Xylan derivatives

Due to the lack of a commercial supply, as well as their usually low molecular weight and poor solubility, xylans have found little industrial utility and interest in their modification has been rather low in comparison to commercially available polysaccharides such as cellulose or starch. With the aim of improving the functional properties of xylans and/or imparting new functionalities to them, various chemical modifications have been investigated during the past decade. Most of them were presented in recent reviews [3,399]. 

Partial etherification of the beech wood MGX with p-carboxybenzyl bromide in aqueous alkali yielded fully water-soluble xylan ethers with DS up to 0.25 without significant depolymerization the Mw determined by sedimentation velocity was 27 000 g/mol [400,401]. By combination of endo- 6-xylanase digestion and various ID- and 2D-NMR techniques, the distribution of the substituents was suggested to be blockwise rather than uniform. The derivatives exhibited remarkable emulsifying and protein foam-stabilizing activi- 

The TMAHP-MGX isolated from cationized aspen sawdust was reported to be applicable as a beater additive it significantly increased the tear strength of bleached spruce organosolv pulp [3]. The TMAHP derivatives prepared from isolated xylans were shown to improve the paper-making properties and 

By the treatment of oat spelt xylan with phenyl or tolyl isocyanate in pyridine the fully fimctionahzed corresponding carbamates were prepared [416]. Xylan 3,5-dimethylphenylcarbamate showed higher recognition abihty for chiral drugs compared to that of the same cellulose derivative [417]. 

In a most recent paper [418] the preparation of corn fiber arabinoxylan esters by reaction of the polymer with C2-C4 anhydrides using methanesul-fonic acid as a catalyst is described. The water-insoluble derivatives with high molecular weight showed glass-transition temperatures from 61 to 138 °C, depending on the DS and substituent type. The products were thermally stable up to 200 °C. Above this temperature their stability rapidly decreased. 

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Thermoplastic xylan derivatives have been prepared by in-hne modification with propylene oxide of the xylan present in the alkaline extract of barley husks [424,425]. Following peracetylation of the hydroxypropylated xylan in formamide solution yielded the water-insoluble acetoxypropyl xylan. The thermal properties of the derivative quahfy this material as a potential biodegradable and thermoplastic additive to melt-processed plastics. Xylan from oat spelts was oxidized to 2,3-dicarboxyhc derivatives in a two-step procedure using HI04/NaC102 as oxidants [426]. 

Macromolecular Symposia, Vol. 232,1, (February 2005), pp. (1-12), ISSN 1521-3900 Ebringerova, A. Heinze, T. (2000). Xylan and xylan derivatives - Biopolymers with valuable properties, 1 - Naturally occurring xylans structures, procedures and properties.. Macromolecular Rapid Communications, Vol. 21, 9, 0une 2000), pp. (542-556), ISSN 1022-1336... 

The film-forming property of xylan derivatives also leads to the inference of an average D. P. greater than about 50. This deduction arises from the general observation that pliable polysaccharide acetate films are only formed from molecules with a D. P. of 50 or more. 

Model building in the computer is used to compare the influence of remote contacts on the stereochemistry and properties of P-1,2-, p-1,3-, and P-1,4-glucans, including their optical rotation behavior, and to explore the possibility of chain folding in cellulose, chltin, and xylan derivatives. 

Refs. 183, 189, and 203). The last two substrates are usually sparingly soluble in water, and are solubilized by treatment with alkali (M sodium hydroxide) followed by neutralization.181,203 Soluble D-xylan derivatives that have been used include O-(carboxymethyl)-D-xylan167,229 and 0-(2-hydroxyethyl)-D-xylan.200,205... 

Ebringerova, A., Heinze, T, (2000). Xylan and xylan derivatives Biopolymers with valuable properties, 1. Naturally occurring xylans structures, procedures and properties. 

K. Petzold-Welcke, K. Schwikal, S. Daus, and T. Heinze, Xylan derivatives and their application potential - Mini-review of own results, Carbohydr. Polym., 100,80-88,2014. 

Figure 3. Effect of H2O2 charge on brightness and hydrolysis residue of xylans derived from non-pressurized and 02-aided extraction (Ref = starting xylans)...

An anionic xylan derivative was produced by carboxymethylation of xylan in homogeneous IN alkali solution using the sodium salt of chloroacetic acid, according to Gustavsson et al. (30). After 3 hr. at 70 C, die reaction mixture was adjusted to pH 10 with HCl and precipitated in ethanol. 

A) Typical telechelic fluorinated cellulose ester copolymer (Tyo-TF) (data are averages of three measurements with a variation of /-0.25 (B) xylan from rye straw (data variation as shown) (C) xylan from yellow poplar and (D) hydroxypropyl xylan derivative. 

In general, HP or AP xylan derivatives (33), produced sharp transitions in surface tension with respect to bulk solution concentration and distinct CMC values (Figure 3D), whereas most (Figure 3D), but not all (Figure 3B), xylan isolated from natural... 

Weak transitions, like the one in Figure 3C, are indicative of ill>defined aggregates in solution with small aggregation numbers. Nonetheless, the ct fiuit xylans wifii different lignin-levels (Figure 3B) or chemical modification by HP or AP derivatives (Fig. 3D) could alter and sharpen the CMC provided encouragement that xylan-derivatives could be made that would adsorb ("dock") more stror y on a cellulose surface. 

Several water-soluble, xykn-rich hetero-polysaccharides and their derivatives were measured in this way widi respect to dieir self-assembly behavior at cellulosic LB film surfaces (i.e., dockiiig behavior). The correqionding eiqierimental results ate sununarized in Figure 6. The structure of the xylan derivatives used is given in Figure 2. 

Based on the above results, it was clear dut more drastic changes in r lan structure were required to promote adsorption ( docking ). Hence cationic and F-containing xylan derivatives were examined given the strong hydrophobic effect seen for F-containing CTP derivatives. Cationically-... 

Figure 7. AFM height image (left) and phase images (right) of a 40-layer cellulose LB film treated with an aqueous solution of the F-containing cationic xylan derivative. Note the spherical particles deposited on the image on the right side.

Jain, Rajesh K., M. Sjdstedt, and W. G. Glasser. 2001. Thennoplastic xylan derivatives with propylene oxide. Cellulose 7(4), 319-336. 

Typical functionalization reactions of xylan are reviewed. Moreover, comments about the analytical characterization of the xylan derivatives are given and some structure-property relationships are discussed. 

In the present article, important functionalization methods for the preparation of xylan derivatives are discussed. In addition, examples for the structure analysis and applications are given. 

Ebringerova, A. Heinze, Th. Xylan and xylan derivatives - biopolymers with valuable properties, l.Macromol. Rapid Commun, 2000,27, 542-556. 

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