Extraction and characterization of hemicelluloses from flax shives by different methods

Hemicelluloses were extracted from flax shives using pressurized low-polarity water (PLPW), pressurized aqueous ethanol (PAE), microwave-assisted water (MW-Water) or aqueous ethanol (MW-EtOH), and precipitated with ethanol. Hemicelluloses still remaining in solution were further separated using ultrafiltration. All samples were characterized with chemical analysis, ion-moderated partition chromatography (IMP), size exclusion chromatography (SEC), and Fourier transform infrared (FT-IR) spectroscopy. PLPW, PAE, MW-Water and MW-EtOH extracted 90, 80, 18, and 40% of the total hemicelluloses, respectively. The molecular weight of the ethanol-precipitated hemicelluloses ranged from approximately 11,000 to 40,000 Da and the ethanol-soluble low-molecular weight hemicelluloses were about 1700 Da. High-molecular weight hemicellulose isolated from PAE extracts contained ∼23% lignin, while that from the PLPW extracts contained ∼5% lignin. Low-molecular weight hemicelluloses separated by ultrafiltration from PLPW and PAE extracts contained similar amounts of lignin (∼20%). However, the yield of low-molecular weight hemicelluloses from PLPW was higher (∼15%) compared to that from PAE (∼6%). The FT-IR results revealed the specific band maximum at 1220 cm−1 and the bands between 1175 and 1000 cm−1 which are typical of xylans.