FIELD OF THE INVENTION

The invention relates to a method for increasing the reactivity of lignin and to the further use of such lignin.

BACKGROUND OF THE INVENTION

Lignin is a natural polymer, which can be extracted from e.g. wood. As lignin is a natural biopolymer its use as a component in glues instead of synthetic materials has been investigated in order to come up with a more environmentally friendly adhesive composition. Especially, the ability to replace synthetic phenol in phenolic resins, such as phenol formaldehyde resin, has been the object of prior art.

Different types of adhesive compositions, such a phenolic glues, can be used with wood products. Examples of such glues include compositions comprising phenol formaldehyde resin. Traditionally synthetic phenol formaldehyde resins are produced by polymerizing phenol and formaldehyde in the presence of a catalyst. Examples of such catalysts are sodium hydroxide (NaOH) and acids. The method for producing phenol formaldehyde resin comprises adding formaldehyde in a stepwise manner to a phenol composition and thereafter rising the temperature of the formed composition up to 80-90° C. The composition is cooked at this temperature until a desired viscosity of the formed resin or polymer chain length is reached.

Lignin can be used for the purpose of decreasing the amount of synthetic phenol in a resin composition. Lignin has previously been used for replacing phenol during the production of lignin-phenol-formaldehyde resin.

It has been possible to replace up to 30 of the synthetic phenol in the final resin, e.g. phenol formaldehyde resin, with lignin, but higher replacement results in unsatisfying properties of the produced glue.

The inventors have therefore recognized a need for a method, which would result in a higher phenol replacement in the composition and thus in a more environmentally friendly binder composition having suitable properties for use in different applications.

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new method for increasing the reactivity of lignin. Further, the purpose of the invention is to provide a new type of method, where the more reactive lignin is used for replacing at least part of the amount of synthetic materials used during the production of a binder composition. Especially the purpose is to produce a more environmentally friendly binder composition to be used e.g. in adhesive applications.

SUMMARY

A alkalated lignin having an opened macromolecular structure according to the present invention is prepared by prepared by a process comprising a) forming, under heating at a temperature of 30-70° C., an aqueous dispersion consisting of alkali and lignin and water, wherein the alkali comprises a hydroxide of an alkali metal, and wherein the concentration of the lignin is 10-50 weight-% based on the total weight of the aqueous dispersion in step a); and b) heating the aqueous dispersion formed in step a) at a temperature of 50-95° C., thereby producing the alkalated lignin, wherein the alkalated lignin has increased reactivity relative to the lignin.

A hydroxymethylated lignin according to the present invention is formed from a reaction of the alkalated lignin detailed above and an aldehyde.

