Color reduction of sulfonated eucalyptus kraft lignin

Area of Science:

• Lignin Chemistry
• Biomass Valorization
• Pulp and Paper Industry

Background:

• Eucalyptus kraft lignin is a byproduct with potential applications.
• Lignin's dark color limits its use in high-value products.
• Developing effective lignin decolorization methods is crucial.

Purpose of the Study:

• To prepare and characterize sulfonated eucalyptus lignins using different methods.
• To investigate the color properties and molecular weight of the prepared lignins.
• To evaluate the effectiveness of butane sultone sulfonation and sodium borohydride treatment for lignin decolorization.

Main Methods:

• Preparation of lignins via high-temperature sulfonation (HSL), sulfomethylation (SML), and butane sultone sulfonation (BSL).
• Characterization using UV-vis spectroscopy, FTIR, 1H NMR, and GPC.
• Brightness testing and color property evaluation of modified lignins.

Main Results:

• BSL exhibited higher molecular weight and lighter color due to phenolic hydroxyl blocking by 1,4-butane sultone (1,4-BS).
• Sodium borohydride treatment of BSL (SBSL) further enhanced color reduction, improving brightness by 76.1% compared to HSL.
• The SBSL process demonstrated superior performance over HSL and SML.

Conclusions:

• Phenolic hydroxyl blocking by 1,4-BS is key to reducing lignin color.
• Sodium borohydride's reducibility significantly contributes to the decolorization of sulfonated eucalyptus kraft lignin.
• The SBSL method offers an effective route for producing brighter lignin.