Below is a glossary of common terminology we refer to on the website and their meanings.
Biodegradation is the degrading or breaking down of materials by nature – by bacteria, fungi, or other biological means. Microorganisms literally feast on the material and poop it out back into the compost or soil for plants to then take up again on the circle of life.
Anything made by nature will biodegrade over time, but that can be from a few weeks to hundreds of years (think of a leaf biodegrading vs a whole tree).
Many packaging items you see are able to use the term ‘biodegradable’ even though they use petrochemical polymers. Chemicals are often added to speed up the biodegradation process but tiny synthetic polymers (microplastics) remain, contaminating the compost or soil.
As mentioned, there are naturally occurring polymers found in plants such as cellulose and lignin. Bioplastics refers to plastics made entirely, or predominantly, of these molecules. You will see them advertised as being ‘biodegradable’ or ‘compostable’.
For the difference between biodegradable and compostable, please see below.
Canvas is a strong woven material that is used to make sails, tents, shoes and as a surface for painters. It was traditionally made using hemp fibres, but it’s more common today for it to be made from linen or cotton.
Plastics that have been certified as compostable are made from 100% naturally occurring molecules like cellulose. They must biodegrade back into carbon, nitrogen and water in a certified amount of time (usually under 12 weeks) and must not contaminate the compost or soil.
Any packaging claiming to be compostable must be certified by one of the international certifying bodies. Most commonly in New Zealand it is the American, European or Australian standards we use.
Most compostable plastics are made from plant starch (more commonly known as sugar which is a polymer chain of glucose). The cheapest form of starch comes from corn, so the majority of compostable plastics are made from corn starch.
Composting compostable plastics
Composting is the process of heaping together organic waste (anything that used to be living) and leaving it for microorganisms to consume, creating a natural fertiliser. There are large variations in the efficiency, quality, smell, leachate and heat of a compost heap which are dependant on the size, oxygen content, carbon/nitrogen ratio and water content of the compost.
Composting can be done anywhere and by anyone, although as explained above there are large variations in the quality of a compost. A commercial compost is a large composting operation which typically involves huge quantities of organic waste (hundreds to thousands of tonnes) and large machinery. Due to the expertise of commercial composters, they typically have very efficient composts that produce high heats and are able to accept compostable plastics, although the quality of the finished product is up for debate.
A home compost is typically too small and too poorly managed to be very efficient or produce enough heat. So they’re often not capable of breaking down most compostable plastics. More and more research is being done around the world to make bags that are compostable at home. This is a problem across the globe and there are many people trying to find solutions.
Cotton is a soft, natural fibre. It’s the most used natural fibre in the world, predominantly by the fashion industry. Intensive cotton farming requires a large amount of water, pesticides and herbicides. Much of today’s cotton crops have been genetically modified. Certified organic cotton has not been genetically modified and is farmed without the use of pesticides and herbicides. There are many types of cotton fabric including denim, calico, corduroy and cotton velvet.
Essentially, everything is degradable. Everything will break down into simpler compounds by stages (for example a plastic bag breaking down into microplastics). It breaks down but then contaminates natural ecosystems with the smaller bits of the same material.
Hemp is one of the world’s fastest and easiest growing plants. It has little or no need for pesticides and herbicides. It is an extremely versatile plant and has many uses including clothing, paper, biofuel, food, compostable plastics and bags.
Jute is a plant fibre that can be spun into long, strong threads. It’s used to make hessian sacks, garden twine, carpets and clothes. Jute plants are easy to grow, have a high yield per acre and have little need for pesticides and fertilisers. As with other all-natural fibres, Jute is biodegradable, so it will break down into naturally occurring substances that continue on the circle of life.
Linen is a smooth material made from the fibres of flax plants. It’s commonly used to make napkins, tablecloths, clothing and bed sheets. Flax grows in cooler regions of the world. It’s also used to make linseed oil and the seeds can be eaten.
Synthetic materials are not made by nature, they’re made in a factory or a lab. So will not biodegrade back into nature’s natural cycle of molecules. All synthetic plastics can break apart into smaller pieces over time, but these smaller pieces are still synthetic and nature can’t biodegrade them.
The research into microplastics and their impacts on the health of natural ecosystems and human health are is still relatively new, but we know they’re already in our food and in our drinking water. New World was the first supermarket in New Zealand to ban products containing microbeads which can wash down the drain and into our waterways. That’s a great move for New Zealand’s sea life.
Monomers and Polymers
A monomer is a single molecular unit. ‘Poly’ means many. So a polymer is many monomers linked together which creates a long chain of that molecule. Think of making a chain with microscopic paperclips. One paperclip could be a monomer of ethylene (a hydrocarbon found in oil), while polyethylene (the world’s most common plastic) would be thousands of paperclips of ethylene all linked together.
The first kind of ‘man-made’ plastic was basically stumbled upon by scientists learning how to join these molecules together – a process known as polymerisation. As the science improved over the years, especially during the World Wars, more and more types of plastics were invented.
All plastics are polymers, but not all polymers are plastic.
Nature produces polymers such as rubber, lignin (commonly found in wood), starch and cellulose – the world’s most common natural polymer.
Different polymers have different qualities and so have different uses. This is why there are so many different types of plastics available. Other chemicals can also be added to plastics to make them different colours, to make them stronger, last longer and so on.
Although there are hundreds of thousands of different types of polymers used to make a huge variety of plastics, they can be classified into two groups: Thermosets and Thermoplastics.
Numbers on plastics –what do they mean?
It may surprise you, but the numbers you see on plastic enclosed by the three triangular arrows are not a symbol of recyclability. They represent what polymer was used to make that product. To learn what each number refers to, check out this Plastics Recycling Guide.
To learn more about the recycling process in New Zealand, check out these videos
Nylon is a light and durable type of plastic made from petrochemicals which is available in many different forms. It is commonly used to make parachutes, brush bristles, mechanical parts, moulds and fishing line. It’s often used in 3D printing.
Oxydegradable plastics are made using petrochemical polymers and adding special chemicals to make them go brittle and degrade quicker when left in the open where there is oxygen. However, they simply degrade into smaller microplastics meaning they are not compostable and can cause severe environmental harm. Some countries have now banned the sale of these plastics.
To make new paper, trees are cut down and then shredded into small woodchips. The woodchips are heated in water creating a big soup-like substance to extract the cellulose. This cellulose soup is then left to dry before being squashed into paper. Often a variety of chemicals are added to change the colour or improve its strength. Making new paper from recycled paper uses the same process. Paper can also be composted after use, but this and the recycling process are compromised if it’s coated with plastic. Trees remove carbon from the atmosphere, so massive deforestation is a big contributor to global warming. It’s best to use wood from sustainable forests and to plant new trees to replace what’s cut down.
As we all know, plastic comes in many different shapes, colours, strengths and sizes. It can be hard to tell what is and isn’t plastic. To be classified as plastic, a material must be made from polymers and it must be malleable – that means to have plasticity.
Recycling is a process of using existing material to produce a product. The actual processes involved in recycling vary significantly from material to material depending on their molecular properties, their abundance, the demand for them and so on.
Usually the whole recycling process is very complex and involves collecting, sorting, cleaning, shredding, melting, reshaping and transporting the materials. Due to the many steps in the process it can be an expensive exercise, both financially and in terms of resources used. For this reason, much of what is technically recyclable will not in fact be recycled. It is often far cheaper in the short term to dump the material in landfills.
The economics of recycling are dependent on many factors including the availability and cost of the virgin material (for example, oil and gas are relatively cheap), the demand for the material, the complexity and cost of recycling and the proximity to the recyclers and how this influences transportation costs.
Due to New Zealand being relatively sparsely populated, it is often the case that the density of the material relative to the distance from the overseas recycling plants makes it too expensive to recycle much of our waste.
This problem has been exacerbated by China’s recent decision to stop accepting large amounts of the world’s waste.
Other problems for recyclers include contamination from food waste and items like straws and lollipop sticks that are just too small for the sorting machines and will not be recycled.
Please visit your local council’s website to ensure you’re recycling correctly and not causing the people at the recycling centres these problems.
- The production of the material: Was virgin rainforest cut down, or were lots of synthetic fertilisers used to grow it? Where does it come from? Is it locally sourced, or transported from half way around the world?
- Usefulness: Will the bag last for just one or two uses, or thousands? This can be affected by the material used, how well it’s made and what the bag is used for.
- The afterlife: Where does the bag end its life? Can it be recycled? If so, how many times and into what? Or can it be composted and returned to nature?
With this in mind, we’ve outlined the most common materials used to make carrier bags. Check out the ‘green credentials’ of these alternative options.
Single-use plastic bags
Acronym alert! Single-use plastic bags (SUPBs) are most commonly made from Low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), or high-density polyethylene (HDPE). Polyethylene is a petrochemical polymer. The difference between the three forms is how strong, dense and flexible they are. SUPBs are made by blowing air into the plastic to create a bubble which is then sealed at the bottom and cut at the top. During the manufacturing process, various chemicals are also added to stop the bags sticking together, make them easy to open and keep them from fading or weakening.
Whatever material your bag is made of, the most important thing is to reuse it as many times as possible. Every time you reuse a bag, you’re potentially keeping another new single-use plastic bag from entering circulation.
Thermoplastics and Thermosets
Thermoplastics can be re-melted, softened and cooled to reform into different shapes many times making them recyclable (think of a plastic drink bottle, or plastic bag). But thermoset plastics can only be moulded into one shape (think of a laptop, or TV screen). They can’t be re-melted or softened, making them much harder to recycle.