Page 624 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Polymer Technology 587

Composites

Particle-reinforced Fiber-reinforced Structural

Large particle Continuous Discontinuous (short) Laminates Sandwich

FIGURE 18.6 Classification of polymer-intense composites.

TABLE 18.7
Materials Used for Heat Protection in the Space Shuttle Orbiter
Maximum Operating
o
Identifi er Temperature ( C) Description of Material
Advanced flexible reusable surface insulation 810 Quartz batting sandwiched between AFRSI

quartz and fibrous glass fabric
Felt-reusable surface insulation 400 Nylon felt with a silicone rubber FRSI
coating
High-temperature reusable surface insulation 1,250 Silica tiles, borosilicate glass coating
insulation HRSI with silicon boride added
Low-temperature reusable surface 650 Silica tiles with a borosilicate coating
insulation—LRSI
Reinforced carbon–carbon–RCC 1,650 Pyrolyzed carbon–carbon coated with
silicon carbide, SiC
The locations are given in Figure 18.7.

Composites are generally composed of two phases, one called the continuous or matrix phase
that surrounds the second called the discontinuous or dispersed phase. There are a variety of poly-
mer-intense composites that can be classified as shown in Figure 18.6. Many of these composite

groups are used in combination with other materials, including different types of composites and
like types of composites except differing in orientation.
Many naturally occurring materials such as wood are reinforced composites consisting of a res-
inous continuous phase and a discontinuous fibrous reinforcing phase.

Composites are also used extensively where light but very strong materials are needed such as in
the construction of the new Boeing 767 where composites play a critical role in the construction of
the exterior. They are also used where excessive high heat stability is needed such as in the reusable
space vehicle (Table 18.7).

Here we will briefly look at each of the main groupings of composites.
18.8.1.1 Particle-Reinforced Composites-Large-Particle Composites
Some materials to which fillers have been added can be considered as composites. These include

a number of the so-called cements, including concrete (Section 12.2). As long as the added par-
ticles are relatively small, of roughly the same size, and evenly distributed throughout the mixture
there can be a reinforcing effect. The major materials in Portland cement concrete are the Portland
cement, a fine aggregate (sand), course aggregate (gravel and small rocks), and water. The aggregate

particles act as inexpensive fillers. The water is also inexpensive. The relatively expensive material

is the Portland cement. Good strength is gained by having a mixture of these such that there is a

9/14/2010 3:43:38 PM
K10478.indb 587 9/14/2010 3:43:38 PM
K10478.indb 587