Desiccant Masterbatch Dosing — When It Fixes Bubbles and When It Hides a Drying Problem
Direct answer
A desiccant masterbatch converts trace moisture in the melt into calcium hydroxide so the water never becomes vapour in the die. It is a genuine fix for the residual moisture carried by recycled polyolefins and mineral fillers. It is not a substitute for drying hygroscopic engineering resins such as PET, PA or PC, where water attacks the polymer chain itself and no scavenger recovers the lost molecular weight.
Read the defect before choosing a dose
- Fine bubbles spread through the film or sheet — typical of dissolved moisture; a scavenger usually works.
- Silver streaks radiating from the gate — moisture in injection moulding; scavenger helps, drying is the reliable fix if the resin is hygroscopic.
- Large irregular voids and a smell of degradation — this is thermal degradation or entrapped air, not water. Adding desiccant here just adds filler.
Dosing logic
Suppliers state a range, and the working point sits inside it based on how wet the feedstock actually is. The practical method:
- Start at the low end of the supplier range for a clean, well-stored feed.
- Move up in single increments only while the defect measurably reduces.
- Stop as soon as the defect clears. Overdosing does not clean the melt further; it loads the compound with reaction product, dulls the surface and can raise screw torque.
- Re-check after any change of supplier, silo or season — winter condensation on cold resin changes the answer.
Where a supplier document states an addition rate for a specific grade, that figure is the starting point recorded against the product; it is not a substitute for a trial on your own line.
Handling matters more than most buyers expect
Calcium oxide is reactive with water by design. An opened bag left on a humid shop floor consumes its own capacity before it reaches the extruder, which is the most common reason a dose that worked last month appears to stop working. Keep bags sealed, use foil-lined packaging where offered, and treat the shelf life on the document as real.
Where the money actually is
If the feedstock is consistently wet, a desiccant masterbatch is an operating cost paid on every kilogram produced. Compare it honestly against a dryer, a covered storage change, or a different regrind supplier. The scavenger is the right answer when moisture is variable and unpredictable; a drying investment is the right answer when it is constant and high.
What to send with the enquiry
Base resin and recycled content, the defect you are seeing with a photograph if possible, film gauge or wall thickness, filler loading, current dosing method (gravimetric or volumetric), throughput, and packaging preference.