Physical Equilibrium
Equilibrium moisture content in textile fibers depends on the direction from which equilibrium is approached. When a fiber is dried from a wet state, the residual moisture at a given relative humidity is higher than when the dry fiber absorbs moisture under the same conditions, a phenomenon known as desorption hysteresis. This differential occurs because the internal structure of the fiber undergoes molecular rearrangements as water leaves, locking some moisture in the crystalline gaps.
Fiber Response
Internal polymer networks in natural fibers create varied bonding potentials for water molecules during the drying phase. In cotton, desorption hysteresis occurs due to the relaxation of internal stress and the closing of transient pores. This means that drying and wetting cycles change the fiber density.
Processing Impact
Fiber processing during high-speed spinning depends on the structural conditioning of the raw material. Spinners use controlled moisture restoration to stabilize yarn before winding. Because of desorption hysteresis, a fiber that has been over-dried is structurally different from a fiber that reached the same moisture content through absorption, directly affecting yarn strength and uniformity.
Testing Limit
Moisture testing instruments require calibration against a fixed reference pathway to ensure reliable measurements. Standard lab methods rely on pre-conditioning samples to a low moisture level before final absorption measurement to eliminate the influence of desorption hysteresis. This prevents false readings during fiber grading.
