Page 48 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Introduction to Polymers 11

TABLE 1.4
Common Polymers
Material/Name Typical Polymer Chapter
Styrofoam Polystyrene 6
PVC pipe Poly(vinyl chloride) 6
Nylon stockings Polyamide, Nylon 6,6 4
Concrete Cement 12
Meat Protein 10
Plexiglass Poly(methyl methacrylate) 6
Automotive bumpers and side panels Polyethylene and polyethylene/polypropylene blends 5,7
Potatoes Starch 9
Compact discs (case) Polycarbonate (polystyrene) 4
Hula hoop Polypropylene, polyethylene 5
Diamond Carbon 12
Silicon sealants Polydimethylsiloxane 11
Bakelite Phenol-formaldehyde cross-linked 4
Super glue Poly(ethyl cyanoacrylate) 18
Cotton T-shirt Cellulose 9
Fiberglass Composite 8
Saran wrap PVC copolymer 7
Velcro Polyamide 4
Rubber band Natural rubber 9
Soda bottle Poly(ethylene terephthalate), PET 4
Tefl on Polytetrafl uoroethylene 6
Orlon sweater Polyacrylonitrile 6
Sand Silicon dioxide 12
Pillow stuffi ng Polyurethane 4
Wood, paper Cellulose 9
Human genome Nucleic acids 10

polymers that are present in many everyday items, either through looking at labels, researching on
the web, simply knowing what certain items are generally composed of, through the feel and gross
physical properties (such as flexibility and stiffness) of the material, and so on.

Further, the properties of essentially the same polymer can be varied through small structural
changes giving materials with differing properties and uses. There is a match between desired prop-
erties and the particular material used. For instance, for plastic bags, strength and fl exibility are
needed. The bag material should be somewhat strong, inexpensive (since most bags are “throw-
away” items), and readily available in large quantities. Increased strength is easily gained from

increasing thickness. But, with increased thickness comes decreased flexibility, increased cost since
more material is needed to make the thicker bags, and increased transportation (because of the addi-
tional weight) and storage costs. Thus, there is a balance between many competing factors. Plastic
bags are typically made from three polymers, HDPE, low-density polyethylene (LDPE), and linear
low-density polyethylene (LLDPE; actually a copolymer with largely ethylene units). These different
polyethylene polymers are similar, differing only in the amount of branching that results in differ-
ing tendencies to form ordered (crystalline) and less ordered (amorphous) chain arrangements. You
will learn more about them in Chapter 5. Grocery bags are generally made from HDPE which is a
largely linear polymer that has a high degree of crystallinity. Here, in comparison to LDPE fi lm with
the same strength, the bags are thinner, allowing a decrease in cost of materials, transportation cost,

and storage space. The thinness allows good flexibility. LDPE is used for dry cleaning garment bags
where simply covering the garments is the main objective rather than strength. The LDPE is less

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