Hemicelluloses extraction

Figure 1. Concentrations of polyuronides and hemicelluloses extracted from strawberry tissues at different stages of ripeness.

O Dwyer22 finds that increased severity in the conditions of drying of English oak decreases the yield of hemicellulose extracted by 4% sodium hydroxide solution. Likewise, Meller23 notes that there occurs an increased amount of pentosan resistant to extraction with 7 % cold alkali whenever wood pulps are dried at high temperatures. Similar changes, associated principally with the furfural-yielding complexes, can be produced in both hard and soft woods.24... 

Whistler, R. L., and Feather, M. S. (1965). Hemicellulose extraction from annual plants with alkaline solutions. Methods in Carbohydrate Chemistry, Vol. V, pp. 144-145. Academic Press, New York. 

In contrast, marked and very similar darkening occurred upon the thermal aging of added-on test sheets at 90 °C and 50 rh, regardless of the particular hemicellulosic extract (Figures lc and 2c). For comparison, the behavior of handsheets made solely from groundwood pulp (gp), notorious for its tendency to discolor, is shown in each figure. 

Tests using hemicellulosic extracts from several different pulp stocks indicate that little if any discoloration is caused by exposure of these components to visible and near-UV radiation or even radiation at 254 nm (UV). In the continuing quest to understand the causes of discoloration in paper, these results support the contention that the tendency of hemicelluloses to lead to discoloration is primarily a thermally induced effect. 

The preparation of the different fuel samples is described elsewhere (10), Special reference needs to be made to sample ENT (Table 1), a steam pre-treated E. nitens stem wood feed stock. This sample was derived from experimental work to evaluate the effect of fuel pre-treatment on combustion behaviour (11). Stemwood chips of E. nitens were treated via a new steam treatment process to produce a clean biomass fuel. The treatment involved steam hydrolysis, hemicellulose extraction and materials drying. 

The FTIR spectra of hemicelluloses extracted from birch wood (commercial xylan, line 1) and wheat straw hemieellulose extracted with 0.25 mol/1 NaOFI/30 °C (line 2),... 

Fig. 5 FTIR spectra of commercial xylan from birch wood (line 1) and FTIR spectra of wheat straw hemicellulose extracted with 0.25 mol/1 NaOH/30 °C (tine 2), 0.50 mol/1 NaOH/30 °C (line 3), 0.25 mol/ 1 NaOH/55 °C (line 4), and 0.50 mol/1 NaOH/55 °C (line 5) all the treatments for 2 h...

Proper extraction process needs special requirements to fractionate a certain hemicellulose or mixture of hemicelluloses. However, the presence of lignin network as well as ester and ether lignin-carbohydrate linkages limits the hemicellulose extraction... 

The isolation of hemicellulose from various materials that have lygnocellulose has been done by several researchers. Numerous researchers have studied the different procedures, solvents, working conditions, and hemicellulose extraction processes. Various procedures have been developed for the isolation of hemicellulose, using sodium and potassium hydroxide, peroxide hydrogen and a base, or with a solution of barium or calcium hydroxide with a wide range of temperatures [7, 9,14, 22, 25, 39, 40]. 

Hosseinaei, Omid., Wang, Siqun., Taylor, Adam.M. Jae-Woo Kim Effect of hemicellulose extraction on water absorption and mold susceptibility of wood-plastic composites. Int. Biodeterior. Biodegradation 71, 29-35 (2012)... 

Modern global tendencies in deep processing of wood biomass are based on green chemistry approach, including simultaneous use of all main wood components (cellulose, lignin, hemicellulose, extractive substances), and also wood wastes (bark, pulp lignin), non-standard and low-value wood. 

Lyytikainen K, Saukkonen E, Kajanto I, Kayhko J. The effect of hemicellulose extraction on fiber charge properties and retention behavior of kraft pulp fibers. BioResources 2011 6(1) 219-31. 

A variety of industrial processes are available for hemicellulose recovery in large scale. They can be classified into processes with lignocelluloses as starting materials or pulps as a source for hemicellulose extraction. Of course the hemicellulose source and the recovery process are of major importance for the chemical and physical properties of the recovered polysaccharides. Hemicellulose fractionation from lignified materials mostly yields... 

Hemicelluloses extracted flora a hardwood and softwood source, namely beech wood sulphite pulp (BS) (19) and Eucalyptus prehydrolysis itraft pulp (EK) (20) respectively, were characterized and the results were compared to the press lye obtained firom the viscose process. Table I contains the standard specification of the starting materials. The characteristic data of press iye (PL) are summarized in Table II. 

The homogeneous acylation of the hemicellulose is mostly carried out in the solvent iV,/V-dimethylformamide (DMF) in combination with LiCl. Hemicellulose extracted from poplar wood chips was acylated with various carboxylic acid chlorides in DMF/LiCl applying triethylamine and 4-N,N-dimethylaminopyridine (DMAP) as base and catalyst (J, Table 1). Depending on... 

After the two-hour extraction, the pump and heater were turned off and a bottom valve opened slowly to relieve the pressure and to withdraw the extract for analysis. The extract was collected through a valve and heat exchanger to cool the sample below the boiling point. The chips were washed thoroughly until a clear liquid was observed. The wash water was not collected. The chips were then placed in a drying oven at 105 C overnight to determine the mass loss of the chips. The % hemicellulose extracted was determined using a NMR... 

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