Christiane Laine

Structural features of water-soluble arabinogalactans from Norway spruce and Scots pine heartwood

Abstract Isolated water-soluble acidic arabinogalactans from Norway spruce and Scots pine heartwood were analysed and compared to Siberian larch heartwood arabinogalactans. The carbohydrate monomer composition was determined by acid methanolysis and gas chromatography, while structural studies were performed by 13C NMR spectroscopy and methylation analysis. The main structural features were found to be the same in the three types of arabinogalactans. However, the structure of the arabinogalactans from spruce and pine were found slightly different from the structure of larch arabinogalactans. The amount of single unit side-chains, consisting of arabinose and glucuronic acid units, was higher in the spruce and pine arabinogalactans than in the larch arabinogalactans. The amount of glucuronic acid was higher in the spruce arabinogalactans than in the pine arabinogalactans. The pine arabinogalactans had a higher amount of side chains with more than two sugar units than the spruce arabinogalactans.

Carbohydrate structures in residual lignin-carbohydrate complexes of spruce and pine pulp

Abstract Residual lignin carbohydrate complexes (RLCC) were isolated enzymatically from spruce and pine pulp. The RLCCs contained 4.9–9.4% carbohydrates, with an enrichment of galactose and arabinose compared to the original pulp samples. The main carbohydrate units present in all studied RLCCs were 4-substituted xylose, 4-, 3- and 3,6-substituted galactose, 4-substituted glucose and 4 and 4,6-substituted mannose. These units were assigned to carbohydrate residues of xylan, 1,4- and 1,3/6-linked galactan, cellulose and glucomannan. RLCCs of surface material and the inner part of spruce kraft pulp fiber were compared to obtain information on the heterogeneity of layers of the fiber wall. The 1,4-linked galactan was the major galactan in RLCC of fiber surface material of spruce kraft pulp. Towards the inner part of the fiber, the proportion of 1,3/6-linked galactan increased relative to 1,4-linked galactan. This finding is presented for the first time. 1,3/6-Linked galactan structures are suggested to have a role in restricting lignin removal from the secondary fiber wall. RLCCs of three different alkaline pine pulps were studied before and after oxygen delignification to evaluate differences resulting from the cooking method. The pulps were conventional kraft pine pulp (PCK), a polysulfide/anthraquinone pine pulp (PPSAQ) and a soda/anthraquinone pine pulp (PSoAQ); all were cooked to approximately kappa number 30. Small differences were found in the carbohydrate structures of the unbleached pulps. The study indicated that the RLCC of unbleached PSoAQ pulp contained longer oligomeric carbohydrate chains and less branched 1,3/6-linked galactan residues than the RLCCs of unbleached PCK and PPSAQ pulps. The RLCC of the unbleached PSoAQ also contained more 1,4-linked glucose units suggesting a greater number of linkages of lignin to cellulose in the PSoAQ pulp than in the other two pulps. All RLCCs of oxygen-delignified pulps had more non-reducing ends and less 1,3/6-linked galactan than the corresponding RLCCs of the unbleached pulps. The RLCC of the oxygen-delignified PSoAQ pulp had a higher ratio of 1,4-galactan to 1,3/6-linked galactan and shorter xylan residues than the RLCCs of oxygen-delignified PCK and PPSAQ pulps.

Methylation Analysis as a Tool for StructuralAnalysis of Wood Polysaccharides

Summary In modern structural analysis of complex mixtures of wood polysaccharides, methylation analysis is still a valuable and powerful tool for linkage analysis. In this paper, methylation analysis is described for the procedure methylation, methanolysis, silylation and GC/MS. The retention time indexes for the partly methylated methyl glycosides of the relevant wood polysaccharides are listed together with the ratios of the isomers of the different structural units. A calculation model for relative molar response factors is suggested based on a published model for FID detection and on experimental data. Tested for oligosaccharides of known structure including xylotetraose, mannotriose and 63, 64-α-D-galactosyl-mannopentaose, the model gives reproducible and sufficiently correct results. The fate of xylose units substituted with 4-O-methyl glucuronic acid at position 2 is investigated with a model compound.

Changes in the fiber wall during refining of bleached pine kraft pulp

Abstract The effect of refining on the fiber wall was studied for bleached kraft pulp fractions from pine first thinnings and pine sawmill chips. Hydrocyclone fractionation of both pulps produced fractions enriched in earlywood and latewood fibers. Some external fibrillation but no changes in fiber wall thickness were observed for the thin-walled earlywood fibers during refining. Refining the thick-walled latewood fibers led to extensive external fibrillation and a decrease in fiber wall thickness. The pore structure of the fiber wall opened up during refining for all pulp fractions. Earlywood fibers were more porous than latewood fibers, and fibers from first thinnings more porous than those from sawmill chips. The earlywood fibers from first thinnings had more large pores than the other fiber fractions. In the region of the smaller pores, the pore volume did not change significantly with refining, whereas in the region of the larger pores it increased markedly. In all the fractions investigated, specific hydrolytic enzymes hydrolyzed cellulose more easily after refining. This is an indication of an increase in cellulose surface area and/or disordering of cellulose as a result of refining, probably due to local disorder of the cellulose in the fibril aggregates. Bonding developed most strongly for the earlywood fiber fraction from first thinnings. This is concluded to be due to a combination of fiber dimensions and fiber wall porosity.

Simultaneous bench scale production of dissolving grade pulp and valuable hemicelluloses from softwood kraft pulp by ionic liquid extraction

Ionic liquid extraction of wood pulp has been highlighted as a highly potential new process for dissolving pulp production. Coproduction with a polymeric hemicellulose fraction was demonstrated in bench scale from softwood kraft pulp using extraction with the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc) and water. In total, the recovered pulp and hemicellulose fraction together yielded 95.5 wt.% of the pulp input. The extracted pulp had a remarkably high purity with an R18-value of 97.8%. The hemicellulose fraction consisted of galactoglucomannan, arabinoxylan and some cellulose and was precipitated from the ionic liquid-water mixture. After hydroxypropylation of the hemicellulose fraction, films were prepared and barrier and strength properties were compared to films from other polysaccharides. Reduced oxygen and water vapor permeation and good strength properties were demonstrated when compared to corresponding films from hydroxypropylated xylan from cold caustic extraction. The films have potential for applications in food packaging and edible films.

Hydrothermal carbonization of pulp mill streams.

The progress of the conversion, the yield, the structure and the morphology of the produced carbonaceous materials as a function of time were systematically studied with pyrolysis-GC/FID and FESEM microscope. The conversion of galactoglucomannan, bleached kraft pulp and TEMPO oxidized cellulose nanofibrils followed the reaction route of glucose being slower though with fibrous material, higher molar mass and viscosity. The conversion of kraft lignin was minor following completely different reaction route. Carbonaceous particles of different shape and size were produced with yields between 23% and 73% after 4h with being higher for lignin than carbohydrates. According to the results, potential pulp mill streams represent lignocellulosic resources for generation of carbonaceous materials.

Submicron hierarchy of cellulose nanofibril films with etherified hemicelluloses

The lack of simple differentiation of all-polysaccharide-film components in nanoscale hinders unveiling their structure-property dependency. Submicron hierarchy of films of cellulose nanofibrils (CNFs) and carbohydrate-based additives was revealed via visualization of the components by their differentiating adhesion to an Atomic Force Microscope (AFM) tip. The differentiation of the film components revealed that distribution of hydroxypropylated hemicellulose in the CNF matrix could be tuned by addition of a plasticizer. The hemicellulose hydroxypropylation degree of substitution (DS) was detected to be another parameter affecting the film structure due to the water-solubility depending on the DS. This was further verified via Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). The translucent, self-standing films comprising CNFs, sorbitol and hydroxypropylated hemicellulose were tested for mechanical, optical and oxygen diffusion performance. The performance was linked to their structural evenness, which confirmed that the oxygen diffusion through the film is tremendously affected by the film nano hierarchy.