Page 296 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Composites and Fillers 259

TABLE 8.1 (continued)
Types of Fillers for Polymers
2. Ground petroleum coke 2. Whiskers (including nonoxide)
3. Graphite fi laments a. Aluminum oxide
4. Graphite whiskers b. Beryllium oxide
E. Polyfl uorocarbons
II. Inorganic materials c. Zirconium oxide
A. Silica products d. Aluminum nitride
1. Minerals e. Boron carbide
a. Sand f. Silicon carbide & nitride
b. Quarts g. Tungsten carbide
c. Tripoli h. Beryllium carbide
2. Synthetic materials G. Calcium carbonate
a. wet-processed silica 1. Calk
b. Pyrogenic silica 2. Limestone
c. Silica aerogel 3. Precipitated calcium carbonate
H. Barium ferrite and sulfate

Among the naturally occurring filler materials are cellulosics such as wood fl our, α-cellulose,
shell flour, and starch, and proteinaceous fillers such as soybean residues. Approximately 40,000

tons of cellulosic fillers are used annually by the U.S. polymer industry. Wood fl our, which is pro-
duced by the attrition grinding of wood wastes, is used as filler for phenolic resins, urea resins,

polyolefins, and poly(vinyl chloride) (PVC). Shell flour, which lacks the fibrous structure of wood

flour, has been used as a replacement for wood flour for some applications.

α-Cellulose, which is more fibrous than wood flour, is used as filler for urea and melamine plas-
tics. Melamine dishware is a laminated structure consisting of molded resin-impregnated paper.
Presumably, the formaldehyde in these thermosetting resins react with the hydroxyl groups in cel-

lulose, producing a more compatible composite. Starch and soybean fillers have been used to make
biodegradable composites and other materials.
Carbon black, which was produced by the smoke impingement process by the Chinese more
than 1,000 years ago, is now the most widely used filler for polymers. Much of the 1.5 million tons

produced annually is used for the reinforcement of elastomers. The most widely used carbon black
is furnace carbon black.
Conductive composites are obtained when powered metal fillers, metal flakes, or metal-plated

fillers are added to resins. These composites have been used to produce forming tools for the aircraft
industry and to overcome electromagnetic interference in offi ce machines.
Calcium carbonate is available as ground natural limestone and as a synthetic chalk. It is widely
used in paints, plastics, and elastomers. The volume relationship of calcium carbonate to resin or

the pigment volume required to fill voids in the resin composite is called the pigment-volume con-
centration (PIVC).
8.2 TYPES OF COMPOSITES
There are a variety of polymer-intense composites that can be classified as shown in Figure 8.1.

Many of these composite groups are used in combination with other materials, including different
types of composites. Many naturally occurring materials such as wood are reinforced composites
consisting of a resinous continuous phase and a discontinuous fibrous reinforcing phase.

Structural composites include laminas that can be sandwich or laminate. At times there is con-
fusion between which materials are sandwich or laminate laminas. Even so, here we will consider

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