'Green' Susana cuts to the chase

Joyee Chan

An award-winning scientist spent two years perfecting a resin to make biodegradable knives and forks

Joyee Chan |

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Susana Kan's many experiments using resins are part of her dream to help end the use of all oil-based plastics.
A YouTube video that instructs viewers to dissolve spoonfuls of tapioca powder in hot water before adding drops of glycerine might make your stomach churn: it's not for eating ... at least not so far.

Yet 14-year-old Susana Kan Wing-yi says it's her favourite recipe. The dish - literally - is an eco-friendly homemade plastic.

The budding scientist, who studies at Maryknoll Fathers' School, in Tai Hang Tung, spent two years perfecting her own recipe - often during her lunch hour and at home - to make "green", biodegradable plastic bookmarks, cutlery and crockery.

She discovered starches can be converted into a plastic-like resin to make things that look and feel like regular plastic, but degrade naturally and safely. "Conventional plastics all have one common flaw - they're non-biodegradable by-products of petroleum that will pollute the environment."

Susana's efforts won her first prize at last month's International Children's Science and Maths Festival, involving 300students - including 50 from Hong Kong, Thailand and Italy - held in India.

Her dream is to help end the use of all oil-based plastics - and slow down the growth of Hong Kong's rubbish mountain.

Hongkongers throw away sixmillion tonnes of waste a year, including 1,000 tonnes of plastic bags each day, says EcoVision Asia, the environmental group that organises the annual Hong Kong Cleanup initiative. The city's three major landfill sites are expected to be at full capacity by 2019.

Susana's first experiment used cornstarch as the main ingredient. But the resulting plastic resin "had an uneven surface and dissolved easily in water", she says.

So she experimented by replacing the cornstarch with tapioca starch - taken from cassava roots - sweet potato starch, green-bean powder and water chestnut powder.

Susana found tapioca starch worked best, producing the most transparent and smoothest resin; all the other starches failed to dry properly, and became mouldy.

After using the tapioca starch to make laminated bookmarks, she experimented further by mixing a variety of starches in different ratios to create three-dimensional plastics.

She found that mixing tapioca starch and mochi (Japanese rice cake) powder forms a strong plastic resin, which can be shaped into spoons, dishes and mugs.

None of her products harms the environment; her bookmarks break down in 20 minutes when soaked in water, depending on the materials, temperature and humidity; her crockery needs up to six hours.

Susana is continuing her research. Ultimately she wants to make her plastics recyclable.

She soaked small broken pieces of her crockery in water. She hoped to use the powdery deposits left behind in another experiment, but the deposits were so fine she lost most of them while straining them.

Her resin products are "theoretically" edible, but more research is needed, she says. Also, the production process might need to be more hygienic.

Yet thanks to advice from a professor at City University's biochemistry department, she is not far off achieving her goals.

Susana will represent Hong Kong at the Intel International Science and Engineering Fair, in the United States, next May