L8. Elastomers / Biopolymers

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Elastomers and Biopolymers

Elastomers have links between the monomers which are flexible even when the Thermoplastic has cooled down. This allows the plastic to have rubber properties.

Elastomers can generally be recycled.

Thermoplastic Elastomers (TPE’s)

Thermoplastic Elastomers (TPE’s) can be processed using conventional moulding equipment i.e. injection moulding and have the advantage of quicker production times compared to natural or synthetic rubbers.

Another advantage is that all waste and scrap material can be recycled.

TPE’s are commonly used for wire and cable coatings, for seals and hoses in the automotive industry as well as over moulding of grips onto power tools casings, toothbrushes, pens and utensils etc...

Liquid Silicon Rubber (LSR)

Liquid Silicon Rubber (LSR) is a thermosetting elastomer made up of two components, of which one is a catalyst.

These can be made using injection moulding techniques and the main advantage of this material is its ability to withstand temperatures ranging from -50C to +250C.

This makes it ideal for use in the automotive industry, for teats on baby bottles and for cooking and medical applications

Biopolymers

Can also be referred to as biodegradable plastics.

Conventional oil-based plastics do not break down easily and, since the bulk of domestic waste comes from this source, they have a significant and negative effect on the environment.

Biodegradable plastics are designed to break down under the right conditions.

The majority of biodegradable plastics are derived entirely from renewable sources.

Starch based polymers are produced from wheat, corn and potatoes (Potatopak).

Polylactide (PLA) is a type of biodegradable plastic used for packaging, gardening products and even some disposable nappies.

They are also used in medical implants and sutures for their ability to dissolve harmlessly into the body over time.

video

This instructional video explains how corn is made into biodegradable polymers.

video

Here is a video showing in more detail how biodegradable polymers and analysis of them as a 'better' alternative..

PHA’s and PHB’s.

PHA’s are better known as Biopol and are made from natural cellulose.

PHA’s have wide ranging applications in the area of medicine in the form of dispersible fixatives such as film, screws and bone plates and also for slow release medication.

PHB’s are a variation of Biopol and are used in packaging as they have similar properties to polypropylene.

While stable in the environment,they will break down in soil.

PHA - Biopol

degradable polymers

Oxo-degradable polymers have additives that promote short degradation e.g. less than five years. These help the polymer break down into a fine powder from the effects of heat, oxygen and moisture.

Photodegradable polymers will break down when exposed to ultraviolet light.

Aditives - It is also possible to help conventional polymers break down more easily by the addition of an additive such as a ‘bio batch’ This can help plastics like PE, PP, PVC, PET or PS break down in less than 5 years rather than the hundred+ currently predicted for oil-based polymers.

The downside of using these type of plastics is the degradation and time limit which could, for example, render a chair unsafe to use before its lifetime use is over or packaging of precious objects could dissolve while stored in plastic bags.

Water Soluble Polymers

Water Soluble Polymers are an increasingly popular area of biodegradation.

Products such as liquid detergent pouches make it possible to introduce the detergent into the washing machine but the pouch will dissolve in warm water releasing the liquid and removing the need for disposable packaging.

Other application include laundry bags in hospitals and any other application where a carrier will no longer be needed once it has served its purpose.

These types of polymer are still more expensive than conventional polymers and this cost is passed on to the consumer which means that only the more environmentally conscious will pay the extra, but prices are falling all the time.

Ecological and social footprint

Oil based polymers are not a sustainable or renewable source of materials.

Sustainable means we can keep supplies of a material going by recycling, repairing or reusing them.

Polymers degrade and we will always need virgin polymers to recycle, so oil based polymers are not sustainable.

To make the use of polymers more sustainable we are looking at natural and renewable sources of polymers. These can include starch based foods such as potato (potatopak) and corn.

Plant and fibre based polymers are constantly being developed that will naturally biodegrade in order to reduce pollution. Scientists are also looking at making plastics from seaweed, coffee grounds and other natural sources.

In the meantime, we all have to take responsibility for our plastic use and be more thoughtful in how we dispose of our plastic products.

Most plastics are derived from crude oil. While this is a naturally occurring source they are fossil fuels which have taken millions of years to produce from rotting vegetation, animals etc.

Given the time taken for these fossils fuels to be formed it is impossible to recreate them artificially.

Most processes involved in the extraction and processing of crude oil into polymers is harmful to the environment.

They are a finite resource which will eventually run out which is why we need to find alternative sources of polymers

Most common plastics will not naturally biodegrade so they end up in land fill and in the oceans.

Single use plastic products are becoming a major concern in terms of pollution of our water and harm to sea creatures.

Micro particles of polymers have made their way into the animals and fish that we eat….we are effectively eating our own waste.

Summary

Polymers are derived from natural sources but more commonly from fossil fuels such as Coal and Oil.
Thermoplastics can be recycled while Thermosetting plastics cannot.
Elastomers are flexible, rubber like plastics.
Biopolymers are derived from plants and starch based foods such as corn and potatoes.
Plastics are increasingly being used to replace wood, metal and glass which are now considered premium materials.
Conventional plastics are derived from a finite source which means they will run out but only a small amount (up to 30%) of recycled plastics can be used with virgin plastic to make new products.
More manufacturers are using plant based plastics in their products. Coke use around 20% recycled, 30% biopolymer and 50% virgin in their plastic bottles.

Revision Notes:

There are three main types of polymer. Elastomers and Thermoplastics can be reformed and are therefore recyclable.
All but one thermoplastics have the term ‘poly’ in their names. All thermosetting polymers either have ‘resin’ or ‘formaldehyde’ in their names.
This will help you remember which category they belong to.
Try and find one good example of a product for each polymer and also how that product is made. This will reinforce your learning on processes later in the course.
All oils are from a natural source (oil, coal) but need to be processed through thermal cracking. These are from a finite source (it will run out)
Biopolymers are sustainable as they are from a renewable source (plants, vegetables etc.)
There are seven categories of materials covered in the syllabus, but you should also be familiar with textiles, glass and ceramics making a total of ten categories. These last three will only be for reference in case an exam question requires reference to them for comparison.
Where possible, these categories have been broken down into three to help you remember more easily. Use this fact to help you identify materials and their uses.
Ensure that you can name one common application for each specific material and never answer a question with a generic term such as ‘wood’ or ‘metal’.
Check your knowledge of these materials at the end of the relevant unit.

Prep 8

L7-8-Polymers.ppsx

L7 -L8 Powerpoint

This powerpoint summarises all the content from L3 - L4 should you wish to review it.

Go to 1.2 Performance characteristics >

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