The effects of holocellulose treatments on the yield and structure of dimethylsulfoxide-extracted birchwood xylans

Xylans with naturally occurring acetylation are vital to the plant cell wall functionalities and are also demonstrating excellent dispersing properties which can be applied in fine chemicals and advanced materials. The acetyl structure of xylan can be maintained by dimethyl sulfoxide (DMSO) extraction. A disadvantage of DMSO extraction is that its yield is much lower than that of alkali extraction, which is unfavorable to the research and application of xylans. In this study, sodium chlorite was used as the delignification method to produce holocellulose from birch wood. The effects of subsequent holocellulose solvent exchange, drying and ball-milling on xylan DMSO extraction were studied. The differences of three successive DMSO extractions from the same holocellulose sample and gradient xylan precipitation from DMSO were also evaluated. The majority of xylans are extracted in the first two extractions, while the xylans extracted in the third extraction usually had low yields and low molecular weights. Xylans extracted directly from aqueously wet holocellulose without drying had a very low yield of less than 1%, while xylans extracted from freeze or vacuum dried holocellulose have total yields of 4–9%. T-butanol or ether washed holocellulose shows slightly lower xylan yield than water washed holocellulose. Ball milled holocellulose has twice the xylan yield of holocellulose sample without ball milling. For gradient xylan precipitation, more than 95% of the xylans precipitate in 50% and 70% ethanol. Gradient ethanol precipitation fractionates xylans by molecular weight, but does not fractionate xylans by degree of acetylation. This study is significant for promoting the researches and applications of DMSO extraction of xylan.