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In steam pretreatment the defibration is usually achieved by an explosion at the end of the treatment, but can also be carried out in a subsequent refiner step. A steam explosion and a steam refining unit were compared by using the same raw material and pretreatment conditions, i.e. temperature and time. Smaller particle size was needed for the steam explosion unit to obtain homogenous slurries without considerable amounts of solid chips. A higher amount of volatiles could be condensed from the vapour phase after steam refining. The results from enzymatic hydrolysis showed no significant differences. It could be shown that, beside the chemical changes in the cell wall, the decrease of the particle size is the decisive factor to enhance the enzymatic accessibility while the explosion effect is not required.

Four xylan samples from different origin were investigated, using a multi-detector, size exclusion, chromatographic system with two chromatographic column sets and mobile phases differing in the DMSO:water ratio. Molar mass distribution could be analysed best using a mobile phase of DMSO:water (90:10) with addition of 0.05 M LiBr, a system offering good solubilisation of the polymers and a proper chromatographic separation. SEC analysis in aqueous systems provided information on solubility and aggregation of xylans. A comparison of UV- and RI-signals in different systems gave further information on lignin impurities, which in some cases were involved in aggregation phenomena. Both analytical systems were applied to study the enzymatic fragmentation of xylans. Combining the information derived from the two systems can differentiate between the enzymatic degradation of the well-dissolved and the associated polymer fractions.