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Bending, shaping and forming plastics
What are Plastics?
What are Plastics?
Plastics is the word given to a broad list of materials made from polymers. Polymers are mostly synthetic (man-made) molecules which form long chains. It is the fact that polymers form long, repeated chains that makes them so special and so versatile. Their properties are homogeneous. That is that they act the same in all directions. It doesn't matter which way you prod, push or pull them, they have the same characteristics in all directions.
Weird fact - Plastics are actually misnamed. This is because the word 'plastic' describes the tendency of a material to stay deformed whereas 'elastic' behaviour is when a material 'retracts' back into its original shape. If you think about it most plastics are actually elastic in behaviour. After all, you wouldn't want a milk bottle that slowly drooped down to the floor as it was filled with milk would you?
Petrochemical 'cracking'
Petrochemical 'cracking'
Cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons such as those found in crude oil are broken down into simpler molecules such as light hydrocarbons.
This is done by breaking of carbon-carbon bonds at a range of high temperatures via a process called fractional distillation.
At various temperatures different chemical by-products are produced. These synthetic by-products are used to produce plastics.
Why are plastics so popular?
Why are plastics so popular?
Plastics are used in a wide variety of products not just in packaging. They compete fiercely with the more traditional materials such as: wood, metal, glass, paper and board. Their popularity has increased because they are cheaper than these traditional materials, self-coloured, self-finished, lightweight and are very good electrical and thermal insulators.
Typical milk containers from a supermarket.
These are cheaper to manufacture than glass bottles. They can be recycled however many end up in landfill sites and cause damage to the environment when people don't recycle properly.
Glass bottles are reusable as they can be cleaned and sanitised between uses however they are easily smashed and are more expensive to recycle than plastic.
What are plastics made from?
What are plastics made from?
The vast majority of plastics in use today are made from non-renewable resources such as: gas, oil and coal. These plastics are referred to as synthetic polymers. There have been increasing developments in semi and non-synthetic plastics. These are made from vegetable and plant fibres, which are deemed to be more environmentally friendly.
In the following video the difference between various types of plastic are discussed as well as how they were accidentally developed in the first place!
There are two main types of plastic.
There are two main types of plastic.
Plastics can be categorised under two main groups: thermoplastics and thermosetting plastics.
Thermosetting Plastics
Thermosetting Plastics
Thermosetting plastics, also know as thermosets, are moulded into shapes using heat and pressure. When a thermoset is heated and moulded there is a chemical change in the structure of the plastic, called ‘cross-linking’. When ‘cross-linking occurs, bonds are formed which link one polymer chain to another. A thermoset plastic cannot be re-melted and re-shaped after it has cured (cross-linking has occurred), therefore, they cannot be recycled. Thermosets have few uses in packaging; however, they are generally stronger than thermoplastics and are suited to high temperature applications, such as kitchen work surfaces.
Thermoplastics
Thermoplastics
Like thermosetting plastics, thermoplastics can be shaped using heat and pressure. However, when they are formed, no ‘cross-linking’ occurs, allowing them to be reheated and remoulded into new shapes. This means many thermoplastics can be recycled offering a better alternative to the environment.
'Natural' plastics (bioplastics)
'Natural' plastics (bioplastics)
Believe it or not plastics also occur naturally in some surprising places. Read below to find out about examples of natural plastics and where they are found.
Animal horn
Animal horn
Rhino horn is made up of a material called keratin. This is a protein. Proteins are large, complex molecules which form long chains. Essentially a polymer! The main product of animal horn is casein. This is used in adhesives (glues).
The ugly side of this
The ugly side of this
Rhino horn is often poached by hunters and sold illegally on the black market for money. This lucrative illegal trade has caused the population of Black Rhinos (as well as other horned animals) to fall to extinction levels.
Click the image to learn more.
Warning - this site contains distressing images.
Animal milk
Animal milk
As with animal horn, the principle protein constituent of milk is casein.
Click the cascamite image lower down to visit a page from Scientific American which explains how to make plastic from milk!
Insects
Insects
A tree dwelling insect called a Lac Bug (Kerria lacca) which lives in India and Thailand secretes a resin-like substance called shellac.
It was discovered that when this substance is dissolved in ethanol it produces liquid shellac.
This tough substance is used to colour plastics, as a natural paint primer, to make food shiny (a glaze), a wood sealant and varnish and even as a blocker to bad odours (smells)!
The ugly side of this
The ugly side of this
To produce industrial quantities of shellac, industrial quantities of lac bugs are needed. This means huge populations of living creatures are literally grown and harvested as a human commodity. Is this ethical? Click the nail varnish image lower down to learn more.
Plants
Plants
The cell walls of green plants contain cellulose. This is a polymer containing hundreds and sometimes thousands of carbon, hydrogen and oxygen atoms.
It is this cellulose that helps keep plants from falling over, keeping them upright and stiff so that they can lean into the sun to photosynthesise.
Cellulose is the most readily available organic (natural) polymer on the planet. This makes it ideal for natural plastics.
Cellulose is used to make paper products (yep, paper contains plastic!). It is also used to create cellophane wrapping, rayon (a fabric fibre) and even used for biofuels.
Cellulose has also been used in (the synthetic, oil-based product) bitumen (the main ingredient of road tarmac and flat roofing material) as a stabiliser or binder (to stop it from losing shape and 'running away').
Trees
Trees
Trees, as with plants contain cellulose fibres.
In addition to this, some trees produce special resins such as tree sap (in canadian maple trees this is called maple syrup - it tastes great on pancakes!), and rosin. Fossilised tree sap is called amber. This is a semi-precious 'stone' (it isn't really a stone though).
Rosin is used in all sorts of products such as sealing wax, soap, solder flux, printing ink, chewing gum and even in laser printer paper. Violinists and Cellists put rosin on their bow strings to create friction which helps make their instruments 'sing' louder and clearer.
Natural rubber is made using a plant material which is harvested from the Amazonian rubber tree (Hevea brasiliensis).
Examples of products derived from natural plastics - Click the images to learn more.
Examples of products derived from natural plastics - Click the images to learn more.
The Environmental Impact of Plastics
The Environmental Impact of Plastics
If plastics are such a wonder material, why are they also so dangerous?
If plastics are such a wonder material, why are they also so dangerous?
Whilst plastics have transformed manufacturing beyond all recognition and have undeniably advantageous properties, it is clear that they have also caused severe damage to the environment globally. Since the first plastics were developed in the 1940's and subsequently mass produced in the 1950's, because of the fact that they (generally) do not break down naturally, they are persistent in the environment. This means that there has not been a way to destroy them safely. Click the arrow to see more information...
Because of the global economy and the constant demand for newer products, the fact that plastics are inexpensive to begin with, this has created a 'disposable culture'. Consumers throw away products and replace them with little regard for the subsequent impact. As a result there are literally mountains of plastic rubbish building up around the world. Plastics can persist without biodegrading fully for many hundreds of years. These can get tangled up in wildlife or even consumed by them as food (except there is little nutritional value in a poisonous plastic!).
As plastics break down (usually triggered by UV radiation from sunlight) they emit toxic chemicals which can get into the water supply, rendering it poisonous to marine life. In addition it has been found that some chemicals are also harmful to humans too. Greenhouse gases are also emitted such as methane which contribute to global warming and are also explosively flammable! A chemical often used in plastics (as a plasticiser to make it more pliable) is Bisphenol A (BPA). This is known to mimic the behaviour of certain hormones and has even altered the gender characteristics of fish populations! BPA is banned in certain countries for the use of plastics for food preparation and consumption.
The images above illustrate the persistence of plastics in the environment.
The information was correct as of 2012. Since then plastic use has continued to increase significantly.
The Plastic ProblemPlastics Negative Impact Videos
Plastics Negative Impact Videos
Environmental issues that surrounds plastics - Click the videos to learn more.
Environmental issues that surrounds plastics - Click the videos to learn more.
A good example of the damage waste chemicals can do is the recent controversy over the damage the chemical company DuPont caused when they dumped unregulated chemicals into water supplies across America whilst producing the popular non- stick compound 'teflon' (used in frying pans).
This was dramatised into a film called 'Dark Waters'. Watch the trailer (left).
Environmentally 'friendly' plastics
Environmentally 'friendly' plastics
A huge amount of research is currently underway regarding the development of environmentally friendly plastics. There are some available already but some of these are more expensive to produce or recycle than their less eco-friendly equivalents. Consumers are reluctant to 'shoulder' the additional cost of processing or reprocessing eco-plastics, so there is a long way to go before they are widely used and accepted.
Starch-based plastics
Starch-based plastics
Starch is a polymeric (behaves like a polymer) carbohydrate. It is formed by a chain of glucose molecules. Starch for plastics can be obtained from all sorts of foodstuffs such as potatoes, corn and rice, even peas!
The ugly side of this
The ugly side of this
As before, the more biodegradable plastic we need, the more starch we need, which requires more land to grow plants. This means clearing natural areas of trees and their indigenous plants and wildlife.
PLA (Polylactic Acid)
PLA (Polylactic Acid)
PLA is an example of a starch based plastic. This is often used in 3D printing of plastic components.
Bamboo 'plastic'
Bamboo 'plastic'
Bamboo itself is not actually a plastic but a cellulose fibre. It can be processed into small fibres or even dust and used as the filler or bulk material in 'bamboo plastic'. It is often blended with epoxy resin to produce the material which is used to make products such as food containers and crockery.
Applying the 6 R's of Sustainability
Applying the 6 R's of Sustainability
3. Recycle
3. Recycle
Recycling is one of the most impactful things that you can do as a consumer to help reduce the impact of plastics on the environment. Recycling is when a material is broken down and reprocessed to produce new raw materials ready for a new product.
In order to avoid cross-contamination of materials it is necessary to sort plastics into their different types. This is because each plastic has different working properties and so cannot be mixed. We use identification codes to help make it easy to pick out what each plastic is.
In recycling centres the plastics are separated and then ground-down into small beads or granules. They are then heated up, softened and forced into new sheets, filaments and extrusions ready for sending back to manufacturers as raw materials.
Not all plastics can be easily recycled. Some require more energy and effort than is actually economically viable.
Watch the video to see how plastic bottles are often recycled.
International plastic resin identification codes
International plastic resin identification codes
These codes are often imprinted into plastic mouldings to make it easily visible to those disassembling the product which plastic the product has been made from. This table also give you a list of the most common household plastics and their purposes.
Note it is important to note that even though a product may have one of these icons, it does not necessarily mean the plastic is recyclable. This was a cunning method used by the plastics industry to make it appear as though plastics are less environmentally damaging than they are. It is important to be aware of what actual plastic your product is made from and what your local council will actively recycle - otherwise your waste product could end up in landfill.
The actual 'recyclable' logo!
Plastic 'stock' types
Plastic 'stock' types
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