Selulosa serat (fibrous cellulose)

Plants contain cellulose, hemicelluloses and lignin. The cellulose appears as micro fibrils with diameter size between 2 to 20 nm and length size of 100 to 40,000 nm. Cellulose has most important use to hold on to water. Water molecule cannot penetrate crystalline cellulose. Dry amorphous cellulose absorbs water to become soft and flexible. If the cellulose has high crystallinity, less water is bound by direct hydrogen bonding. However some fibrous cellulose can hold on to considerable water in pores and its typically straw-like cavities. Water holding ability correlates with the amorphous surface area effect and porosity.

Fig. Cellulose structural unit

Plant fibers are group into seed fiber (cotton, kapok), leaf fiber (sisal, banana, agave), bast (stem skin) fiber (flax, jute, kenaf, hemp, ramie, rattan), fruit fiber (coconut/coir), and stalk fiber (straws of wheat, rice, barley, bamboo and grass). Cellulose content in each plant does not similar. For examples in dry basis, hardwood contains 42% cellulose, sugarcane baggage contains 41% and rice straw contains 45%. The characterization and its potential application of fibrous cellulose have being studied in the world.

Fig. Study on fibrous cellulose during last century

(Courtesy of Forest Product Laboratory, 1994)

Hemicelluloses refer to polysaccharide filling between fibrous cellulose in the plant walls. Hemicelluloses are polysaccharide that can be extracted by base solution. Hemicelluloses are mainly arranged by D-glucose chain monomers and other monosaccharide. The main component of hemicelluloses at dicotyledoneae is dominated by xiloglukan, whereas its composition may vary in monocotyledoneae. In wheat plant, it is dominated by arabinoxylane, whereas at barley and haver is dominated by betaglukan.

Lignin plays role as a binder of other components in plant tissue. If cellulose consists of carbohydrate groups, then chemical structure of lignin is very complex and has random pattern. Aromatic group is found in lignin, and cross linked by aliphatic chain consists of 2 to 3 carbons. In physical chemical process, lignin and hemicelluloses are usually separated from its cellulose to find better mechanical properties of new product involving as much as cellulose content.