Modification of lignin structure by amine group introduction

• Amination of lignin conducted simply by Mannich reaction is an important mean for lignin structural and value upgradation. However, there is a lack of powerful analysis for quantification of the amine groups introduced and at the meantime for supplement of structural information about e.g. binding positions and side reactions etc. Various types of NMR analysis have thus been performed for the analysis of Mannich reaction products from lignin model, 4-hydroxy-3-methoxyacetophenone (HMAP), and from industrial spruce Kraft lignin. As revealed by NMRs, the reaction was very selective at C-5 position of guaiacyl lignin units and complete under acidic conditions with 11-fold amounts of reagents of piperidine (PIP) or dimethylamine (DMA) and formaldehyde over HMAP. No side reactions took place at the aromatic structure. For industrial lignin, 13.5 (by PIP) and 15 (by DMA) nitrogen atoms were introduced per 100 aromatic rings. Using other analytical methods, the aminated lignin was found with higher molecular weights, reaching Mp of 5.06kDa from the original 3.92kDa by DMA modification, and with a sharp increased solubility especially in acetic acid aqueous solution, 31.2 mg/ml after DMA modification. A preceding phenolation of the lignin resulted in a 70% increase of available aromatic rings and an introduction of 56 amine groups over 100 original aromatic rings after Mannich reaction by using DMA, which caused increases of molecular weights to 5.11kDa (Mp) and of solubility in acetic acid aqueous solution up to 77.2 mg/mL. Potential applications of these modified lignins of high values include many applications in different fields such as surfactant chemicals, polycationic materials and slow released fertilizers etc.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Pappers-, massa- och fiberteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Paper, Pulp and Fiber Technology (hsv//eng)

Nyckelord

Aminated lignin

Mannich reaction

NMR

Phenolation

Solubility

4-Hydroxy-3-methoxyacetophenone

Acidic conditions

Amine groups

Analytical method

Aromatic rings

Aromatic structures

Dimethylamines

Guaiacyl lignin units

Kraft lignin

Lignin models

Lignin structure

Mannich reactions

Modified lignins

Nitrogen atom

NMR analysis

Potential applications

Side reactions

Structural information

Upgradation

Acetic acid

Amination

Aromatization

Lignin

Molecular weight

Nuclear magnetic resonance

Organic compounds

pH

Phenols

Solutions

Surface active agents

Wood

Lignins

Reaction Kinetics

Publikations- och innehållstyp

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