Dimitri Areskogh

Investigation of the molecular weight increase of commercial lignosulfonates by laccase catalysis.

Lignosulfonates are by-products from the sulfite pulping process. During this process, lignin is liberated from pulp fibers through sulfonation and washed away. As a consequence, the lignosulfonate molecules contain both hydrophobic and hydrophilic moieties. Lignosulfonates are low-value products with limited performance and are used as such as binders, surfactants, and plasticizers in concrete. Lignosulfonates face strong competition from synthetic petroleum-based plasticizers with superior quality. Therefore, increasing the performance of lignosulfonates is desirable not only from a sustainability point of view but also to expand their usage. One important aspect that describes how well lignosulfonates can act as plasticizers is the molecular weight. In this paper, the molecular weight of four commercial lignosulfonates is increased through oxidation by two laccases without utilization of mediators. Different parameters to obtain maximal molecular weight increase were identified and the technical significance of the experiments is discussed.

Oxidative polymerisation of models for phenolic lignin end-groups by laccase.

Abstract The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5′ and 4-O-5′ bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the α-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.

Enzyme catalyzed cross-linking of spruce galactoglucomannan improves its applicability in barrier films

Hemicelluloses are one of the main constituents of plant cell walls and thereby one of the most abundant biopolymers on earth. They can be obtained as by-products from different wood based processes, most importantly from the mechanical pulping. Hemicelluloses have interesting properties in e.g. barrier film applications. However, their relatively low molecular weight after isolation and co-extraction with lignin has limited their use. In this work, we present a novel technique for increasing the molecular weight of different wood hemicelluloses from mechanical pulping process waters as well as from pre-hydrolysis extracts. This is achieved by enzyme-catalyzed cross-linking of aromatic moieties bound to the hemicelluloses. The cross-linking treatment resulted in significantly improved mechanical properties in barrier films made with spruce galactoglucomannan. To our knowledge, this is the first time that wood hemicelluloses have been cross-linked by utilizing the bound aromatic moieties and creates new possibilities for utilizing this raw material source.

Investigation on Enzymatic Oxidative Polymerization of Technical Soda Lignin

Enzyme, including laccase and peroxidase, catalyzed oxidative polymerization of technical bagasse soda lignin and low molecular weight ultra-filtrated kraft pulp lignin in methanol-water solution w ...