting operation." Although the films aren't recyclable Narayan argues that recycling isn't appropriate for "certain packaging and single-use materials because of their very low volumes or contamination with other organic wastes." For these applications composting is a more effective solid waste disposal solution he maintains. Of course even if the film blends succeed on a technical level their popularity ultimately depends on how much the still-young U.S. composting infrastructure grows. While the films can get their start today in lawn and leaf bag applications Narayan acknowledges their widespread adoption for packaging applications is dependent on the growth of the composting infrastructure. "We're looking five ten years down the road when these infrastructures grow and [packaging made from these plastics] would fit into such an infrastructure." Narayan can be reached at 517/432-0775 or narayan@pilot.

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