Abstract
This paper presents an enzyme biocatalytic method for grafting lignin (grafting bioprocess) with aniline, leading to an amino-derivatized polymeric product with modified properties (e.g., conductivity, acidity/basicity, thermostability and amino-functionalization). Peroxidase enzyme was used as a biocatalyst and H2O2 was used as an oxidation reagent, while the oxidative insertion of aniline into the lignin structure followed a radical mechanism specific for the peroxidase enzyme. The grafting bioprocess was tested in different configurations by varying the source of peroxidase, enzyme concentration and type of lignin. Its performance was evaluated in terms of aniline conversion calculated based on UV-vis analysis. The insertion of amine groups was checked by 1H-NMR technique, where NH protons were detected in the range of 5.01–4.99 ppm. The FTIR spectra, collected before and after the grafting bioprocess, gave evidence for the lignin modification. Finally, the abundance of grafted amine groups was correlated with the decrease of the free –OH groups (from 0.030 to 0.009 –OH groups/L for initial and grafted lignin, respectively). Additionally, the grafted lignin was characterized using conductivity measurements, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), temperature-programmed desorption (TPD-NH3/CO2) and scanning electron microscopy (SEM) analyses. The investigated properties of the developed lignopolymer demonstrated its disposability for specific industrial applications of derivatized lignin.
Highlights
Lignin was mentioned for the first time as lignum (Latin word for wood) by the Swiss botanistA.P. de Candolle in the 19th century [1]
We developed a biocatalytic alternative for the derivatization of lignin based on a grafting approach using aniline as the co-monomer (Scheme 1)
The screening ofbiocatalytic peroxidase enzymes was performed by testing the biocatalytic capacity the of the biocatalytic process was evaluated based onevaluated aniline conversion (aniline attached/inserted toofthe performance of the process was based on aniline conversion (aniline peroxidase fromIn sources forInthe grafting of lignin (AL) with
Summary
Lignin was mentioned for the first time as lignum (Latin word for wood) by the Swiss botanist. A.P. de Candolle in the 19th century [1]. It was characterized from the beginning as a fibrous biomass (10–25% lignin in biomass) insoluble in water/alcohol and soluble in weak alkaline solutions. The research interest in lignin increased exponentially, especially due to its widespread nature. The paper pulp industry provides lignin as a waste byproduct, which is quite underutilized [3]. From the chemical point of view, lignin is a complex heterogenous biopolymer with a 3D structure, which contains phenylpropane units with/without one or two methoxy groups in ortho positions toward
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