Drying Parameters Overview
There are different drying parameters that have their distinct role in the process of drying the resins. Here we describe the these parameters and their effects that help processors to put them in use accordingly.
Drying Parameter: Heat
Heat is considered as the first fundamental drying parameter that can be used with any kind of polymer. Here is how heating affects hygroscopic materials & non-hygroscopic polymers.
In the Hygroscopic polymers, the water molecules are present in the molecular structure of the substance and thus they have a strong attraction for water. The heat works on the force that binds these water molecules with the molecular chains, casting them out of the material more vigorously & efficiently. At a certain temperature, the binding force finally weakens and thus the water molecules are led free in the air, moving freely and assisting in the drying process.
In non-hygroscopic materials, heat is used to eliminate the surface moisture as the molecular structure of these materials does not allow water molecules to enter in the pellet. Thus the moisture collects externally on the surface which is eliminated by heat.
Drying Parameter: Dew Point
The second fundamental drying parameter is Dew Point. It is primarily used for drying hygroscopic polymers and assists in many drying processes.
The temperature at which the moisture in the air starts condensing is known as ‘Dew Point’. When exposed to dry air, the free moisture molecules present in the hygroscopic materials are forced to migrate to the surface of the pellet.
Drying Parameter: Drying time
Offering plastic pellets enough time to dry is another fundamental drying parameter. The pellets need sufficient time to release the moisture molecules when heated and then to defuse these molecules to the surface of the pellet as an effect of the dry air.
Drying Parameter: Airflow
Airflow is one such parameter that aids in the entire drying process. It assists in carrying the heat & dry air into the drying hopper. If you are working on non-hydroscopic materials, you need hot airflow exposed to the pellet to let the surface dry.
In the case of the hygroscopic polymer, low dew point heated air is forced on the pellet to disintegrate the bond between the molecular chain and water molecule and force it away on the pellet surface from where it is finally carried away.
The volume of the dry air is responsible for developing and maintaining the desired temperature profile in the drying hopper. Any deviation in between can cause harm to the plastic and hamper the drying process.