Subcritical water is a high potential green chemical for the hydrolysis of cellulose. In this study microcrystalline cellulose was treated in subcritical water to study structural changes of the cellulose residues. The alterations in particle size and appearance were studied by scanning electron microscopy (SEM) and those in the degree of polymerization (DP) and molar mass distributions by gel permeation chromatography (GPC). Further, changes in crystallinity and crystallite dimensions were quantified by wide-angle X-ray scattering and (13)C solid-state NMR. The results showed that the crystallinity remained practically unchanged throughout the treatment, whereas the size of the remaining cellulose crystallites increased. Microcrystalline cellulose underwent significant depolymerization in subcritical water. However, depolymerization leveled off at a relatively high degree of polymerization. The molar mass distributions of the residues showed a bimodal form. We infer that cellulose gets dissolved in subcritical water only after extensive depolymerization.

The Lyocell process is a modern 'green' industrial fiber-making technology, which employs N-methylmorpholine-N-oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluorideacetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.

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Xylo-oligosaccharides (XOS) have gained growing interest during the past decade owing to their beneficial influence on health. At the same time, a trend to a more effective utilization of biomass and biomass degradation products can be observed. As a consequence, also the steeping-lye of the viscose process is discussed as a potential source of new products based on xylans, xylooligosaccharides, xylose, and different xylose degradation products, thus being a driving force for the development of appropriate production processes. Therefore, xylan isolated from the steeping-lye was subjected to hydrothermal degradation for production of xylooligosaccharides (XOS). The experiments were carried out at 120, 150, and 180 8C, respectively. This hydrothermal treatment led to a soluble fraction, consisting of neutral and acidic XOS, and an insoluble residue predominantly made up of highly crystalline cellulose. A mass balance was established to calculate the activation energy for hydrothermal xylan degradation from weight loss kinetics. The degree of polymerization (DP) of the neutral product fraction could be influenced in a wide range by the reaction conditions applied. Acidic XOS were further characterized using mass spectrometry (MS). A 4-O-methylglucuronic acid residue a-(1,3)-linked to the xylose backbone was detected as a new structural element in alkaline degradation products derived from beech wood xylan.