Understanding Plastics

What is a key characteristic of thermoplastics?

• They cannot be remoulded once set.

• They can be remoulded multiple times.

• They are always biodegradable.

• They are always transparent.

Answer explanation

A key characteristic of thermoplastics is that they can be remoulded multiple times when heated, allowing for flexibility in manufacturing and recycling. This distinguishes them from thermosetting plastics, which cannot be reshaped once set.

What happens to thermoset plastics when they are heated after setting?

• They melt and can be reshaped.

• They become softer but retain their shape.

• They burn or char.

• They dissolve in water.

Answer explanation

Thermoset plastics do not melt upon reheating; instead, they undergo degradation, often burning or charring. This is due to their cross-linked structure, which prevents them from being reshaped like thermoplastics.

Which of the following is an example of a thermoplastic?

• Epoxy resin

• Polyethylene

• Bakelite

• Melamine

Answer explanation

Polyethylene is a thermoplastic, meaning it can be melted and reshaped multiple times. In contrast, epoxy resin, Bakelite, and melamine are thermosetting plastics, which harden permanently after being set.

Why are thermoset plastics often used in high-temperature applications?

• They are cheaper than thermoplastics.

• They are more flexible.

• They do not melt when heated.

• They are transparent.

Answer explanation

Thermoset plastics are ideal for high-temperature applications because they do not melt when heated. Unlike thermoplastics, which can soften and lose shape, thermosets maintain their structure and integrity under heat.

Which of the following is a disadvantage of thermoplastics?

• They are difficult to recycle.

• They can melt when exposed to high temperatures.

• They are always brittle.

• They are not available in different colours.

Answer explanation

Thermoplastics can melt when exposed to high temperatures, making them unsuitable for applications requiring heat resistance. This characteristic is a significant disadvantage compared to other materials.

What is the primary difference between thermoplastics and thermoset plastics?

• Thermoplastics are always heavier.

• Thermoset plastics can be remoulded.

• Thermoplastics can be remoulded multiple times.

• Thermoset plastics are always transparent.

Answer explanation

The primary difference is that thermoplastics can be remoulded multiple times when heated, while thermoset plastics cannot be reshaped after curing. This makes thermoplastics more versatile for various applications.

Which of the following is a property of thermoset plastics?

• They are soluble in water.

• They can be reshaped after setting.

• They are rigid and heat-resistant.

• They are always flexible.

Answer explanation

Thermoset plastics are known for being rigid and heat-resistant, making them suitable for high-temperature applications. Unlike thermoplastics, they cannot be reshaped after setting, which distinguishes their properties.

What is a common application of thermoplastics?

• Circuit boards

• Car tyres

• Plastic bottles

• Ceramic tiles

Answer explanation

Plastic bottles are a common application of thermoplastics due to their lightweight, durability, and ease of molding. Unlike circuit boards, car tyres, and ceramic tiles, which use different materials, plastic bottles are primarily made from thermoplastics.

Which of the following materials is a thermoset plastic?

• Polyvinyl chloride (PVC)

• Nylon

• Polyester resin

• Polypropylene

Answer explanation

Polyester resin is a thermoset plastic, meaning it hardens permanently when cured. In contrast, PVC, nylon, and polypropylene are thermoplastics, which can be remelted and reshaped.

Name the main sources of Polymers

• Crude Oil

• Coal

• Ores

• Natural Gas