Monopoly: The Materials Edition

NATURALS

RUBBER

Raw material

Rubber

rubber tree

Natural rubber is a naturally occurring elastic polymer (or elastomer) made from latex. Latex is a natural form of polyisoprene produced by the rubber tree. The trees are native to South America but the majority of commercial plantations are in Thailand, Indonesia and Malaysia.

Latex is collected by making a diagonal incision in the bark of the tree and collecting the liquid latex in a cup. This tapping process takes about 6 hours and produces around 8 litres of latex. The tree can usually be tapped again the next day. The latex is filtered and mixed with acid to thicken it. It is then rolled into sheets to remove water, dried and smoked to improve mould resistance. The majority of natural rubber is used to make tyres but the rubber sheets can also be manufactured into products using processes such as injection moulding and extrusion

Synthetic rubber is made from various chemicals sourced from crude oil that can be combined to produce elastic polymers. The properties of synthetic rubbers can be tailored by changing their chemical composition. For example, neoprene is soft and foamy and is used to make wetsuits whilst silicone is flexible and chemically unreactive and is used in medical implants.

Around 11.5 million tonnes of natural rubber were produced in 2012 compared with just over 15 million tonnes of synthetic rubber. Synthetic rubbers generally have better resistance to heat and chemicals but they are less elastic and are not a sustainable resource.

Uses

Elastic Band

elastic bands

Most elastic bands are made from natural rubber because of its superior elasticity. They are made by extruding a rubber tube of the desired diameter which is then vulcanised (see raw material pdf) and sliced into bands.

As well as general purpose uses, elastic bands can be utilised in more specialist applications.
Elastration is a method of bloodless castration used in male sheep, goats and cattle. Special pliers are used to place a tight rubber ring around the base of the scrotum. This is usually done in the first few weeks of life. The ring stops the blood supply to the scrotum and it will fall off after about 2 weeks. The same principle can be used to dock the tails of sheep.

Creating jewellery and charms from coloured elastic bands has become a popular craft in recent years. Model makers use the energy stored in a stretched elastic band to propel model cars and planes (see pdf).

Gloves

rubber gloves

Gloves made from different grades of natural and synthetic rubber are used in a range of applications when the hands require protection ranging from household chores such as the washing up to surgical gloves used in medical applications. Rubber is chosen because it is waterproof, elastic, and resistant to some chemicals. Rubber gloves can be manufactured quickly and cheaply which is important for a disposable product.

Tyres

In order to provide a safe and comfortable journey, car tyres need to be sufficiently strong to support the weight of the vehicle and its contents without distorting, provide good traction with the road surface and absorb some of the bumps in the road. Global production is expected to exceed 1.7 billion tyres by 2015 and the tyre industry is a major user of rubber.

tyres

Tyres are assembled on a drum. Manufacture starts with the bead which is a loop of rubber-coated high strength steel cord. It provides rigidity and enables the tyre to be mounted on the wheel rims. The body of the tyre is made up of layers of fabric called plies. Adding more plies increases the strength of the tyre; standard tyres have 2 plies but specialist tyres such as those used on aircraft landing gear may have up to 30. The side walls of the tyre are made of rubber, they provide lateral stability so the tyre keeps its shape when inflated and during cornering. The tread is the part of the tyre that contacts the road and is typically made of a mixture of natural and synthetic rubbers with carbon black added as a filler to improve abrasion resistance. Once the tyre is assembled it is vulcanised by heating under pressure to achieve its final shape and properties.

Links

Rubber
How rubber is made – discovery channel (5 mins)
http://www.youtube.com/watch?v=CKq42J7SaWw

 

Elastic band
Rubber band aeroplane
Instructions: http://www.rubber-power.com/make-it.htm
Youtube video (6 mins): http://www.youtube.com/watch?v=N-BLpmQXGoU
The first in a whole series of rubber band car projects by GrandadIsAnOldMan
http://www.youtube.com/watch?v=ClNHPuH99DU&list=TLBYF6kZ0VdY8DlUkk3a-5rz2UeWjgHTbi

What happens when you heat a rubber band?
http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/heat-shrink

 

Gloves
How rubber gloves are made (4 mins)
http://www.youtube.com/watch?v=h-sLHYvqT7I