Abstract
A novel and efficient one-pot system for green production of artificial lignin bio-composites has been developed. Monolignols such as sinapyl (SA) and coniferyl (CA) alcohols were linked together with caffeic acid (CafAc) affording a polymeric network similar with natural lignin. The interaction of the dissolved SA/CA with CafAc already bound on a solid support (SC2/SC6-CafAc) allowed the attachment of the polymeric product direct on the support surface (SC2/SC6-CafAc-L1 and SC2/SC6-CafAc-L2, from CA and SA, respectively). Accordingly, this procedure offers the advantage of a simultaneous polymer production and deposition. Chemically, oxi-copolymerization of phenolic derivatives (SA/CA and CAfAc) was performed with H2O2 as oxidation reagent using peroxidase enzyme (2-1B mutant of versatile peroxidase from Pleurotus eryngii) as catalyst. The system performance reached a maximum of conversion for SA and CA of 71.1 and 49.8%, respectively. The conversion is affected by the system polarity as resulted from the addition of a co-solvent (e.g., MeOH, EtOH, or THF). The chemical structure, morphology, and properties of the bio-composites surface were investigated using different techniques, e.g., FTIR, TPD-NH3, TGA, contact angle, and SEM. Thus, it was demonstrated that the SA monolignol favored bio-composites with a dense polymeric surface, high acidity, and low hydrophobicity, while CA allowed the production of thinner polymeric layers with high hydrophobicity.
Highlights
Together with cellulose and hemicellulose, lignin is one of the most abundant natural polymers (Zakzeski et al, 2010)
The bio-composites construction was performed in one-pot system by enzyme oxi-copolymerization of monolignols (e.g., coniferyl alcohol (CA) or SA) directly on the surface of the previously prepared supports (SC2/SC6 functionalized with caffeic acid (CafAc), section SC2/SC6 functionalization)
The oxi-copolymerization of monolignols (e.g., CA or SA) was directly performed on the supports (SC2 and SC6) surface functionalized with CafAc (SC2-CafAc and SC6-CafAc) in the presence of the 2-1B mutant of versatile peroxidase as catalyst using an adapted procedure (Opris et al, 2018)
Summary
Together with cellulose and hemicellulose, lignin is one of the most abundant natural polymers (Zakzeski et al, 2010). Particles functionalized with CafAc were used as solid supports allowing the synthesis of bio-composites. For the attachment of the lignin polymer, the solid supports SC2 and SC6 were functionalized with CafAc in order to ensure the phenolic structures on the particles surface.
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