Woods, metals and plastics

According to their origin, materials can be natural, derived (processed from a natural material) or synthetic (man-made). Classify these materials: pine wood, plastic, steel, cotton, glass. Explain the criteria you followed in each case.

The figure shows the classification tree of materials according to their origin, with examples in each branch, but one card is covered with a question mark, as shown in the diagram.

What example of a synthetic material could be hidden behind the covered card? Explain what each of the three branches means and add a new card, with its example, to each branch.

The figure shows two production chains going from the raw material to the finished object, but one link is covered, as shown in the diagram.

Which link is missing in the second chain? Explain the difference between raw material, material and object, and build a completely new chain starting with 'sand' and ending with 'window'.

A natural wooden board and a piece of plywood can be distinguished at a glance. Explain what differences can be seen (continuous grain versus thin glued layers) and why plywood is considered a processed wood material and not natural wood.

Manufactured boards (plywood, MDF, chipboard) have replaced solid wood in most furniture. Explain two advantages of manufactured boards (price, large stable panels, use of wood waste) and one disadvantage (they get damaged by moisture, joints hold less weight).

A table can be made of pine (softwood) or oak (hardwood). Compare the price, hardness and ease of working with each wood, and choose one for the workshop workbench, which will suffer knocks and scratches daily. Justify your choice.

Match each material to its family: (a) pine, (b) plywood, (c) steel, (d) aluminium, (e) PVC. Families: 1. non-ferrous metal; 2. natural wood; 3. plastic; 4. manufactured board; 5. ferrous metal.

Metals are divided into ferrous (containing iron, like steel) and non-ferrous (like copper or aluminium). Compare their typical properties (hardness, oxidation, electrical conductivity, weight) and match each metal with a common use: steel, copper and aluminium with tools and structures, electrical cables, and cans and window frames.

Electrical cables are almost always made of copper rather than steel, even though steel is cheaper and stronger. Reason which properties win out in this decision (copper conducts electricity much better and is ductile: it can be drawn into thin wires) and why price is not everything when choosing a material.

True or false? Justify each answer: (a) aluminium is a ferrous metal; (b) most plastics are obtained from crude oil; (c) wood is a renewable material if forests are replanted; (d) all metals oxidise with the same ease.

Window frames are usually made of aluminium or PVC, rarely of steel. Explain which properties make steel impractical for this use (weight, rusting/corroding with rain) and what each of the two materials that are used contributes.

A simple pen combines several different plastics: the rigid body, the soft grip section and a transparent part to see the ink. Explain why a single plastic is not used for everything and what property each part aims for.

Match each item of waste with its destination: (a) a plastic bottle, (b) an old newspaper, (c) a glass jar, (d) a broken wood and metal chair. Destinations: 1. green bin; 2. blue bin; 3. yellow bin; 4. household recycling centre. Explain why the chair does not go into any of the first three.

An old mobile phone contains plastic, glass, copper, aluminium and even a pinch of gold. Explain why it should not be thrown in the normal bin, what a household recycling centre is, and which materials you think can be recovered and for what purpose.

A company markets a cleaner in a container consisting of a PET plastic bottle, a polypropylene cap, and a PVC wrap-around label attached with permanent adhesive. Although all three plastics are theoretically recyclable separately, in the recycling plant this container is almost impossible to recover and is downgraded to low-quality waste. Explain why this happens on a technical level compared to recycling a steel can, and redesign the container by applying ecodesign criteria to ensure it can be recycled with high quality.