Branching of hemicelluloses through an azetidinium salt ring-opening reaction

• Carbonyl groups and uronic acids are favorable for the reaction between azetidinium salts and hemicelluloses and are the target for the branching reaction.
• Introduction of carbonyl groups to the hemicellulose polymer through TEMPO-oxidation increases reaction efficiency with azetidinium salts.
• Azetidinium containing compounds gives a Y-shaped branching where smaller functional groups give higher substitution.
• The glucuronic acids in xylan were almost fully substituted when reacted with azetidinium salt prepared from diethylamine.

During the last century there has been a steady increase in the number of publications on practical applications of hemicellulose. Due to the water and moisture sensitivity, poor film-forming ability and lack of thermal processability most of the hemicelluloses need to be chemically modified prior to processing into materials. Within this study we present the results of azetidinium salts as a new functional group for conjugation to polysaccharides. The reactivity of three azetidinium salts on xylan, arabinoxylan and galactoglucomannan was investigated. Carbonyl groups were found to be favorable for the reaction with azetidinium salts and thus the glucuronic acid content in the hemicellulose determines the degree of substitution. TEMPO-oxidation of the hemicelluloses was done which successfully increased the degree of substitution. The highly reactive azetidinium salts are easily synthesized from secondary amines and epichlorohydrin and can be used as a new tool toward functionalization of hemicelluloses into the after sought properties.

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