Plastic shopping bags have been banned in San Francisco and other cities around the world. Some municipalities are slapping on taxes and fees in an effort to cut waste. Even individual companies are taking a stand on the environmental debate over plastic bags, with some shopping centers requiring their tenant stores to stop handing them out. In Sweden, about a billion plastic shopping bags are used each year, most for a one-way trip from a store to the home and straight to the trashcan.

One argument against plastic bags is that they are made from polyethylene, which in turn is produced from non-renewable petroleum raw materials. Another is that disposable containers of all types add to society’s enormous waste mountain. And when they get thrown away outdoors, plastic bags often add to long-lived litter since they aren’t readily broken down by micro-organisms and sunlight. And even when properly disposed of, plastic is often burned in municipal incinerators, where it contributes to the carbon dioxide emissions believed to cause global climate change.

Early adopter of bioplastics

It’s been 30 years since chemical engineer Gerth Jonsson began thinking about developing biodegradable plastics. But it wasn’t until about five years ago that a real market emerged. Noting an interest in green alternatives among its customers, the Swedish grocery chain ICA was looking for a more environmentally sound plastic bag. By the time Jonsson and his son, Magnus Jaeger, founded Tenova Bioplastics AB in 2003, compostable bags had been around for a few years.

Tenovas production of bioplastic has now grown to about 2500 tons per year. ICA, still the company’s largest customer, buys about 100 million biodegradable plastic bags per year, about one-third of the number it hands out to its shoppers. In 2009, Tenova was acquired by the Swedish packaging giant Billerud.

Based on polylactic acid

Corn, sugar beets and grasses can be used as raw material for modern plastics.

Corn, sugar beets and grasses can be used as raw material for modern plastics.

Tenova’s plastic for shopping bags contains about 45 percent polylactic acid (PLA) combined with an added polyester known as Ecoflex, which is supplied by the German chemical manufacturer BASF. PLA is derived mainly from corn, though sugar beets and grasses may also used as raw materials. If the ratio of PLA is increased in creating the composite substance, the mechanical performance of the resulting plastic suffers, but Tenova and BASF are working together to develop a new formulation of Ecoflex that will reduce cost by allowing an increase in the amount of PLA in the mixture to over 60 percent.

For the time being, however, bags made from bioplastic are considerably more expensive than traditional polyethylene bags.

Bioplastic breaks down naturally, and can be added to industrial composters, although smaller home composters cannot handle the material in large amounts. Left outdoors, the bags will break down within a few months in warmer weather. The material meets EU requirements for compostability, and measured over the entire lifecycle, bioplastics release less carbon dioxide than traditional polyethylene.

Green polyethylene

Conventional plastics made from polyethylene can also be more environmentally adapted. Derived from ethylene, the most-produced organic molecule in the world and an important industrial raw material, polyethylene is used in the synthesis of many chemical products.

Ethylene is conventionally produced through chemical reactions that utilize oil as a raw material, but “greener” alternatives are emerging, for example starting with ethanol and removing a hydrogen molecule through a process known as dehydration. Several plants for dehydration of ethanol have been built or are under construction in Sweden, with a combined capacity of 550,000 tons per year. However, current methods for producing “green” polyethylene are 30 to 40 percent more expensive than conventional processes.

One of the driving forces behind Billerud’s acquisition of Tenova was a plan to develop renewable plastic films that can be laminated with paper and cardboard. The company believes bioplastics have an important role to play in the future of packaging.

Article published in July 2009