One of the advantages of plastic is that it does not rust or rot. But this can also be a problem – plastic cups, bags, wrappers and containers litter the countryside and beaches all over the world. Unless they are picked up, they go on accumulating year after year.
To deal with the problem, various forms of degradable plastic have been developed. The secret is to incorporate into the plastic a chemical that can be attacked by light, bacteria or other chemicals.
Biodegradable plastics can be made by adding starch. If the plastics are buried, bacteria that feed on starch will gradually break them up into tiny pieces that disappear harmlessly into the soil.
Chemically degradable plastics can be broken up by spraying them with a solution that causes them to dissolve. They can be used, for example, as a protective waxy covering for new cars, and washed off at the dealer’s garage by a specially formulated spray. This reacts with one of the components in the plastic and causes it dissolve into harmless materials which can be flushed down the drain.
One of the most successful uses of degradable plastics is in surgery, where stitches are now often made using plastics which dissolve slowly in body fluids, saving the patient the anxiety of having the stitches removed. Drugs are often prescribed in plastic capsules which dissolve slowly, releasing the rug into the bloodstream at a controlled rate.
Photodegradable plastics contain chemicals that slowly disintegrate when exposed to light. In France, strips of photodegradable plastic about 3ft (1m) wide are used in the fields to retain heat in the soil and produce early crops. They last for between one and three years before rotting into the soil. But they have to be used in a country with a consistent amount of sunshine so they decay at a predictable speed.
In the USA, about one-quarter of the plastic ‘yokes’ that link beer cans in a six-pack are made of a plastic called Ecolyte, which is photodegradable. But to stop them decaying too early they must be stored away from direct sunlight, which can be an inconvenience for the retailer.
Degradable plastic has other problems. For example, it cannot be recycled because there is no easy way to measure its remaining life span. The biggest drawback has been the cost of producing it, but Japanese scientists believe they will soon be able to produce a much cheaper multipurpose biodegradable plastic.
Picture Credit : Google