大学入学共通テスト2022(R)⑨第６問B

Recycling Plastic
ーWhat You Need to Knowー

ー The world is full of various types of plastic. Look around, and you will see
dozens of plastic items. Look closer and you will notice a recycling symbol on
them. In Japan, you might have seen the first symbol in Figure 1 below, but
the United States and Europe have a more detailed classification. These
recycling symbols look like a triangle of chasing pointers, or sometimes a
simple triangle with a number from one to seven inside. This system was
started in 1988 by the Society of the Plastics Industry in the US, but since 
2008 it has been administered by an international standards organization, 
ASTM (American Society for Testing and Materials) International. Recycling
symbol provide important data about the chemical composition of plastic 
used and its recyclability. However, a plastic recycling symbol on an object 
does not always mean that the item can be recycled. It only shows what type
of plastic it is made from and that it might be recyclable.

ー So, what do these numbers mean? One group (numbers 2,4, and 5) is
considered to be safe for the human body, while the other group (numbers 1,
3, 6, and 7) could be problematic in certain circumstances. Let us look at the
safer group first.

ー High-density Polyethylene is a recycle-type 2 plastic and is commonly
called HDPE . It is non-toxic and can be used in the human body for heart
valves and artificial joints. It is strong and can be used at temperatures as low
as -40℃ and as high as 100℃. HDPE can be reused without any harm and is
also suitable for beer-bottle cases, milk jugs, chairs and toys. Type 2 products
can be recycled several times. Type 4 products are made from Low-density
Polyethylene (LDPE) . They are safe to use and are flexible. LDPE is used for
squeezable bottles, and bread wrapping. Currently, very little Type 4 plastic is
recycled. Polypropylene (PP), a Type 5 material, is the second-most widely
produced plastic in the world. It is light, non-stretching, and has a high
resistance to impact, heat, and freezing. It is suitable for furniture, food
containers, and polymer banknotes such as the Australian dollar. Only 3% of
Type 5 is recycled.

ー Now let us look at the second group, Types 1, 3, 6, and 7. These are more
challenging because of the chemicals they contain or the difficulty in recycling
them. Recycle-type 1 plastic is commonly known as PETE (Polyethylene
Terephthalate), and is used mainly in food and beverage containers. PETE
containers – or PET as it is often written in Japan – should only be used once
as they are difficult to clean thoroughly. Also, they should not be heated
above 70℃ as this can cause some containers to soften and change shape.
Uncontaminated PETE is easy to recycle and can be made into new containers,
clothes, or carpets, but if PETE is contaminated with Polyvinyl Chloride (PVC),
it can make it unrecyclable. PVC, Type 3, is thought to be one of the least
recyclable plastics known. It should only be disposed of by professionals and
never set fire to at home or in the garden. Type 3 plastic is found in shower
curtains, pipes, and flooring. Type 6, Polystyrene (PS) or Styrofoam as it is
often called, is hard to recycle and catches fire easily. However, it is cheap to
produce and lightweight. It is used for disposable drinking cups, instant noodle
containers, and other food packaging. Type 7 plastics (acylics, nylons, and
polycarbonates) are difficult to recycle. Type 7 plastics are often used in the
manufacture of vehicle parts such as seats, dashboards, and bumpers.

ー Currently, only about 20% of plastic is recycled, and approximately 55%
ends up in a landfill. Therefore, knowledge about different types of plastic
could help reduce waste and contribute to an increased awareness of the
environment.