07 - Recycling

What’s are the different types of recycling methods?

Give a short definition for each

Material recycling mechanical recycling)

→ process of transforming used plastics into new plastic products w/ changing the chemical structure of the polymer

→ used if parts can be collected & separated correctly

Recycling of raw material (chemical recycling)

→ process of breaking the polymer chains to get chemicals that can be used to make new plastics

→ suitable for mixed & impure components

Energy recovery

→ process of burning the plastic & using the released energy to produce electricity, steam, heat…

→ the material itself is lost

→ suitable for mixed, impure & polluted/ contaminated components

Special case: biodegradable plastics

→ can be composted or fermented

→ the recycling method is chosen based on the quality of the waste

What does the separation process consist of? Why do we do that?

What are the 2 ways of separating?

Consists of sorting out the different plastics to avoid poor-quality recycled plastic

• Manual separation: people sort the waste by hand

• automatic separation: machines & sensors are used instead of people

What’s the chemical recycling of plastics or biomaterials called?

What’s the purpose?

How does it work?

Pyrolysis

→ organic materials are decomposed by exposing them to high temperatures in an oxygen-free environment

Goal: to recover chemicals that can be used as raw materials in the chemical or petrochemical industries

1. The plastic is heated to high temperatures, which breaks the polymer chains = thermal degradation

2. The plastic doesn’t burn because there is no oxygen

What’s pyrolysis?

Chemical recycling process in which plastics are heated to high temperatures in an oxygen-free environment, which leads to the degradation of the polymer chains into smaller valuable molecules, that can be reused

What are the conditions for a plastic to be classified as compostable?

The plastic must…

• decompose within a specified time (can’t take 10 years)

• Leave no harmful residues (toxic substances/ chemicals/ heavy metals…)

• Fully decompose into natural products (visible plastic shouldn’t be left)

Official statement (standard):

• at least 90% of the plastic must be biologically decomposed by microorganisms

• This must happen within 90 days

• It must occur under the controlled conditions of an industrial composting plant

What are the 2 types of composting?

What’s the difference between them?

Industrial composting

• takes place in industrial composting plants

• The composting process carefully controlled with specific conditions (temp & moisture) that allow the plastic to break down efficiently

Home composting

• no specific conditions

• No predetermined time