Meaning
Environmental measurement instruments monitor the concentration of water vapor present in the surrounding air or process gas. A relative humidity sensor is commonly installed in polymer drying hoppers to ensure that the air used for drying is sufficiently dry. This measurement prevents the introduction of moisture into moisture-sensitive resins.
Resin Prep
Hygroscopic polymers like polyamide or polycarbonate absorb moisture from the air, which can cause hydrolysis during processing. Placing a relative humidity sensor in the dryer’s return line helps verify that the desiccant beds are functioning correctly. Excess moisture in the feed causes cosmetic defects such as splay marks.
Defect Avoidance
Hydrolytic degradation occurs when wet polymer is melted, which breaks the polymer chains and reduces their molecular weight. Monitoring the drying process with a relative humidity sensor prevents this irreversible damage. The resulting reduction in molecular weight leads to a significant decrease in the impact strength of the molded parts.
This can cause the parts to fail prematurely when subjected to mechanical stress in the field. By ensuring the air has a low dew point, the sensor protects the mechanical integrity of the finished product.
Energy Economy
Dryers can run on closed-loop feedback systems that adjust heating and regeneration cycles based on actual air humidity. Using a relative humidity sensor prevents the system from running unnecessary regeneration cycles. This reduction in energy usage lowers the operating cost of the compounding or molding facility.
