Page 47 - Carrahers_Polymer_Chemistry,_Eighth_Edition

10 Carraher’s Polymer Chemistry

plastic models, toy cars, dolls, skip ropes, hula hoops, and corvettes. Our food is polymer intense
as meat, vegetables, breads, and cookies. In history, polymers have been the vehicle for the Magna
Carter, Torah, Bible, Koran, and our Declaration of Independence. Outside our homes they are
present in our flowers, trees, soil, spider webs, and beaches. In fact, it is improbable that a polymer

is not involved in your present activity—reading a paper book, holding a plastic-intense writing
device, sitting on a cloth-covered chair or bed, and if your eyes need corrective vision, glasses of
one variety or another.
Polymers gain their importance because of their size. Many polymers are made from inexpensive
and readily available materials, allowing vast quantities of products to be made for a high increase
in value, but they are typically inexpensive compared to nonpolymer alternatives. They also often
have desirable physical and chemical properties. Some polymers are stronger on a weight basis than
steel. Most are resistant to rapid degradation and rusting. You will learn more about these essential
materials for life and living in this text.
Polymers are often divided according to whether they can be melted and reshaped through appli-
cation of heat and pressure. These materials are called thermoplastics. The second general clas-

sification belongs to compounds that decompose before they can be melted or reshaped. These
polymers are called thermosets. While both thermoset and thermoplastic polymers can be recycled,
because thermoplastics can be reshaped simply through application of heat and pressure, recycling
of thermoplastics is easier and more widespread.
In general groups, synthetic polymers are often described by their “use” and “appearance” as
fibers, elastomers, plastics, adhesives, and coatings. A common toothbrush illustrates the three

major physical forms of synthetic polymers—the rubbery (elastomeric) grips, plastic shaft, and
fibrous brussels. The rubbery grips have a relatively soft touch; the plastic shaft is somewhat fl exible

and hard, and the brussels are highly fl exible. Another illustration of the breath of polymers about
us is given in Table 1.4 where polymers are divided according to the source.
To get an idea of the pervasiveness of polymers in our everyday life, we can look at containers.
Most containers are polymeric—glass, paper, and synthetic polymer. It is relatively easy to identify
each of these general categories. Even, within the synthetic polymer grouping, it has become rela-
tively easy to identify the particular polymer used in some applications, such as with disposable con-

tainers. Most of these synthetic polymers are identified by an “identification code” that is imprinted

somewhere on the plastic container, generally on their bottom. The numbers and letters are described
in Figure 1.1. The recycling code was developed by the Society of Plastics Industry for use with con-
tainers. Today, the “chasing-arrows” triangle is being used more widely for recycling by the public.
A colorless somewhat hazy water container has a “2” within the “chasing” arrows and underneath it
“HDPE,” indicating that the bottle is made of HDPE. The clear, less flexible soda bottle has a “1” and

“PETE,” both signifying that the container is made out of PET, a polyester. A brownish clear medi-
cine container has a “5” and the letters “PP” on its bottom conveying the information that the bottle
is made of polypropylene. Thus, ready identification of some common items is easy.

But, because of the use of many more complex combinations of polymers for many other items,
such identification and identification schemes are not as straightforward. For some items, such as

clothing and rugs, labels are present that tell us the major materials in the product. Thus, a T-shirt
might have “cotton” on its label indicating that the T-shirt is largely made of cotton. A dress shirt’s
label may say 55% cotton and 45% polyester meaning it is made from two polymers. Some items are
identifi ed by trade names. Thus, a dress advertised as being made from Fortrel (where “Fortrel” is
a trade name) means it is made largely of a polyester material, probably the same polyester, PET or
PETE, which made our soda bottle. Some everyday items are a complex of many materials but only
some or none are noted. This is true for many running shoes and tires. Tires will often be described
as being polyester (again, probably the same PETE) or nylon (or aramid). This describes only the
composition of the tire cord but does not tell us what other materials are included in the tire’s com-
position. Yet, those that deal with tires generally know what is used in the manufacture of the tire in

addition to the “stated ingredients.” You will be introduced, gently, to the identification of the main

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