Just as polyethylene naphthalate is beginning to crack into commercial packaging applications, researchers have taken steps to make the expensive plastic easier to recycle.
Long heralded as a packaging polymer of the future, PEN's properties make it more valuable than its polyester cousin, PET.
Five companies — a recycling equipment firm, two material suppliers, a soft drink manufacturer and a major recycler — have formed a cooperative program to develop technology to automatically sort naphthalate polymer containers from PET containers.
The group completed its first phase this spring, according to Nashville, Tenn.-based Magnetic Separation Systems Inc. If the results of the second set of tests conducted this summer are successful, the equipment may be on the market this fall, said MSS President Garry Kenny.
Naphthalate polymers are high-performance analogs of PET and can be categorized into three product types: PEN homopolymer; copolymers of dimethyl-2, 6-naphthalene dicarboxylate (NDC) with terephthalate monomers; and blends of these materials with PET.
MSS expects its latest machine to perform as well or better than its existing products, which do color and resin sorting. The company expects results of at least 95 percent accuracy, depending on the quality of the bottles, Kenny said.
The other companies involved in the naphthalate/PET separation technology are Amoco Chemical Co., Shell Chemical Co. and Coca-Cola Co., which are funding the work, and Wellman Inc., which is evaluating the technology.
Amoco, based in Chicago, is the world's largest producer of NDC, a raw material used to modify polyesters.
Amoco's Decatur, Ala., facility began producing commercial quantities of NDC April 1. By early 1998, the plant is scheduled to reach design capacity of 54 million pounds per year. Though Amoco can accommodate existing customers' needs, the company said it would not accept new business until it has more capacity.
``The development of a commercially viable means to automatically sort naphthalate polymers from PET is one responsible way to continue to advance PET recycling,'' said Amoco Chemicals' technical development manager, Greg Schmidt.
``We are also addressing reclaimers' concerns that spikes of some types of naphthalate polymers in the PET recycling stream could impact the downstream operations of their customers.''
Schmidt serves as chairman of the Naphthalate Stewardship Committee, a subcommittee of the Naphthalate Polymers Council, which is part of the Society of the Plastics Industry Inc. in Washington. The committee works with industry on PEN recycling issues.
An efficient automatic sortation process would give recyclers the ability to control the level of naphthalate in the PET stream.
One company interested in the PET/PEN separation and recycling technology is Wellman. The Shrewsbury, N.J., company claims to be the world's largest PET recycler, and is also a manufacturer of virgin PET.
Wellman, which uses a range of automatic sortation machines, is evaluating the MSS prototype.
``With improvements, the prototype shows promise,'' said Pete Booth, Wellman's research and development manager of recycling. ``The technology can be of commercial value. We look at this technology as we would any technology — from the standpoint of economic viability.
``After assessing the technology, we look at the economic reality of the marketplace,'' he added.
Wellman analyzed data after field-testing the separation equipment on four samples of baled and labeled containers with varying degrees of naphthalate content. The bales represented typical deposit, deposit/curbside, curbside and mixed plastics post-consumer PET streams.
Separation systems at recyclers will be necessary as PEN becomes more popular. The properties that make naphthalate-based plastics attractive for packaging applications are an improved gas barrier, high temperature resistance, higher strength and a greater barrier to ultraviolet light, said Bob Minney, manager of recycled programs for the polyester business at Houston-based Shell.
``As we get the material approved and into the market, we need to find the best way to recycle NDC materials in the PET stream in a way that is readily acceptable,`` he said.
Minney said he does not think creating a new SPI resin identification code for PEN would be conducive to recycling. By working with MSS, he hopes to show that NDC polymers can be handled automatically in the PET stream. NDC polymers are relatively expensive, costing $3-$5 per pound, and are not widely used yet in consumer packaging.