Basic lignin characterization

As simple as the solid content determination in various biorefinery streams by means of conventional drying might appear at a first glance, there are major pitfalls and a significant risk or errors. Usually the solid content is determined by drying a sufficiently large amount of sample to constant weight in an oven at 105 ± 3°C. However, most lignocellulosic materials and products from biorefinery streams are comprised of quite reactive compounds and/or process chemicals, such as bases or acids, which inevitably bring about reactions, in particular when exposed to air, and inaccurate results.

Within the ALICE core facility, we offer an optimized and very accurate approach for the determination of solids content and for dry sample preparation for further analysis in general. The drying process is conducted by means of freeze-drying and/or vacuum oven drying.

HT-GC-MS/FID of extractives: LMW: low molar mass compounds; FA: Fatty acids, RS: Resin acids; ST: Sterols; LG: Lignans; DG: Diglycerides; SE: Steryl esters; TG: Triglycerides

Extractive substances in lignocellulosic biomass refer to the components that can be extracted by various solvents of different polarities (e.g. water, ethanol, acetone, hexane and others). Extractive substances in lignins comprise various classes of chemical compounds, such as fatty and resin acids, fats, waxes, proteins, terpenes, gums, resins, simple sugars, starches, phenolics, essential oils, pectins, glycosides and saponins, sterols, flavonoids and others (Holmbom, 1999).

Within pulp and paper biorefineries, the extractive substances are separated from the spent liquors and usually processed into crude tall oil, which can be further fractionated and modified into a broad variety of value-added products. Therefore, the quantitative and qualitative analysis of extractives may allow the assessment of the product characteristics, perform process monitoring, or evaluate the isolation efficiency. The characterization of extractives plays an important role in further analysis of lignocellulosic materials since these compounds can impair accuracy and precision of those tests.

The isolation of extractives is performed by accelerated solvent extraction (Dionex™ ASE™ 350) with different solvents (depending on the material). Analysis of isolated substances is conducted by means of GC-MS/FID after derivatization following thoroughly optimized protocols.

For specific research questions we offer UPC2-qToF analysis for structure identification based on data mining with a specific extractive data base.

Sample amount required: 20 mg.

References

Holmbom, B. (1999).
Extractives.
In E. Sjöström & R. Alén (Eds.), Analytical Methods in Wood Chemistry, Pulping, and Papermaking (pp. 125-148). Berlin, Heidelberg: Springer Berlin Heidelberg.

Thermal analysis is an indispensable technique for determining the physical and chemical properties of polymeric materials, and evidently also of lignin.

ALICE offers thermogravimetry (TG), differential scanning calorimetry (DSC) and simultaneous thermal analysis (STA). The last method combines both TG and DSC, however, with lower precision and accuracy for higher sample throughput.

TG is a technique that measures the weight change of a sample as a function of temperature or time. It is used to measure degradation, oxidation, reduction, evaporation, sublimation, and other heat-related changes occurring in polymers (Hatakeyama and Hatakeyama, 2005). Being quite flexible in terms of measurement settings and sample composition, the method can be applied for the characterization of isolated lignins and of biorefinery streams directly, as well as for the analysis of possible products, such as modified lignins or even lignin-based composites. Moreover, TG under oxidative conditions is an alternative for the determination of inorganic residues (ash).

TG analysis is carried out on TG 209 F1 Iris Netzsch® instrument (temperature range 25 - 1000 ^oC). Samples are preferred in a powder or particle form.

Sample amount needed: 50 mg.

DSC provides information on the enthalpy changes associated with the phase transition occurring on heating or cooling (Hatakeyama, 1992). One of the most common application of DSC is the determination of the heat capacity of the material and the glass transition temperature (Tg) of lignin. Lignin, being an amorphous polymer, undergoes chain segment motion upon heating, which is indicated by an endothermic shift in DSC curves and hence allows determination of Tg. Tg is crucial when considering the use of lignins in composite applications, such as polymer blends, adhesives, thermosets and others. In addition, DSC allows to investigate the occurrences of reactions, for example, between lignin and other components of an adhesive system.

DSC analysis is carried out on DSC F3-MAIA Netzsch® instrument over a temperature range between 25 and 1000 ^oC. Samples are preferred in a powder or particle form.

Sample amount needed: 50 mg.

References

Hatakeyama, T. & Hatakeyama, H. (2005)
Thermal Properties of Green Polymers and Biocomposites.
Springer Netherlands. Vol.4., 332 Pages. doi: 10.1007/1-4020-2354-5

Hatakeyama, H. (1992).
Thermal Analysis.
In S. Y. Lin & C. W. Dence (Eds.), Methods in Lignin Chemistry (pp. 200-214). Berlin, Heidelberg: Springer Berlin Heidelberg.

The reliable determination of the lignin content in lignocellulosic materials or biorefinery streams is far from being a trivial task. This analysis is performed for characterizing lignocellulosic materials, for assessing the effects of chemical, physical, and biological treatments of wood and pulp, for monitoring effluents in wood-processing biorefineries, etc. There are several methods for lignin determination. We offer Klason lignin determination and acetyl bromide lignin determination (Dence, 1992, Iiyama & Wallis, 1988). Klason total lignin content of biomass or pulps is estimated from the sum of the acid-insoluble and acid-soluble lignin components obtained after digesting the samples with sulfuric acid. The acid-insoluble and acid-soluble constituents are determined by gravimetric and UV- techniques, respectively. 

Alternatively, lignin can be quantified by measurement of UV absorbance of wood and wood pulp samples after complete digestion and dissolution in acetyl bromide/acetic acid mixture. In contrast to the Klason approach, the acetyl bromide method requires much smaller amounts.

Sample amount needed: 100 mg.

References

Dence, C. W. (1992).
The Determination of Lignin.
In S. Y. Lin & C. W. Dence (Eds.), Methods in Lignin Chemistry (pp. 33-61). Berlin, Heidelberg: Springer Berlin Heidelberg.

Iiyama, K., & Wallis, A. F. A. (1988).
An Improved Acetyl Bromide Procedure for Determining Lignin in Woods and Wood Pulps.
Wood Science and Technology, 22(3), 271-280. doi: Doi 10.1007/Bf00386022