Thioacidolysis, periodate oxidation and size exclusion chromatography (SEC) were used for the analysis of spruce lignin samples. The standard thioacidolysis method was modified by including a pre-swelling of the lignocellulosic sample before the reaction, and this gave a higher yield of monomer products. Middle lamella and compression wood lignin was found to contain a larger amount of oligomers after thioacidolysis than normal wood lignin. Analysis by thioacidolysis of a thermomechanical pulp (TMP) revealed that approximately 10% of the β-O-4 structures in the lignin were cleaved due to the mechanical grinding effect. From kraft pulp, the mixture of thioacidolysis products contains a major fraction having a considerably larger molecular mass than the products from spruce wood and TMP. The structure of this material is still unknown.
Bauer-McNett fractions of an aspen chemi-thermomechanical pulp showed a significant variation
with respect to lignin content and sugar composition, and two of the fractions were found to be
particularly rich in middle lamella and secondary wall material, respectively. The secondary wall
lignin of aspen was found to contain larger amounts of non-condensed β-O-4 aryl ether structures
than the middle lamella lignin and the difference was attributed to a larger amount of syringyl
structures as revealed by thioacidolysis. Size exclusion chromatography of the thioacidolysis products
from birch and spruce wood showed a larger part of lignin oligomers being present in the degraded
spruce lignin. Moreover, birch lignin had a lower phenolic content than both aspen and
spruce lignin. Thioacidolysis followed by Raney-nickel desulphuration was used for the analysis of
hardwood lignin trimers.
A new method for the quantitative preparation of pulp representative lignin-carbohydrate complexes
(LCC) has been developed, in which LCC has been systematically prepared at quantitative
yield, fractionated and qualitatively determined. At least 90% of residual lignin in softwood kraft
pulp is proposed to be chemically bonded to carbohydrates. A major part of LCC (92%) in softwood
kraft pulp was observed between lignin, xylan and glucomannan, whereas a minor part (8%)
was linked to cellulose. Half of the hemicelullosic LCC is a lignin-glucomannan complex. The other
half is lignin-xylan complex and xylan-lignin-glucomannan complex. Thus, part of the residual
lignin in softwood kraft pulp crosslinks xylan and glucomannan. The proposed linkages are of covalent
type. At most 10% of the residual lignin is not bonded covalently to carbohydrates.
The steam explosion process was used to separate the components of aspen wood. The main goal was to
obtain a material with a molecular weight distribution similar to that of dissolving pulp. To achieve
variations in fibre structure and molecular weight, two series of steam explosions were made in which
the time and temperature were varied according to factorial designs. The resulting pulps were very dark
and were therefore bleached with hydrogen peroxide. The bleaching was sufficient to increase the
brightness of the exploded material significantly. The resulting lignocellulosic materials as well as the
washing water were characterised by carbohydrate analysis, lignin analysis and size-exclusion chromatography.
A large variation in the pulp composition as well as in cellulose and hemicellulose
molecular weight was obtained merely by varying the time and temperature of the explosions. The
results showed that pulps with properties ranging from a high xylan content (7%) and high molecular
weight cellulose (900 000) to a low xylose content (< 1%)and low molecular weight cellulose (<40 000)
were produced. The exploded material consisted mainly of cellulose, hemicellulose and degraded
polysaccharides. The degraded polysaccharides showed up as lignin in the Klason lignin analysis and in
measurements of kappa number.
Electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (MS) and
size exclusion chromatography (SEC) was utilised for analysis of milled wood lignin (MWL) and
lignin model compounds degraded by thioacidolysis. MS and SEC showed that thioacidolysis was
an efficient method for degradation of the β-O-4 bond in lignin. Moreover, the molecular weight of
thioacidolysed pinoresinol and MWL were analysed using matrix assisted laser desorption ionisation
time-of-flight mass spectrometry. Tandem MS was successfully applied for the structural determination
of thioacidolysed pinoresinol with and without acetylation of the product. The MS results
of thioacidolysis on MWL resulted in the identification of a tetrameric lignin structure
containing a 5-O-4, 5-5, β-1 linkage pattern.
Analytical and structural studies were done on different types of alkaline pulps and their isolated residual
lignins. Although having the same degree of delignification after cooking, some pulps were easier to
bleach than others. All isolated residual lignins were found to contain β-aryl ether (β-O-4) structures in
reasonable amounts when analysed by thioacidolysis (≥10 % of the native lignin value). At decreasing
kappa numbers, there was also a corresponding decrease in the amount of β-aryl ether structures in the
residual lignin. Moreover, a high β-aryl ether content in the unbleached residual lignin after cooking was
found to contribute to a better bleachability of the pulp, especially when hydrogen peroxide stages were
involved. At the same degree of delignification, the superior bleachability of alkaline sulfite pulps over
kraft pulps was shown to be attributable to a higher content of β-aryl ether linkages in the former type
Cellulases isolated from Trichoderma reesei and Phanerochaete chrysosporium were screened for hemicellulolytic,
pectinolytic and cellulolytic activity using locust bean mannan, birchwood xylan, citrus fruit
pectin and carboxymethylated cellulose (CMC) as substrates. The purpose of this work was to choose
appropriate enzymes to include in a “miniature cellulase system” with minimal hemicellulase activity
for the preparation of lignin-carbohydrate complexes (LCCs). The endoglucanases showed CMC activity
whereas activity towards the substrate was not detected for the CBHs. Xylanase activity was observed
for EG I and EG 38 whereas mannanase activity was observed for EG 44. None of the enzymes degraded
pectin. The results suggest that CBH I, CBH II, CBH 58, EG II and EG III are good candidates for
the effective preparation of LCCs. The possible biological function for the hemicellulolytic activity of
cellulases is discussed.
Lignin content and composition are important traits in
several tree breeding programs, but very little is known
about their natural variation. This study compares the lignin
content in 1-year-old plants and 9-year-old trees of
Norway spruce belonging to the same full-sib families. It
is shown that the lignin content, according to the modified
acetyl bromide method, does not vary significantly
within or among the different full-sib families either as
plants or as young trees. There is, however, on average
4.0% higher lignin content (31.4% versus 27.4%) and
lower standard error for the trees than for the plants. The
number of C9-units g−1 lignin, analyzed by thioacidolysis,
ranges from 516 to 1186 μmmol C9-units g−1 lignin in
plants and from 716 to 953 μmmol C9-units g−1 lignin in
trees, with no significant differences among the families.
However, the extent of change in C9-units g−1 lignin varies
among the families with age. The ratio of erythro and
threo stereoisomers does not vary significantly among
the families. However, the ratio changes differently with
age among the families similar to the C9-units g−1 lignin.
Additionally, the content of p-hydroxyphenyl (H) lignin is
0.6% higher in the trees than in the plants (1.4% versus
0.8%), estimated indirectly from GC-MS data by a novel
subtractive technique, indicating a higher degree of compression
wood in the young trees. In conclusion, the
amount and composition of lignin does not vary within
or among the families at the same age. However, the
amount of lignin increases with age while the change in
lignin composition varies between family and age.
Development of eco-friendly binders with no harmful emission during its complete life cycle is of high interest for the wood-based industry. In this paper, a fully renewable binder based on activated lignin and poly-furfuryl alcohol and a partly renewable lignin based phenol-formaldehyde (PF) binder were evaluated. Activation of kraft and soda lignins, isolated respectively from softwood and non-woods, by periodate oxidation was performed to improve lignin reactivity and application in wood adhesives. Periodate oxidation of lignin leads to higher lignin acidity, formation of quinonoid groups under more severe conditions, higher molar mass and higher reactivity towards the curing of furfuryl alcohol within a temperature range currently used in industry. Comparison of a 100% furan-based glue with a furan-based glue substituted by 10% lignin yields comparable product properties. However, periodate-activated lignin leads to lower wood failure, which might be caused by incompletely solubilised lignin particles in the acidic formulation disturbing crosslinking of the furan resin. Unmodified softwood kraft lignin performs well in a PF resin formulation at substitution levels up to 30% (w/w). Periodate oxidation of soda lignins enhances the glue performance because higher wood failure is attained. The higher molar mass after periodate treatment could be an important parameter for development of a stronger wood binder.
Functional properties of technical lignins need to be characterized in more detail to become a higher added value renewable raw material for the chemical industry. The suitability of a lignin from different plants or trees obtained by different technical processes can only be predicted for selected applications, such as binders, if reliable analytical data are available. In the present paper, structure dependent properties of four industrial lignins were analyzed before and after successive organic solvent extractions. The lignins have been fractionated according to their molar mass by these solvents extractions. Kraft and soda lignins were shown to have different molar mass distributions and chemical compositions. Lignin carbohydrate complexes are most recalcitrant for extraction with organic solvents. These poorly soluble complexes can consist of up to 34% of carbohydrates in soda lignins. Modeling by principle component analysis (PCA) was performed aiming at prediction of the application potential of different lignins for binder production. The lignins and their fractions could be classified in different clusters based on their properties, which are structure dependent. Kraft softwood lignins show the highest potential for plywood binder application followed by hardwood soda lignin and the fractions of Sarkanda grass soda lignin with medium molar mass. Expectedly, the softwood lignins contain the highest number of reactive sites in ortho positions to the phenolic OH group. Moreover, these lignins have a low level of impurities and medium molar mass.