The Effect of Crosslinking Agents

Compounds like dimeric sugars (e.g. sucrose) or polyacids (e.g. H3BO3), are of the hydrogen-bonding type. In the case of fibers from AN/VA (3.1 %), the addition of H3BO3 or sucrose to the polymer, prior to spinning, improved the carbon fiber properties substantially fibers from AN/VBr, however, did not show this positive response (see Table 8). 

Crosslinking by chemical bond formation was tried with maleic anhydride. It is known that the addition of dienophiles such as maleic anhydride or acrylamide reduces color formation ( discoloration ) in acrylic fibers. A reasonable explanation for this phenomenon has been given by Marien It is based on a Diels-Alder reaction of the dienophile with cis-dienic structures created during the oligomerization of the 

A polymer solution containing AN/MMA copolymer plus 5% (referred to polymer) of maleic anhydride gelled completely, indicating that the expected crosslinking actually took place. As the maleic anhydride concentration was reduced to 0.5%, fiber spinning was no longer a problem. However, at this low concentration the beneficial effect on carbon fiber properties was only minor (see Table 8). 

The question of reduced stabilization time has not been investigated, since the standard conditions have been applied throughout. Only in one case it was observed that a fiber of AN/MMA (3.2%) with 0.5% of maleic anhydride was fully stabilized in one hour at 250 °C, whereas the parent fiber (no additive) was not, under the same conditions. 

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