Page 313 - Carrahers_Polymer_Chemistry,_Eighth_Edition

276 Carraher’s Polymer Chemistry

As with organic-matrix composites, advances with MMCs are continually being made to answer
the call for better materials to meet the ever increasingly restrictive requirements and the ever
broadening applications.

8.9 SUMMARY
1. Fillers are relatively inert materials that usually add bulk, but when well chosen they can enhance
physical and chemical properties. Many natural and synthetic materials are used as fi llers today.
These include polysaccharides (cellulosics), lignin, carbon-based materials, glass, and other inor-
ganic materials.
2. The most important reinforced materials are composites. They contain a continuous phase and
a discontinuous phase. There are a variety of composites. These include particulate composites,
structural composites, and fi ber composites.
3. Fiber-reinforced composites contain strong fibers embedded in a continuous phase. They form

the basis of many of the advanced and space-age products. They are important because they offer
strength without weight and good resistance to weathering. Typical fi bers are fi brous glass, car-
bon-based, aromatic nylons, and polyolefins. Typical resins are polyimides, polyesters, epoxys,

phenol-formaldehyde, and many synthetic polymers. Applications include biomedical, boating,
aerospace and outer space, sports, automotive, and industry.

4. Nanocomposites employ nanofibers that allow for much greater fiber–resin surface contact per

mass of fiber, and consequently they generally offer greater strength in comparison to similar
nonnanocomposites.
5. Concrete and particle board are examples of particulate composites. Plywood and Formica are
laminate composites.
6. Metal-matrix composites offer a number of possible advantages over classical organic compos-
ites, including greater radiation resistance, greater strength, greater fi re resistance greater stiff-
ness, and higher thermal and electrical conductivities.

GLOSSARY
Aspect radio: Ratio of length to diameter.
Comminuted: Finely divided.
Composites: Materials that often contain strong fibers embedded in a continuous phase called

a matrix or resin,
Diatomaceous earth: Siliceous skeletons of diatoms.
Discontinuous phase: Discrete filler additive, such as fibers, in a composite.

Extender: Term sometimes applied to inexpensive fi ller.
Fiberglass: Trade name for fi brous glass.
Fibrous filler: Fiber with an aspect ratio of at least 150:1.

Fibrous glass: Filaments made from molten glass.

Filament winding: Process in which resin-impregnated continuous filaments are sound on a
mandrel and the composite is cured.
Filler: Usually a relatively inert material used as the discontinuous additive; generally
inexpensive.
Fuller’s earth: Diatomaceous earth.

Graphite fibers: Fibers made by the pyrolysis of polyacrylonitrile fi bers.
Lamellar: Sheet like.
Laminate: Composite consisting of layers adhered by a resin.

Pultrusion: Process in which bundles of resin-impregnated filaments are passed through an
orifice and cured.

9/14/2010 3:40:36 PM
K10478.indb 276 9/14/2010 3:40:36 PM
K10478.indb 276