Why are control samples of each plastic kept in the dark during a photodegradation experiment?

Dark controls show whether a change is caused by ultraviolet light rather than by heat, moisture or time alone.

State the independent and dependent variables in a UV propagator experiment comparing two plastics.

The independent variable is the type of plastic, or the time spent under ultraviolet light. The dependent variable is a measure of degradation, such as breaking force or brittleness.

Which variables must be controlled when comparing plastic samples in a propagator?

Strip size and thickness must be the same for both plastics. The distance from the bulbs, exposure time, temperature and humidity must also be kept constant.

What results would you expect after several weeks of UV exposure in a propagator?

The photodegradable plastic becomes brittle, discoloured and cracked, and may crumble when handled. The polythene strip shows little visible change.

CCEA A-Level Environmental Technology 3930

Fossil Fuels

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Global Action on Energy Conservation and Climate Change

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Macrogeneration

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Microgeneration

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Energy From Wind

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Energy From the Sun

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Energy Storage

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Plastics for the Future

Topic overview Crude oil as a fuel and a feedstock Refinery gases and the making of polymers Persistent plastic waste and the Great Pacific Garbage Patch Toxic gases from incinerating plastics Biodegradable, photodegradable and compostable plastics Testing photodegradable plastic against polythene Bio-derived polyethylene and a sustainable plastics future

Renewable Energy Investigations

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Sustainable Development

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Waste Management

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Waste to Energy Technologies

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Land Contamination and Remediation

Topic overview Contaminated land, risk and traditional remediation Bioremediation principles and bioreactor systems Micro-organisms that degrade named pollutants Bioremediation benefits and genetically engineered microbes Phytoremediation of metals and other elements Phytoextraction with Indian mustard and alpine pennycress Biohydrometallurgy and phytomining of ores

Hydrogen Fuel Cells

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Transport System Challenges

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Energy Performance of Buildings

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Emerging Technologies

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Sustainable Urban and Rural Communities

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The Code for Sustainable Homes

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Plastics for the Future

Testing photodegradable plastic against polythene

3 things to know
AS 1

Overview

The UV propagator experiment, controls and variables, expected results, tensile strength and the Newton meter, worked strength loss and stress calculations, repeats, limitations, UV safety and real-world conditions.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Evaluation

What are the limitations of using a simple Newton meter for tensile testing?

Key term

What is a propagator, and why is it used in plastic degradation experiments?

Key term

Outline a method to compare the degradability of photodegradable plastic and polythene.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a propagator, and why is it used in plastic degradation experiments?
Model answer
A propagator is a covered tray, often with a heated base, normally used to raise seedlings. UV bulbs fitted in the lid expose plastic samples to steady ultraviolet light and warmth.
2
Outline a method to compare the degradability of photodegradable plastic and polythene.
Model answer
Identical strips of each plastic are placed under UV bulbs in a propagator for several weeks. Samples are removed at intervals and checked for brittleness, cracking and loss of strength.
3
Why are control samples of each plastic kept in the dark during a photodegradation experiment?
Model answer
Dark controls show whether a change is caused by ultraviolet light rather than by heat, moisture or time alone.
4
State the independent and dependent variables in a UV propagator experiment comparing two plastics.
Model answer
The independent variable is the type of plastic, or the time spent under ultraviolet light. The dependent variable is a measure of degradation, such as breaking force or brittleness.
5
Which variables must be controlled when comparing plastic samples in a propagator?
Model answer
Strip size and thickness must be the same for both plastics. The distance from the bulbs, exposure time, temperature and humidity must also be kept constant.
6
What results would you expect after several weeks of UV exposure in a propagator?
Model answer
The photodegradable plastic becomes brittle, discoloured and cracked, and may crumble when handled. The polythene strip shows little visible change.

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Fossil Fuels

Global Action on Energy Conservation and Climate Change

Macrogeneration

Microgeneration

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