CRYSTALLINE AND AMORPHOUS REGIONS

In the textile fibres there are organized (crystalline- where molecules are arranged in a regular pattern), and disorganized (amorphous- where molecules are not arranged in a regular pattern) components.

Figure 2: Amorphous and crystalline regions.

The relative properties of crystalline and amorphous regions can be ascertained in a number of ways. One of the simplest is by density. It is possible to calculate the density of the crystalline region from a knowledge of the spacing between the molecules and molecular weight of the units in the chain. Since the density of the fibre is less than the theoretical density of the crystalline portions, it is easy to determine how much is amorphous, whereas randomly arrange molecules only give one.

From the relation intensities of the absorption bands, it is possible to calculate the proportion of crystalline structure in the fibre. From the X-ray diffraction pattern degree of crystallinity of the fibre can be known chemically, amorphous region are more accessible to chemicals than the crystalline ones.

The intermolecular forces may exist in crystalline regions are of three kinds:

1. Chemical linkages: These are found in the naturally occurring protein fibres. Salt linkage between adjacent amino and carboxyl groups exist in wool.

R-NH₂ + HOOC-R' = R-NH₃^+- OOC-R'

2. Hydrogen bonds: Hydrogen bond is not as strong as other chemical linkage. Its bond energy is low.

3. Van der waals’ forces: There are the attraction forces between adjacent chain. Polyethylene, for instance, the straight, (-CH₂-CH₂-CH₂-CH₂-) has no scrope for H-bonding or chemical linkage is quite absent.