Environmentally friendly plastic film of potato starch

Plastic made of potato starch is a promising material for packaging, which is a big new application for starch plastics. This is shown in Åsa Rindlav-Westling’s doctoral dissertation, which was carried out in Paul Gatenholm’s research team in polymer technology at Chalmers University of Technology, Sweden.

Our huge quantities of refuse could be reduced and a greater proportion than today could be composted. Combustion of materials from oil, such as conventional plastics and fossil fuels, raise levels of carbon dioxide in the atmosphere, increasing the risk of the greenhouse effect and environmental problems. Starch polymers, extracted from potatoes, corn, and wheat, for instance, can be used as raw materials for biologically degradable plastics. Today the EU has a surplus of agricultural products, and a certain share could be used as raw materials in the production of plastics. At present disposable eating utensils and packaging chips are made from starch. A major new field of use for plastic films made of starch could be packaging. Starch films have excellent oxygen-barrier properties and in some cases can replace aluminium when it comes to protecting oxygen-sensitive foods.

Potato starch is produced from carbon dioxide and water with the help of energy from the sun when potatoes grow. Åsa Rindlav-Westling’s doctoral work deals with plastic films made from potato starch. Her work has involved studying starch-film structure, which affects its properties. By varying the conditions under which the film is produced, she has been able to control the structure. Slow formation of film results in starches that exhibit well-ordered films, and crystallinity is high. Film properties like strength and elasticity are affected by crystallinity.

The films exhibited excellent properties as oxygen barriers. In high humidity, however, both the barrier properties and the strength of the films deteriorated. This is due to softening caused by the penetration of moisture. A new theory is presented regarding how water is redistributed in the film after heating, thereby influencing properties. One way to prevent water from penetrating the film is to treat its surface, and experiments were made involving plasma treatment, in which a glass-like surface or a strongly water-repellent surface was formed. A further possibility is to add water-repellent substances to the film, which will deposit themselves on the surface. Proteins in the starch turned out to migrate to the surface, which thereby became more water-resistant.

The study shows that starch is an extremely promising material for use in biodegradable and renewable plastics. The knowledge yielded by this work will be of use the development of new and environmentally friendly plastics. The dissertation Crystallinity and Morphology of Starch Polymer of Films was publicly defended on March 15.

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