Meaning
Analytical gravimetric method used to measure the volatile content of a material by heating it and recording the change in weight. In polymer processing, loss on drying is a fast method used to check the dampness of resin pellets before they are fed into an extruder.
Gravimetric Procedure
A wet sample is weighed before being placed into a heated chamber or under an infrared lamp to evaporate volatile substances. The sample is weighed again after a set drying period to determine the mass difference. This weight reduction represents the total amount of volatile material driven off during the test.
Measurement Limitation
This technique cannot distinguish between water and other volatile substances like residual solvents or plasticizers. Consequently, loss on drying can overestimate the actual moisture content of compounded resins that release additives when heated. For highly sensitive resins, more specific chemical titration methods are required to obtain an accurate moisture reading.
Moulding Control
Despite these limits, the method provides a rapid screening tool on the production floor. Operators can run the test next to the injection moulding machine to quickly confirm that the drying hopper is functioning. This immediate feedback helps avoid the production of weak, degraded parts with surface splay.
