Holocellulose from wood

Holocellulose Cellulosic material obtainable from wood after removal of lignin. The term therefore means total carbohydrates (cellulose and hemicellulose) present in the wood (Refs 1 2) Ritter (Ref 3) succeded in isolating holocellulose from wood pulp by repeated chlori-nations, followed by extraction with alcohol containing 3% of monoethanolamine. The resulting product was white but changed color on standing... 

Another method of isolating holocellulose from wood and similar lignified tissues by the use of sodium chlorite and acetic acid was devised by Jayme and modified by Wise, Murphy and D Addieco. The latter... 

Partially degraded cellulose is called hydrocellulose or oxycellulose, depending on the agent used for degradation. The term holocellulose is used to describe the residue after lignin has been removed from wood pulp. 

The whole procedure normally takes about 1 hr. The acid is then evaporated, and the dry matter can be analyzed. This method can be applied to cellulose from wood, as a-cellulose or pulp, or to other celluloses (e.g., cotton) as well as to cellulosic materials with higher amounts of other polysaccharides (e.g., holocellulose). The chromatograms of the hydrolysates of a-cellulose from beechwood and of holocellulose from sprucewood (Figure 6) are examples of the application of this method. Compared with sulfuric acid hydrolysis, the total sugar yield from the spruce holocellulose is higher after the hydrolysis with concentrated TFA (Table II). Regarding the individual sugars, it can be seen that the... 

Figure 6. Chromatograms of the hydrolysates of a-cellulose from beech-wood and holocellulose from sprucewood...

Woods contain a number of acyl (mainly acetyl) groups, and it is probable that these are associated with the xylan components of the hemicellulose fraction. Evidence for the original esterification of aspen-wood xylan comes from the observation that the isolated xylan (obtained by alkaline extraction) is readily cleaved by periodate, whereas only a small proportion of the D-xylose residues in the wood itself are oxidized under similar conditions.66 Hemicelluloses still containing acyl groups may be extracted from wood holocelluloses by means of dimethyl sulfoxide, and further quantities... 

Holocellulose. Holocellulose is the total polysaccharide (cellulose and hemicelluloses) content of wood, and methods for its determination seek to remove all of the lignin from wood without disturbing the carbohydrates. The procedure generally used (34) was adopted as Tappi Standard T9m (now useful method 249), and as ASTM Standard D 1104. Extracted wood meal is treated alternately with chlorine gas and 2-aminoethanol until a white residue (holocellulose) remains. The acid chlorite method is also used (3). The... 

Figure 3. Infrared spectra of methyl isocyanate-modified southern pine. Key A, unreacted wood (control) B, 17.7 WPG C, 47.2 WPG D, holocellulose from sample treated to 17.7 WPG E, lignin from sample treated to 47.2 WPG.

The phenomena which have been observed on extraction of wood with aqueous sodium hydroxide - also occur, albeit to a smaller extent, with holocelluloses the restriction to dissolution is, in this case, mostly due to the fiber structure itself. In a study of the extraction of a chlorine holocellulose from European beech with sodium hydroxide solutions of various concentrations, Corbett and Ewart found that 87% of the (4-0-methyl-glucurono) xylan could be removed under mild conditions, and another 10% by extraction with hot alkali, but that 1.3% remained associated with the cellulose. The same authors have also described an apparatus suitable for the alkaline extraction of wood or holocellulose in an atmosphere of nitrogen. 

Bird and Ritter isolated, from wood of white oak, a chlorine holocellu-lose which contained all of the 0-acetyl groups present in the wood. Mitchell and Ritter later extracted a chlorine holocellulose from sugar maple with water and obtained a xylan in a yield of 3.4% of the wood. This polysaccharide contained 9.2% of 0-acetyl groups. A xylan which had been obtained in the same way, from aspen, by Wise and Jones, was, on treatment with periodate, oxidized almost to completion. When the wood itself was similarly treated, most of its xylan escaped oxidation. Although it appears evident that all of the xylan in the wood could not possibly have been accessible to the aqueous reagent, it was concluded that the lack of oxidation was most probably due to the fact that the native xylan was partly 0-acetylated. After treatment of wood from Eucalyptus regnans with methanol at 150°, Stewart and coworkers obtained, on extraction with water, a xylan (in a jdeld of 3.7%) which contained 5-6% of acetate... 

A chlorite holocellulose from white-birch wood, on extraction with methyl sulfoxide, gave a xylan containing 5.3 0-acetyl groups per ten xylose residues. In this case, the yield was only 5% of the original wood. The hemi-cellulose contained 58.1% of unsubstituted, 11.8% of 2-0-substituted, 24.0% of 3-0-substituted, and 6.1% of 2,3-di-O-substituted xylose residues. The 0-acetyl groups in native hardwood xylans are thus distributed between C-2 and C-3 of the xylose residues, with the majority located at C-3. It should, perhaps, be pointed out that, so far, only this species has been investigated, and moreover, only a minor part (15%) of the xylan portion of this wood has been studied. 

Following previous attempts to isolate a pure mannan from wood, Hess and Liidtke reported the isolation of such a polymer from a spruce sulfite pulp. Husemann, much later, obtained a similar product from a spruce holocellulose. It is now clear that these polysaccharides could not possibly have been mannans. Wise and Ratliff found that over half of the D-mannose residues in black spruce wood are intimately associated with the a-cellulose portion, perhaps as an integral part of the cellulose. A skinlike substance, insoluble in cuprammonia, was isolated by Rollin-... 

However, there are some methods for extraction of cellulose from plants. Han and Rowell s (1996) method describes a procedure for extraction of holocellulose, hemicelluloses, cellulose and lignin [18]. The method consists of four principle steps (1) preparation of sample (grinding of the wood), (2) removal of extractives, (3) preparation of holocellulose (removal of lignin), (4) preparation of a-cellulose (removal of hemicellulose). Several other procedures for a-cellulose extraction from wood samples have already been described during the last decades. Older methods used benzene-methanol instead of toluene-ethanol as organic solvent for the second step. Toluene-ethanol works as well as benzene-methanol mixture, and reduces health risks associated with the use of benzene and methanol. 

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

For the study of soluble polysaccharides, a treatment with diluted TFA is sufficient and the reaction time can be kept short (7). Soluble polysaccharides of wood are separated from holocellulose by extraction with alkali. Wise et al. (10) term the extract with 5% KOH polyoses (hemicelluloses) A. Polyoses A can be hydrolyzed completely with 2N TFA within 1 hr. The chromatograms of the hydrolysates of polyoses A from spruce and beech holocelluloses recorded with a sugar analyzer (Biotronik ZA 5100) are shown in Figure 1. 

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