Industrial lignins comprise a mixture of substances, including volatile, low-molecular weight compounds. In material applications of lignins, these volatiles contribute to the malodor of the finished product. We developed a method based on solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) to assay qualitatively and quantitatively the volatiles emitted from lignin samples. Substances were identified by mass spectra and retention indices, while quantitation was achieved by multiple headspace sampling (MHS). Guaiacol and dimethyl disulfide were calibrated as representative compounds for the most prominent substance classes. The method was validated and gave good recovery, ranging from 89 to 123% for dimethyl disulfide and 90 to 105% for guaiacol, a measurement range of several dozen nanogram to a few micrograms, which can be extended by adjusting the sample amount, and limits of detection of 86 ng for dimethyl disulfide and 25 ng for guaiacol. Sample preparation is limited to weighing of the sample into a headspace vial and requires no consumables or auxiliaries. The entire analytical workflow was automatized, including the necessary data evaluation, which combines the outcome of repeated analyses of the same sample. The concentrations of guaiacol in four representative lignin samples ranged from 0.4 to 1200 ppm, while dimethyl disulfide was detected only in a single sample.

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A method for lignin quantification is presented that is based on densitometry and multivariate calibration by partial least squares (PLS). Densitometry removes interferences otherwise caused by undissolved liquor components and solvents, while multivariate calibration accounts for interferences by other sample components, such as extractives or chromophoric compounds. Method validation predicted a bias very close to 0% and an uncertainty of 10% (kraft) to 20% and less (lignosulfonate). In trials with three industrial kraft liquors, biases from 0 to 5% were observed; for a tested lignosulfonate, a bias of 6% was obtained. By combining this method with thin-layer chromatography, other liquor components can be determined simultaneously with the lignin content, for example monosaccharides in sulfite liquors (total time per sample: 13 min). If only the lignin content is of interest, chromatography is unnecessary, and more than 200 samples can be applied to the plate in a dense pattern (time per sample: 2 min). Compared to other methods, this measurement is fast, gives correct results, is inert toward matrix components, and can be coupled with a chromatographic analysis. Its only prerequisite is the isolation of a suitable reference lignin to be used as an external standard.

Lignin is a major constituent of renewable plant resources. Its complete utilization is therefore a key element in a biobased economy. Lignin products can fail to be accepted commercially if they release volatile organic compounds, since they must conform to emission standards, and consumers must not reject them due to a repulsive smell. We therefore investigated low-odor kraft lignins for the stability of their volatile profiles, both on the long and the short term. With an increase in temperature, the emitted amount of volatile compounds increased, while the types of volatiles remained unchanged. The activation energy for the release was found to be in the area of physical desorption. It is therefore unlikely that chemical degradation processes contribute to the release of volatiles up to a temperature of 100 °C, and lignin can in principle be deodorized without degradation. Humidity had a stronger effect on the release of volatiles than temperature. When the relative humidity exceeded 60% or liquid water was added to a lignin powder, the detected volatiles multiplied. While we were unable to elucidate the underlying mechanism, our observations indicate a physical release, which is probably caused by the displacement of adsorbed organic molecules by water. Based on these findings, the influence of highhumidity conditions and elevated temperature must be taken into account during the development of lignin-based products to guarantee their stability.

2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ, 1) is the most prominent representative of cellulosic key chromophores, which occur almost ubiquitously in all types of aged cellulosics. The degradation of DHBQ by chlorine dioxide under conditions of industrial pulp bleaching (''D stage'') was studied, i.e. in moderately acidic medium (pH 3) at temperatures between 50 and 90°C. The degradation in the presence of excess ClO 2 generates rhodizonic acid (RhA, 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone, 2) as a secondary chromophore which is even more stable and more potent as a chromophore than the starting DHBQ, especially in the form of its salts. At least a threefold ClO 2 excess is needed for complete DHBQ consumption. The reaction from DHBQ to RhA involves pentahydroxybenzene (PHB, I) as an intermediate which is either readily further oxidized to RhA by excess ClO 2 or slowly reconverted to DHBQ in the absence of ClO 2. The RhA yield after 30 min reaction time had a maximum of 83% at a DHBQ/ ClO 2 molar ratio of 1:5, and decreased with increasing ClO 2 charge, reaching 38% at a DHBQ/ClO 2 ratio of