No abstract

Scots pine samples, heat-treated (225°C under steam) and reference (kiln-dried), were exposed to natural weathering for 7 years in Espoo, Finland. The weathered and unweathered samples were examined with FTIR, UV resonance Raman, and 13 C CPMAS NMR spectroscopies. The spectroscopic results revealed that the lignin contents of the weathered heat-treated and especially of the weathered reference softwood samples diminished significantly. The surface of the weathered heat-treated sample was still rich in aromatic and conjugated carbonyl structures, whereas the surface of the reference sample was enriched with cellulose. These results indicated that weathering products of lignin were leached out with water from the reference sample, whereas in the heat-treated wood they were largely unleachable. The structure of the heat-treated wood was modified and degradation products did not leach out as easily as in the case of the reference sample. The weathering also resulted in a decreased content of amorphous polysaccharides of the reference sample, whereas the changes in the polysaccharide contents between weathered and unweathered heat-treated samples were not as dramatic because the amorphous carbohydrates were already degraded in the heat treatment. The results indicated that heat-treated wood is more resistant to natural weathering than untreated wood.

The variation in the mass fraction of crystalline cellulose (crystallinity of wood), the intrinsic crystallinity of cellulose, and the thickness of cellulose crystallites in early wood of Norway spruce [Picea abies (L.) Karst.], and Scots pine (Pinus sylvestris L.) grown in Finland were studied using wide angle X-ray scattering and nuclear magnetic resonance spectroscopy. The mass fraction of crystalline cellulose in wood increased slightly with the distance from the pith and was about 30€4% in mature wood of both species. The crystallinity of cellulose and the thickness of cellulose crystallites were almost constant for both species. The crystallinity of cellulose was 52€3% for both species and the average thickness of the cellulose crystallites was 32€1 and 31€1 for Norway spruce and Scots pine, respectively. The mass fraction of cellulose in wood, calculated from the crystallinity values, increased with the distance from the pith for both species.

In this paper we have investigated the changes in kraft lignin structure and morphology upon hydrothermal carbonization (HTC) at 240°C with and without the presence of carbonization catalysts. The main conclusion of this study is that the structure of kraft lignin was altered only slightly during the hydrothermal carbonization. The main changes in the kraft lignin's structure were demethylation and dealkylation as well as cleavage of β-O-4 bonds. The final product had a more thermally stable and complex cross-linked structure. More pronounced changes occurred in the material structure and morphology upon the addition of catalysts. The energy density of the

Twenty-five tropical hardwoods from Ghana were examined with Fourier transform infrared (FTIR), ultraviolet resonance Raman (UVRR), and 13 C-NMR crosspolarization/magic-angle spinning spectroscopy. FTIR and UVRR spectral data were subjected to principal component analysis, whereas four selected samples exhibiting large structural and compositional variation were investigated in more detail by NMR spectroscopy. The acetyl bromide lignin and ␣-cellulose contents of the samples and the amount of acetone-soluble substances were also determined. The most prominent principal components of the FTIR spectral model separated samples mainly due to the variations in lignin structures and carbohydrate contents and the amount and type of carbonyl structures, whereas UVRR spectral data distinguished between various aromatic and other unsaturated structures. The presence of condensed lignin/tannin-type structures were detected from UVRR and FTIR loading line plots of the minor principal components. Condensed tannins were also observed in the dipolar dephasing NMR spectra. Furthermore, the NMR results showed variations in the amount of crystalline cellulose and hemicelluloses and in the syringyl/guaiacyl proportions in lignin. Both NMR and FTIR data suggest that in most cases, a higher amount of guaiacyl units correlated with higher levels of acetyl bromide lignin and better bioresistance of the samples.