Conclusion

The reduction or even elimination of defects is a major challenge in industrial polymer extrusion practice. Identifying the type of mechanism responsible for the appearance of these defects provides an effective means of defining corrective measures.

Surface deformations initiated at the die outlet can be effectively prevented, but by different means than those used to prevent volume deformations initiated at the die inlet. The most conventional approach is to reduce local stress below a critical level of around 0.1 to 0.2 MPa. This can be achieved by changing the polymer architecture, modifying extrusion conditions or blending the polymer with oligomers to reduce viscosity and create a lubricating layer on the die wall.

Alongside surface and volume deformations, we can observe the formation of "plugs", a periodic phenomenon presenting successively...