Hexenuronic acid

Hexenuronic_acid.svg

Hexenuronic acid is a compound that is formed during the kraft process of pulping wood. It is a derivative of 4-deoxy-β-L-threo-hex-4-enopyranosyluronic acid and is known to affect the bleaching process of pulp (paper).

Formation

Hexenuronic acid is formed from the xylan component of wood during the kraft pulping process. The formation occurs when the 4-O-methylglucuronic acid groups attached to the xylan backbone are converted into hexenuronic acid under the alkaline conditions of the kraft process.

Impact on Pulp Bleaching

Hexenuronic acid has a significant impact on the bleaching of kraft pulp. It consumes bleaching chemicals, such as chlorine dioxide and ozone, which increases the cost and environmental impact of the bleaching process. Additionally, hexenuronic acid can contribute to the formation of colored compounds, which can affect the brightness and quality of the final paper product.

Removal

To mitigate the effects of hexenuronic acid, various methods have been developed to remove it from kraft pulp. One common method is the use of acid hydrolysis, which breaks down hexenuronic acid into smaller, more easily removable components. Another approach is the use of specific enzymes, such as xylanase, which can selectively degrade hexenuronic acid without damaging the cellulose fibers in the pulp.

Research and Development

Ongoing research in the field of pulp and paper science is focused on finding more efficient and environmentally friendly methods to remove hexenuronic acid from kraft pulp. This includes the development of new chemical treatments, enzymatic processes, and modifications to the kraft pulping process itself.

See Also

• Kraft process
• Pulp (paper)
• Xylan
• Bleaching of wood pulp
• Chlorine dioxide
• Ozone