13 Mai 2011

Styrofoam from milk and other developments in biodegradable Polystyrene

Foam-like materials hold promise for a wide range of applications

Expanded Polystyrene (EPS) is made from polystyrene impregnated with a blowing agent (typically pentane). Expanding beads fuse together to form the finished product, which is 95-98% air and 2-5% polystyrene. It finds application in cups and containers, shape-molded packaging, expanded loose-fill packaging. It insulates, is lightweight, and resists moisture.

US scientists have used the protein in milk and clay to develop a new lightweight biodegradable styrofoam material which they claim could be a substitute for traditional foamed plastics. The results of the study, published in Biomacromolecules, shows that a material produced using cow’s milk is both biodegradable and strong enough for commercial uses with almost a third of the material breaking down within 30 days. 80% of the protein in cow milk is a substance called casein, which is already used in making adhesives and paper coatings. According to the researchers, casein shows good film-forming and coating properties as well as excellent barrier properties to non-polar substances (oxygen, carbon dioxide, and aromas). This makes it an excellent candidate for numerous applications, such as paper coatings, adhesives and food packaging.

However, casein on its own has limited mechanical strength and is water sensitive, which can restrict its practical applications. To make the casein more resilient and boost its resistance to water, the scientists blended in a small amount of clay and a reactive molecule called glyceraldehyde, which links casein’s protein molecules together. The scientists freeze-dried the resulting mixture, removing the water to produce a spongy aerogel, a lightweight material. To make the gossamer foam stronger, they cured it in an oven and then tested its sturdiness. These foam-like materials hold promise for a wide range of applications where the low density and environmental friendliness are of great importance; the ultra-low-density layered architectures result in favourable mechanical and thermal insulation properties.

The research began with an accidental discovery in the lab. One of Schiraldi’s students freeze-dried clay and got something intriguing enough to warrant a closer look. So the team started mixing the clay with a variety of materials. When they added a cow’s milk protein called casein, they ended up with a super-light, fluffy and foam-like material. The final ingredient is a tiny amount of a glycerol-based material, which basically stiffens up the solution’s chemical bonds. The dirty-looking water was poured into molds and frozen like ice-cubes and then freeze-dried to get all the water out.

The result is a material that has all the same properties of Styrofoam, but is 98% bio-based. At 100 degrees Celsius (212 degrees Fahrenheit), the milk-containing foam lets out a few drops of water. But it stays sturdy up to 200 degrees Celsius (392 degrees Fahrenheit). Before milk-based plastics will go mainstream, though, there are technological hurdles to overcome. For example, scientists will need to make sure that the new material doesn’t smell like sour milk.

In a commercial development, Synbra Technology has introduced BioFoam®, a new biodegradable EPS. This environmentally friendly material is made from plant and vegetable waste. Initially, BioFoam® will be used by Synbra’s subsidiaries for packaging industry applications.

Victorian-based technology company RMAX is partnering with the CSIRO to develop the world’s first fully biodegradable foam beads, an environmentally sustainable alternative to polystyrene. Designed for use initially in packaging and building, the biodegradable alternative to polystyrene foam has the potential to significantly reduce the amount of polystyrene waste, and eventually enable packaging waste to be turned into composted garden products. With nearly 1 million cubic metres of expandable polystyrene (EPS) packaging ending up in permanent landfill each year, this product could have huge environment and sustainability benefits for industry and the wider community.

RMAX, a leading manufacturer and supplier of moulded EPS products in Australia and New Zealand, anticipates the new material will be manufactured in its existing moulding plants based in Melbourne and could be on the global market within three years. RMAX received an $800,000 Victoria’s Science Agenda Investment Fund (VSA IF) sustainability grant to help it develop the biodegradable packing material in collaboration with the CSIRO.

Source: Plastemart, 2011-05-13.

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