Materials: woods, metals, plastics and composites

ZIMSEC O Level · Design and Technology · Form 1, Form 2

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Woods

Hardwoods (mukwa, teak), softwoods (pine) and manufactured boards (plywood, MDF, chipboard).

Metals

Ferrous (mild steel, cast iron, stainless steel) and non-ferrous (aluminium, copper, brass).

Plastics

Thermoplastics soften when heated and can be reshaped: acrylic (Perspex), polythene, PVC, polystyrene. Used for bottles, pipes and signs.
Thermosetting plastics set permanently and do not soften: melamine (worktops), urea-formaldehyde (electrical fittings), epoxy resin.

Plastics are light, waterproof and easily shaped, but many are non-biodegradable.

Composites

Two or more materials combined: reinforced concrete, glass-reinforced plastic (fibreglass), plywood, carbon fibre.

Smart and modern materials

Thermochromic materials change colour with temperature; shape-memory alloys return to their original shape when heated.

Choosing materials

Consider strength, weight, appearance, durability, ease of working, cost, availability and environmental impact. Reusing waste materials (tyres, bottles, scrap metal) is sustainable and cheap.

Exam tip: Give the property that makes a material suitable – “acrylic: easily shaped by heat and comes in bright colours”.

Check yourself

Distinguish between thermoplastics and thermosetting plastics.
Give one example of a composite material.
Name a material suitable for a weatherproof sign and give a reason.

Show answers

Thermoplastics can be reheated and reshaped; thermosets set permanently and cannot.
Any one: reinforced concrete, fibreglass, plywood, carbon fibre.
Acrylic – waterproof, durable and easily cut and shaped (aluminium is also acceptable).

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