Composite materials
A composite materialMaterial made from two or more different materials with contrasting properties. consists of two or more materialsThings that are used, sometimes to make other things. with contrasting propertiesThe characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point.. They are combined to produce a material with improved properties.
Most composite materials have two components:
- the reinforcementFibres or other material that make up the bulk of a composite material.
- the matrixThe substance that binds the reinforcement together in a composite material., which binds the reinforcement together
The table shows some examples of composite materials.
| Composite material | Reinforcement | Matrix |
| Concrete | Sand and gravel | Cement |
| Fibreglass | Glass fibres | Polymer resin |
| Carbon fibre reinforced polymer | Carbon fibres | Polymer resin |
| Chipboard | Wood chips | Resin glue |
| Composite material | Concrete |
|---|---|
| Reinforcement | Sand and gravel |
| Matrix | Cement |
| Composite material | Fibreglass |
|---|---|
| Reinforcement | Glass fibres |
| Matrix | Polymer resin |
| Composite material | Carbon fibre reinforced polymer |
|---|---|
| Reinforcement | Carbon fibres |
| Matrix | Polymer resin |
| Composite material | Chipboard |
|---|---|
| Reinforcement | Wood chips |
| Matrix | Resin glue |
It is often possible to separate the reinforcement from the matrix by physical processes. For example, concrete can be broken up using machinery. This is one stage in recycling the components of concrete.
Fibreglass and carbon fibre reinforced polymer
The fibresLong, thin strands. in these composite materials have a low densityA measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3).. They are strong in tensionPulling force exerted by each end of an object such as a string or rope., so they are not easily stretched, but they are brittleIf something is brittle it is easily broken..
The polymer resinRaw plastic, especially when in semi-liquid form. which binds the fibres together is not strong, but it is stiff and hardwearing. The composite materials show a combination of these properties. They are strong, stiff, hard and lightweight.
Chipboard
Wood itself is a natural composite material. It consists of a reinforcement of celluloseA carbohydrate. It forms the cell wall in plant cells. fibres bonded together by a matrix of ligninCarbohydrate material lining the xylem vessels providing strength and support.. The fibres are aligned alongside each other, so wood is stronger in one direction than it is in the other.
Chipboard contains randomly arranged wood chips bonded together by a glue, so it is strong in all directions.
Question
Chipboard may be supplied with a thin polymerA large molecule formed from many identical smaller molecules known as monomers. layer glued to its surfaces. Suggest reasons that explain why this material is more suitable than chipboard alone for making self-assembly furniture.
The polymer can be coloured or patterned to look like wood. It makes the surface waterproof so it is protected from spills and can be cleaned more easily.
Reinforced concrete
The properties of concrete can be improved by reinforcing it with steel rods or mesh. The compressive strengthA measure of how well a material resists being crushed when a force is applied. of concrete is higher than its tensile strengthThe tension a material can withstand without breaking., but the tensile strength of steel is higher than its compressive strength. The combination of the two materials is strong in tension and in compressionBeing squashed.. Reinforced concrete is therefore strong and slightly flexible, whereas concrete alone is brittle.