Sorption of corn cob and oat spelt arabinoxylan onto softwood kraft pulp

Arabinoxylans from corn cob and oat spelt were studied in sorption experiments onto bleached and unbleached softwood kraft pulp. The corn cob (CC) xylans were produced by steam extraction (SE-CC) and alkaline extraction (NaOH-CC), while the oat spelt xylan (NaOH-OS) was obtained by alkaline extraction. Both alkaline extracted xylans exhibited a high degree of polymerization (DP) (230-240), whereas the steam extraction induced a significant degradation resulting in DPs around 36. Investigation of the xylan addition mode revealed that adding xylan before beating of pulp is most effective for increasing the beating degree and the strength properties. The tensile and burst indices are improved by xylan addition over the whole range of beating degrees. In contrast to that, the tear strength is increased significantly for unbeaten pulps but declines after beating, compared to the reference. Xylan sorption rates are increased with prolonged beating. Highest sorption rates are observed for the NaOH-OS (12-32%) and lowest for the SE-CC xylan (6.6-14%). In general, the alkaline extracted xylans have a better performance, most likely as a result of their higher molar masses.