How to avoid blooming in rigid and flexible PVC

Blooming is the migration of formulation components to the polymer surface. In PVC, it usually appears as a white film, loss of gloss or a waxy feel after storage, thermal exposure or contact with moisture.

The most common causes are incompatibility between lubricant and matrix, over-dosing, poorly calibrated thermal stabilizer, mineral filler moisture and aggressive thermal history during extrusion.

The safest strategy is to balance internal and external lubrication. Metal stearates control stability and flow, while PE waxes help with release and surface finish. The recurring mistake is fixing torque by adding too much wax, increasing migration risk.

Plectus recommends step-dosage trials and simultaneous reading of torque, gloss, color and dimensional stability to locate the robust process window.

Before replacing the entire formulation, validate critical process variables. Small changes in temperature, residence time and addition order can eliminate the defect without sacrificing productivity.