A new barrier resin is closing in on commercialization in the form of polyglycolic acid (PGA), developed by Kureha Chemical Industry, Tokyo. The material boasts excellent barrier properties in high-humidity environments, and as it is a polyester, its processing window is very similar to that of PET.

PGA can be readily employed in multilayer stretch blowmolding, biaxially oriented films, and blown films.

PGA is currently manufactured on a pilot scale at Kureha, and the company plans to start developing global markets in earnest in 2004 in anticipation of European and U.S. regulatory approval for food packaging applications. Full-scale commercial production at a plant with a capacity of 10,000 tonnes annually is planned for 2006. "At this scale, we should be able to supply the market with PGA priced at a similar level to competing barrier materials such as EVOH and polyamide MXD6," says Toshio Mizuno, VP and general manager of business planning and development at Kureha''s packaging materials division.

A key to successful development of PGA as a barrier material was preventing hydrolysis during processing and usage. This was accomplished through incorporation of proprietary comonomers and additives. PGA is normally easily hydrolyzed, and when Kureha started out on development, multilayer films lost their barrier properties after several weeks. Refinements have seen barrier life extended to 20 months. Barrier properties, which can be tailored to last for between two weeks and 20 months, are primarily derived due to the material''s high density of 1.6 g/cu cm.

Where PGA comes into its own is in high-humidity environments such as packaging of wet products like beverages and solid foods in brine. At a relative humidity of 80%, the resin outscores its key competitors by an order of magnitude for oxygen and carbon dioxide permeability. "If we keep PGA''s price down to a par with its competitors, processors will save as they can use less material," says Mizuno.

In films, PGA can be processed in combination with mainstream plastics such as PP, PE, and polyamide, in addition to, of course, PET. The processing temperature window for biaxial orientation is 40 to 100C vs. just 80 to 90C for EVOH (ethylene content = 47 mol%). PGA''s window overlaps favorably with LLDPE (60 to 100C), nylon 6 and 66 (70 to 90C), and PET (80 to 100C). And as it is a polyester, PGA can be coextruded or blowmolded in multilayer structures incorporating PET without the need for an adhesive layer. Puncture strength is an order of magnitude higher than EVOH.

PGA is not Kureha''s first barrier material. The company also markets Besela, a lamination film comprised of a PET, oriented nylon, or oriented PP film substrate and a 1-µm polyacrylic acid barrier film. Oxygen barrier properties of Besela are in the same range as inorganic SiOx film-based products, while moisture permeability is very similar to EVOH. As Besela is an organic film, Kureha says it stands up better to severe abuse compared with inorganic barrier films and metallized films.

Besela has scored commercial success since 2001 in consumer retortable stand-up pouches for products such as mushrooms, sweet corn, soybeans in brine, and soups. It has also been used to package 5-kg servings of apple preserves and 1-kg servings of mixed beans and tuna spread for institutional use.

The next target markets are substitution for bottles, cans, and metallized films, while starting around 2006, Kureha plans to target the paper laminate market. The eventual aim is to secure markets worth ¥10 billion (US$86 million) for both Besela and PGA.

Stephen Moore [email protected]