1Polymer composites.ppt (Size: 3.64 MB / Downloads: 88)
What are polymer composites?
A composite is any material made of more than one component. There are a lot of composites around you. Concrete is a composite. It's made of cement, gravel, and sand, and often has steel rods inside to reinforce it.
Polymer composites are composites made from polymers, or from polymers along with other kinds of materials.
These are materials in which a fiber made of one material is embedded in another material.
Modern composites are usually made of two components, a fiber and matrix. The fiber is most often glass, but sometimes Kevlar, carbon fiber, or polyethylene. The matrix is usually a thermoset like an epoxy resin, polydicyclopentadiene, or a polyimide.
The fiber is embedded in the matrix in order to make the matrix stronger. Fiber-reinforced composites are strong and light. They're often stronger than steel, but weigh much less. This means that composites can be used to make automobiles lighter, and thus much more fuel efficient. This means they pollute less, too.
A common fiber-reinforced composite is FiberglasTM. Its matrix is made by reacting a polyester with carbon-carbon double bonds in its backbone, and styrene.
The styrene and the double bonds in the polyester react by free radical vinyl polymerization to form a crosslinked resin. The glass fibers are trapped inside, where they act as a reinforcement.
Matrix holds the fibers together. A loose bundle of fibers wouldn't be of much use.
Though fibers are strong, they can be brittle. The matrix can absorb energy by deforming under stress. This is to say, the matrix adds toughness to the composite.
While fibers have good tensile strength (that is, they're strong when you pull on them), they usually have bad compressional strength. That is, they buckle when you squash them. The matrix gives compressional strength to the composite.
Measuring up fibers
Glass is the most popular fiber because it's really cheap. When glass is spun into really tiny fibers, it acts very different. Glass fibers are strong, and flexible.
Other fibers include Kevlar, carbon fiber, or Spectra.
Applications of fiberglass
Gliders, kit cars, sports cars, microcars, karts, bodyshells, boats,kayaks, flat roofs, lorries.
Pods, domes and architectural features where a light weight is necessary.
High end bicycles.
Storage tanks, piping, house building.