ALBERT

Description: 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.

Description: 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.

Description: Summary The present paper aims at elucidating the effect of high-temperature defibration at different temperatures on the bulk and surface chemical properties of defibrated birch, aspen and eucalypt. The results indicate that defibration of these hardwoods results in partial depolymerization of fiber lignin via (homolytic) cleavage of interunit alkyl-aryl (β-O-4) ether bonds. This increases the phenolic hydroxyl content and produces relatively stable (phenoxy) radicals. Syringyl-type lignin is more extensively depolymerized than guaiacyl-type lignin. Defibration generates water-extractable material, which is enriched in hemicellulose-derived carbohydrates and has a substantial content of aromatic compounds rich in phenolic hydroxyl groups. The amount of water-extract and the extent of lignin interunit ether bond cleavage increase with an increase in defibration temperature. The differences between various hardwood species in this respect are small. The surface chemical composition of the fibers differs considerably from their bulk composition, but is not significantly influenced by variations in defibration temperature. Lipophilic extractives cover a large portion of the fiber surface, while the lignin content of lipophilic extractives-free fiber surfaces is 2–3 times as high as the bulk lignin content of the fibers.

Description: Summary Fiberboard was manufactured without synthetic resins from spruce and beech fibers activated by treatment with Fenton's reagent (H2O2/FeSO4) and the formation of radicals in the fibers by the action of Fenton's reagent was studied. The treatment resulted in a strong improvement of board strength and a large increase in fiber free radical content. The improved adhesion is probably largely due to interfiber bonds formed by reactions of radicals or other reactive groups generated in the fibers by Fenton's reagent. The reactivity of spruce fibers in terms of radical formation increased as defibration temperature increased. The thickness swell of the boards depended more on the amount of sizing agent or other additive than on the defibration temperature or fiber reactivity toward Fenton's reagent.

Description: 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.