The move came into effect June 30 and is part of a restructuring of the Teijin global business instigated by the economic slowdown, the Osaka-based company said.

Minnetonka, Minn.-based NatureWorks was set up in 1997 as a joint venture between Minneapolis-based Cargill and Dow Chemical Co. Teijin took a 50 percent share in the venture in 2007, following Dow’s decision to exit the business.

The NatureWorks manufacturing plant in Blair, Neb., is currently the world’s largest PLA bioplastic production plant. The company recently started up a second polymerization line at the facility, taking its annual capacity to around 140,000 metric tonnes per year.

In a statement, NatureWorks CEO Marc Verbruggen said the Teijin decision will have no effect on its day-to-day operations and said that the company retains strong prospects for continued growth for its Ingeo branded bioplastic.

“While the economic downturn slowed sales growth, we still show growth, which can’t be said of many conventional materials today,” he said.

“Sales have notably rebounded since January -- a clear demonstration that the Ingeo product traits and environmental advantages are important to customers even in times of lower oil prices.”

Earlier this year, Verbruggen said current sales are close to 70,000 metric tonnes per year, but that growth had been slowed by the widening price gap between its Ingeo product and conventional petrochemical polymers as a result of the slump in commodity polymer prices.

Natureworks cut around one third of its staff back in March, when it also announced that it had initiated an evaluation study to establish a second manufacturing plant. Verbruggen said then that a second plant -- which will be located outside of the United States -- could be required as early as 2013.

Teijin said that the decision to exit the Natureworks joint venture was not an indication of a lack of commitment to the bioplastics sector. However, the company said it plans to focus its commercial and technological resources in future on development of its BioFront heat-resistant PLA polymer.

In a statement, it said: “Teijin believes that cooperative efforts among industry players are essential for continued market expansion going forward and intends to maintain co-operative relations with NatureWorks and Cargill, which share the same belief.”

Teijin, which is active in the synthetic fibers, plastic films and pharmaceuticals sectors, posted consolidated sales for 2008 of 943 billion yen ($9.75 billion).

In April, the company announced plans to “drastically restructure” some of its plastics businesses, including its PET film and fibers and polycarbonate resin. It also said it would freeze major capital investment for two years and cut capital spending for 2009 by almost 50 percent.

Teijin said the cost of the NatureWorks ownership transfer was included in its fiscal 2008 results, and will have no impact in the current fiscal period.