Why fibrous material has only one falling period in drying curve?

Answer 1

Fibrous material has only one falling period in its drying curve due to the nature of its structure. Fibers are composed of long slender elements that contain mostly air. As the material is heated this air is expelled from the fibers resulting in a decrease in the water content of the material. This is the first falling period in the drying curve. Once the air within the fibers has been expelled further drying is not possible resulting in a plateau in the drying curve. This plateau indicates that the material has reached its equilibrium moisture content. Since the equilibrium moisture content is independent of the drying temperature further drying will not result in any further decrease in the water content.

Answer 2

Fibrous material has only one falling period in the drying curve because the process of drying involves moisture being removed from the material by evaporation. Once the moisture content drops below a certain level, the fibrous material becomes structurally rigid and loses the ability to continue releasing moisture. This results in a single falling period in the drying curve.