EGEE 439
Alternative Fuels from Biomass Sources

6.2c Hemicellulose

6.2c Hemicellulose

As seen in previous lessons, lignocellulosic biomass contains another component, hemicellulose. Rather than being a typical polymer where units repeat over and over again, hemicellulose is a heteropolymer. It has a random, amorphous structure with little strength. It has multiple sugar units rather than the one glucose unit we’ve seen for starch and cellulose, and the average number of sugar units is 500-3000 (glucose units with the starch and cellulose). The monomer units include: xylose, mannose, galactose, rhamnose, and arabinose units (see Figure 6.8 with a chemical structure of each). The various polymers of hemicellulose include: xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan (see a couple of examples in Figures 6.9a and 6.9b).

monomomer units and their chemical structures: xylose, mannose, galactose, rhamnose, and arabinose,
Figure 6.8: Monomer sugars found in hemicellulose.
Credit: Wikipedia page for each chemical, a) xylose wiki, b) mannose wiki, c) galactose wiki, d) rhamnose wiki, e) arabinose wiki
Example of polymers in hemicellulose (xylan)
Figure 6.9a: Example of polymers in hemicellulose (xylan).
Example of polymers in hemicellulose (arabinoxylan)
Figure 6.9b: Example of polymers in hemicellulose (arabinoxylan).