Hemicelluloses softwood

Further studies on hemicelluloses of hardwoods have shown that these may exhibit a considerable range in the content of xylan and 0-methylhexuronic anhydride. In a recent review of hemicelluloses, Wise suggests that hardwood hemicelluloses may have a rather simple, architectural pattern, consisting predominantly of n-xylose units and smaller amounts of 0-methyluronic acid units. Softwood hemicelluloses also contain this fundamental structural unit consisting of a mono-O-methyluronic acid in combination with n-xylose units. In the case of pine, this fundamental unit may be associated with a part of the maiuian. ... 

Hardwoods also contain minor amounts (2-5%) of a glucomannan, which contains one to two mannose units for every glucose. In general, hardwood hemicelluloses are characterized by high concentrations of xylose and acetic acid structural units, whereas softwood hemicelluloses are relatively rich in mannose. 

J. Hartman, A.-C. Albertsson, M.S. Lindblad, and J. Sjoberg, Oxygen barrier materials from renewable sources Material properties of softwood hemicellulose-based films. J. Appl. Polym. Sci. 100, 2985-2991 (2006). 

Figure 10 shows the derived values of the glass transition temperature for the birch xylan and the glucomannan as a function of moisture ratio compared with data for the transition temperature for softwood hemicelluloses taken from literature (4). In the xylan, the glass transition temperature at 50°C and 1 Hz occurred at 76 %RH, which corresponded to a moisture ratio of 22%, whereas for the glucomannan at 50°C and 1 Hz it occurred at 65 %RH, corresponding to a moisture ratio of 16%. 

Figure 3.8 Principal structure of the main softwood hemicellulose type, galactoglucomannan, and of the main hardwood hemicellulose type, 4-Omethyl glucuronoxylan.

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