Polymers are long chains of molecules that make up many everyday materials, especially plastics. Think of them as a string of beads where each bead is a small molecule. The way these beads connect determines how the plastic behaves.
Some plastics are very flexible (like a rubber band), while others are rigid (like a plastic bottle). Flexibility means the polymer chains can slide past each other easily, which makes the material soft. Rigid plastics have tightly packed chains, so they resist bending.
Thermal stability is how well a plastic can withstand heat. High thermal stability plastics can be melted and reshaped without breaking apart. Low thermal stability plastics melt at lower temperatures.
Some plastics resist chemicals like acids and bases, while others are easily attacked. This property affects how they can be reused or recycled.
| Plastic | Chemical Resistance |
|---|---|
| PET | Good |
| PVC | Poor |
Why are plastics hard to dispose of?
When plastics end up in landfills, they occupy space and can leach chemicals into the soil and groundwater. Imagine a giant pile of plastic bags that never shrinks – that’s the problem.
Plastics that wash into rivers can travel to oceans, where they break into microplastics. These tiny particles are eaten by fish and eventually reach our plates.
Recycling plastics requires energy to melt and reform them. The more energy used, the higher the carbon footprint.
Plastics are shredded, melted, and reshaped. This works best for polymers that can withstand repeated heating, like PET.
Plastics are broken down into their monomers and then re‑polymerised. This can handle more types of plastics but is currently more expensive.
Made from plant materials, these plastics can break down faster in the right conditions. However, they still need proper composting facilities.
Key points to remember:
Exam Question Example:
“Explain how the thermal stability of a polymer influences its suitability for recycling. Use examples of PET and PVC.”
Answer tip: Mention that PET has a high \$T_d\$ (~250 °C) making it suitable for repeated melting, whereas PVC degrades at lower temperatures (~200 °C) and releases HCl, making recycling more problematic.