Reducing the content of VOCs of softwood kraft lignins for material applications

Abstract

Three laccases, functioning in mild acidic, and one in slightly alkaline conditions, were evaluated in order to reduce low-molecular phenolic VOCs of kraft lignins, which could be used in lignin/natural fibers composites. The potential of a sulfhydryl oxidase to catalyze the oxidation of sulfur containing VOCs (thiols) was also tested in combination with the laccase-catalyzed oxidation. In addition, oxidation at alkaline pH at room temperature that may induce polymerization of phenolics in an analogous manner to the laccase-catalyzed reaction was investigated. Enzyme reactivity towards lignin was evaluated as consumption of oxygen in the reaction solution. The effect of treatments on VOC reduction was determined both by sensing (odorimetry) and chemical (TD-GC/MS, SEC) analyses. Laccases, Lcc2, and MaL from Thielavia arenaria and Melanocarpus albomyces, respectively, showed potential in reducing odors. The most promising results were obtained by oxidizing lignin with O2 at alkaline pH. However, the odor threshold values of the main VOC compounds are extremely low, which poses a challenge to VOC reduction.

Slow‐release fertilizers using lignin: Challenges and future prospects

“…55 At a very high pH, the oxygen molecule converts into the superoxide anion (O2•-), which, on further protonation, results in the production of hydroperoxyl anion (HOO-). Out of all these derivatives of oxygen (O2• -, HOO-and HOO•), HOO• and O2• -work as electrophiles and attach the lignin at high-density electron sites like an aromatic ring and phenoxy ion, 56 whereas, HOO-works as a nucleophile and targets the low electron density sites of the lignin, such as carbonyl. This can convert the quinones into carboxylates, which can result in the right opening.…”