On Laccase-Catalyzed Polymerization of Biorefinery Lignin Fractions and Alignment of Lignin Nanoparticles on the Nanocellulose Surface via One-Pot Water-Phase Synthesis

Rajesh Koppolu,Martti Toivakka,Liqiu Hu,Luyao Wang,Stefan Willför,Bas Van Bochove,Chunlin Xu,Jukka V Seppälä,Liji Sobhana Seleenmary Sobhanadhas,Teija Tirri,Petri Ihalainen,Liping Tan,Xiaoju Wang

doi:10.1021/acssuschemeng.1c01576

Rajesh Koppolu, Martti Toivakka + Show 11 more

Open Access

https://doi.org/10.1021/acssuschemeng.1c01576

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Abstract

Two series of well-defined lignin fractions derived from birch and spruce alkaline lignin (AL) by sequential solvent fractionation (i-PrOH-EtOH-MeOH) were engaged in a structure–property-application relationship study. The bacterial-derived alkaliphilic laccase (MetZyme) extensively catalyzed the oxidation and polymerization of AL fractions in an aqueous alkaline solution (pH 10). Lignin fractions with low molar mass reached a higher polymerization degree due to more phenolic-OH groups serving as reactive sites of oxidation and better lignin-laccase accessibility arose from a lower lignin condensation degree than the high molar mass ones. In comparison, AL fractions from spruce were found to be less reactive toward the laccase-catalyzed polymerization than those from birch, which was attributed to the much pronounced aryl-vinyl moieties’ oxidation. Furthermore, in situ polymerization of birch AL fractions using microfibrillated cellulose as a structural template was conducted in an aqueous medium and a dispersion of nanocellulose with its fiber network evenly coated by aligned lignin nanoparticles was obtained. The present study not only provides fundamental insights on the laccase-assisted oxidation and polymerization of lignin but also presents a new perspective for valorizing lignin in biobased fiber products through green processing of solvent fractionation and enzymatic treatment.

Highlights

In plant cell walls, lignin is synthesized mainly from sinapyl alcohol (S), coniferyl alcohol (G), and p-coumaryl alcohol (H) monomers via an enzyme-initiated radical polymerization, resulting in an amorphous and three-dimensional polymer with both ether (e.g., β-O-4′, 4-O-5′, and α-O-4′) and carbon− carbon (e.g., β-1′, β−β′, and 5−5′) interunit linkages.[1]
We reported on a lignin structure−property-application relationship of hardwood alkaline lignin (AL) that is isolated from a novel biorefinery process in the field of lignin-containing phenol-formaldehyde adhesive by solvent fractionation methodology.[14]
The isopropyl alcohol (i-PrOH)-soluble (i-PrOH-s) fraction from birch AL had the highest S/G ratio of 3.3, which decreased with increasing molar mass of the lignin fractions

Summary

■ INTRODUCTION

Lignin is synthesized mainly from sinapyl alcohol (S), coniferyl alcohol (G), and p-coumaryl alcohol (H) monomers via an enzyme-initiated radical polymerization, resulting in an amorphous and three-dimensional polymer with both ether (e.g., β-O-4′, 4-O-5′, and α-O-4′) and carbon− carbon (e.g., β-1′, β−β′, and 5−5′) interunit linkages.[1]. It is interesting to note that the film prepared with the unfractioned birch AL with MFC through the in situ polymerization approach showed a deteriorated profile of E′ in comparison with that of the MFC film (Figure 6d) This confirms that the sequential solvent lignin fractionation is strategically significant in deriving high performance for this type of lignin-containing materials. As strongly inferred by the mechanical properties, wettability, and water vapor transmission of the nanocomposite films as-fabricated, this one-pot, water-phase synthesis has potential in development of functional biobased packaging taking the advantages of the holistic processing approach being green and sustainable

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES