Although all polymers absorb some amount of moisture, on none does it have such a significant effect as on nylons. Table 6.1 illustrates the moisture absorption levels of various types of nylons. 12 0.7 1.4 Water molecules produce polar bonds with the amide groups in the nylon molecules. Although small, water molecules take up space and displace the nylon molecules. This results in the nylon molecular matrix swelling.
Molecular mobility is increased through the absorption of water.
The increase in spacing between nylon molecules lowers the secondary forces allowing easier translational motion. This is the major reasons for the change in physical properties discussed above. There is less resistence to applied stress from the decrease in intermolecular friction. The change in molecular mobility is significant enough that molded nylon parts can relieve molded in stresses as they absorb moisture. The absorption of moisture by nylon is a completely reversible physical reaction.