Abstract
Lignin derivatives have potential as antioxidants in advanced packaging materials through their ability to scavenge oxygen in reactions catalyzed by phenol-oxidizing enzymes, such as laccase. The effects of size fractionation of lignosulfonates on laccase-catalyzed reactions were investigated in experiments with aqueous solutions, films, and coated paperboard. Four industrial lignosulfonate preparations were compared: Feed (unfractionated), Prod (5–60 kDa enriched), Conc (≥60 kDa enriched), and Perm (≤60 kDa enriched). Extraction of lignosulfonates from films showed that the enzymic reaction increased the average molecular weight from <10,000 to up to 66,000. The enzymatic reaction resulted in an increase in the water contact angle of the films from the range 25–49° to 56–81°. The four preparations showed relatively small differences with regard to their ability to scavenge oxygen in aqueous solution and in experiments with coated paperboards in sealed chambers. Coatings with lignosulfonates where the contents of low-molecular weight material had been reduced (i.e., Prod and Conc) showed improved water resistance after the enzymic reaction. Thus, in both aqueous and solid media, fractionation of lignosulfonates had little effect on oxygen scavenging, but fractionation was beneficial for other reasons, such as improved cross-linking resulting in higher molecular weight and superior water resistance.
Highlights
Lignin is one of the main constituents of wood and is a major residue from chemical pulping processes [1,2,3,4,5]
The influence of size fractionation of lignosulfonates on oxygen-scavenging catalyzed by the phenol-oxidizing enzyme laccase was investigated in aqueous solutions, films, and paperboard coatings
The investigation covered the effects of the enzymatic reaction on the average molecular weight of the lignosulfonates, the contact angle of lignosulfonate-containing films, the mechanical properties of lignosulfonate-containing films, the capability to scavenge oxygen, and the water resistance of lignosulfonate-containing films
Summary
Lignin is one of the main constituents of wood and is a major residue from chemical pulping processes [1,2,3,4,5]. Useful as an energy source, it would be highly advantageous to utilize at least a part of the lignin for advanced high value-added products. Lignosulfonates are co-products of sulfite pulping and are mainly used as additives to concrete [3,4,6]. While many other lignin derivates show poor solubility in water, the sulfonation that occurs during sulfite pulping renders lignosulfonates soluble even under neutral and moderately acidic conditions. Previous studies indicate that lignosulfonates and other lignin derivatives have potential as antioxidants in enzyme-catalyzed oxygenscavenging formulations, for example, in advanced packaging systems [7]. Lignin fractions may be used as antioxidants due to their free radical and oxygen radical scavenging properties [8]
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