Modification of xylan

Abstract

The invention provides a method of modifying soluble xylan which contains glucuronic acid and / or arabinose side chains so that it can be adsorbed onto other substrates. The method includes the steps of enzymatically modifying the xylan by selectively removing glucuronic acid and / or arabinose side chains from the xylan with α-D-glucuronidase and / or α-L-arabinofuranosidase, and allowing the modified xylan to adsorb onto the substrate. The substrate may be a cellulosic substrate like pulp or paper or a non-cellulosic substrate. The enzymes are able to remove a sufficient number of the xylan side chains so as to decrease water solubility of the xylan, induce xylan precipitation and allow adsorption of the xylan onto other substrates. A pulping process which incorporates modification of xylan and adsorption onto cellulosic material is also provided, as are products which contain the modified xylan.

Description

FIELD OF THE INVENTION[0001]This invention describes a method for enzymatically modifying xylan so that it can be adsorbed or coated onto a substrate, a product comprising modified xylan adsorbed or coated onto the substrate and a pulping process incorporating the method.BACKGROUND TO THE INVENTION[0002]The principal components of plant biomass are lignin, cellulose and hemicellulose. Cellulose in the plant cell wall is present in close association with hemicellulose in a matrix encrusted by lignin. One of the major hemicelluloses in most plant cell walls is xylan. Xylan is a polymer consisting of a 1,4-β-linked D-xylose backbone chain substituted with L-arabinose, D-glucuronic acid or both and various short oligosaccharide chains consisting of D-xylose, -L-arabinose, galactose, glucuronic acid, and O-acetyl groups. Depending on the plant biomass source, morphological plant part and physiological stages of plant maturity, the xylan contained therein may also contain feruloyl and p-c...

AI Technical Summary

Benefits of technology

The patent text is about a way to modify a type of sugar called xylan to make it less soluble in water. This can be useful in certain applications where reducing water solubility is important.

Problems solved by technology

However, because xylan is soluble, an undesirable side effect of this process is that xylan is removed along with the lignin, resulting in reduced pulp yields and reduced fibre strength.

Not only is this a waste of a valuable resource, but it is also an environmental hazard, as the degraded xylans release organic acids and chromophogenic compounds which, when coupled with large amounts of chemical discharges from the kraft process, increase the COD loading of waste water streams.

These methods, however, result in random desubstitution and undesirable depolymerisation of the xylan.

Although additives such as clay, derivatised starch and cellulosic products are often added to increase yield and improve the pulp fibre function, higher loading of these additives is associated with retention, dusting and fibre-to-fibre contact problems.

Inter-fibre bonding is consequently weakened, further reducing paper strength.

Images