Meaning
Visual anomalies on the surface of polymeric materials result from melt fracture or uneven crystallization during the manufacturing run. When polymer melts exit the die, extruded surface haze appears as a matte finish that reduces the clarity of the finished part. This phenomenon indicates that the cooling and shaping process did not occur uniformly.
Chemical Origin
Incompatible additives or moisture in the raw resin can migrate to the boundary layer during extrusion. This migration creates a microscopically rough surface that scatters light, and this extruded surface haze is often the result of using resin lots with high moisture content. It can also stem from the thermal degradation of processing aids that were designed to reduce friction in the barrel.
Physical Measurement
Quality control teams use glossmeters and spectrophotometers to quantify the level of light scattering on the plastic sheet. In many cases, extruded surface haze is compared against a validated baseline to determine whether a batch should be rejected. The measurement process requires a flat sample and a standardized light source to ensure repeatable results.
Production Adjustment
Operators can mitigate the defect by altering the temperature profile of the die or reducing the screw speed. Adjusting these parameters directly affects the shear rate of the polymer, helping to eliminate extruded surface haze without changing the material formulation. Increasing the die gap is another operational change that relieves the pressure that causes surface roughness.
This solution is often preferred over lowering production throughput because it maintains the factory’s established output rates while resolving the cosmetic issues.
