Antioxidant function and solubility in water are highly desirable in many applications of chitosan.In this paper,a xylan/chitosan composite was prepared in an ionic liquid system using glutaraldehyde as a crosslinking agent.The antioxidant activity,reducing capacity and metal ion chelating ability of the resulting composite were determined.The chemical structure and thermal stability were analyzed by FT-IR,XRD and TGA.The results showed that chitosan was successfully cross-linked with xylan by glutaraldehyde in the ionic liquid system.Compared to pure chitosan,the ABTS·+scavenging activity of the xylan/chitosan composite increased from 10.56%to 97.59%.After cross-linking with xylan by glutaraldehyde,the reducing power of xylan/chitosan composite increased from 0.054 to 2.109.The capacity of chelating metal ion of the composite also increased from 42.35%to 86.71%compared to that of pure chitosan.An underlying mechanism was proposed to account for the improvement of the chemical properties of the chitosan in the composite.
Poplar wood chips were extracted in an acetic acid/sodium acetate(SA/AA)buffer solution at 180ºC for 60 minutes,with a solid-to-liquid ratio of 1:6,to investigate the effect of pH on the extraction performance in terms of chemical compositions of the extract.The pH was controlled by varying the concentrations of sodium acetate and acetic acid in the buffer system.Results showed that the SA/AA system could promote the dissolution of hemicellulose,obtaining more oligosaccharides and monosaccharides,and could also inhibit the excessive decomposition of monosaccharides.When extracting poplar wood chips in a SA/AA system of pH=3.7,the yield of oligosaccharides was the highest,while the contents of furfural and hydroxymethyl furfural decreased by 25%and 30%,respectively,compared to conventional water extraction systems.Moreover,the amount of lignin extracted in the S/AA process was also higher than that in a conventional hot water extraction process.
Hydrothermal pretreatment of poplar wood chips was performed in an acetic acid/sodium acetate buffer medium.To characterize the structural changes of lignin in the pretreatment process,milled wood lignin(MWL)was isolated from both the un-treated and treated poplar wood chips,and analyzed by ^(1)H-NMR,^(13)C-NMR,^(31)P-NMR,FT-IR,and GPC-MALLS.Results showed that the lignin in the pretreated wood chips had more phenolic OH groups,less aliphatic OH groups,higher molecular weight,and narrower polydispersity,in comparison with the lignin in the un-treated wood.The acetic acid-sodium acetate buffer pretreatment facilitated the removal of-OCH_(3) groups and the cleavage of the inter-unit linkages ofβ-O-4 bond in the lignin.Furthermore,the re-polymerization of lignin in the acetic acid-sodium acetate buffer pretreatment was found to be less than that in autohydrolysis.
