Using Plastics

Polymers have many useful applications and new uses are being developed, for example: –new packaging materials, –waterproof coatings for fabrics, –dental polymers, –wound dressings, –hydrogels, –smart materials, including shape memory polymers.

PolymerUse Polyethene (PE) Plastic Bags, Bottles Polychloroethene (PVC) Water (& drain) pipes and insulation on electricity cables Polystyrene (PS) Plates, Rulers, expanded as insulation and packaging Polypropene (PP) Ropes and crates

Polymers have properties that depend the chain length. Longer molecules can get tangled up in each other. They also stick together better. This means that substances made of longer molecules are harder and have higher melting points.

Polymers have properties that also depend on what they are made from and the conditions under which they are made. For example –If poly(ethene) is produced under high pressure then the low density (LDPE) form is made. It has many side branches –If poly(ethene) is produced under low pressure using catalysts then the high density (HDPE) form is made. It has few side branches and so is stronger

Polymers are usually made by heating the monomer and passing it over a catalyst. The sort of catalyst used can affect how much the polymer chain branches. Polymer branches are like the branches of a tree – they are made of the same stuff as the main chain but go off in a different direction.

Main Chain Side Branch

If the polymer chains have no branches, they pack in close to each other and the material has a high density. The chains close together so there are more chain in the same volume, making the material stronger. 3 chains

If the polymer chains have a lot of branches then the chains cannot pack together as closely and the material has a lower density. The chains are further apart so there are less chains in the same volume, meaning the material is weaker 3 chains

The properties of PVC are modified through the use of additives: –It can be made softer and more flexible by the addition of plasticisers –Most plastics break down in UV light (from the sun), but the addition of a stabiliser to the PVC allows it used outdoors for window frames and drain pipes

The chains with small plasticiser molecules between them slip and slide over each other more easily. This makes the plastic more flexible. Without plasticiser molecules the plastic is tougher and more rigid because the chains line up in rows and hold on to each other more tightly.

Example PVC If plasticisers are added to PVC then it behaves like a fabric It is used for, amongst other things, clothing and shower curtains

uPVC stands for unplasticised PVC and it remains rigid. It is used in place of wood in buildings, as it is virtually maintenance free. Commonly used for double glazing windows and doors, guttering and siding

Poly(ethenol) dissolves in water to form a ‘slime’ The slimes can have different viscosities depending on: –how much water is used –if a crosslinking additive, like borax is used

The links stop the molecules moving over each other so the structure is more rigid. The substance made of molecules that are cross-linked is harder and less flexible than the one without crosslinks. Cross link

Summary A Polymer’s properties are affected by: –Chain Monomer type Length –Additives Plasticises Stabiliser Crosslinker –Conditions of production Catalysts Pressure

There are two main types of plastics: –Thermoplastics –Thermosetting When thermoplastics are heated they soften and can go back to their original shape The polymer chains are given enough heat energy to vibrate themselves into line and so they shrink back to their original form

Thermoset plastics are different When they are heated, they form cross- links between chains through side branches. This is how that are formed into a solid If they are subsequently heated they do not soften like thermoplastics, they form extra cross-links or burn.