Meaning
Polymer conditioning processes remove moisture from hygroscopic resins before they are subjected to high temperature melt processing. For nylon materials, polyamide 66 drying is necessary because this resin possesses a high affinity for water due to its polar amide groups. If the moisture is not reduced to below zero point two percent by weight, the polymer will undergo severe hydrolysis in the molding machine.
This process requires a desiccant air dryer operating at elevated temperatures.
Drying Mechanism
High temperature air heats the pellets and increases the diffusion rate of water from the pellet core to the surface. Effective polyamide 66 drying relies on circulating air with a dewpoint below minus forty degrees Celsius through the hopper. The dry air sweeps away the evaporated water, preventing it from being reabsorbed by the polymer.
Mechanical Impact
Parts molded from inadequately dried polyamide 66 exhibit low impact strength, excessive flash, and surface splay. This occurs because the water acts as a plasticizer and reduces the melt viscosity, causing the material to leak through mold parting lines. Proper drying ensures that the polymer chains remain long and strong, providing the expected mechanical performance.
Technical Limit
Over-drying must also be avoided as it can cause the polyamide to become too viscous and difficult to process. If the water content falls below zero point zero five percent, the resin may struggle to fill thin sections.
