Xylan derivatives and their application potential - mini-review of own results

The chemical modification of xylan is a promising path to new biopolymer ethers and esters with specific properties depending on the functional groups, the degree of substitution, and the substitution pattern. The reaction of 4-O-methylglucuronoxylan (GX) from birch with sodium monochloroacetate and 2,3-epoxypropyltrimethylammonium chloride in aqueous sodium hydroxide/slurry medium is described. The influence of the conditions of activation on product structure and properties are discussed in some detail. Methylation of GX was investigated under completely heterogeneous conditions or starting with dissolved polymer using methyl halides as reagents in the presence of NaOH. An activation of the biopolymer has been carried out before the reaction to enhance the accessibility of the reagents. Furthermore, novel xylan esters were efficiently synthesized by conversion of the hemicellulose with furan- and pyroglutamic acid as well as ibuprofen and N,N'-carbonyldiimidazole as activating agent under homogeneous conditions in dimethyl sulfoxide. This conditions are also appropriate to synthesize novel xylan ester containing xylan-4-[N,N,N-trimethylammonium]butyrate chloride moieties. Homogeneous syntheses of xylan sulfates could be carried out in a N,N-dimethylformamide (DMF)/LiCl as solvent applying sulfur trioxide complexes with DMF or pyridine. Advanced analytical techniques including NMR spectroscopy, HPLC, scanning electron microscopy, rheology, measurements of turbidity and surface tension allow description of structure-property-relationships; selected results will be briefly discussed. Xylan esters may form spherical nanoparticles of a size down to 60 nm and a narrow particle size distribution applying a simple dialysis process and may be used for drug delivery applications. For cationic xylan derivatives a wide range of applications as paper strength additives, flocculation aids, and antimicrobial agents are proposed.