Kiwi firm leads way with its sweet plastic bottle

Scientists have discovered that ethanol, used to make polyethylene, can come from renewable sources such as the sugarcane plant.

Find your nearest plastic bottle or tub and turn it over. You are likely to see a number inside a triangle which corresponds to it being a recyclable product.

The actual numbers run from 1-7 and describe the type of plastic that the object is made from.

No 1 is PET, short for polyethylene terephthalate, and used in fizzy drinks bottles, No 5 is PP, or polypropylene, probably housing your takeaway meal.

Although all plastics with these numbers - apart from No 7 - can theoretically be recycled, in fact many items such as polystyrene food trays with No 6 on the bottom must be sent to landfill because of their possible contamination with meat products.

Scientists and engineers call plastics "polymers", which derives from Greek origins: "poly" means many and "mer" means parts.

Plastic to us describes the way a material responds to force. If you remove the applied force and it springs back like a rubber band we call it elastic deformation, if it permanently bends or changes shape we call that plastic deformation.

If you had a microscope that could look at the molecular structure of a polymer you would see long spaghetti-like structures made up of many repeating parts joined together.

One of the most common plastics, polyethylene is made up of molecules of ethylene lined up in long chains.

Polyethylene is represented by two recycle numbers, 2 and 4. No 2 is HDPE, or high-density polyethylene, which has many more molecules packed into its structure making it stronger and more dense, ideal for milk and washing up-liquid bottles which need to be sturdy and stand upright with fluid inside.

Recycle No 4 is LDPE, or low-density polyethylene, which is weaker and more flexible so used to make plastic carrier bags and bin liners.

To make polyethylene, the alcohol ethanol (C2H6O) is dehydrated down to ethylene (CH2=CH2) which is then polymerised by breaking the double bond to form chains with many ethylene groups attached ( - CH2-CH2-CH2-CH2-).

Plastic usually uses non-renewable petroleum sources such as crude oil for its raw material source, but scientists have discovered ethanol can come from renewable sources as well, including the sugarcane plant.

Chemically there is no difference in polyethylene produced from petroleum or plants - they look the same, feel the same and importantly can be recycled in the same way. One big advantage of using sugarcane is its ability to capture the greenhouse gas carbon dioxide from the atmosphere which it uses for photosynthesis as it grows. Analysis shows each tonne of sugarcane-produced polyethylene avoids the emission of 2 to 2.5 tonnes of CO2 that would have been created with the petroleum-based version.

Leading the way in this new plastic-bottle material innovation is Kiwi natural cleaning supplies company ecostore, which just switched 98 per cent of its bottled products over to sugarcane HDPE.

The sugarcane agro-ecological zoning policy ensures sugarcane can't be grown in areas with high levels of biodiversity, protecting the Amazon, Pantanal biomes, indigenous and environmentally protected lands to ensure that both environmental and social sustainability are considered.

This isn't the first time a Kiwi firm has innovated in the plant-based sustainable bottle industry. Charlie's honest water eco bottles are made from PLA or polylactide, a plastic derived from lactic acid produced by bacterial fermentation of sugarcane and corn and are compostable if you live near a rare industrial composter.

The new face of plastic is green and hopefully more New Zealand companies will be bringing them to a supermarket shelf near you.

Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science.