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. 2018 Feb 10;23(2):377.
doi: 10.3390/molecules23020377.

Quantification and Variability Analysis of Lignin Optical Properties for Colour-Dependent Industrial Applications

Olumoye Ajao  1 , Jawad Jeaidi  2 , Marzouk Benali  3 , Andrea M Restrepo  4 , Naima El Mehdi  5 , Yacine Boumghar  6
Affiliations

Quantification and Variability Analysis of Lignin Optical Properties for Colour-Dependent Industrial Applications

Olumoye Ajao et al. Molecules. .

Abstract

Lignin availability has increased significantly due to the commercialization of several processes for recovery and further development of alternatives for integration into Kraft pulp mills. Also, progress in lignin characterization, understanding of its chemistry as well as processing methods have resulted in the identification of novel lignin-based products and potential derivatives, which can serve as building block chemicals. However, all these have not led to the successful commercialization of lignin-based chemicals and materials. This is because most analyses and characterizations focus only on the technical suitability and quantify only the composition, functional groups present, size and morphology. Optical properties, such as the colour, which influences the uptake by users for diverse applications, are neither taken into consideration nor analysed. This paper investigates the quantification of lignin optical properties and how they can be influenced by process operating conditions. Lignin extraction conditions were also successfully correlated to the powder colour. About 120 lignin samples were collected and the variability of their colours quantified with the CIE L*a*b* colour space. In addition, a robust and reproducible colour measurement method was developed. This work lays the foundation for identifying chromophore molecules in lignin, as a step towards correlating the colour to the functional groups and the purity.

Keywords: bioplastic; biorefinery; carbon black; colour; lignin; non-destructive measurement; optical properties.

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Conflict of interest statement

The authors declare no conflict of interest. The funding sponsors and the lignin suppliers had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
Measured colour for 45 lignin samples arranged in order of decreasing brightness.
Figure 2
Figure 2
Some chromophores and leucochromphores from lignin.
Figure 3
Figure 3
Samples and parameters evaluated for lignin characterization.
Figure 4
Figure 4
Schematic diagram of lab scale black liquor precipitation using carbon dioxide.
Figure 5
Figure 5
Experimental set-up for carbon black preparation.
Figure 6
Figure 6
Illustration of the CIE L*a*b* colour space.
Figure 7
Figure 7
Lignin colour variability depending on (A) feedstock and types of (B) black liquors.
Figure 8
Figure 8
Contrast in lignin colour when precipitated at different 65, 75 and 85 °C.
Figure 9
Figure 9
Effect of precipitation agent and pH on lignin colour.
Figure 10
Figure 10
Correlation lignin colour properties to precipitation conditions.
Figure 11
Figure 11
Reflectance spectrum for the lignin samples.
See this image and copyright information in PMC

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