Sorption Hysteresis

Molecular Cause

Internal structures within the cellulose or protein chains resist the movement of water molecules as they enter or leave the amorphous regions. In sorption hysteresis, the energy required to break hydrogen bonds during drying is higher than the energy released when those bonds form during wetting. This leads to a loop on the moisture isotherm graph where the absorption and desorption curves do not overlap.

The size of this loop indicates the degree of internal friction and the number of available bonding sites within the fibre. Understanding this behavior is necessary for predicting how fabrics will change in weight and dimension as they move through different climates.

Commercial Impact

Weight discrepancies in bulk yarn shipments often result from this physical lag. If a sample is conditioned from a dry state versus a wet state, the recorded equilibrium moisture content will differ, leading to potential disputes over the invoiced weight of the goods.

Industrial Application

Drying processes in the mill must account for this lag to ensure consistent results in dyeing and finishing. When a fabric exhibits high levels of sorption hysteresis, it may require more energy to reach a target dryness level than a simple linear model would predict. Engineers use these data to calibrate oven temperatures and line speeds for different fibre types.

Accurate moisture management prevents issues like mildew in storage or brittle fibres during high-speed weaving.