F5chapter 7

Why thermosetting plastic cannot be
soften/ remoulded?

Thermosetting plastic molecules have cross-
links between polymer chains.

Prevent polymer chains slide over each other-
cannot be remoulded

Thermosetting plastic

 If reheated it- not soften again
Can the thermosetting plastic be recycled???

Non-recyclable

Examples of thermosetting plastics

Melamine

Hard
Heat-resistant

Bakelite

Uses:
Buttons
Car bumper
Electrical plugs and switches
Handle of cookware/iron

Epoxy resin

Use:
As adhesive /glue for metals, glass, wood,
leather, concrete

Analysing Plastic Topic 7 Synthetic Materials I

Plastics Examples and uses of plastic
Polythene
Polyvinyl chloride Uses
Plastic bags, plastic container.
(PVC) Food trays, cling film, bottles for mineral water,
Polystyrene shampoo, garden hose, toys.
Foam trays, protective packaging for electrical goods
Perspex Substitute glass window for aeroplane
Bakelit Electric switches and sockets, handles of kettles
Melamine
Epoxy Plates, bowls.
Adhesives, epoxy glues.

Past Year

Topic 7 Synthetic material in industry

Analysing plastics

Comparison between thermoplastics and thermoset

Thermoplastics Thermoset

Polymer chains Polymer chains are
slide over one holded by cross-
another without links which prevent
intersecting. polymer chains
Cross links from sliding over
Characteristics one another
Characteristics
I. Melt when reheated but harden
when cooled. I. Do not melt when reheated.

II. Soft II. Hard

III. Can be moulded repeatedly, it III. Can be moulded only once,
cab be recycled. can not be recycled.

IV. No colour and transparent. IV. Usually opaque.

ITeach – Science Form 5

Nowadays, plastic can replace many
materials such as metal, wood and

glass to make things.

What are the characteristics of plastic
that make it widely used in our daily life?

 Strong
 Light
 Easily washable
 Can be moulded into different shapes
 Can be coloured
 Cheap

A modern type of plastics was invented.
Composite plastics – made from different types

of plastics ( much stronger than usual plastic)

Astronaut’s
clothing

Bulletproof Fireman’s
vest clothing

Topic 7 Synthetic Materials In Industry

Practicing Responsible Attitude In The Disposal Of Synthetic Polymers

Example of synthetic fibre

Synthetic fibre Uses

Nylon Nylon strings, textiles, carpets, fishing Nylon bristles
net Nyloonf tsoooctkhsbrushes
Nylon rope
Polyester Textiles, threads, strings
Polyester sail
Example of composite Plastic

Composite plastic Uses

Kevlar Bulletproof vest, racing helmet,
yacht, aircraft

Nomex Firefighting clothes, racing vehicle
industries, racing glove

Teflon Non-stick coating pan and
cookware, pipelines.

Mylar Electronic and electrical industries

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ITeach – Science Form 5

The effects of improper disposal of
plastic

Plastic
pollution

Why is the drain clogged?

 Plastics are thrown into
the drains.

Will the plastic
decompose?

- No, because plastic is non-
biodegradable materials.

-Remain in the
environment for
hundreds of years.

What will happen
if the drain/ river
is clogged by
plastic rubbish?



Breeding of Aedes mosquito in clogged
drain/river ( stagnant water)

Plastic thrown on land – destroy the
beauty of surroundings

What will happen if the plastics bags
are thrown into the sea?

The marine
animals
may die
when
entangled
in plastics.

The turtle or seabirds died after they
mistakenly ate the plastic bag.

Plastic bag
Toxic
Block the stomach –
- cause starvation

Plastic bags looks like jellyfish – food
for some marine animals

Open burning of plastics releases:

The gases released can cause acid rain.

Destroy
forest

Kill the
marine
life

Carbon dioxide – Greenhouse effect

Carbon monoxide

Breathing carbon monoxide can cause
Headache
Dizziness
vomiting and nausea.

Black smoke – toxic gas ( dioxin)

 Asthma
 Bronchitis
 Cancer
 destroy

immune system
/ reproductive
system and
nervous system.

Effects of improper disposal of plastics

1. Clog drains/rivers
- Cause flash flood / breeding of Aedes mosquito

2. Marine animals died when
- Entangled by plastics
- Mistakenly ate the plastic

3. Destroy the beauty of the environment

4. Burning of plastics cause air pollution.
-Greenhouse effect / global warming
-Acid rain

- Release toxic gas – harmful to human health

What are the ways to control plastic
waste disposal?

1. Practising 3R

Plastic materials

Reduce

Bring your own shopping bag when go to the
market.

Bring your own food containers to buy food.

Reuse

1. Reuse plastic bags ( don’t just throw away after
use once)

2. Donate plastic toys to orphanage.
3. Other examples :





Recycle

2. Use biodegradable plastic

Can be decomposed by bacteria.

3. Burn the plastic waste products in
an enclosed incinerators.

Air cleaning
system
filter the smoke
before

releasing into
the air.

Ways to control plastic waste disposal

1. Reduce, reuse and recycle plastic materials.
2. Use biodegradable 可被分解的 plastics.
3. Burn the plastic waste products in an

enclosed incinerator 焚化炉 equipped with
air cleaning systems.