Getting to the bottom of biodegradable bags

There are two main types of plastic bags: those that are biodegradable are those that are not.

Biodegradable bags are created from a plastic called polylactide, which is produced after starch obtained from corn or potatoes is converted into lactic acid and polymerised. Biodegradation is triggered by ultraviolet light, heat or mechanical stress. As the plastic begins to oxidise it becomes brittle and susceptible to the usual agents of degradation, such as moisture and microbes. When discarded, plastic bags can take as little as a few months to degrade.

Non-biodegradable bags are generally made from polyethylene, which is derived from natural gas and petroleum. In a process called photodegradation, they are broken down by sunlight into smaller and smaller pieces. Estimates at the length of time this can take range between 400 and 1000 years.

Although the far shorter lifespan of biodegradable bags has clear benefits, both types of bags pose environmental problems. These include the amount of energy required to manufacture and transport them, which in turns eats up more resources and contributes to global warming.

The toxic chemical ingredients needed to make bags are a cause of pollution. In the case of non-biodegradable plastic, prospecting and drilling for their component materials contribute to the destruction of fragile habitats and ecosystems. For example, between 500 billion and 1 trillion plastic bags are used each year worldwide. To manufacture them, 60-100 million barrels of oil are required.

Careless disposal of bags, whether biodegradable or not, poses an extreme threat to wildlife and natural resources – in the latter case, the toxins left behind to enter the soil and, potentially, aquifers. In terms of manufacturing, plastic bags are arguably not as bad as production of other large-scale items products, especially cars. But plastic bags are being produced on a huge, arguably unnecessary, scale and are one problem that can be easily tackled through promoting green thinking.

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