Extraction of polymeric hemicelluloses from okoume sapwood by steam explosion: Use of non-destructive characterization methods

The hemicelluloses, which represent an important family of polysaccharides constituting approximate to 20-30% of the plant wall are currently one of the most poorly valorized fractions of the biomass. Extracted in polymeric form, hemicelluloses could be used for innovative material applications, replacing fossil materials. Five cumulative pretreatments involving bleaching and/or steam explosion (SE) and/or alkaline extraction processes have been studied for polymeric hemicelluloses extraction from Okoume ' sapwood. Morphological analysis of the cell wall of untreated and steam exploded wood was performed by optical and fluorescence microscopy after staining. Near infrared spectroscopy combined with multivariate calibration modeling were also performed for evaluating hemicellulose extraction. Hemicelluloses extracts were characterized by HPEAC/PAD ion chromatography, size exclusion chromatography (SEC), and high-performance liquid chromatography (HPLC), FTIR and HSQC NMR spectroscopy analyses. Alkali extraction of bleached wood led to high yields (approximate to 19%) of high molecular weight hemicelluloses (Mw approximate to 65 kDa) while neutral SE pretreatment allowed the recovery of highly acetylated polymers with a low degree of branching. A bleaching step prior to SE increased accessibility to hemicelluloses extraction but weakened the pulp and led to the removal of micro-particles of wood during the SE.