Material SelectionThe plastics that have been considered and can be used with rotational moulding are polypropylene, polyethylene, and polypropylene. The requirements from the material are strength to hold the water and the forces that it is going to be sub-jected to in use. Material also must crucially be able to manufactured with the method of rotational moulding.

Properties of plastics:

PolypropyleneWeight: Polypropylene is a lightweight material.Tensile strength: Its tensile strength is quite high. It shows strong resistance towards stress and cracking.Shape: Polypropylene is crystalline in nature and possesses a regular geometrical shape.Insulation: It acts as an excellent insulator. That means, it prevents flow of electricity through it.Moisture Absorption: Polypropylene does not get damaged by water exposure because its moisture absorption is very low.Melting Point: Melting point of polypropylene is 160°C. Therefore, unlike other polymers like polyethylene, it is capable of being operational at a very high temperature.Corrosion: This polymer remains unaffected when it comes in contact with chemicals such as alkaline substances, acids, deCorrosion: This polymer remains unaffected when it comes in contact with chemicals such as alkaline substances, acids, de-greasing agents, electrolytic attacks, etc. However, its resistance towards aromatic or aliphatic hydrocarbons, chlorinated solvents and ultraviolet radiation is not very strong.Other Useful Properties:It is a non-toxic substance.It does not get stained very easily.It can be easily fabricated.It can retain its stiffness and flexibility intact even at very high temperatures.

The secondary material in this design that has been considered are stainless steel , oak and birch, the application of the sec-ondary material is a base for the primary component raising it off the ground. The requirements needed from this material are resistance to the elements such as rain and strength to withstand the forces exerted upon them.

Properties:Oak: Oak is the most widely used hardwood. There are more than 60 species of oak grown in the U.S., which can be sepa-rated into two basic varieties; white and red. The red variety is also known as black oak (a reference to its bark).Properties: Oak is a heavy, strong, light coloured hardwood. It is ring porous, due to the fact that more and larger conduc-tive vessels are laid down early in the summer, rather than later. Prominent rings and large pores give oak a course texture and prominent grain. Oak also has conspicuous medullary rays which can be seen as "flakes" in quarter sawed oak lumber.

Birch: There are many species of birch. The yellow birch is the most commercially important. European birch is fine grained, rare and expensive.Properties: Birch is a hard, heavy, close grained hardwood with a light brown or reddish coloured heartwood and cream or light sapwood. Birch is often rotary or flat sliced, yielding straight, curly or wavy grain patterns. It can be stained to resem-ble mahogany or walnut.

Stainless steel : Stainless steel can be explained as a metal alloy that contains about 30% of chromium (Cr) and approxi-mately 50% of iron (Fe). It is named as 'stainless' due to its highly stain resistant properties. The formation of an invisible chromium-rich oxide surface film gives stainless characteristics to steel. Hardness shows resistance to penetration. Heat re-sistance of stainless steel varies depending upon the type of steel. Grade 316H is the most resistant to high temperatures. It has the properties of being a touch metal resistance to impact and resistant to rust due to it being an alloy.

With researching these materials the ones that will be used in the final design are polyethylene for the main component due to the strength of the material and the resistance to the water, and it can also be manufactured using the process of ro-tational moulding. And for the secondary material for the base I have chosen stainless steel. This material has been chosen for these two components to for the as it has the property requirements to meet the designs needs of strength and element resistance.