Question

Answer the reason why the cellulose is resistance to chemical attack. ( i.e. chemical structure bonding and so on )

Answer 1

Cellulose molecules form into fibrils, or bundles of molecular chains that combine in groups to form the cellulose fibres. Each fibre is composed of many cellulose molecules. These are not arranged in a completely parallel manner; or rather although certain portions of the fibre may have the molecules lying parallel other areas are characterized by a somewhat random molecular arrangement. The parts of the fibre where molecules lie side by side and are held together by many associated forces are called crystalline. If the molecules, as well as lying side by side, are parallel to the longitudinal axis, there is a high degree of molecular orientation. Usually, high orientation and crystallinity imply strength, rigidity, low elongation, and low pliability.

The strength of cellulose fibres is also influenced by the degree of polymerization (dp) as well as by the molecular arrangement. The higher the dp, the stronger the fibre. A typical degree of polymerization for a native cellulose fibre is about 10,000; for regenerated cellulose, such as rayon, it is only about 500. The molecules within the fibre are usually held in place by hydrogen bonding. When cellulose fibres are bent, the hydrogen bonds are broken, and new ones form, causing creases or wrinkles that do not hang out. This is why all products made from cellulose fibres have the same tendency to crease. Removal of the hydroxyl unit may result in cross-linking of the cellulose molecules so that they are more stable, helping to form cellulose fibres that have a higher resistance to and recovery from creasing.

Because of the hydroxyl (–OH) groups in cellulose, these fibres usually have a high attraction for water. This means that in hot weather, perspiration from the body will be absorbed in fabrics made from cellulose fibres, transported along the yarns to the outer surface of the cloth, and evaporated into the air. Thus, the body maintains its temperature and feels comfortable.

Cellulose fibres also tend to burn easily and fast with a yellow flame, giving off a smell like burning paper or leaves, then depositing a light, fluffy, greyish residue or ash. Cellulose is usually decomposed by acid solutions, especially strong mineral acids, but it has excellent resistance to alkaline solutions. In general, cellulose is low in elasticity and resilience, so it is prone to creasing unless treated. The fibres are laundered readily and can withstand strong detergents, high temperatures, and bleaches (if used properly). This group of fibres is seldom damaged by insects, but fungi, such as mildew, will destroy cellulose or at least stain it severely.