Reaction of ozone with individual wood component such as cellulose and lignin.

In reactions with lignin and cellulose, ozone behaves as a highly selective reactant, which can be documented by the values of the corresponding rate

constants, reaching ~104 M-1⋅s-1 when reacting with lignin compounds and ~10-1 M-1⋅s-1 in reactions with carbohydrate type substances at pH 2.

Stemming from the rate constant ratio, it can be concluded that the selectivity of ozone reactions ranges between 105 - 106 . Given the selectivity dependence on pH, it can be supposed that ozone reacts predominantly with

lignin during plasma treatment. This hypothesis is based on the acidic character of the reaction media stabilizing ozone against its decomposition. Due to plasma treatment, acid components (formic acid and acetic acid) are formed, the wood surface becomes more acidic which, in turn, leads to

increased selectivity of ozone reactions with wood components.

The elementary steps of the mechanism for reaction of lignin with ozone may involve:

• electrophilic substitution and 1,3-dipolar insertions;

• oxidative cleavage of C=C;

• syn-anti zwitterion isomerization;

• Criegee rearrangement;

• dimerization and polymerization via diperoxides and polymeric peroxides;

• cleavage of the carbon-carbon bonds of aromatic ring via 1,3 dipolar cycloaddition

• electrophilic substitution on aromatic rings, resulting in hydroxylation and

quinone formation;

• attack at acarbon-hydrogen bond adjacent to a1,3 dipolar insertion to hydrotrioxide;

• cleavage between the ring carbons bearing the hydroxyl and metoxyl substituents;

• oxidative radical coupling involving the phenoxy radical condensation of phenolic compounds during the first time of ozonisation;

• autoxidation of lignin initiated by ozone

Further information in article: Jablonsky, M., Smatko, L., Botkova, M., Tino, R., Sima, J. Modification of wood wettability (European Beech) by diffuse coplanar surface barrier discharge plasma, Cellulose Chem. Technol., 50 (1), 41-48 (2016)

Article Modification of wood wettability (European Beech) by diffuse...