Mathematical Model
Mathematical models describing the relationship between ambient humidity and fiber moisture content often reveal a gap between the wetting and drying paths. A dual curve isotherm represents this behavior by plotting two distinct lines that show how a fabric absorbs water as humidity increases and how it releases it as humidity decreases. The path taken depends entirely on the previous moisture state of the material.
Sorption Differential
Differences between the absorption and desorption curves indicate the energy required to rearrange the molecular structure of the fiber during moisture exchange. For natural fibers like wool, the dual curve isotherm shows a wide gap, meaning the material holds more water at a given humidity when it is drying out than when it is being wetted. This lag is a result of the internal friction and mechanical resistance of the fiber cells.
Milling Application
Factories use these charts to predict how fabric will behave during the transition from a wet finishing stage to a dry packing environment. Knowing the dual curve isotherm for a specific blend allows the mill to set the correct target humidity in the warehouse to prevent mold. It also helps in predicting the final weight of the goods after they have equilibrated to the shipping conditions.
Data Constraint
Validity of the model is restricted to a constant temperature, as thermal changes shift the position of both curves. Most dual curve data is generated at 20 degrees Celsius to match international testing standards. If the temperature fluctuates during the measurement, the two curves may overlap or distort, making the data unusable for precision weight calculations.
