Carbon Fiber

Carbon fiber

Carbon fibers are produced by using heat to chemically change rayon or acrylic

fibers. Carbonization occurs at temperatures of 1000° C to 2500° C in an inert atmosphere. Carbon fibers are converted to graphite at temperatures above 2500° C. Carbon and graphite fibers can also be made from pitch, a residual petroleum product. Products that use carbon fibers include heat-shielding materials, aircraft fuselages and wings, spacecraft structures, and sports equipment. You can golf, ride, sail, tennis, drive, cycle, fish, decorate or even fly Carbon Fiber! Carbon fibers are derived from one of two precursor materials Pitch and Pan.

Pitch is based carbon fibers have lower mechanical properties and are therefore rarely used in critical structural applications. Pan based carbon fibers are

under continual development and are used in composites to make materials of

great strength and lightness.

The raw material of Pan, acrylonitrile, is a product of the chemical industry and can be manufactured as follows: Acrylonitrile is used as a raw material in acrylic fibers, ABS resin, AS resin, synthetic rubber, acrylamide and other materials. Global

production capacity is 4.67 million tons, approximately 60% of which is

consumed for acrylic fibers. In the early manufacturing processes acetylene and

hydrogen cyanide were used as a raw material, whereas today nearly all AN

is manufactured using what is called the Sohio process, whereby an ammoxidation

reaction are applied from inexpensive propylene and ammonia. Technological

advances, particularly surrounding research into improved catalysts for the

Sohio process, are proceeding, promoted by a concern for energy conservation

and lessening the environmental loading. The research aims include improved

productivity, reduced byproducts, and lesser wastewater and waste gas.

The Sohio process was perfected in 1960 by The Standard Oil Co. of Ohio, owing

to the development of an epoch-making catalyst that synthesizes AN in a single-

stage reaction using propylene and ammonia. The reaction took place using the

fluid-bed od. The P-Mo-Bi group is used as the catalyst and favorable fluidized

conditions are maintained by adjusting the physical properties of the

catalyst. The reaction gas contains not only AN, but also acetonitrile, hydrogen cyanide

and other byproduct gasses, so AN products are obtained by having the reaction

gas absorbed into water, then using evaporation separation. The Sohio process was epoch-making at the time it was developed, but improvements have been made in response to the following conditions: The AN yield of approximately 60% was not very high; The process circulated and used large amounts of water, requiring a lot of

energy. Approximately 1.5 tons to 2 tons of wastewater was generated for every ton

of AN produced. Treatment technology for the waste gas was incomplete.

The conversion of Pan to carbon fibers is normally made in 4 continuous stages

Oxidation, Carbonization (Graphitization), Surface treatment, and Sizing. Oxidation involves heating the fibers to around 300 deg C in air. This evolves hydrogen from the fibers and adds less volatile oxygen. The polymer changes from a ladder to a stable ring structure and the fiber changes color from white though brown to black. In this picture you see the fiber changing color. The white Pan strands at the bottom pass through the air heated oven and begin to darken Quite quickly they turn to black and carbon fiber is like the Ford T, As Henry said "Its any color you want, as long as it's black"

Photo courtesy of Akzo NobelThe resulting material is a textile fiber which is fireproof, some companies actually sell this as an end product for example SGL Technic, under the trade name Pan ox.

A summary of typical properties of the various grades of carbon fibers is

given by Toray, although the units of tensiometry are imperial sizing is a neutral finishing agent to protect the fibers during further processing (prepregging) and to act as an interface